Review

We investigate the transient dynamics of cavity-EIT-based all-optical switching in a system of trapped ions coupled to an optical cavity through numerical simulations. In contrast to steady-state analysis, the time-dependent response provides direct insight into the switching speed, transient dynamics, and achievable switching contrast. We consider three distinct switching schemes and systematically compare their performance as a function of the relevant system parameters. The switching contrast is evaluated from the time-dependent cavity output and used to characterize the performance of each scheme. For the four-level N-type system, we find distinct trade-offs between switching through suppression of the cavity-EIT signal and switching through resonance shifting, with the former exhibiting a faster temporal response. The corresponding three-level scheme can achieve near-unity switching contrast with substantially shorter switching pulses, although it does not provide an independent switching control field. These results establish the performance limits and trade-offs of different cavity-EIT-based switching schemes and provide guidelines for optimizing their operation for applications such as high-speed optical gating, frequency-selective photon routing, frequency-multiplexed quantum communication, etc.

We report on hyperfine structure measurements of the $1s2s\,{}^{3\!}S_1 \rightarrow 1s2p\,{}^{3\!}P_{0,2}$ fine-structure transitions in the spectrum of $^{11}$B$^{3+}$ ions. The helium-like ions were created in an electron beam ion trap (EBIT) and ejected after a short production period of 15 ms. A challenge of the experiment was the treatment of the complex energy-time-profile of the created ion bunches and the sensitivity of the collinear laser spectroscopy to the starting potential inside the EBIT. Despite these complications and the low statistics of the experiment, we were able to confirm and improve the results of a previous measurement of these transitions. While we find moderate tension in the results for the hyperfine parameters of the $^{3\!}P_{0,2}$ levels, their fine-structure level energies are in reasonable agreement between experiments and with theory.

Existing quantum simulations of the two-flavor Schwinger model have run at a single lattice size, and it is not known how far the variational approach can be pushed or which weakness stops it first. Following the model from N = 2 to 6 staggered lattice sites, we find that the binding constraint at reachable sizes is hardware noise rather than circuit expressibility or trainability, and identify N = 3 as the immediately viable extension of existing trapped-ion experiments. The energy error of a charge-conserving ansatz collapses onto one function of p/d, the ratio of variational parameters to physical-sector dimension, and falls by more than two orders of magnitude as p/d rises through order unity, giving the expressibility condition L(4N - 1) >= binom(2N,N) for L circuit layers. The condition is local in chemical potential: at N = 3 the layer count sufficient at zero chemical potential leaves a 74.38% error near the first-order boundary, while one further layer reaches 0.08%. Charge conservation also protects trainability and prevents charge-sector leakage: as the qubit count doubles from 4 to 8, the normalized gradient variance falls to 1/3.56 of its starting value for the constrained ansatz, versus 1/13.57 for an unconstrained circuit. Comparing a global contraction with per-gate local noise, a fixed-parameter control shows that the noise model, not whether the optimizer runs inside the noisy loop, sets how strongly noise degrades the first-order transition. At N = 4, a noiseless control reaches 0.12% mean error, whereas the same circuit at 1.00% depolarizing noise reaches 25.69 to 52.81%.

Merging trapped ions with cold atomic clouds offers intriguing prospects for quantum chemistry and many-body quantum simulations. Especially when going beyond the standard alkali atomic baths by using lanthanide atoms, opportunities arise to study the interplay between the intermediate-range atom-ion interaction and the tunable long-range dipolar atom-atom interactions. However, the high total angular momentum of the ground-state of open-shell lanthanides, e.g. $^{5}I_{8}$ for dysprosium, affects the atom-ion potential. Here, we discuss the implications for long- and short-range atom-ion interactions and present a novel apparatus which combines an ytterbium ion (Yb$^{+}$) with dipolar dysprosium (Dy) atoms. We highlight the consequences of this novel Dy-Yb$^{+}$ mixture for observing buffer gas cooling, (non-) radiative charge transfer, and three-body recombination. While the energy-averaged rates are dominated by radiative charge transfer, particularly radiative association, we find that three-body recombination can compete with molecular-ion formation at Dy densities $n\gtrsim 10^{12}$ cm$^{-3}$. This competition is further enhanced by the expected non-thermal distribution of ion energies. These processes could be experimentally characterised through controlled variation of the atom-ion interaction parameters, providing a direct test of our theoretical predictions.

The decoder is a critical component of a fault-tolerant quantum computer, computing corrections based on parity-check measurements performed throughout the computation. A soft decoder supplements its output with a confidence score which, when used alongside post-selection, can substantially improve logical performance. We introduce a soft beam search decoder for quantum low-density parity-check codes that uses internal decoder data as a confidence metric, removing the need for extra computation. We perform circuit-level simulations of five quantum LDPC codes relevant for superconducting and trapped ion architectures equipped with our global soft decoder and we obtain up to $580\times$ logical-error suppression at a physical error rate of $10^{-3}$ while rejecting only $0.1\%$ of shots. Then, we simulate an error detected measurement, which is a core logical operation of the walking cat architecture, using a streaming version of soft beam decoder and we achieve up to $210\times$ error suppression while increasing the rejection probability by only $0.5$ percentage points. Finally, we revisit recent quantum LDPC code memory experiments on trapped ions, demonstrating that our soft decoder doubles the logical qubit lifetimes at the price of a mean rejection rate of $2.6\%$--$5.6\%$ per syndrome round, bringing all five codes into the beyond-breakeven regime.

Linear radio-frequency quadrupole (RFQ) traps are crucial for ion and phase-space manipulation across diverse physics platforms, including quantum information processing, precision atomic spectroscopy, and high-resolution mass or laser spectrometry. We present the design, electrostatic field optimization, and performance characterization of a scalable, multi-layer printed circuit board (PCB) linear RFQ trap. By utilizing a PCB-based "stacked-electrode" geometry to generate high-quality quadrupolar fields, this architecture suppresses higher-order multipole field components by up to an order of magnitude compared to planar "flat surface-electrode" designs and allows for reclaiming up to 60% of the radial pseudopotential-well depth of an ideal hyperbolic quadrupole. Following a thorough optimisation and characterization using both simulations and experiments, we demonstrate its suitability as a cooler buncher, showing rapid helium buffer-gas cooling with time constants between 34 +/- 3 us and 412 +/- 23 us, and achieving a highly compressed longitudinal phase-space emittance of only 58 +/- 4 eV*ns. The low beam emittance provides flexible control of the extracted bunch properties: weak extraction fields yield energy spreads down to 2.5 +/- 0.4 eV, whereas strong fields produce ultra-narrow temporal widths down to 2.6 +/- 0.3 ns. The results establish our PCB-RFQ platform as a versatile, scalable, and cost-effective alternative to traditionally machined rod-based RFQ assemblies for advanced ion-trapping, beam-preparation, or quantum applications.

Characterizing the phonon distribution of trapped-ion motional states is essential for many applications in quantum information processing, but existing methods become ill-conditioned beyond the Lamb-Dicke regime. We overcome this limitation by recasting phonon-state reconstruction as a filter-function inversion problem. Using composite pulses on the carrier and multiple sidebands, we engineer well-conditioned filters in phonon space to characterize pure and mixed states, study heating dynamics, and reconstruct Fock states up to $n=250$.

We propose a protocol for extracting work from a coherent quantum battery state by exploiting measurement-assisted feedback mediated by a continuous-variable pointer. The scheme relies on the unitary operator $U = \exp(-i k t \, \hat{H} \otimes \hat{P}/\hbar)$, which generates entanglement between the battery's energy eigenstates and the position of an auxiliary pointer. A subsequent projective measurement of the pointer's position conditionally prepares the battery in a pure state from which work can be extracted via a feedback unitary. We analyze the protocol for a two-level quantum battery and a Gaussian pointer, computing the conditional states and the corresponding daemonic ergotropy. For the pure initial state considered, we find that the daemonic ergotropy equals the standard ergotropy for all interaction strengths, demonstrating that the measurement-assisted feedback recovers the full extractable work that would otherwise become inaccessible due to entanglement with the pointer when its degrees of freedom are traced out. The protocol thus provides a physically transparent realization of a quantum Maxwell demon, where the pointer acts as a quantum measurement ancilla whose position becomes correlated with the battery's energy. The scheme is amenable to experimental implementation in trapped-ion systems, and it contributes to the ongoing efforts to understand the role of quantum coherence and measurement in thermodynamics.

Trapped ions excited to high-lying electronic states, so-called Rydberg states, open new opportunities for quantum simulation and quantum computing. Generally, the fidelity of quantum coherent operations critically depends on the longevity of Rydberg states. However, scaling laws predict that the lifetimes of Rydberg states in singly charged alkaline-earth metal ions are 16 times shorter, compared to their neutral atom counterparts. Here, we show that this is not generally the case. We report an anomalous lifetime enhancement of certain low angular momentum ionic Rydberg series by factors larger than eight. The anomaly is present at both zero and finite temperature, although it is caused by different mechanisms. At zero temperature, the anomalously enhanced lifetimes are caused by accidental cancellations of the relevant dipole transition matrix elements, while at room temperature the anomaly originates from the enlarged energetic separation of ionic Rydberg levels with respect to neutral-atom levels.

Scalable quantum computation is expected to rely on fault-tolerant quantum computation (FTQC), in which quantum error correction (QEC) suppresses physical errors sufficiently to support reliable logical operations. This requires quantum compilation to move beyond general-purpose circuit optimization toward encoding-aware and protocol-structured compilation across the full stack of fault-tolerant quantum computers. Beyond circuit synthesis and hardware mapping, an FTQC compiler must lower algorithm-level operations into the logical gate set supported by the chosen code, coordinate encoded data and ancilla resources, realize logical operations together with repeated syndrome extraction under hardware constraints, and provide the resulting measurement stream to real-time decoding. This survey presents a full-stack view of compiler design for QEC-protected quantum computation. We organize existing work into three interacting layers: logical-level QEC compilation, physical-level QEC realization, and decoder runtime integration. At the logical level, we review surface-code lattice-surgery compilers, beyond-surface-code code-surgery frameworks including emerging qLDPC approaches, and compilation support for non-Clifford operations such as magic-state distillation and code switching. At the physical level, we survey hardware-aware QEC realization on superconducting, trapped-ion, and neutral-atom platforms. We further examine decoder models, real-time decoding systems, and frame-management mechanisms that close the feedback loop during fault-tolerant execution. Finally, we identify open challenges in cross-layer optimization, qLDPC compilation, compiler-decoder co-design, runtime adaptivity, and the development of integrated and benchmarkable FTQC compilation stacks. An actively maintained paper list is available at: github.com/chenghongz/QEC-compiler-design.

At atomic resonance the Jaynes--Cummings (JC) vertex of a single bosonic mode coupled to a two-level emitter is blind to $f=ω/λ$ at zero detuning and Kerr; the anti-Jaynes--Cummings (AJC) vertex is not. We show that the mean-rung excited population of the AJC block equals exactly $1/4$ at $f_\star=\sqrt{\bar n+1}$, while the JC population at the same point is $1/2$. The Poisson-averaged packet value at $\bar n=16$ is $0.24650$, within $3.5\times 10^{-3}$ of the exact value, with the deviation reproduced by $-\bar n/[16(\bar n+1)^2]$. At $f_\star$ the modulation depth of the AJC inversion is $1/2$ and the relative sensitivity of the continuum revival-time ratio $r=t_R^{\rm AJC}/t_R^{\rm JC}$ is maximal with value $1/(2\sqrt{\bar n+1})$. Full diagonalization on $2(n_{\max}{+}1)$ states confirms the analytic values. The $1/4$ value can be generated by Floquet-engineered counter-rotating coupling provided that the static transverse rate satisfies $g_0\ll g_1$. Parameter translations for an ideal trapped-ion blue sideband and a flux-tunable circuit-QED coupler are reported.

Finite-component light-matter systems realize dissipative phase transitions in a single controllable atom-cavity setup, but how atomic dephasing - ubiquitous in real cavity- and circuit-QED devices - affects this criticality remains unknown. We study the anisotropic open Rabi model under cavity decay, spontaneous emission, and atomic dephasing together. We show that when spontaneous emission stabilizes a long-lived metastable superradiant phase, atomic dephasing actively competes with it - eroding its coherence and shortening the lifetime. This direct competition reveals that a dissipation channel's microscopic character, not its strength, controls its nonequilibrium criticality - a distinction directly tunable via independent spontaneous-emission and dephasing rates in circuit-QED and trapped-ion platforms.

Understanding how thermal fluctuations modify or suppress quantum-enhanced sensing is a central problem in quantum metrology. Closely related questions arise in quantum thermodynamics, particularly regarding the relation between the work induced by a signal and the information acquired by a sensor. Here, we establish general relations among the sensitivity of thermal quantum states, as quantified by different quantum Fisher information metrics, their temperature dependence, and the work induced by a unitary signal. We further show that, at high temperature, all monotone QFI metrics coincide to leading order with a universal quantity that can be expressed as the variance of a simple observable and itself defines a lesser-known QFI metric. This emergent uniqueness is reminiscent of the uniqueness of classical Fisher information in information geometry. In continuous-variable systems, the infinite-temperature limit is finite and generically non-zero for quadratic Gaussian signals, while it diverges for higher-degree signals. Remarkably, for any purely quadratic signal generator, the infinite-temperature QFI is at least twice the zero-temperature SLD QFI or, equivalently, at least eight times the ground-state variance of the generator. Consequently, the Cramér--Rao lower bound on the estimator variance is reduced by at least a factor of two. We illustrate these results using harmonic chains of bosonic modes relevant to trapped-ion platforms and quantum field-theoretic models.

Precision metrology, quantum information, and quantum-controlled chemistry studies all have many implementations in trapped ion systems that require a precise understanding of the motional dynamics of ions. Between the well-studied Coulomb-crystal and gaseous regimes lies the intermediate liquid-like regime whose properties and boundaries have largely eluded experimental investigation. Here, we track the entire liquid-to-gas transition process by leveraging direct velocity measurements using our newly developed ion-trap with integrated velocity map imaging. We demonstrate that the colder the ensemble, the more viscous the ion motion becomes until radial localization emerges, which marks the onset of the liquid regime at a temperature warmer than commonly assigned. At even hotter temperatures, we observe an abrupt change in the heating rate power-law, which indicates the maximum density threshold. The enhanced sensitivity of direct velocity measurements reveals the full transition process from a fluid with short-range order to a weakly-interacting gas.

The laboratory-frame anti-Jaynes--Cummings (AJC) interaction retains a residual detuning $2fλ$ that is absent from the rotating-frame model. We map two proposed remedies---a Kerr shift $χ(\hat a^\dagger\hat a)^2$ and collective Dicke coupling of $N$ two-level emitters---for a squeezed vacuum on that ladder ($r=1$, $\langle n\rangle=\sinh^2 r\simeq 1.38$). All quoted contrasts are the amplitude of the first turning point of the atomic ground-state population, which coincides with the two-level formula $\mathcal{C}=1/[1+(2f+χ)^2]$ at $r=0$ to $10^{-9}$. Three results follow. (i)~A single Kerr strength never restores unit contrast at $r=1$; the $r=0$ $n$-dependent shift $χ(2n+1)$ cannot cancel $2fλ$ on every occupied Fock component. (ii)~The exact $r=1$ contrast at $χ=0$ is not reproduced by an incoherent sum $\sum_n P_n(r)\,\mathcal{C}_n$ built from the $r=0$ two-level formula; pointwise deviations are several tenths. (iii)~Collective coupling raises the contrast systematically. At $f=5$ one finds $\mathcal{C}=0.140$ ($N=1$) and $\mathcal{C}=0.575$ ($N=8$), above the unsqueezed value $8/[8+(2f)^2]=0.074$. The $N=16$ point at this $f$ remains truncation-limited and is not quoted to three digits. The same $N\sim(2f)^2$ estimate for $\mathcal{C}=1/2$ places trapped-ion values $f\sim 10^{2}$--$10^{3}$ outside the present construction. The relevant platform is ultrastrong circuit QED with $f\sim 1$--$10$. The calculation is a numerical control landscape, not a new solvable limit.

Change detection in synthetic aperture radar (SAR) and interferometric synthetic aperture radar (InSAR) underpins disaster response, infrastructure monitoring and land-use enforcement. Detection is limited by the background estimator, which conventionally forms a conditional expectation directly from observed pixel statistics and degrades where those statistics are sparse, including the regime produced by the heavy-tailed marginals of sub-meter-resolution radars. In this work, we integrate state-of-the-art satellite imagery with quantum machine learning on IonQ trapped-ion-based quantum processors. By replacing the empirical conditional with a quantum circuit Born machine (QCBM)-sampled generative model in Copula space, we substantially improve change detection on sparse real-world images. On Capella Space satellite image acquisitions, the generative estimator matches conventional methods when the observed statistics are adequate, and substantially outperforms them when they are not. Executing the trained model on IonQ trapped-ion based hardware reproduces the results of the ideal and noisy simulations and demonstrates up to par, or even better, performance with the classical state-of-the-art methods. For a SAR dataset of an airport, QPU circuit evaluations for both training and inference achieved a maximized filtered F1 score of 0.32, compared with 0.16 and 0.24 for the two classical baselines. For an InSAR dataset of a volcanic lava flow, all three methods reached a maximum filtered F1 of approximately 0.66. These experiments demonstrate the feasibility of executing a QCBM-based background estimator on trapped-ion hardware. We further demonstrate that the QCBM method successfully extends to interferometric coherence data, achieving performance comparable to classical approaches.

We investigate how Kerr nonlinearity modifies quantum synchronization in a squeezed quantum van der Pol oscillator. We show that the Kerr interaction produces an amplitude-dependent frequency shift that drives a saddle-node bifurcation, transforming the classical phase-space structure from bistable to monostable dynamics. In the quantum regime, this transition manifests as systematic frequency pulling and spectral broadening, while the steady-state Wigner function reveals a continuous correspondence between the quantum state and the semiclassical attractor despite finite quantum fluctuations. By constructing global synchronization phase diagrams in the squeezing--Kerr parameter space, we uncover a remarkably linear dependence of the critical squeezing strength required to maintain phase locking on the Kerr nonlinearity. We further demonstrate that the synchronization boundary does not coincide with the crossover between super- and sub-Poissonian photon statistics, showing that synchronization and photon-number statistics characterize distinct aspects of the quantum steady state. These results provide quantitative design principles for controlling quantum synchronization through Kerr nonlinearity, with potential relevance to trapped-ion, superconducting-circuit, and optomechanical platforms.

Universal quantum computation with continuous variables cannot be attained solely with a set of Gaussian operations, it requires the addition of a non-Gaussian element, at least of third order in the quadrature operators, such as the cubic phase state. In this work, we present a method to generate a quantum state in the vibrational mode of a trapped ion that exhibits characteristics compatible with the cubic phase state, such as the distinctive oscillating pattern in its Wigner function. This state emerges from the nonlinear Jaynes-Cummings interaction native to the trapped-ion model, and under the assumption of an initial coherent vibrational state with a large occupation number. Consequently, the evolved vibrational state approximates the cubic phase state with high fidelity, and we use the variance of a nonlinear combination of the quadratures to characterize it. Finally, we provide an analytical expression for its cubicity that shows the high performance of the approximate vibrational cubic phase state.

Maximizing gas throughput in transmission networks under hydraulic and operational constraints is a combinatorial problem whose complexity grows exponentially with network size, making it computationally intensive to solve exactly. This paper addresses the graph-based optimization problem by optimizing nodal-pressure assignments under the Panhandle-B hydraulic equation. By framing the problem as a search over discretized nodal-pressure assignments coupled with a cost Hamiltonian that encodes both the delivery objective and physical-constraint penalties, we establish a unified formulation suitable for the Quantum Approximate Optimization Algorithm (QAOA). The mathematical model is adapted to a Quadratic Unconstrained Binary Optimization (QUBO) formulation and implemented using the Classiq quantum software platform. In simulator-based experiments, QAOA recovered the maximum-throughput valid operating point, consistent with classical exhaustive evaluation and classical hydraulic simulation reference solutions. A distinctive contribution of this work is the end-to-end execution of a reduced problem instance on the IonQ Forte-1 trapped-ion quantum processor. Remarkably, the hardware implementation used only $p=2$ QAOA layers, substantially fewer than the $p=30$ layers used in the simulator-based study. Despite this significant reduction in circuit depth, the QPU produced physically valid and interpretable candidate solutions that bracketed the continuous classical optimum, with each located within one pressure-discretization step of it. These results demonstrate that meaningful gas-network optimization behavior can be obtained using considerably shallower QAOA circuits than initially expected and provide an end-to-end proof of concept for near-term quantum-assisted gas-network optimization.

We investigate the dynamics of a quadratically coupled system under the influence of an external drive applied to the second oscillator, where the coupling facilitates a high-order synchronization with phase-locking emerging in the form of 2:1 between the oscillators. Our analysis reveals a synchronization blockade in the first oscillator, characterized by the complete suppression of conventional 1:1 phase-locking with the drive. In contrast, we observe that the directly driven second oscillator synchronizes with the drive, showing 1:1 phase-locking but notably at second harmonic frequency. A classical mean-field analysis of the corresponding equations of motion reproduces this asymmetric phase-locking geometry which demonstrates that the phase-locking structure itself can be understood from the nonlinear classical dynamics. The quantum analysis, however, reveals the microscopic origin of the synchronization blockade. Furthermore, we show that the system exhibits mutual synchronization when both the oscillators satisfies the resonance condition, enabling coherent energy exchange facilitated by nonlinear quadratic coupling. The mutual synchronization shows synchronized regimes and also subtle suppression of synchronized regimes near resonance occurring due to spectral splitting of the energy states. Using perturbation analysis of the master equation within the low excitation subspace, we analyze steady-state phase distribution and synchronization measures, supported by population statistics and spectral responses. We also propose possible experimental realizations in trapped-ions and optomechanical setups. These findings highlight the crucial role of quadratic coupling in enabling nonclassical synchronization phenomena, offering deeper insights for quantum control strategies and the development of quantum information platforms.

Real-time quantum error correction requires classical decoders to process growing syndrome workloads with low and predictable latency. For quantum low-density parity-check (qLDPC) codes, iterative belief propagation (BP) repeatedly updates messages over sparse Tanner graphs, creating substantial memory-access and data-movement demands. We map normalized Min-Sum BP decoding of the [[144,12,12]] Bivariate Bicycle qLDPC code onto a DPU-based Processing-in-Memory (PIM) architecture. Within each DPU, 11 tasklets cooperatively decode one syndrome, while multiple DPUs process independent syndrome instances in parallel. Using uPIMulator and a data-qubit Pauli error model with ideal syndrome measurements, we compare throughput, per-syndrome processing time, logical error rate (LER), and single-syndrome tail latency against a 16-logical-CPU baseline. At a component-wise physical error probability of p=0.001 and one BP iteration, the projected aggregate kernel throughput of 2,560 DPUs reaches 1.071 x 10^7 decodes/s, compared with 1.22 x 10^6 decodes/s for the CPU, an 8.8x improvement. From two iterations onward, the measured LER remains below the physical error probability for every evaluated value of p. For one to five iterations, the maximum sampled serialized X+Z DPU compute latency remains below the 1 ms decoder-side reference for trapped-ion QEC, reaching approximately 0.873 ms at five iterations. These results show that near-memory processing can provide high aggregate throughput and sub-millisecond compute latency for qLDPC BP decoding under the evaluated conditions.

Spin-boson models are paradigmatic examples of open quantum systems and serve as the theoretical paradigm for current quantum computers based on single-ion trap technology. Despite their ubiquity, a complete spectral diagonalization of these models remains an open problem, except in highly singular regimes. This paper establishes a rigorous framework for the approximate diagonalization of generalized spin-boson systems. Our approach is inspired by the Brockett-Wegner double-commutator flow, which is a non-linear differential equation governing the evolution of (here unbounded) operators. Unlike relatively recent applications of this flow to quadratic Hamiltonians in quantum field theory, it does not close in the spin-boson context. We overcome this fundamental obstruction by performing a detailed analysis of the resulting non-closed algebraic structure, allowing us to explicitly bound the higher-order error term with respect to the spin-boson coupling strength. Consequently, this work provides the first mathematically rigorous justification for several heuristic diagonalization techniques widely employed in the theoretical physics literature for small-coupling regimes, in the simplest non-trivial cases. More broadly, our framework renders a flow-based algorithm feasible for systematic higher-order diagonalization and self-energy renormalization. This strategy is conceptually akin to multi-scale analysis, or, much more recently, to the iterative, local Lie-Schwinger block-diagonalization method by Fröhlich and Pizzo.

Quantum federated learning enables collaborative model training across quantum devices without sharing raw data, and it faces the data and hardware heterogeneity inherent to noisy quantum devices. Utilizing the quantum geometric tensor is a natural remedy, yet pure-state approaches and diagonal approximations discard the correlations that encode parameter incompatibility. To address this, we extend the parameter-space geometry to the mixed states that noisy clients actually prepare. The real part of the resulting mixed-state geometric tensor is the Bures metric, which measures how fast the physical state changes under parameter variation, and the imaginary part is the mean Uhlmann curvature, which quantifies the incompatibility of estimating multiple parameters simultaneously. Accordingly, we employ the Bures metric as a local preconditioner and use the mean Uhlmann curvature to develop an achievable-precision aggregation rule that dynamically down-weights unreliable clients. Furthermore, we establish theoretical guarantees by proving a convergence theorem and a variance-dominance proposition. Empirical evaluations on a trapped-ion quantum emulator demonstrate that the proposed method maintains high accuracy across diverse device-heterogeneity conditions and outperforms standard federated averaging, whose accuracy degrades under strong noise.

We show a finite-time Otto-like quantum thermodynamic cycle that preserves the adiabatic population structure of a time-dependent harmonic oscillator in the non-quasi-static regime. In the conventional energy representation, finite-rate driving induces non-adiabatic population redistribution and leaves residual excitations after the Hamiltonian has returned to its initial value. We show that this difficulty can be avoided by formulating the dynamics in the Lewis-Riesenfeld invariant representation, without modifying the physical Hamiltonian through auxiliary counterdiabatic driving. For a parametric Mathieu protocol, quantum inertia produces a mismatch between the spatial width of the working mode and its transient dressed energy scale. We propose an experimental implementation of this scheme in a trapped-ion Paul trap using stimulated Raman interactions, with independent control of the laser detuning and beam intersection angle. This provides a finite-time implementation in which the invariant population structure is preserved while the physical trap frequency evolves non-quasi-statically. Our results establish a clear distinction between adiabatic operation and quasi-static driving, providing a route toward finite-time quantum thermal cycles that retain the adiabatic energy structure without requiring the quasi-static limit.

Plasma rotation together with corrugation of magnetic field can result in coupling acoustic waves with different azimuthal wavenumbers and formation of eigenmodes with discrete frequency spectrum and zero longitudinal group velocity in a helical magnetic mirror. Such eigenmodes can be destabilized by plasma rotation as well as resonant interaction with trapped ions. Equations describing these waves in the linear approximation are derived and results of numerical solving the equations are discussed. Probably these eigenmodes may drive anomalous ions scattering which is needed for effective suppressing flow of rarefied plasma through a helical mirror.

End-to-end quantum-hardware scores need not transfer across workloads, compilations, or execution times. We specify a compilation-explicit screen-and-stress profile whose opening diagnostic is round-trip state echo (RTSE): prepare one of four tetrahedral qubit states at a route root, move it out and back by swaps, apply inverse preparation at the root, and record zero. An execution snapshot means a dated submitted task batch together with its captured capability document where available, not a certified calibration epoch. On sparse superconducting hardware, a byte-identical communication rerun changed route-level contrasts although the aggregate RTSE estimates differed by only 0.00125. In a separate prospectively frozen two-window length study, RTSE and the remote-inverse do-nothing predecessor's root marginal both fell from length 2 to length 10; the prespecified interaction did not support superior RTSE retention. The mean selected-output return probability across 64 deletion-recovery cells changed from 0.738 to 0.624 between IQM execution snapshots. On a trapped-ion service advertising all-to-all connectivity among five submitted virtual wires, recovery was 0.911 and 0.923 in two windows, exceeding the frozen two-thirds reference; recovery-minus-adjoint-control differences were 0.446 and 0.443. These are execution-workload diagnostics, not coding-gain, error-suppression, physical-loss, fault-tolerance, or architecture-ranking claims. The results support assessment indexed by workload, placement or virtual-wire contract, compilation, architecture, and execution snapshot.

We ask how passive conducting geometry determines the spatial structure of electric-field noise seen by trapped ions. From a boundary-potential covariance and the Dirichlet Green function we construct the $N$-ion electric-field cross-spectral matrix and its blockwise motional Kossakowski generator. In a parallel slab, billiard unfolding turns the electrostatic response into a return-depth measure and yields an exact return-pair functional for arbitrary stationary surface spectra. For every finite equal-height ion array, the passive cover increases the normal-field covariance matrix in the positive-semidefinite ordering and decreases the tangential-field covariance matrix in the same ordering: all collective normal-field coordinates acquire more absolute noise, while all collective tangential coordinates acquire less. At $h=2d$ the local-noise single-ion ratios are exactly $ζ(3)$ and $η(3)$. Diagonalizing the equal-frequency covariance identifies collective environmental noise eigenchannels and a geometry-dependent noise rank; within a degenerate frequency block these become the Lindblad jump channels. In a ten-ion example, closing the cover to $h=2d$ lowers the participation rank from 5.61 to 5.11 while increasing the leading channel's share from 23.7% to 28.6%; a primitive Mølmer-Sørensen calculation shows how the projected covariance sets the weak-heating gate exposure. Beyond parallel walls, specular paths emerge as large-$q_z$ saddles of the screened boundary operator. Across 16 curved covers, the fitted electrostatic decay exponent correlates at 0.9991 with the independently computed shortest specular excess length, while separate tests resolve focusing and competing saddles.

Extreme-ultraviolet (XUV) spectroscopy represents an important new direction in precision physics, with potential applications ranging from the metrology of fundamental constants to tests of physics beyond the Standard Model. However, the application of quantum control methods for precision spectroscopy remains an open challenge in the XUV range. Here we present a novel quantum logic (QL) spectroscopy method for precision spectroscopy of weak XUV transitions, and numerically validate its feasibility for the $1S-2S$ transition at 40.81\,eV in singly-ionized helium (He$^{+}$). We propose a scheme based on a single He$^{+}$ ion co-trapped with a Be$^{+}$ ion in a Paul trap, and He$^{+}$ excitation with pairs of frequency-comb (FC) laser pulses upconverted to the XUV via High-Harmonic Generation (HHG). We investigate a nondestructive QL scheme to detect $1S-2S$ excitation, and compare its performance with a destructive readout based on state-selective ionization. Phase coherence of the XUV light is modelled and an optical cavity is used to filter the FC pulses prior to HHG. We model the motional excitation dynamics of trapped ions outside the Lamb-Dicke regime, and numerically validate a scheme we proposed in \cite{Grundeman} to cancel the first-order Doppler broadening and the recoil shift by synchronizing the ion's secular period with the time delay between the two excitation pulses. We show that precision spectroscopy of the $1S-2S$ transition in He$^{+}$ at the 10 kHz level is feasible, for improved tests of quantum electrodynamics (QED), a measurement of the Rydberg constant $R_{\infty}$ independent of hydrogen measurements, or an improved determination of the alpha particle and helion charge radii. The proposed method may also be applied to XUV spectroscopy of other ions outside the Lamb-Dicke regime.

We experimentally demonstrate continuous-angle logical $Z$ rotations in the $[[7,1,3]]$ Steane code on the IonQ Forte trapped-ion processor. A round of the protocol applies a transversal physical $Z$ rotation by $θ$, followed by Steane syndrome extraction and decoding, which induces a syndrome-dependent logical $Z$ rotation. We analytically derive the effect of dephasing noise on the logical rotation angle and logical dephasing rate. Using logical Ramsey interferometry, we observe coherent syndrome-dependent logical rotations from a single round of the protocol. We find that the logical channel reconstructed from process tomography is a noisy logical $Z$ rotation well explained by a dephasing model. We further implement a two-round protocol applying physical rotations $+θ$ and $-θ$, and observe cancellation of the total logical angle with low logical dephasing for repeated trivial syndromes. This constitutes a proof-of-principle demonstration of continuously tunable non-Clifford logical gates by transversal rotations and standard error correction in a small quantum code.

When a charged particle in a Paul trap is displaced from the node of the AC trapping field, excess micromotion arises as an undesired effect. Excess micromotion heats the particle, limits the precision with which the particle can be localised, and acts as a decoherence channel in quantum mechanical experiments. However, thus far there is no standard procedure for micromotion compensation with mesoscopic particles. Here, we experimentally demonstrate three different methods for minimizing the micromotion of a nanoparticle in a linear Paul trap along three axes. The most precise method allows us to nullify the stray field to within 2.9 V/m, which is comparable to reported values in trapped-ion experiments.

Noisy intermediate-scale quantum computers are constrained by circuit depth, while product-formula simulation of spin systems leads to narrow and deep circuits. Here we introduce a fan-out-based gadget compiler that trades circuit depth for width in simulations of Heisenberg-type nuclear magnetic resonance (NMR) Hamiltonians. Each logical spin is encoded into a small repetition-code register sized by its interaction degree, so that all pairwise interactions of a given Pauli type execute in parallel after a logarithmic-depth CNOT fan-out, and the redundant registers provide error detection for post-selection at no additional algorithmic overhead. The central result is a fixed-protocol resource comparison of the two compilations, transpiled to heavy-hex superconducting and all-to-all trapped-ion targets across a set of NMR spin systems. For interaction graphs with a high-degree hub the volume-optimal schedule halves the two-qubit depth and reduces the volume 1.7-fold for the 13-spin demonstration, which on heavy-hex also lowers the two-qubit gate count, and the depth reduction rises to 2.5-fold on all-to-all for the highest-degree molecule studied. On all-to-all the two-qubit gate count rises for every system, so the volume reduction is a benefit on depth-limited hardware. The gain grows with the degree inhomogeneity of the interaction graph and vanishes for dense uniform graphs, where the optimum is the sequential circuit. We simulate the zero-field NMR spectrum of tetramethylsilane, a 13-spin star system. Under a noise model scaled from a published present-day processor calibration, the shallower gadget circuits match or surpass the sequential compilation only after post-selection on their built-in error detection, once error rates improve by one to one and a half orders of magnitude. We verify the spectra against an independent classical computation.

We investigate the self-assembly of polar molecules around a single ion immersed in an ultracold, dilute two-dimensional molecular gas. The ion aligns and attracts the molecules through charge-dipole interactions, producing a strong electrostrictive accumulation around the impurity, while intermolecular repulsion limits further densification and favors spatially extended configurations. By combining global optimization with diffusion Monte Carlo, we calculate the evaporation energy as a function of the number of molecules bound to the ion. In contrast to conventional charged and van der Waals clusters, the evaporation energy exhibits a plateau-like dependence on cluster size, reflecting the sequential formation of concentric molecular rings. These structures are governed by the topology of the ion's electric field and by the competition between attractive ion-molecule interactions, repulsive intra-ring interactions, and attractive correlations between neighboring rings, rather than by conventional coordination or icosahedral packing. In the weak-interaction regime, the resulting structures form extended mesoscopic molecular ions, whereas stronger interactions produce increasingly rigid, crystal-like molecular rings. We further analyze their stability against thermal perturbations and the time-dependent ion trap and find that a broad range of clusters remain stable under experimentally relevant conditions. The intermolecular repulsion and dipolar geometry also suppress close-range ion-molecule encounters, suggesting an intrinsic shielding mechanism. Our results establish ion-bound polar-molecule clusters as a distinct class of mesoscopic molecular ions and open a route to studying charged impurities in quantum baths with anisotropic interactions.

Fractionalizing a quantum two-level system is usually associated with encodings based on pairs of Majorana fermions---an operational fractionalization. We show an alternative algebraic fractionalization by embedding Székely's classical ``half-coin'' into a non-Hermitian Krein space. The coefficients of $(q+pz)^{1/2}$ define a signed sequence and a normalized, non-Hermitian biorthogonal operator describing a biorthogonal half-qubit. We prove that two such objects fuse into an arbitrary pure qubit through the signed Vandermonde convolution that the collective $N\ge2$ vectors are null in Krein space. $L_1$ norm of the half-qubit follows in closed form, $\lVert p\rVert_1 = 2\sqrt{q}-\sqrt{q-p}$. Its $L_1$ norm increases monotonically with the bias and attains its supremum $\sqrt{2}$ precisely at the unbiased point $p=q=1/2$. Interestingly, we identify two structural results as follows. First, number parity and the $η$-metric generate a distinguished commuting $\mathbb Z_2\times\mathbb Z_2$ subgroup. Second, we find the $η$-metric obstructs any local $η$-self-adjoint partner of the parity, so a half-qubit carries a $\mathbb{Z}_2$ observable but no local $SU(2)$. The full Pauli algebra emerges only upon fusion. We then show that the construction survives truncation of the Fock basis: the fused qubit is exact at every cutoff, and the Vandermonde cancellation is visible in sign-weighted photon-number statistics, and can be tested using existing cavity and trapped-ion state-synthesis methods. Finally, we generalize this algebraic fractionalization to a $1/n$-qubit, which can be achieved by replacing the square root with an $n$th root.

We investigate how nonequilibrium quantum initial states can reduce the finite-time thermodynamic cost of Landauer erasure. Considering a general finite-dimensional quantum memory coupled to a thermal reservoir via a Davies generator, we show that the dissipated heat at a fixed operational erasure fidelity is largely controlled by the overlap of the initial state with the slowest Liouvillian relaxation mode. We derive a modified finite-time Landauer bound in which the excess dissipation above the quasistatic limit scales quadratically with this slow mode projection, and we prove a sufficient Mpemba Landauer condition under which a hotter state can erase faster and dissipate less heat than a colder preparation, without violating Landauer's principle. A minimal qutrit model illustrates these quantum Mpemba speedups and reveals broad parameter regimes where coherence and Hamiltonian-induced modes conspire to suppress finite-time entropy production. We further identify practical control knobs, including temperature tuning, coherence engineering, and Hamiltonian shaping of Liouvillian spectra, which enable Mpemba-enhanced erasure to be directly tested on platforms such as superconducting circuits, trapped ions, semiconductor quantum dots, and solid-state spins.

Can a high-quality quantum gate be certified when uncharacterized state-preparation and measurement errors are dominant? Can this be achieved with low experimental overhead? Here, we introduce a sound black-box certification protocol for a single-qubit gate based on a small set of fixed, deterministic sequences. From the data, the protocol derives finite-sample bounds on the gate's rotation eigenvalue, a gauge-invariant property. Its phase reveals the accuracy of the rotation angle, while its modulus quantifies the loss of coherence under repeated gate applications. We implement the protocol on a $^{40}\mathrm{Ca}^{+}$ trapped-ion processor and certify the $\sqrt{\mathrm{X}}$-gate rotation eigenvalue using $22\,000$ circuit executions, and demonstrate the robustness of certification to state-preparation and measurement errors by deliberately degrading the readout. Finally, we prove that these spectral constraints imply, up to a physically meaningful unitary change of basis, a rigorous average gate-fidelity lower bound for every time-independent qubit model compatible with the data. In both readout settings, the spectral bounds yield the same fidelity certificate of $99.94(3)\%$ with $99\%$ confidence. Our results establish a new standard for quantum-gate certification by combining soundness and experimental efficiency without requiring trusted reference operations, randomized circuits, or model fitting.

The trapped-ion optical-metastable-ground ($\textit{omg}$) architecture for quantum processors promises the full functionality of two-species experiments, including sympathetic cooling and non-destructive ancilla readout, without the corresponding hardware overhead. We confirm that we can cool a global motional mode of a mixed metastable-ground state Coulomb crystal to the motional ground state via dissipative operations on the ground ($\textit{g}$) qubit without disturbing coherence of the metastable ($\textit{m}$) qubit. This enables quantum logic spectroscopy to non-destructively readout the state of the $\textit{m}$ qubit using fluorescence detection of the $\textit{g}$ qubit. Extensions of these demonstrations to larger system sizes should enable the mitigation of motional heating after ion shuttling and syndrome extraction for quantum error correction, both crucial primitives for future fault-tolerant quantum computers based on trapped ions.

We present an ion-trap platform on borosilicate glass with an integrated femtosecond-laser-written waveguide for on-chip light delivery. The optical layer is physically separated from the electrode substrate and bonded atop the trap, remaining compatible with silicon-based integration. We engineer single-mode low-loss guidance at 729 nm with tunable mode-field diameter and achieve low-loss curved waveguides down to a radius of curvature of 6 mm. We also extend single-mode operation to a wavelength of 405 nm. The fabrication process is compatible with the industrial fabrication of a single-metal-layer surface-electrode trap, including active fiber alignment and bonding. We validate the platform in a cryogenic trapped-ion system with $^{40}$Ca$^+$, demonstrating trapping, shuttling the ion to a zone in front of the waveguide, and coherent operations driven by 729 nm light delivered through the integrated waveguide. We characterize the effect of the exposed dielectric on the ion and measure stray electric fields that show slow drift at a timescale of hours. The architecture is compatible with hybrid micro-optics (e.g. pick-and-place lenses) to realize single ion addressing and provides a robust, scalable route to integrated light delivery for trapped-ion devices.

Certifying genuine multipartite entanglement in quantum systems can require a number of measurements that grows exponentially with the system size. Here we introduce a criterion based on correlation-tensor subsector lengths restricted to local measurement planes and show that it can be evaluated using partially randomized measurements without an explicit exponential dependence on the number of qubits. We derive the corresponding bounds for $k$-separable states and illustrate the criterion using representative families of multipartite entangled states. Finally, we demonstrate the practical applicability of the method on an ion-trap quantum computer by certifying genuine five-partite entanglement.

Generating entanglement rapidly and reliably is essential for quantum information processing, communication, and metrology. Dissipative preparation is attractive because engineered reservoirs robustly drive a system toward an entangled target, yet relaxation can carry a substantial time cost. Here we formulate the entanglement Mpemba effect, whereby an initially less entangled state overtakes a more entangled state under the same open-system dynamics. This effect turns initial-state engineering into a route for faster preparation without altering the dissipative protocol. We derive a general criterion for the reversal from the relaxation spectrum, applicable even when entanglement evolves nonmonotonically. A reversal of deterministic local operations and classical communication (LOCC)-reachability preorder provides a measure-independent certificate of reversed entanglement order. Exactly solvable models show that initial-state selection can substantially shorten the time required to reach high entanglement. We further propose an experimentally relevant trapped-ion protocol that can realize the entanglement Mpemba effect.

Deviations from both the ideal linear Paul trap (LPT) geometry as well as the ideal quadrupole driving scheme introduce imperfections to ion trapping potentials. We investigate the effects of these imperfections in a LPT operated in a conventional dipole-drive configuration. We demonstrate the trapping of the Li$^+$ ions along the axial direction with zero and negative end-cap voltages. This occurs due to the modified axial $a-q$ space resulting from radial-to-axial coupling of the electric field. The dipole drive configuration lifts the degeneracy of the radial trapping potentials, resulting in unequal radial secular frequencies, and this is demonstrated experimentally. The combined effects of dipole drive and trap dimensions are summarized in a two-dimensional map that quantifies deviations from ideal behaviour. Based on this map, we propose a geometric modification that significantly reduces radial-to-axial coupling of the potential.

We compare different measures for photon localization in terms of two-dimensional Gaussian wave packets. We find that all measures start to coalesce if the wave packet has evolved for times which are larger than a few times the inverse momentum-space width of the package. However, the Landau-Peierls wave function yields the largest positive offset <r>-ct>0 while the scalar Fourier transform of the wave packet yields the smallest offset and converges towards <r>-ct=0 fastest. We also discuss local detection of photons through a model detector consisting of ions in ion traps. The position-dependent detection probabilities are inferred from the scattering matrix. We find that the local detection probability for photons can be expressed in terms of three of the proposed localization measures, viz. the Landau-Peierls wave function, the energy wave function, and the Hawton density. Those three porposals also remain close throughout the time evolution of the single-photon wave packet.

Whether a quantum Mpemba effect occurs can depend on how distance from stationarity is measured. We show that agreement across normalized operator-convex Petz divergences is decided by a one-parameter $χ^2$ profile. Its sign fixes the common order, alternating sign margins guarantee repeated crossings, and finite dimension yields a polynomial positivity test. The same profile explains diagnostic-independent late-time order for a simple real slow mode and isolates coherence as the local source of diagnostic dependence. In a trapped-ion qutrit ideal model, the reported preparation gives diagnostic-selective crossings, while a nearby preparation is a floating-point candidate for two family-wide reversals. The framework turns diagnostic robustness into a tractable control problem.

We propose a fast laser pulse sequence for the generation of non-thermal Fock state mixtures of the motion of a trapped ion, targeted at displacement metrology beyond the standard quantum limit. Using a polaron-frame description of the ion-laser interaction, we identify a resonant operating point-zero detuning and a Rabi frequency matching the trap frequency-at which selective population trapping survives strong driving, enabling preparation speeds beyond the weak-driving limit of previous protocols without requiring ground-state cooling. We trace the residual infidelity at large Lamb-Dicke parameter $η$ to a single coherent process, the counter-rotating blue-sideband term neglected in the rotating-wave approximation, and show that it is suppressed by two routine calibrations: a percent-level refocusing of the pulse duration and a small compensating Bloch-Siegert detuning. Numerical simulations of the full sequence show that this refinement keeps the preparation error at or below the $10\%$ level up to $η\approx0.5$ and restores the displacement-sensing Fisher information that the uncorrected protocol loses at strong coupling, recovering up to 9 dB relative to the nominal sequence.

Trapped-ion quantum computers rely on shuttling compilers, which cast an input algorithm into a sequence of ion-qubit movements within a given architecture. We present the first study in which a single frontier large language model (LLM), Claude Opus 4.7, generates and iteratively refines the full Python code of shuttling compilers from written specifications. We start with a compiler for (i) a linear segmented trap, extend it to (ii) a trap with junctions, and finally achieve efficient compilation for (iii) a broad class of connected trap graphs. The compilers for the more general cases are seeded with code from the previous ones. We benchmark the LLM-generated compilers against state-of-the-art hand-crafted ones using a common suite of quantum circuits. The number of shuttling timesteps is reduced by up to 76% for (i) and up to 39% for (ii). For the broad case (iii) of freely connected architectures, we find large variations in the required number of shuttling timesteps, depending on the connectivity. A densely connected, junction-rich architecture yields an order-of-magnitude reduction in shuttling timesteps compared to a corridor-like one. Repeating the complete generation and evaluation with a second frontier LLM, Claude Fable 5, reproduces these findings, with the Fable 5 compilers surpassing the hand-crafted ones more often on the largest circuits. Our results show that an unmodified frontier LLM can produce working, correct, and competitive shuttling compilers without additional manual algorithmic engineering, thus reducing the development time for new architectures from several months to a few days.

Trapped ions provide a high-fidelity platform for quantum information processing, yet delivery of multiple, distinct wavelengths across large networks of interaction zones remains a bottleneck. Conventional free-space light delivery lacks scalability, while on-chip grating couplers suffer from narrow operational bandwidth that increases circuit footprint and optical interfacing complexity. Here we show a broadband photonic integrated circuit capable of addressing individual ions. The circuit combines a planar waveguide lens with a micromirror fabricated using two-photon polymerization at wafer scale. This implementation can address three individual ions from $λ$ = 405 - 880 nm with -27 dB average intensity crosstalk at $5\,μ\mathrm{m}$ pitch. We trap $^{40}\mathrm{Ca}^{+}$ and $^{138}\mathrm{Ba}^{+}$ ions above such devices, characterize optical crosstalk with barium ions, and demonstrate individual repumping of calcium ions. This monolithic photonic architecture brings broadband addressing in an on-chip modality to trapped-ion technology. More generally, integrating additive manufacturing into quantum devices is poised to unlock expanded design space for implementing novel quantum architectures.

Multi-wavelength optical control is a scaling bottleneck for trapped-ion hardware: separate surface emitters consume trap area, interrupt the electrode plane, and expose charge-sensitive dielectric near the ions. Here, a vertically stacked silicon-nitride bilayer routes the $^{40}\text{Ca}^+$ qubit and repump fields-729.4 and 854.2 nm-through one electrode aperture and focuses them $70~μ\text{m}$ above the chip. Three-dimensional FDTDX predicts $0.10~μ\text{m}$ color separation and near-diffraction-limited spots along the ion-chain axis. Multi-level depth-allocation apodization enables this architecture by encoding the coupling envelope in discrete etch levels rather than sub-resolution linewidths. Every feature satisfies a strict $\ge 125\text{ nm}$ deep-UV rule using two etch depths per film. Full-3D Ansys Lumerical simulations independently corroborate directionality, spot size, and repump efficiency. At a common 50 nm reporting grid, the DUV-compatible device matches a 63 nm electron-beam design on the qubit channel (focusing efficiency 0.286 vs 0.288; crosstalk -24.0 vs -24.3 dB). Vertical integration therefore converts wavelength scaling from a lateral-footprint penalty into a layer-allocation problem, providing a pathway toward compact multi-color photonic interfaces for trapped ions and other chip-addressed quantum emitters.

Conventional laser control schemes for cooling and gate operation of trapped ions are limited to the regime of weak laser intensities and small Lamb-Dicke parameters. To overcome this limitation, we present the concept of dark polarons: spatially extended states of pseudospin polarization that are fully decoupled from a lambda laser configuration. In this picture, all high-order Lamb-Dicke terms collapse into a single linear coupling independent of laser intensity. We apply it to definitively elucidate the reasons behind cooling rate limitations observed in recent experimental implementations of electromagnetically induced transparency with high-intensity lasers.

We discuss the experimental realization of the rotating radio-frequency (rrf) trap, proposed by Hasegawa and Bollinger [Phys. Rev. A 72, 043403 (2005)]. Compared to a traditional linear rf (lrf) Paul trap, the rrf trap is a closer analogy to the popular mechanical lecture demonstration for a Paul trap. In an ion trap with reslistic, non-ideal electrode geometry, the rrf trap averages over angular variations in the effective potential. This averaging provides more uniform confinement and reduces ion loss at equal confinement strength compared with the lrf trap. This feature makes the rrf trap configuration advantageous for precision metrology application, such as electron electric dipole moment (eEDM) measurements.

Formation dynamics and stability starting from various phase space vortex (PSV) or Bernstein-Greene-Kruskal (BGK) structures i.e electron acoustic wave (EAW), Langmuir (LAN) waves is investigated in the presence of a quasi-stationary ion scale (QSIS) inhomogeneity using high resolution Vlasov-Poisson simulations with VPPM-OMP 1.0 solver. In a one dimensional, collisionless, periodic, unmagnetized plasma with kinetic ions and kinetic electrons, we first create a QSIS inhomogeneity using low amplitude electric field drive at ion acoustic (IA) frequency with k eq = mk min [where m = 2 is the mode number, k min corresponds to the longest scale in the system]. While creating QSIS inhomogeneity, we have demonstrated the existence of ion trapped particle instability (ITPI) which saturates as the amplitude of sideband modes become comparable to that of the primary nonlinear mode (quite analogous to the trapped particle instability in large amplitude electron plasma waves). Also, mode transition from m = 2 to m = 1 is observed during relaxation period due to the energy cascading process. Finally, an electron acoustic (EA) perturbation of scale k p = k min [m = 1] is applied on top of the QSIS inhomogeneity to determine its response in the presence of background ion scale inhomogeneity. Some key observations such as formation of transient PSV, wave-wave mode coupling interaction and various frequency generation alongwith comparative investigation with EA perturbation launched in the absence of ion scale inhomogeneity is also reported.

In Part I of the companion paper [Ref Part I], we have extensively discussed about the creation of quasi-stationary ion scale (QSIS) inhomogeneity using a constant frequency external drive at ion-acoustic time scales, resulting in ion trapped particle instability (ITPI), wave-wave mode coupling interaction and energy cascading. QSIS thus formed is perturbed by applying small amplitude electron acoustic (EA) mode leading to the several key plasma response features. In this Part II, using electrostatic, unbounded, OpenMP Vlasov-Poisson solver i.e VPPM-OMP 1.0, we have investigated the formation of various phase space vortices (PSV) (generated using two step or one step time dependent downward frequency chirping drives) in the presence of background QSIS inhomogeneity obtained in Part I. In addition, we have also performed one to one comparison of individual cases with their homogeneous counterparts with exact simulation parameters. In presence of QSIS inhomogeneity, we have observed interesting phenomenon such as early onset of Langmuir (LAN) mode, suppression of PSV sizes, omission of PSVs when compared to the homogeneous cases. Also, for different two step or one step downward chirp perturbation cases, particle trapping or untrapping fractions and its response to the increasing chirp intervals are respectively reported.

Motion-mediated trapped-ion interactions commonly coordinate state-dependent forces on both target ions. Sequential optical access reduces the number of concurrent target channels but makes the relative phase between disjoint force windows a control variable. We derive a complex near-resonant description in which each window generates a displacement vector and ordered symplectic products between vectors on different ions produce the ZZ phase. Only relative boundary phases affect this area; a common phase shift is a gauge transformation. Building on the experimental precedent for alternating single-ion addressing, we develop matched-envelope phase and contrast controls that isolate this boundary-phase dependence without target-window overlap or hidden force in the dark gaps. The analysis separates phase generation from differential closure, projector-common motion, deterministic local-Z phases, spectator coupling, and control-parameter transfer. A conditional-Ramsey sequence gives continuous and reset contrasts of 0.998 and 0.996, with a reset-induced phase separation of 0.581 rad modulo $π/2$. In the representative comparison, sequential control uses fewer concurrent target channels but greater normalized force action than independently calibrated simultaneous control. All results are model-level estimates within the stated Lamb-Dicke, rotating-wave, and apparatus-input limits.

The slowest Liouvillian mode often bottlenecks the relaxation of an open quantum system to its steady state. Standard strategies circumvent this bottleneck by selecting special initial states or engineering the dissipator. Here we show that neither is necessary. We introduce a pre-dissipative geometric steering protocol that reshapes any given pure or mixed state before relaxation begins -- coherent rotations interleaved with nonselective projective measurements -- at fixed Lindblad generator. By steering the state's Bloch direction along geodesic paths, the protocol suppresses its overlap with the slowest Liouvillian modes. The prepared state then starts farther from equilibrium yet relaxes faster, realizing the quantum Mpemba effect, whenever two computable conditions hold: reduced slow-mode overlap and a larger initial distance to stationarity. Our framework treats real and complex spectral gaps uniformly, and we demonstrate robust Mpemba acceleration in driven qubit and multiqubit systems using operations available in trapped-ion and superconducting platforms.

Large ion crystals in diverse geometries are a key resource for quantum simulation experiments. In this work, we introduce a macroscopic rf trap that supports a wide variety of one-dimensional ion configurations as well as lateral two-dimensional crystals with more than 100 ions. Our design is based on precision-machined fused silica wafers that are stacked to form the trap structure. Ten independently biased electrodes provide flexible control over the axial potential, enabling long one-dimensional crystals, isospaced ion strings, split-well chains, and two-dimensional arrays with tunable aspect ratios. We present the design and fabrication process for this trap and demonstrate the ability to tune the radial secular frequencies, detect and compensate micromotion, rotate the principal axes, and characterize trapped ion heating rates. All trap design and documentation files are freely available alongside this work, to facilitate adoption and further development within the ion trap community.

Entangling gates of trapped ions are typically mediated by collective motional degrees of freedom. Weak coupling between qubit and motional degrees of freedom and the resulting harmonic dynamics give access to a broad range of gate schemes, but also impose strict limitations on achievable gate times. In this paper, we devise optimally designed driving schemes for the realization of fast, high-fidelity entangling gates mediated by anharmonic dynamics. The driving can also be optimized to achieve resilience to multiple system imperfections, and the anharmonicity in the motional dynamics can be used to enhance such resilience.

The unification of quantum mechanics and general relativity remains one of the major open problems of theoretical physics. The Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence provides a valuable theoretical framework for this effort via a holographic duality between a theory of quantum gravity in asymptotically AdS spacetime and a conformal quantum field theory on the lower-dimensional boundary. Here, we implement a toy model of this duality called the HaPPY code, a quantum error-correcting code in the form of a tensor network with hyperbolic entanglement patterns, on a trapped-ion quantum computer. We present the first experimental confirmation of the Faulkner-Lewkowycz-Maldacena formula in this model - a key test of the holographic correspondence. We then enrich it with non-stabilizerness, or magic, and observe entropic precursors expected of emergent gravity. Finally, we present and measure a code construction whose entropic behavior is reminiscent of a highly quantum wormhole. Our experiments illustrate how quantum computers can serve as testbeds for modeling the emergence of spacetime.

Strong electromagnetic backgrounds make quantum electrodynamics a real-time nonperturbative problem involving dressed fermions and dynamical photons. We propose a trapped-ion protocol for simulating intense-field QED in $3+1$ dimensions in the Furry picture. The construction encodes photon modes in collective phonons and Volkov-dressed fermion modes in ion spins, combining native spin-phonon couplings with Clifford circuits that compress nonlocal Jordan--Wigner strings. For nonlinear Breit--Wheeler pair production, the protocol has polynomial resource scaling and is benchmarked against exact single-mode dynamics with controlled Trotter errors. With experimentally motivated phonon heating and dephasing, zero-noise extrapolation substantially reduces deviations in photon-survival and pair-production signals. These results provide a hardware-efficient route to intense-field particle-production dynamics beyond perturbative or static-field descriptions.

Dynamical structure factors (DSF) measured with neutron-scattering experiments provide key insights into the structure of materials. Their computation requires both the preparation of an equilibrium state and the implementation of Hamiltonian dynamics. We demonstrate the feasibility of computing DSF on the Quantinuum Reimei trapped-ion quantum computer, comparing the DSF of 1D Heisenberg model on $20$ sites, and that of the copper sulfate crystal. To that end, we introduce a pumping approach for computing the DSF $S(q,ω)$ on quantum computers that enables targeting specific arbitrary values of frequencies $ω$. This method time-evolves the initial state using a time-dependent Hamiltonian perturbed by a source term oscillating at the target frequency $ω$. When targeting only a few frequency values, this approach provides a significant reduction in shot overhead compared to previous methods.

The performance of variational quantum algorithms depends in general on the structure of the parametrized quantum circuit, but the most common ansätze are typically based on local couplings. Motivated by the extended connectivity available with neutral atoms and trapped ions, we examine when structured long-range connectivity provides a useful resource, focusing on sparse power-of-two (PWR2) coupling graphs. Using dynamical Lie-algebra analysis, approximate unitary-design diagnostics, and finite-depth measures of expressibility and entanglement, we examine how these geometries enlarge the accessible operator space. This enlarged space alone is not sufficient to ensure trainability of the parameterized circuit for given target problems, and we explore performance across example problems with and without long-range coupling, identifying where sparse coupling graphs are or are not likely to provide an advantage. We also introduce a variational scheme that maps hierarchical long-range Hamiltonians to geometrically local ones that can be optimized with short-range circuits. Together, these results identify circuit geometry and qubit reconfigurability as task-dependent resources for variational algorithms, relevant to ongoing developments in quantum hardware with long-range connectivity.

We report precision measurements of the ratio of Landé $g$ factors between the $3^2D_{5/2}$ and $4^2S_{1/2}$ states of a single trapped $^{40}\text{Ca}^+$ ion. The measurements are performed in two distinct ion trap apparatus: a cryogenic surface electrode radiofrequency Paul trap and a room-temperature permanent magnet Penning trap. The Penning trap measurements yield a ratio of $0.599~488~813~3(2)$, which represents a more than 40-fold uncertainty reduction compared to previous work. The radiofrequency trap measurement yields a concurring value of $0.599~488~813(6)$. We estimate that systematic shifts for each system are well below the respective statistical uncertainty.

Bound states in the continuum (BICs) are counterintuitive localized states that lie within the continuum of extended states. While extensively realized and utilized in classical wave systems, it is still unclear what a close analog of BICs would be, and how to extract their experimental signature in quantum-optical settings -- where the wave field itself is quantized into bosonic excitations. Here, we present a paradigmatic quantum-optical model consisting of a driven multi-level Jaynes-Cummings (JC) system, featuring few quantum degrees of freedom yet capable of hosting a BIC. Using the concept of a Fock-state lattice (FSL), this model can be mapped to an extended structure comprising two semi-infinite inhomogeneous Su-Schrieffer-Heeger (SSH) chains coupled to a common continuum. An appropriate quantum superposition of two topological zero modes from the separate chains forms a BIC that remains perfectly localized in the Fock-state dimension within the continuum spectrum, due to complete decoupling from the common continuum via destructive quantum interference. We further develop a method to extract the spectroscopic signature of the BIC -- a discrete peak embedded in a continuous background -- by Fourier-transforming the time-dependent dynamics of the system's chiral-symmetry operator. A highly feasible experimental proposal using a single trapped ion is provided. Our work bridges BIC physics with quantum optics, opening a pathway to harnessing such exotic states at the quantum limit.

Present-day quantum computing is cloud-based, where a user submits a circuit to a service provider's proprietary backend hardware. While providers may wish to hide implementation details, scheduling choices, or even which physical device was used, noisy finite-shot outputs can carry backend-specific fingerprints: information imprinted in the classical output distribution that can reveal the backend identity. So far, such fingerprints have mostly been studied from a benchmarking perspective, with limited attention to privacy considerations for users and providers. This work develops the first formal framework for backend identifiability and its privacy implications. We introduce a backend-identifiability game and use it to formalise routing anonymity as a security notion for quantum cloud services. We show that backend identifiability is a hypothesis-testing problem and prove that, under passive i.i.d. access to a single backend, routing anonymity decays exponentially at the Chernoff rate. We also establish a utility-anonymity trade-off, imposing fundamental limits on how much backend-specific information can be removed from classical outputs without degrading their usefulness. In addition, we observe that, for noisy quantum hardware, identifying fingerprints are inherently an intermediate-depth phenomenon, and establish a depth principle using Pauli-transfer-matrix tools. We complement the theory with experiments on Amazon Braket on AWS, using ion-trap and superconducting quantum processors. We observe 87-90% classification between superconducting backends and 96-100% classification across physical platforms, and find that identifiability can survive natural forms of post-processing. Overall, these results establish routing anonymity as a distinct security requirement for quantum cloud computing, and provide a framework for quantifying and controlling the utility-anonymity trade-off.

This work presents the design and fabrication of a compact permanent magnet based on an optimized stacked structure of fifteen NdFeB rings. The tunable NS-SN-NS configuration generates a central magnetic field of 0.8T with a reconstructed uniformity of 99.988% within a 1mm radius spherical volume. The remaining field inhomogeneity is dominated by radial dipole components. Requiring neither cryogenics nor external power, this design provides a high-performance and cost-effective alternative to superconducting magnets for applications in ion-trap development and Fourier-transform ion cyclotron resonance mass spectrometry.

We demonstrate an end-to-end, multi-stage attack against a quantum neural network (QNN) model that is executed on a trapped-ion quantum computer. Our chain combines side-channel reconnaissance, crosstalk characterization, adversarial example generation, and a physical crosstalk attack that realizes the adversarial perturbation on the device. We cover the full attack chain on ion traps and report the corresponding superconducting-hardware experiments in the appendix. We discuss implications for QaaS providers and hardware mitigations.

State-of-the-art two-qubit gates with trapped ions employ open-loop control that rely on simplified models to precompute control sequences. Our aim is to introduce closed-loop control for two-qubit gates to correct disturbances as they occur during the gate implementation. We introduce a spectator ion into the ion chain used for quantum logic processing, where it couples with the other ions through collective motional modes. The spectator ion's position is continuously monitored by driving dipole transitions and detecting the resultant fluorescence. We show that incorporating a spectator ion is feasible for linear Paul trap implementations and is expected to reduce the two-qubit gate Bell-state preparation infidelity by an order of magnitude with the deleterious effects of position monitoring being negligible compared to the thermal effects that exist in the system, even in the absence of the spectator ions. Mathematically, we describe driven ion-trap dynamics, including the spectator ion, by a stochastic quantum master equation involving the amplitude-modulation multimode-motional coupling gate, motional drift, thermal effects, recoil from photon scattering, spontaneous decay, and light shift. Our on-the-fly control method employs reinforcement learning with the reward function based on the actual geometric phase of the spectator ion. A key advantage of our approach is that we introduce a control method that involves `learning' and correcting disturbances happening in the trap on-the-fly, thus achieving high-fidelity gates. Our approach will lead to a significantly higher two-qubit gate fidelity at a reduced calibration overhead owing to the small parameter drift in the control system.

The electron shell of the Thorium ion with the $M$1(8.4~eV) transition between levels and the doublet of the $^{229}$Th nucleus ground state with the similar transition represent two qubits spatially inserted one within the other. In the case of relative proximity of the energies of these transitions, weakly damped energy oscillations can be excited between qubits, namely, multiple coherent energy transfer from the electron shell to the nucleus and vice versa. This process in the $^{229}$Th ions does not require resonant (within the width of the levels) coincidence of the transition energies due to the relatively high interaction energy of the electron and nuclear currents. The electron shell ``breathes'', periodically decreasing and increasing in size. The effect can be observed in an ion trap by the intensity of light scattered by thorium-229 ions. This extends the energy range for the $^{229m}$Th$(3/2^+,8.4$~eV) isomer excitation via an electron bridge. Furthermore, the system under consideration is transformed into a nuclear quantum battery when exposed to coherent laser radiation. To ``charge'' the battery, i.e. to excite $^{229m}$Th, one can use developed methods for charging quantum batteries, in particular, coherent excitation of the electron shell followed by coherent transfer of excitation energy to the nucleus (the coherent electron bridge). This opens the way for the design of the $^{229}$Th nuclear quantum battery at the current level of technological development.

Standard gate-level transpilation introduces significant physical noise and overhead for high-precision quantum algorithms, such as the Quantum Singular Value Transformation (QSVT), on near-term trapped-ion hardware. Current compilers treat quantum operations as discrete units, forcing the physical control layer to execute highly fragmented laser pulses. To address this hardware-software disconnect, this work introduces a holistic pulse synthesis strategy that bypasses discrete gate-stitching to compile algorithms directly into continuous compound pulse gadgets. As a proof-of-concept, we target Hamiltonian simulation of the $H_2$ molecule, block-encoding the problem into a QSVT circuit to approximate the time-evolution operator $U = e^{-i H t}$ across 3 computational ions (2 system, 1 ancilla). We utilize the Gradient Ascent Pulse Engineering (GRAPE) algorithm to generate these compound gadgets and evaluate our methodology using noisy Lindblad master equation simulations. Preliminary observations indicate that the proposed strategy achieves significant temporal compression, reducing the total pulse schedule duration compared to standard compilers. Furthermore, synthesizing operations holistically eliminates the control-layer latency associated with discrete pulse lookup overhead. By streamlining the physical control schedule, this methodology offers a promising pathway to execute operations faster, highlighting the potential for compound gadgets to increase the computational depth achievable within fundamental $T_2$ decoherence limits.

We determine with high accuracy the energy of the inner-shell transition $1s^2 2s^2~{}^1\mathrm{S}_0 \rightarrow 1s~2s^2~2p_{3/2}~{}^1\mathrm{P}_1$ ${}^{16}\mathrm{O}_{Kα}^{4+}$ at $554.372(3)~\mathrm{eV}$ ($λ$ = $22.36480(12)~\unicode{x212B}$) as well as its small shift of $2.2 \pm 1.3~\mathrm{meV}$ ($Δλ$ = $0.089(52)~\mathrm{m}\unicode{x212B}$) for the ${}^{18}\mathrm{O}$ isotope. This transition blends with a $K_α$ line of $\mathrm{O}^{5+}$ used in astrophysical diagnostics, potentially affecting its reliability. In contrast to our experimental uncertainty of $\pm 3~\mathrm{meV}$, advanced electronic structure predictions for this four-electron system, including quantum electrodynamic (QED) corrections on the order of $100~\mathrm{meV}$, still scatter by more than $\pm 250~\mathrm{meV}$. Ions generated and stored in an electron beam ion trap were excited at the ELETTRA synchrotron facility with monochromatic soft x rays, with photon energies corrected by an additional spectrometer. Upon resonant excitation of $\mathrm{O}^{4+}$ and subsequent autoionization, we separate the photoions of each isotope by a time-of-flight measurement. This way, we resolve soft x-ray isotopic shifts of a few meV, obtain very accurate data on an essential astrophysical ion, and test calculations down to the level of QED contributions.

Two-qubit-gate error dominates the failure budget of near-term quantum circuits, so the decomposition chosen for each Toffoli (CCX) gate should minimize hardware two-qubit infidelity, not gate count. The cheapest decompositions - relative-phase and approximate Toffolis - are only correct in context: their residual phase or bounded error must be cancelled or absorbed downstream. We present the first compiler pass that selects a per-Toffoli decomposition to minimize a two-qubit-infidelity error budget. It admits each context-dependent decomposition only when an exact, instance-specific equivalence check certifies its validity in that circuit context, coupling an error-budget objective with per-instance verification and closing the gap between context-aware-but-unverified and verified-but-context-free optimizers. The central result is a safety one: pattern-matched relative-phase substitution is silently incorrect. Our verifier flags 66 library rewrites of a deployed open optimizer as non-equivalent without a context check, and count-greedy substitution silently corrupts 6 of 12 benchmark circuits; the verification gate certifies 0 errors while still applying every valid decomposition. The two-qubit-gate reduction is real but workload-dependent: up to 39.5% fewer two-qubit gates and 36.7% lower infidelity over exact-only on a compute/uncompute-heavy suite (approx. 39%/35% versus Qiskit opt-3 and tket), and 15.6% aggregate on a larger 12-24-qubit suite, with decision-diagram checking certifying every substitution past the exhaustive-verification limit. At current superconducting and trapped-ion error rates, the certified substitutions lower estimated circuit infidelity by 36-43%, and on a quantum state-resetting circuit, the pass removes 48.8% of the native two-qubit gates, every substitution verified.

We investigate the formation of a barrier to evaporation that develops when levitated nanoscale Au nanoparticles are exposed to pulses of 532 nm laser radiation in a high vacuum (pressure $p=10^{-8}-10^{-7}$ Torr) environment. Our data are derived from precision measurements of the charge to mass ratio ($Q/M$) of $\sim$200 nm diameter Au particles confined in a quadrupole ion trap. We characterize the development of the barrier over time as the particle is repeatedly heated with laser pulses and determine the impact of variations of the interval between pulses and of exposure to several gases added to the vacuum chamber. We observe a slow increase in the mass of particles upon prolonged exposure to the vacuum, which we attribute to the growth of a barrier layer. For particles that have acquired a barrier during exposure to CO, we observe a rapid decrease in their mass upon subsequent exposure to O$_2$. These findings are consistent with the growth and subsequent oxidation of a graphene layer on the Au that forms the barrier to evaporation. However, we have not found that the rate of formation of the barrier depends on the pressure of carbon-containing gases (CO, C$_2$H$_4$, CO$_2$) we have added to the chamber. We hypothesize that a rare surface state on the solid Au particle catalyzes the reaction that introduces C to the particle. Repeated laser pulse heating is necessary--either to enable diffusion away from this state or to create fresh states that allow continued C uptake--to facilitate the growth of the surface graphene layer.

Hamiltonian dynamics have been widely implemented on noisy intermediate-scale quantum devices in recent years. In contrast, experimental demonstrations of Markovian quantum dynamics remain limited, because implementing nonunitary evolution on quantum computers is challenging. Quantum collision models provide a natural approach to this problem by coupling the system to ancillas to realize dissipation. However, previous implementations of quantum collision models on quantum computers have typically been restricted to one or two system qubits and fewer than 12 time steps, owing to noise, circuit depth, the overhead of ancilla reset, and limited qubit resources. In this work, we experimentally simulate Markovian quantum processes with local and nonlocal dissipation on both trapped-ion and superconducting quantum computers. By employing hardware-specific ancilla strategies, we realize simulations with up to seven system qubits, corresponding to 13 qubits in total, and 40 time steps. Our results demonstrate that, even for the same physical model, the optimal implementation strategy depends strongly on the hardware characteristics of the quantum computer.

Verifiable blind quantum computing (VBQC) enables a resource-limited client to securely delegate computations to an untrusted quantum server while maintaining privacy and detecting deviations from the prescribed computation. The noise-robust VBQC protocol of Leichtle et al. achieves this through a round-based structure: the client delegates multiple computation rounds and test rounds, using the test outcomes to detect cheating while tolerating honest hardware noise. The protocol's security proof involves numerous interdependent parameters, making it non-trivial to find a valid parameter set for a given hardware noise level and security target. We formalize this as a constrained optimization problem and develop a practical framework to solve it. The framework yields the protocol parameters that minimize the number of rounds for any given setup. We derive a heuristic formula for the minimal number of rounds to help understand the scaling with noise and security targets and to provide rapid resource estimation. Since the number of rounds depends on noise while the time per round depends on hardware rate, the framework also enables optimization of rate-fidelity trade-offs to minimize end-to-end runtime. We demonstrate both applications through a case study of a trapped-ion server with a measurement-only client, showing how the client's polarization control hardware specifications translate into protocol parameters and runtime estimates, providing concrete guidance for near-term implementations.

The $^{229}$Th nucleus possesses an isomeric state at an excitation energy of $\sim 8$ eV, the lowest known nuclear transition energy, placing its frequency in the vacuum-ultraviolet range and making it directly accessible to laser spectroscopy. In this review, we discuss the $^{229}$Th isomer from three connected perspectives: experimental spectroscopy and clock development, nuclear structure theory, and applications to precision tests of fundamental physics. We first trace the experimental progress from indirect $γ$-ray energy inference to resonant laser excitation, absolute frequency comparison with an atomic clock, and feedback-loop operation of a solid-state nuclear clock, and discuss trapped-ion, highly charged ion, and solid-state platforms together with mechanisms for nuclear-state manipulation and readout. We then review, from the nuclear-structure perspective, how the near-degeneracy of the $5/2^+[633]$ and $3/2^+[631]$ neutron Nilsson configurations, together with Coriolis mixing and octupole correlations, underlies the anomalously low transition energy and its electromagnetic properties. Comparisons among different phenomenological and microscopic models show that octupole correlations are a common structural ingredient, while magnetic moments and transition strengths remain sensitive tests of the calculated wave functions. Finally, we discuss how the near-cancellation of MeV-scale nuclear contributions into an eV-scale transition can enhance sensitivity to variations of fundamental constants, signatures of ultralight dark matter, CP-violating interactions, Lorentz-invariance violation, and possible nuclear quantum technologies.

We propose an array of Ramsey-type interferometers using $N$ superposition states, $(\vert 0 \rangle + \vert 1\rangle)^{\otimes N}$, as a sensor to detect wave-like dark matter. After exposure to the dark matter wave, which induces coherent qubit transitions, the signal is the imbalance between the numbers of 0 and 1 outcomes. The signal-to-noise ratio in this scheme is proportional to $N α^2$, where $α$ is the coupling of dark matter to the qubits, and thus the sensitivity to the coupling scales as $δα\sim 1 / \sqrt{N}$. For comparison, in the detection scheme based on the Rabi-type transition, $\vert 0 \rangle \to \vert 1\rangle$, this scaling is achieved only when $N$ highly entangled qubits are used. Since the Ramsey-type measurement does not require entangled states, one can consider much larger $N$ by simply placing a large number of qubits within the de Broglie wavelength of the dark matter. We demonstrate that, using trapped-ion qubits in linear Paul traps as the sensor, the projected sensitivity to the coupling matches or surpasses existing laboratory, astrophysical, and cosmological bounds for $N \gtrsim 10^6$-$10^8$. We also evaluate its sensitivity to high-frequency gravitational waves. Our general framework should, in principle, be useful for other quantum sensing platforms.

A quantum battery charged through a lossy intermediate state faces a structural trade-off between charging speed and dissipation. We show that an exact algebraic cancellation removes it in a driven three-level cell: the radiatively decaying state is fed by a single bright amplitude, and a counterdiabatic field annuls the lone residual source that drives it, holding the lossy state identically empty. Charging is then lossless -- not one photon is emitted through the bridge -- at any one-photon detuning, coupling, linewidth, and speed down to the rotating-wave limit, with no adiabatic elimination, so the charging power is bounded by the drive amplitude (a quantum speed limit) rather than by dissipation. Crucially, this losslessness is independent of the reservoir: because the dark sector never engages the system-bath coupling, the emission vanishes exactly for an arbitrary spectral density, Markovian or not, as an exact damped-pseudomode treatment confirms to machine precision across all memory times. The entire non-Hermitian structure -- a Markovian second-order exceptional point that reservoir memory promotes to a third-order one, and the attendant dissipation phase diagram -- lives in the bright sector, from which the protocol is by construction exempt. This inverts dissipation-engineered charging, where an exceptional point or reservoir memory is a resource; here the lossy sector is never populated at all. The same dark-state structure protects the stored charge, converting fast radiative self-discharge into the slow metastable lifetime, with residuals quadratic in the control error. We detail experimental requirements and representative parameters for neutral alkaline-earth atoms, trapped ions, transmons, and defect centers.

We describe apparatus and experimental procedures for high stability precision measurements of levitated nanoscale particles confined in an ion trap in high vacuum. We discuss methods for particle generation and collection using electrospray emission, for rapid characterization by direct imaging of thermal motion, and for transfer of the particle from the trap where it is collected to a separate analysis trap in order to achieve better vacuum and lower noise. In the analysis trap at high vacuum (pressure $p\simeq10^{-8}$ Torr), we employ thermostatic control of the trapped particle oscillation amplitudes, allowing long-term, precision measurements of oscillation frequencies, from which the charge to mass ratio ($Q/M$) can be deduced. Under these conditions, we achieve $Q/M$ measurement precision approaching $10^{-5}$. This sensitivity will enable, for example, investigations of the surface chemistry of $μ$m-scale levitated materials in ultra-high vacuum environments.

Direct motional coupling of opposite-charge trapped-ion pairs could provide a pathway to extend ultra-low temperatures and quantum control to negative ions that lack the suitable electronic energy structures required for direct laser cooling. Because positive and negative ions cannot be confined within a single electrostatic potential well, I investigate a configuration where single ions are trapped in close proximity within separate potential wells to couple their motion. I analytically and numerically evaluate the electrostatic trapping requirements. As a concrete implementation, I present an optimized segmented surface Paul trap design to couple an antimatter hydrogen molecular ion ($\bar{H}_2^-$) and a beryllium ion ($^9 Be^+$). A motional coupling frequency of 5 kHz can be achieved at an ion-ion separation of $35 μm$, with an ion height of $50 μm$, axial trap frequencies of 4 MHz, and static trap voltages with a magnitude of $\approx 20 V$. Finally, I outline three applications for this technique: quantum logic spectroscopy of $\bar{H}_2^-$ for matter-antimatter comparisons, the preparation of cold neutral deuterium atoms via near-threshold photo-detachment of $D^-$ for optical trapping, and quantum information processing using equal-mass opposite-charge ion pairs.