M. I Hussain

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.

Well isolated quantum systems are exquisite sensors of electromagnetic fields. In this work, we use a single trapped ion for characterizing chirped ultraviolet (UV) picosecond laser pulses. The frequency swept pulses resonantly drive a strong dipole transition via rapid adiabatic passage, resulting in near deterministic population exchange caused by absorption or stimulated emission of photons. When subjecting an ion to counterpropagating pulse pairs, we observe the loss and revival of atomic coherence as a function of the pulse pair spatial overlap enabling quantification of the temporal pulse broadening caused by a frequency chirp in shaped UV pulses with a very low peak power. We find good agreement between measured and applied chirp. The ultrafast population exchange imparts an impulsive force where the estimated change in the mean phonon numbers of 0.5 is measured for two pairs of pulses. The resonant ultrafast kicks could be applied to matter wave interferometry experiments and present a step towards ultrafast entanglement operations in trapped ions.

The conventional approach to perform two-qubit gate operations in trapped ions relies on exciting the ions on motional sidebands with laser light, which is an inherently slow process. One way to implement a fast entangling gate protocol requires a suitable pulsed laser to increase the gate speed by orders of magnitude. However, the realization of such a fast entangling gate operation presents a big technical challenge, as such the required laser source is not available off-the-shelf. For this, we have engineered an ultrafast entangling gate source based on a frequency comb. The source generates bursts of several hundred mode-locked pulses with pulse energy $\sim$800 pJ at 5 GHz repetition rate at 393.3 nm and complies with all requirements for implementing a fast two-qubit gate operation. Using a single, chirped ultraviolet pulse, we demonstrate a rapid adiabatic passage in a Ca$^+$ ion. To verify the applicability and projected performance of the laser system for inducing entangling gates we run simulations based on our source parameters. The gate time can be faster than a trap period with an error approaching $10^{-4}$.

We propose a new protocol to implement ultra-fast two-qubit phase gates with trapped ions using spin-dependent kicks induced by resonant transitions. By only optimizing the allocation of the arrival times in a pulse train sequence the gate is implemented in times faster than the trapping oscillation period $T<2π/ω$. Such gates allow us to increase the number of gate operations that can be completed within the coherence time of the ion-qubits favoring the development of scalable quantum computers.

Trapped ions are a well-studied and promising system for the realization of a scalable quantum computer. Faster quantum gates would greatly improve the applicability of such a system and allow for greater flexibility in the number of calculation steps. In this paper we present a pulsed laser system, delivering picosecond pulses at a repetition rate of 5 GHz and resonant to the S$_{1/2}$ to P$_{3/2}$ transition in Ca$^+$ for coherent population transfer to implement fast phase gate operations. The optical pulse train is derived from a mode-locked, stabilized optical frequency comb and inherits its frequency stability. Using a single trapped ion, we implement three different techniques for measuring the ion-laser coupling strength and characterizing the pulse train emitted by the laser, and show how all requirements can be met for an implementation of a fast phase gate operation.

All physical interactions are mediated by forces. Ultra-sensitive force measurements are therefore a crucial tool for investigating the fundamental physics of magnetic, atomic, quantum, and surface phenomena. Laser cooled trapped atomic ions are a well controlled quantum system and a standard platform for precision metrology. Their low mass, strong Coulomb interaction, and readily detectable fluorescence signal make trapped ions favourable for performing high-sensitivity force measurements. Here we demonstrate a three-dimensional sub-attonewton sensitivity force sensor based on super-resolution imaging of the fluorescence from a single laser cooled $^{174}$Yb$^+$ ion in a Paul trap. The force is detected by measuring the net ion displacement with nanometer precision, and does not rely on mechanical oscillation. Observed sensitivities were 372$\pm$9$_\mbox{stat}$, 347$\pm$12$_\mbox{sys}\pm$14$_\mbox{stat}$, and 808$\pm$29$_\mbox{sys}\pm$42$_\mbox{stat}$ zN/$\sqrt{\mbox{Hz}}$ in the three dimensions, corresponding to 24x, 87x, and 21x of the quantum limit. We independently verified the accuracy of this apparatus by measuring a light pressure force of 95 zN on the ion, an important systematic effect in any optically based force sensor. This technique can be applied for sensing DC or low frequency forces external to the trap or internally from a co-trapped biomolecule or nanoparticle.