Q. Quraishi

Advances in the distribution of quantum information will likely require entanglement shared across a hybrid quantum network. Many entanglement protocols require the generation of indistinguishable photons between the various nodes of the network. This is challenging in a hybrid environment due to typically large differences in the spectral and temporal characteristics of single photons generated in different systems. Here we show, for the first time, quantum interference between photons generated from a single atomic ion and an atomic ensemble, located in different buildings and linked via optical fibre. Trapped ions are leading candidates for quantum computation and simulation with good matter-to-photon conversion. Rydberg excitations in neutral-atom ensembles show great promise as interfaces for the storage and manipulation of photonic qubits with excellent efficiencies. Our measurement of high-visibility interference between photons generated by these two, disparate systems is an important building block for the establishment of a hybrid quantum network.

We demonstrate a simple pulse shaping technique designed to improve the fidelity of spin-dependent force operations commonly used to implement entangling gates in trapped-ion systems. This extension of the Mølmer-Sørensen gate can theoretically suppress the effects of certain frequency and timing errors to any desired order and is demonstrated through Walsh modulation of a two-qubit entangling gate on trapped atomic ions. The technique is applicable to any system of qubits coupled through collective harmonic oscillator modes.

We demonstrate the use of an optical frequency comb to coherently control and entangle atomic qubits. A train of off-resonant ultrafast laser pulses is used to efficiently and coherently transfer population between electronic and vibrational states of trapped atomic ions and implement an entangling quantum logic gate with high fidelity. This technique can be extended to the high field regime where operations can be performed faster than the trap frequency. This general approach can be applied to more complex quantum systems, such as large collections of interacting atoms or molecules.