David Lucas

Abstract:

We present a design study into an ion trap electrode geometry for applying near-field microwave two-qubit gates. This design features an ‘S’-shaped meander electrode to passively null the microwave field. It has ground planes separating the meander electrode from all of the DC and single-qubit microwave electrodes, which should reduce the sensitivity of the microwave field distribution to the boundary conditions of these electrodes. We show that it is possible to design a single-layer trap with this geometry such that the simulated microwave field null overlaps with the RF field null, and that the positions of these nulls can be simulated to a precision of 100 nm with moderate computing resources. We also show that such a trap can be designed such that ion chains can be trapped, transported and split with feasible DC and RF voltages. While this particular design is optimized for 43Ca+ ions, our approach could be applied to other ions by changing the microwave frequency to match the corresponding qubit transition frequency

Abstract:

We integrate a long-lived memory qubit into a mixed-species trapped-ion quantum network node. Ion-photon entanglement first generated with a network qubit in 88Sr+ is transferred to 43Ca+ with 0.977(7) fidelity, and mapped to a robust memory qubit. We then entangle the network qubit with another photon, which does not affect the memory qubit. We perform quantum state tomography to show that the fidelity of ion-photon entanglement decays ∼ 70 times slower on the memory qubit. Dynamical decoupling further extends the storage time; we measure an ion-photon entanglement fidelity of 0.81(4) after 10 s.

Abstract:

A single bichromatic field near resonant to a qubit transition is typically used for σx or σy Mølmer-Sørensen-type interactions in trapped-ion systems. Using this field configuration, it is also possible to synthesize a σz spin-dependent force by merely adjusting the beat-note frequency. Here, we expand on previous work and present a comprehensive theoretical and experimental investigation of this scheme with a laser near resonant to a quadrupole transition in Sr+88. Further, we characterize its robustness to optical phase and qubit frequency offsets, and demonstrate its versatility by entangling optical, metastable, and ground-state qubits.