High-Fidelity Bell-State Preparation with $^{40}$Ca$^+$ Optical Qubits

Abstract

Entanglement generation in trapped-ion systems has relied thus far on two distinct but related geometric phase gate techniques: Mølmer-Sørensen and light-shift gates. We recently proposed a variant of the light-shift scheme where the qubit levels are separated by an optical frequency [B. C. Sawyer and K. R. Brown, Phys. Rev. A 103, 022427 ( 2021)]. Here we report an experimental demonstration of this entangling gate using a pair of 40 Ca + ions in a cryogenic surface-electrode ion trap and a commercial, high-power, 532 nm Nd:YAG laser. Generating a Bell state in 35 µs, we directly measure an infidelity of 6(3) × 10 −4 without subtraction of experimental errors. The 532 nm gate laser wavelength suppresses intrinsic photon scattering error to ∼ 1 × 10 −5 . This result establishes our scheme as competitive with previously demonstrated entangling gates.

Entangling gates for trapped-ion quantum computation and quantum simulation

“…Fast gate with fidelity of 99.8% in 1.6 µs has been achieved on 43 Ca + hyperfine qubits [96]. Bell-State with infidelity of 6(3)×10 −4 without subtraction of experimental errors has been directly measured with 40 Ca + optical qubits [97].…”

A trapped ion quantum computer with robust entangling gates and quantum coherent feedback

“…MS gates are very successful in two-ion chains [35][36][37][38]. However, in long ion-chains, the gates have an increased sensitivity to even small implementation imperfections.…”

Transport-enabled entangling gate for trapped ions

“…The transport gate technique demonstrated here could be extended to longer ion strings with different motional modes and ion species with appropriate changes in beam geometry. In particular, the scheme is amenable to σ z σ z interactions such as the optical-transition dipole force gate [25,26] where the Stark shift effects could be eliminated entirely with an echo pulse.…”