Two-qubit Quantum Logic Gates for Neutral Atoms Based on the Spin-Flip Blockade

The "spin-flip blockade" was first demonstrated in 2016 by Jau et al. [1]. Analogous to the "Rydberg blockade" for optical excitations, here the spin of one neutral alkali atom in its ground state can be induced to flip between hyperfine manifolds through absorption of a microwave photon, while the two-spins are blockaded from flipping simultaneously. The blockade is caused by the additional energy imparted by a light-shift resulting from Rydberg dressing in the presence of Van der Waals forces. This effect was used to demonstrate the generation of Bell states with fidelity >81% (>90% after SPAM correction). We describe here how to extend this to generate universal two-qubit quantum logic gates. We show that many protocols designed for the optical regime can be translated into the microwave regime and analyze their potential for high-fidelity operation. In comparison to the optical protocols, the ultra-precise control is more easily achieved in the microwave regime, which results in the potential for fast quantum logic gates with reduced noise and low decoherence. We also consider various dressing schemes with different advantages. Finally, we use robust control techniques to make our gates robust against perturbations in hard-to-control parameters.
Sandia National Labs is managed and operated by NTESS LLC, a subsidiary of Honeywell Intl., Inc., for the US DOE's NNSA under contract DE-NA0003525.
[1] Y.-Y. Jau, A. Hankin, T. Keating, I. Deutsch, and G. Biedermann, Entangling atomic spins with a Rydberg dressed spin-flip blockade, Nature Physics 12, 71 (2016).