Quantum gates between distant atoms mediated by a Rydberg excitation antiferromagnet

Abstract

We present a novel protocol for implementing quantum gates between distant atomic qubits connected by an array of neutral atoms that play the role of a quantum bus. The protocol is based on adiabatically transferring the atoms in the array to an antiferromagnetic-like state of Rydberg excitations using chirped laser pulses. Upon exciting and de-exciting the atoms in the array under the blockage of nearest neighbors, depending on the state of the two qubits, the system acquires a conditional geometric $π$-phase, while the dynamical phase cancels exactly, even when the atomic positions are disordered but nearly frozen in time, which requires sufficiently low temperatures. With experimentally relevant parameters, using smooth pulses minimizing the Rydberg-state decay and non-adiabatic errors, we obtain the gate times of $2-3\:μ$s and gate fidelities of 0.99-0.98 for a pair of atoms separated by $L=20-30\:μ$m and connected by a quantum bus of several ($3-6$) atoms. Optimizing the pulses, we can obtain faster gates exhibiting even better fidelities than those with smooth adiabatic pulses.