An asymmetric and fast Rydberg gate protocol for entanglement outside of the blockade regime

TL;DR

This paper introduces a modified Rydberg gate protocol that achieves high fidelity without requiring strong interactions, using quantum control techniques for robustness and generalization.

Contribution

It presents a new Rydberg gate design based on the $-2-$ protocol with added detuning, enabling high-fidelity operation outside the blockade regime.

Findings

Achieves fidelity within a factor of 2.39 of the fundamental limit for equal Rabi frequencies.

Generalizes the gate to arbitrary controlled phases and designs optimal phase waveforms.

Identifies the constant-phase protocol as time-optimal under certain conditions.

Abstract

We analyze a new Rydberg gate design based on the original $\pi-2\pi-\pi$ protocol [Jaksch, et. al. Phys. Rev. Lett. {\bf 85}, 2208 (2000)] that is modified to enable high fidelity operation without requiring a strong Rydberg interaction. The gate retains the $\pi-2\pi-\pi$ structure with an additional detuning added to the $2\pi$ pulse on the target qubit. The protocol reaches within a factor of 2.39 (1.68) of the fundamental fidelity limit set by Rydberg lifetime for equal (asymmetric) Rabi frequencies on the control and target qubits. We generalize the gate protocol to arbitrary controlled phases. We design optimal target-qubit phase waveforms to generalize the gate across a range of interaction strengths and we find that, within this family of gates, the constant-phase protocol is time-optimal for a fixed laser Rabi frequency and tunable interaction strength. Quantum control techniques are used to design gates that are robust against variations in Rydberg Rabi frequency or interaction strength.