Neutral atom entangling gate in the ultrastrong coupling regime

TL;DR

This paper introduces a method for deterministic entanglement of qubits in the ultrastrong coupling regime, enabling the creation of entangled, squeezed, and Schrödinger cat states through tunable qubit-boson interactions.

Contribution

It presents a novel entangling gate design that operates effectively in the ultrastrong coupling regime, with tunable interaction strength for state preparation.

Findings

Gate time inversely proportional to interaction strength

Able to generate maximally entangled and squeezed states

Can produce Schrödinger cat states with multiple qubit ensembles

Abstract

We propose a method to deterministically entangle qubits or ensembles of qubits interacting with a shared bosonic mode in the ultrastrong coupling regime. We show that the resulting gate is a product of two unitaries: one unitary acts only on the quantum state of the qubits and entangles them, while the other acts only on the quantum state of the boson, producing a phase shift. We find that the gate time is inversely proportional to the qubit-boson interaction strength, and by tuning the qubit-boson interaction strength, one can prepare a maximally entangled state or a squeezed state. Applying the quantum gate to multiple qubit ensembles, we show that the quantum gate prepares a Schr\"odinger cat state. We also examine imperfections such as including free evolution of the qubits, and show that this produces an effective mixing. Our proposal is feasible for ultrastrong coupling experiments.