Parallel two-qubit entangling gates via a quantum nondemolition interaction controlled by rotation

TL;DR

This paper introduces a protocol for parallel two-qubit entangling gates using quantum nondemolition interactions controlled by rotations, enabling deterministic nonlocal operations and entanglement in multimode light-atom systems.

Contribution

It proposes a novel protocol leveraging QND interactions and rotations to perform parallel two-qubit gates with specific nonlocal operations and entanglement capabilities.

Findings

Realizes deterministic nonlocal SWAP operation.

Achieves entangling √SWAP operation with probability 1/3.

Enables parallel two-qubit operations in multimode light-atom systems.

Abstract

The paper presents an analysis of entangling and nonlocal operations in a quantum nondemolition (QND) interaction between multimode light with orbital angular momentum and an atomic ensemble. A protocol consists of two QND operations with rotations of quadratures of atomic spin coherence and light between them. This protocol provides a wide range of two-qubit operations, while the multimode nature of the chosen degrees of freedom allows the implementation of parallel operations over multiple two-qubit systems. We have used the formalism of equivalence classes and local invariants to evaluate the properties of two-qubit transformations. It is shown that, when selecting suitable values of the governing parameters, such as the duration of each of the two QND interactions and the rotation angles of the qubits, the protocol allows to realize a deterministic nonlocal $SWAP$ operation and entangling $\sqrt{SWAP}$ operation with probability 1/3.