Interference-based universal decoupling and swapping for multimode bosonic systems

TL;DR

This paper introduces interference-based protocols that enable decoupling and swapping of modes in multimode bosonic systems without beam-splitters, facilitating quantum operations in hybrid systems.

Contribution

The authors develop novel interference-based protocols for mode decoupling and swapping that do not require beam-splitters, broadening operational capabilities in bosonic quantum systems.

Findings

Protocols require only multiple uses of a coupler and single-mode Gaussian unitaries.

Decoupling and swapping can be achieved with constant-depth sequences.

Methods are broadly applicable to various bosonic platforms.

Abstract

Beam-splitter operations are widely used to process information encoded in bosonic modes. In hybrid quantum systems, however, it might be challenging to implement a reliable beam-splitter operation between two distinct bosonic modes. Without beam-splitters, some basic operations such as decoupling modes and swapping states between modes can become highly non-trivial or not feasible at all. In this work, we develop novel interference-based protocols for decoupling and swapping selected modes of a multimode bosonic system without requiring beam-splitters. Specifically, for a given generic coupler characterized by a Gaussian unitary process, we show how to decouple a single mode or swap any pair of modes with a constant depth sequence of operations, while maintaining the coupling for the remaining system. These protocols require only multiple uses of the given coupler, interleaved with single-mode Gaussian unitary operations, and thus enable efficient construction of operations crucial to quantum information science, such as high-fidelity quantum transduction. Our results are directly derived from fundamental physical properties of bosonic systems and are therefore broadly applicable to various existing platforms.