Reservoir-engineered spin squeezing: macroscopic even-odd effects and hybrid-systems implementations

TL;DR

This paper analyzes dissipative protocols for generating spin-squeezed states, revealing macroscopic even-odd effects, long transient squeezing regimes, and proposing hybrid-system implementations that are versatile across various quantum platforms.

Contribution

It uncovers the even-odd sensitivity in steady states, identifies a long transient squeezing regime under weak dephasing, and introduces a hybrid-systems approach for dissipative spin squeezing without complex resources.

Findings

Steady state sensitivity to even or odd number of spins.

Existence of a long transient regime with strong squeezing.

Compatibility of the protocol with multiple quantum platforms.

Abstract

We revisit the dissipative approach to producing and stabilizing spin-squeezed states of an ensemble of $N$ two-level systems, providing a detailed analysis of two surprising yet generic features of such protocols. The first is a macroscopic sensitivity of the steady state to whether $N$ is even or odd. We discuss how this effect can be avoided (if the goal is parity-insensitive squeezing), or could be exploited as a new kind of sensing modality to detect the addition or removal of a single spin. The second effect is an anomalous emergent long timescale and a "prethermalized" regime that occurs for even weak single-spin dephasing. This effect allows one to have strong spin squeezing over a long transient time even though the level of spin squeezing in the steady state is very small. We also discuss a general hybrid-systems approach for implementing dissipative spin squeezing that does not require squeezed input light or complex multi-level atoms, but instead makes use of bosonic reservoir-engineering ideas. Our protocol is compatible with a variety of platforms, including trapped ions, NV defect spins coupled to diamond optomechanical crystals, and spin ensembles coupled to superconducting microwave circuits.