Non-Gaussian generalized two-mode squeezing: applications to two-ensemble spin squeezing and beyond

TL;DR

This paper generalizes two-mode squeezed states to finite-dimensional bipartite systems, enabling Heisenberg-limited multi-parameter estimation and stable state preparation, with applications to spin squeezing and quantum metrology.

Contribution

It introduces a framework for non-Gaussian two-mode squeezing applicable to spin systems, extending quantum metrology beyond Gaussian states with simple stabilization methods.

Findings

Generalized two-mode states enable multi-parameter estimation.

States can be stabilized via Markovian dissipative processes.

Applicable to spin ensembles for enhanced quantum sensing.

Abstract

Bosonic two-mode squeezed states are paradigmatic entangled Gaussian states that have wide utility in quantum information and metrology. Here, we show that the basic structure of these states can be generalized to arbitrary bipartite quantum systems in a manner that allows simultaneous, Heisenberg-limited estimation of two independent parameters for finite-dimensional systems. Further, we show that these general states can always be stabilized by a relatively simple Markovian dissipative process. In the specific case where the two subsystems are ensembles of two-level atoms or spins, our generalized states define a notion of two-mode spin squeezing that is valid beyond the Gaussian limit and that enables true multi-parameter estimation. We discuss how generalized Ramsey measurements allow one to reach the two-parameter quantum Cramer-Rao bound, and how the dissipative preparation scheme is compatible with current experiments.