Collective States and Symmetric Local Decoherence in Large Ensembles of Qubits

TL;DR

This paper introduces a new class of collective states in large spin ensembles that remain invariant under symmetric local decoherence, with implications for preserving quantum properties in noisy environments.

Contribution

It develops a novel class of collective states invariant under symmetric local decoherence and analyzes their dynamics in relevant quantum states.

Findings

Hilbert space dimension scales as N^2 for these states

Non-classical states like Schrödinger cat and spin squeezed states are studied under decoherence

Invariant states offer potential robustness against certain decoherence processes

Abstract

The symmetric collective states of an atomic spin ensemble (i.e., many-body states that are invariant under particle exchange) are not preserved by decoherence that acts identically but individually on members of the ensemble. We develop a class of collective states in an ensemble of N spin-1/2 particles that is invariant under symmetric local decoherence and find that the dimension of the Hilbert space spanned by these collective states scales only as N^2. We then investigate the open system dynamics of experimentally relevant non-classical collective atomic states, including Schroedinger cat and spin squeezed states, subject to various symmetric but local decoherence models.