Extreme depolarization for any spin

TL;DR

This paper investigates how highly non-classical states of quantum spins of arbitrary size decohere under depolarization, revealing links between superdecoherence, entanglement decay, and the role of anticoherent states in generating bound entanglement.

Contribution

It provides a detailed analysis of superdecoherent states under depolarization, establishing a connection between decoherence and entanglement, and explores the generation of bound entangled states from anticoherent states.

Findings

Entanglement survival time scales with Hilbert space dimension.

Anticoherent states can generate bound entangled states through depolarization.

Collective depolarization causes rapid decay of quantum properties in high-dimensional spins.

Abstract

The opportunity to build quantum technologies operating with elementary quantum systems with more than two levels is now increasingly being examined, not least because of the availability of such systems in the laboratory. It is therefore essential to understand how these single systems initially in highly non-classical states decohere on different time scales due to their coupling with the environment. In this work, we consider the depolarization, both isotropic and anisotropic, of a quantum spin of arbitrary spin quantum number $j$ and focus on the study of the most superdecoherent states. We approach this problem from the perspective of the collective dynamics of a system of $N=2j$ constituent spin-$1/2$, initially in a symmetric state, undergoing collective depolarization. This allows us to use the powerful language of quantum information theory to analyze the fading of quantum properties of spin states caused by depolarization. In this framework, we establish a precise link between superdecoherence and entanglement. We present extensive numerical results on the scaling of the entanglement survival time with the Hilbert space dimension for collective depolarization. We also highlight the specific role played by anticoherent spin states and show how their Markovian isotropic depolarization alone can lead to the generation of bound entangled states.