Decoherence induced spontaneous symmetry breaking

TL;DR

This paper investigates how decoherence from classical and quantum noise affects the exchange symmetry of Bell states over time, revealing that some states preserve symmetry while others do not, with decoherence identified as the main symmetry-breaking mechanism.

Contribution

It provides a comparative analysis of classical and quantum noise effects on Bell state symmetry, highlighting decoherence as a key factor in symmetry breaking.

Findings

Two Bell states preserve exchange symmetry with probability 1.

Remaining Bell state maintains symmetry with maximum probability 0.5 asymptotically.

Decoherence is identified as the primary cause of symmetry breaking.

Abstract

We study time dependence of exchange symmetry properties of Bell states when two qubits interact with local baths having identical parameters. In case of classical noise, we consider a decoherence Hamiltonian which is invariant under swapping the first and second qubits. We find that as the system evolves in time, two of the three symmetric Bell states preserve their qubit exchange symmetry with unit probability, whereas the symmetry of the remaining state survives with a maximum probability of 0.5 at the asymptotic limit. Next, we examine the exchange symmetry properties of the same states under local, quantum mechanical noise which is modeled by two identical spin baths. Results turn out to be very similar to the classical case. We identify decoherence as the main mechanism leading to breaking of qubit exchange symmetry.