Polaron formation in a spin chain by measurement-induced imaginary Zeeman field

TL;DR

This paper introduces a measurement-based method to induce and stabilize spin polarons in a quantum spin chain, enabling control over non-unitary evolution and state distillation.

Contribution

It presents a novel high-rate projective measurement protocol that creates and stabilizes spin polarons via an effective imaginary Zeeman field in a quantum chain.

Findings

Local measurement of an external spin induces stable spin polarons.

The protocol can distill non-decaying states from superpositions.

Stable non-decaying states determine the long-term polaron shape.

Abstract

We present a high-rate projective measurement-based approach for controlling non-unitary evolution of a quantum chain of interacting spins. In this approach, we demonstrate that local measurement of a single external spin coupled to the chain can produce a spin polaron, which remains stable after the end of the measurement. This stability results from the fact that the Hilbert space of the chain contains a subspace of non-decaying states, stable during the nonunitary evolution. These states determine the resulting final state of the chain and long-term shape of the polaron. In addition to formation of the spin polarons, the presented measurement protocol can be used for distillation of non-decaying states from an initial superposition or mixture.