A quantum phase transition in a quantum external field: Superposing two magnetic phases

TL;DR

This paper demonstrates how a quantum superposition of magnetic phases in an Ising chain can be prepared via adiabatic driving in a quantum magnetic field, revealing critical properties through magnetization.

Contribution

It introduces a method to create superpositions of ground states in an Ising chain using a quantum magnetic field modeled by a coupled central spin.

Findings

Superposition of ferromagnetic and paramagnetic phases achieved

Magnetization encodes critical point and universal exponents

Ground state fidelity can be inferred from magnetization

Abstract

We study an Ising chain undergoing a quantum phase transition in a quantum magnetic field. Such a field can be emulated by coupling the chain to a central spin initially in a superposition state. We show that - by adiabatically driving such a system - one can prepare a quantum superposition of any two ground states of the Ising chain. In particular, one can end up with the Ising chain in a superposition of ferromagnetic and paramagnetic phases -- a scenario with no analogue in prior studies of quantum phase transitions. Remarkably, the resulting magnetization of the chain encodes the position of the critical point and universal critical exponents, as well as the ground state fidelity.