Driven Gaussian quantum walks

TL;DR

This paper introduces driven Gaussian quantum walks, a nonlinear extension of quantum walks using a pump-controlled two-mode squeezer, enabling new quantum phenomena and applications in quantum simulation.

Contribution

It develops a full framework for driven Gaussian quantum walks, including methods to characterize nonlinear quantum effects and proposes an experimental realization scheme.

Findings

Generation of multimode entanglement and squeezing during the walk

Demonstration of quantumness of the evolution independent of input states

Amplification leading to increased correlated quantum particles

Abstract

Quantum walks function as essential means to implement quantum simulators, allowing one to study complex and often directly inaccessible quantum processes in controllable systems. In this contribution, the notion of a driven Gaussian quantum walk is introduced. In contrast to typically considered quantum walks in optical settings, we describe the operation of the walk in terms of a nonlinear map rather than a unitary operation, e.g., by replacing a beam-splitter-type coin with a two-mode squeezer, being a process that is controlled and driven by a pump field. This opens previously unattainable possibilities for quantum walks that include nonlinear elements as core components of their operation, vastly extending their range of applications. A full framework for driven Gaussian quantum walks is developed, including methods to dynamically characterize nonlinear, quantum, and quantum-nonlinear effects. Moreover, driven Gaussian quantum walks are compared with their classically interfering and linear counterparts, which are based on classical coherence of light rather than quantum superpositions. In particular, the generation and boost of highly multimode entanglement, squeezing, and other quantum effects are studied over the duration of the nonlinear walk. Importantly, we prove the quantumness of the evolution itself, regardless of the input state. A scheme for an experimental realization is proposed. Furthermore, nonlinear properties of driven Gaussian quantum walks are explored, such as amplification that leads to an ever increasing number of correlated quantum particles, constituting a source of new walkers during the walk. Therefore, a concept for quantum walks is proposed that leads to -- and even produces -- directly accessible quantum phenomena, and that renders the quantum simulation of nonlinear processes possible.