Driven Gaussian quantum walks

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.

Automated summary

This article introduces the concept of a driven Gaussian quantum walk, which describes the walk process using a nonlinear map instead of a unitary operation. This expands the applications of quantum walks by incorporating nonlinear elements into their operation. An entire framework for understanding driven Gaussian quantum walks is developed, including methods for characterizing nonlinear, quantum, and quantum-nonlinear effects. The article compares driven Gaussian quantum walks with their classical counterparts and explores the generation and enhancement of quantum effects during the nonlinear walk. The quantumness of the evolution is proven regardless of the input state. A proposed experimental realization scheme and exploration of nonlinear properties of driven Gaussian quantum walks are also discussed.