Dynamic conditioning of two particle discrete-time quantum walks

TL;DR

This paper investigates how particle losses influence the behavior of two-photon quantum walks, combining theoretical modeling and experimental implementation to understand their effects on output distributions and system dynamics.

Contribution

It introduces a theoretical framework and experimental platform for controlled particle losses in two-photon quantum walks, revealing their impact on output distributions.

Findings

Localized particle losses alter output distributions

Losses do not change asymptotic spreading properties

Develops a quantum civilization problem for two walkers

Abstract

In real photonic quantum systems losses are an unavoidable factor limiting the scalability to many modes and particles, restraining their application in fields as quantum information and communication. For this reason, a considerable amount of engineering effort has been taken in order to improve the quality of particle sources and system components. At the same time, data analysis and collection methods based on post-selection have been used to mitigate the effect of particle losses. This has allowed for investigating experimentally multi-particle evolutions where the observer lacks knowledge about the system's intermediate propagation states. Nonetheless, the fundamental question how losses affect the behaviour of the surviving subset of a multi-particle system has not been investigated so far. For this reason, here we study the impact of particle losses in a quantum walk of two photons reconstructing the output probability distributions for one photon conditioned on the loss of the other in a known mode and temporal step of our evolution network. We present the underlying theoretical scheme that we have devised in order to model controlled particle losses, we describe an experimental platform capable of implementing our theory in a time multiplexing encoding. In the end we show how localized particle losses change the output distributions without altering their asymptotic spreading properties. Finally we devise a quantum civilization problem, a two walker generalisation of single particle recurrence processes.