Postselective quantum interference of distinguishable particles

TL;DR

This paper demonstrates that completely distinguishable particles can exhibit quantum interference through postselection, revealing new ways to manipulate and understand particle indistinguishability without directly altering their distinguishing features.

Contribution

It introduces a method for postselective interference of distinguishable particles using a family of three-mode interferometers, and develops a general approach based on Schmidt decomposition to analyze distinguishability.

Findings

Distinguishable particles can interfere postselectively without changing their internal states.

A family of three-mode interferometers enables such interference effects.

The approach provides new insights into the relationship between different quantum representations.

Abstract

We show that it is possible for completely distinguishable particles to interfere postselectively without operating on, or indeed having any knowledge of, the distinguishing degree of freedom. In particular, we find a family of three-mode spatial interferometers that, upon inputting, say, a red photon in port 1 and a green photon in port 2, produce a state such that when vacuum is detected at one output, the two photons in the other two outputs will pass a HOM test, despite their frequency degree of freedom remaining untouched. In doing so we develop a general approach to distinguishability based on the Schmidt decomposition between particles' "System" and "Label" degrees of freedom, corresponding to what has been called unitary-unitary duality in many-body physics. This also gives insight into the relationship between the first and second quantized pictures, which is useful in bringing other quantum information concepts across from the former to the latter.