Unambiguous joint detection of spatially separated properties of a single photon in the two arms of an interferometer

TL;DR

This paper demonstrates the unambiguous joint detection of different properties of a single photon in separate interferometer arms, revealing new ways to explore quantum superposition and information processing.

Contribution

It provides the first experimental realization of simultaneous property detection in spatially separated regions of a single quantum system.

Findings

Significant pointer shifts (~50 microns) observed in each arm.

Joint observation of spatial and polarization properties achieved.

Opens new avenues for quantum information and mesoscopic system tests.

Abstract

The quantum superposition principle implies that a particle entering an interferometer evolves by simultaneously taking both arms. If a non-destructive, minimally-disturbing interaction coupling a particle property to a pointer is implemented on each arm while maintaining the path superposition, quantum theory predicts that, for a fixed state measured at the output port, certain particle properties can be associated with only one or the other path. Here we report realization of this prediction through joint observation of the spatial and polarization degrees of freedom of a single photon in the two arms of an interferometer. Significant pointer shifts ($\sim$50 microns) are observed in each arm. This observation, involving coupling distinct properties of a quantum system in spatially separated regions, opens new possibilities for quantum information protocols and for tests of quantumness for mesoscopic systems.