Detecting an Itinerant Optical Photon Twice without Destroying It

TL;DR

This paper demonstrates a method to repeatedly detect a single photon traveling through a long optical fiber without destroying it, using cascaded nondestructive detectors that significantly improve signal-to-noise ratio.

Contribution

The work introduces a cascaded nondestructive photon detection scheme that enhances detection fidelity and allows tracking of a photon without absorption.

Findings

Signal-to-noise ratio improves by about two orders of magnitude with cascaded detectors.

Successfully tracks a photon over a 60-meter optical fiber.

Verifies practical advantage of nondestructive detection over traditional absorbing methods.

Abstract

Nondestructive quantum measurements are central for quantum physics applications ranging from quantum sensing to quantum computing and quantum communication. Employing the toolbox of cavity quantum electrodynamics, we here concatenate two identical nondestructive photon detectors to repeatedly detect and track a single photon propagating through a $60\,\mathrm{m}$ long optical fiber. By demonstrating that the combined signal-to-noise ratio of the two detectors surpasses each single one by about two orders of magnitude, we experimentally verify a key practical benefit of cascaded non-demolition detectors compared to conventional absorbing devices.