Velocity-Controlled Directional Readout of Single Photons

TL;DR

This paper demonstrates how moving photodetectors can encode photon direction information via Doppler shifts, enabling velocity-controlled directional readout without decoherence.

Contribution

It introduces a novel approach showing that detector motion influences single-photon detection POVMs, linking motion to measurement bias and direction sensitivity.

Findings

Motion Doppler-shifts alter detection bias without decoherence.

Finite bandwidth converts propagation direction into detection bias.

Readout transitions from phase-sensitive to direction-sensitive near a Doppler branch.

Abstract

Photodetection is usually treated in the frame in which the detector is at rest relative to the optical apparatus. We show that uniform motion of an electric Glauber detector changes the single-click POVM realized on two counterpropagating single-photon modes. Motion Doppler-shifts the alternatives in the detector frame; finite bandwidth then converts propagation direction into a detection bias without decohering the photon. For a Lorentzian response near one Doppler branch, the readout crosses from phase-sensitive to direction-sensitive with a quality-factor-enhanced onset. Finite-time integration adds Doppler-beat visibility loss, separating passive covariance from measurement change.