Quantum radar with unreflected photons

TL;DR

This paper explores two theoretical models for quantum radar that estimate reflectivity without measuring scattered photons, analyzing their sensitivities and limitations in noisy environments.

Contribution

It introduces and compares two novel descriptions of quantum radar systems that do not rely on photon reflection measurements, highlighting their sensitivities and background noise effects.

Findings

Hamiltonian dynamics model shows exponential cost with transmitter intensity.

Optical quantum circuit model achieves about half the optimal sensitivity.

Both models' sensitivities are affected by thermal background noise.

Abstract

Two descriptions are introduced and analyzed for a reflectivity estimation and detection scheme that does not involve measurement of photons scattered by the target. One description, provided by the Hamiltonian dynamics of the full transmitter/receiver optical system, incurs an exponential cost in transmitter intensity for a given estimation sensitivity but is linearly improved with the intensity of the thermal background. The other description, based on optical quantum circuits, exhibits sensitivity around a factor of 1/2 of the optimal entanglement-assisted scheme, but incurs an inverse linear reduction in sensitivity with increasing thermal background. The results have applications for the design of optically active receivers based on combining echo-seeded spontaneous parametric downconversion and induced coherence due to photon indistinguishability.