Bi-frequency illumination: a quantum-enhanced protocol

Abstract

We propose a quantum-enhanced sensing protocol to measure the response of a target object to the frequency of a probe in a noisy and lossy scenario. In our protocol, a bi-frequency state illuminates a target embedded in a thermal bath, whose reflectivity η(ω) is frequency-dependent. After a lossy interaction with the object, we estimate the parameter λ = η(ω2)−η(ω1) in the reflected beam, which captures information about the response of the object to different electromagnetic frequencies. Computing the quantum Fisher information H relative to the parameter λ in an assumed neighborhood of λ ∼ 0 for a two-mode squeezed state (HQ), and a coherent state (HC ), we show that a quantum enhancement in the estimation of λ is obtained when HQ/HC > 1. This quantum advantage grows with the mean reflectivity of the probed object, and is noise-resilient. We derive explicit formulas for the optimal observables, and propose a general experimental scheme based on elementary quantum optical transformations. Furthermore, our work opens the way to applications in both radar and medical imaging, in particular in the microwave domain.

Propagating quantum microwaves: towards applications in communication and sensing

“…Quantum advantages in the sensing of dielectric properties could enhance these protocols. A first proof of advantage in the computation of reflectivity gradients, using bi-frequency entangled probes, has been theoretically proposed [182]. An QI-based medical imaging device avoids the first and third objections to the quantum radar in the previous paragraph, with idler storage times 5 orders of magnitude shorter (from km to cm), and a static target.…”

Quantum-Enhanced Doppler Radar/Lidar

“…Quantum metrology exploits quantum mechanical resources, such as entanglement and squeezing, to measure a physical parameter with higher resolution than any strategy with classical resources. Many quantum metrology protocols in the photonic regime [1] have been proposed such as quantum illumination (QI) [2][3][4][5], quantum enhanced position and velocity estimation [6][7][8][9][10][11][12], quantum phase estimation [13,14], transmission parameter estimation [15][16][17][18][19], noise estimation [20], and estimation of separation between objects [21,22], among others. In these protocols, information about an object is retrieved by interrogating it with a signal beam.…”