Bi‐Frequency Illumination: A Quantum‐Enhanced Protocol

Abstract

Quantum‐enhanced, idler‐free sensing protocol to measure the response of a target object to the frequency of a probe in a noisy and lossy scenario is proposed. In this protocol, a target with frequency‐dependent reflectivity ηfalse(ωfalse)$\eta (\omega )$ embedded in a thermal bath is considered. The aim is to estimate the parameter λ=η(ω2)−η(ω1)$\lambda = \eta (\omega _2)-\eta (\omega _1)$, since it contains relevant information for different problems. For this, a bi‐frequency quantum state is employed as the resource, since it is necessary to capture the relevant information about the parameter. Computing the quantum Fisher information H relative to the parameter λ in an assumed neighborhood of λ≈0$\lambda \approx \ 0$ for a two‐mode squeezed state (HnormalQ$H_\text{Q}$), and a pair of coherent states (HnormalC$H_\text{C}$), a quantum enhancement is shown in the estimation of λ. This quantum enhancement grows with the mean reflectivity of the probed object, and is noise‐resilient. Explicit formulas are derived for the optimal observables, and an experimental scheme based on elementary quantum optical transformations is proposed. Furthermore, this work opens the way to applications in both radar and medical imaging, in particular in the microwave domain.

Quantum-enhanced Doppler 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][6] , quantumenhanced position and velocity estimation [7][8][9][10][11][12][13] , quantum phase estimation 14,15 , transmission parameter estimation [16][17][18][19][20] , noise estimation 21 and estimation of separation between objects 22,23 , among others. In these protocols, information about an object is retrieved by interrogating it with a signal beam.…”

Quantum-Enhanced Pattern Recognition

“…gain a quantumadvantage. Efforts to design and engineer such protocols have been widely successful, with applications in datareadout [13][14][15][16][17][18][19][20][21][22], target detection [23][24][25][26][27][28][29][30][31][32][33][34][35][36], cryptography [37,38], fundamental physics research [39][40][41] and imaging [42][43][44].…”