Bi-Frequency Illumination: A Quantum-Enhanced Protocol

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 eta(omega)$\eta (\omega )$ embedded in a thermal bath is considered. The aim is to estimate the parameter lambda=eta(omega 2)-eta(omega 1)$\lambda = \eta (\omega _2)-\eta (\omega _1)$, 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 lambda in an assumed neighborhood of lambda approximate to 0$\lambda \approx \ 0$ for a two-mode squeezed state (HQ$H_\text{Q}$), and a pair of coherent states (HC$H_\text{C}$), a quantum enhancement is shown in the estimation of lambda. 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.

Automated summary

In this paper, a quantum-enhanced, idler-free sensing protocol is proposed to measure the response of a target object to the frequency of a probe in a noisy and lossy scenario. The use of a bi-frequency quantum state as the resource allows for more accurate estimation of the parameter lambda, and the quantum enhancement is shown to be noise-resilient and dependent on the reflectivity of the probed object. The study also proposes an experimental scheme based on elementary quantum optical transformations and highlights potential applications in radar and medical imaging.