Quantum illumination with nonzero-mean signal-idler states via noise-enhanced heterodyne work extraction

Abstract

Room temperature microwave and low-THz links exhibit large thermal occupations, making phase sensitive signal-idler correlations difficult to recover after loss. We introduce a work-extraction-based quantum-illumination receiver in which the returned mode $\hat{a}_R$ is measured via heterodyne detection and the outcome is fed forward to a locally stored, possibly displaced idler. For a noisy two-mode-squeezed resource, the receiver is characterized by the heterodyne correlation parameter $x_{\rm h}=\eta c^2/[a(b+\nu_{\rm h})]$. The calibrated displaced-idler work score has Chernoff exponent $\xi_{\rm h}=x_{\rm h}/4+O(x_{\rm h}^2)$, which becomes linear in the target transmissivity $\eta$ in the weak-return, background-dominated regime, matching the leading-order performance of an ideal OPA receiver, but achieved here via a linear and directly measurable correlation mechanism. Unlike OPA-based schemes, the present protocol does not require zero first moments and does not rely on weak-probability nonlinear detection. In our scheme, extracted work converts hard-to-measure second order moment correlation information into an accessible first moment signal. Moreover, preparation noise $\bar{n}_p$, naturally present at room temperature in the microwave and THz regimes, can be directly harnessed when correlated prior to transmission, whereas a classical coherent signal cannot utilize such incoherent thermal photons without first converting them into usable signal energy.