Fig. 1. (a) Represents the principle of the quantum-enhanced photonic radar system, comprising three main modules: squeezed light generation, signal acquisition, and signal processors. (b) depicts a module for squeezed light generation, while (c) illustrates the photonic radar RF acquisition and balanced homodyne detection. EOM, electro-optic modulator; MC, mode cleaner; OPA, optical parameter amplification; SHG, second-harmonic generation; PS, phase shifter; BS, beam splitter; DBS, dichroic beam splitter; BHD, balanced homodyne detector; EOT, electro-optic transducer; RF, radio-frequency.

Fig. 2. The displacement measurement by fixing the RF amplitude and automatically scanning the RF phase. The purple spheres: the measured displacement for different RF phases; the black curve: a sinusoidal fitting for experimental data; the shaded area, the noise variances of the estimation results.

Fig. 3. (a) The estimated noise variances with the coherent state by fixing the RF phase to ϕ₁ (dark blue) and ϕ₂ (light blue). (b) The estimated noise variances for RF phases ϕ₁ (dark red) and ϕ₂ (light red) with the squeezed state. (c) The contrast of distinguishable RF amplitudes by utilizing the squeezed state and the coherent state.

Fig. 4. The reconstructed Wigner function for RF signal estimation with the (a) coherent state and (b) phase-squeezed state.