This study investigates the effect of a partially temporally coherent pump on the nonclassical properties of squeezed vacuum and single-photon subtracted squeezed vacuum state, which could be useful for quantum communication, metrology, and sensing.
We discuss nonclassical properties of single-photon subtracted squeezed vacuum states in terms of the sub-Poissonian statistics and the negativity of the Wigner function. We derive a compact expression for the Wigner function from which we find the region of phase space where Wigner function is negative. We find an upper bound on the squeezing parameter for the state to exhibit sub-Poissonian statistics. We then study the effect of decoherence on the single-photon subtracted squeezed states. We present results for two different models of decoherence, viz. amplitude decay model and the phase diffusion model. In each case we give analytical results for the time evolution of the state. We discuss the loss of nonclassicality as a result of decoherence. We show through the study of their phase-space properties how these states decay to vacuum due to the decay of photons. We show that phase damping leads to very slow decoherence, slower than the photon-number decay.
We investigate the behavior of squeezing in combined quadratures of biphotons generated in the parametric downconversion process for partially coherent pump beams in spatial, temporal, and spatiotemporal domains compared to fully coherent beams. These beams involve both stationary (continuous-wave) and non-stationary (pulsed) processes. This study also involves the derivation of complex Gaussian representation for a partially spatially coherent pump modeled as a Gaussian Schell model beam, which is more resistant to the effects of turbulence. Our findings illustrate that by employing the partially coherent pump, one can generate a squeezed state possessing partially coherent properties without compromising in squeezing by optimizing pump field amplitude, interaction length, and degree of coherence of the pump. We anticipate these results to be useful in limiting the possibility of eavesdropping in noisy channels and optical high-precision measurements in the case of continuous-variable quantum key distribution based on two-mode squeezed states.