Scalable Squeezed-Light Source for Continuous-Variable Quantum Sampling

We propose a squeezed-light source meeting the stringent requirements of continuous-variable quantum sampling. Using the time-dependent effective second-order nonlinear interaction induced by a strong driving beam in the presence of the ${\chi }_3$ response in a microresonator, our approach is compatible with established nanophotonic platforms. With typical realistic parameters, squeezed states with a mean photon number of 10 or higher can be generated in a single consistent temporal mode at repetition rates of over 100 MHz. Over 15 dB of squeezing is expected in existing ultralow-loss platforms.

Figure 1

(a) A microring resonator side-coupled to a channel waveguide. (b) Tuning the resonance condition for parametric fluorescence via self- and cross-phase-modulation. (c) A virtual-level diagram for dual-pumped spontaneous four-wave mixing (SFWM); the strong cw drive beam mediates an effective second-order parametric nonlinearity ${\chi }_2^{\mathrm{eff}}$.

Figure 2

The system performance for a device with realistic parameters (details in text). (a) The variance relative to vacuum of the squeezed quadrature (bottom solid curve) and the antisqueezed quadrature (top solid curve) for the dominant mode. The dashed curve shows the variance of the antisqueezed quadrature for an ideal pure state; some excess antisqueezing is evident from the finite escape efficiency. (b) The mean photon number of the first ten Schmidt modes as a function of the pulse energy; the dominant mode (top curve) consistently lies about $100\times$ above the next-largest mode. (c) The intensity (virtually identical solid curves) and phase (dashed curves) of the temporal-mode profile for the squeezed pulses generated for five pulse energies spanning 1–100 pJ. The intensity profile is virtually unchanged across this range; the phases show only very small progressive deviations due to cross-phase-modulation from the pulsed pump as the energy is increased. (d) The Schmidt number is consistently close to unity across a wide range of pump-pulse energies and squeezing levels. (e) The fidelity between the dominant complex temporal-mode profile at varying pulse energies and that at the lowest pulse energy. Only very slight degradation of this fidelity is predicted, primarily due to the slight phase variations shown in (c). More details of how these quantities are extracted from the output moments can be found in Appendix pp2.

Figure 3

The purity of the generated Gaussian state as a function of the target squeezing level for a device with 90% escape efficiency.