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Physical Review A

Strong squeezing in periodically modulated optical parametric oscillators

Hayk H. Adamyan, János A. Bergou, Narine Gevorgyan, Gagik Yu. Kryuchkyan

Published Nov 6, 2015• 14 citations
Publisher

Abstract

We consider specific signatures of squeezing for time-modulated light fields and propose the scheme of an optical parametric oscillator driven by a continuously modulated pump field. The application of a periodically modulated driving field instead of a continuous wave field drastically improves the degree of quadrature integral squeezing. This quantity goes below the standard limit of 50% relative to the level of vacuum fluctuations. We develop semiclassical and quantum theories of an optical parametric oscillator under the influence of a pump field with harmonically modulated amplitude for all operational regimes, including numerical simulations at the threshold point. The results can be directly applied in time-resolved quantum communication protocols.

DOI
10.1103/physreva.92.053818

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Physical Review A•Dec 8, 2017•21 citations
We consider specific signatures of squeezing for time-modulated light fields and propose the scheme of an optical parametric oscillator driven by a continuously modulated pump field. The application of a periodically modulated driving field instead of a continuous wave field drastically improves the degree of quadrature integral squeezing. This quantity goes below the standard limit of 50% relative to the level of vacuum fluctuations. We develop semiclassical and quantum theories of an optical parametric oscillator under the influence of a pump field with harmonically modulated amplitude for all operational regimes, including numerical simulations at the threshold point. The results can be directly applied in time-resolved quantum communication protocols.
A degenerate optical parametric oscillator (DOPO) in the above threshold regime is a prominent source of squeezed field. In this study, a driven DOPO whose pump mode is coupled to a thermal bath while the signal mode is coupled to a squeezed vacuum reservoir is explored to understand the effect of the external squeezed light and the thermal fluctuations on the squeezing properties of both the intracavity and output pump and signal modes. Our findings showed that the injected squeezed vacuum reservoir enables the intracavity squeezing to surpass the maximum squeezing limit of 50% attainable in a DOPO coupled to an ordinary vacuum reservoir. We also found that the maximum squeezing of the output signal mode shifts from resonance to off-resonance in the presence of the injected squeezed vacuum field. Furthermore, the output pump mode exhibits nearly perfect squeezing for a squeezing parameter of r=2. Unlike the output signal mode, the maximum squeezing of the output pump mode occurs at resonance in the presence of the injected squeezed vacuum reservoir. Moreover, a considerable amount of squeezing is observed even in the presence of thermal fluctuations, as they are counterbalanced by the external squeezed light. Notably, relative damping rate between the pump and signal modes is observed to be a parameter that significantly influences squeezing, indicating the importance of optimizing the amount of damping depending on the intended purpose of the DOPO.
The optical parametric oscillator is one of the most well-characterized devices in nonlinear optics, with many useful applications, especially as a frequency converter and as a wide-band amplifier. Novel discoveries made with these devices in the quantum domain include demonstrations of large amounts of both single-mode and two-mode squeezing, and, in the two-mode case, significant quantum intensity correlations between the two modes and quadrature correlations, which provided the first experimental demonstration of the original Einstein–Podolsky–Rosen (EPR) paradox. In this chapter, a systematic theory is developed of quantum fluctuations in the degenerate parametric oscillator. The quantum statistical effects produced by the degenerate parametric amplifier and oscillator have been intensely studied. As we have seen, the amount of transient squeezing produced in an ideal lossless parametric amplifier was calculated using asymptotic methods by Crouch and Braunstein. It was found to scale inversely with the square root of the initial pump photon number. When the system is put into a cavity, and driving and dissipation are introduced, we find that the steady state of a driven degenerate parametric oscillator bifurcates. There is a single steady state at low driving strengths, but, as the driving field increases, a threshold value is reached and the single state splits and forms two stable states. Below the threshold, a linearized analysis of squeezing in the quantum quadratures is possible; while above this threshold, or critical point, the tunneling time between the two states due to quantum fluctuations can be calculated.
We propose a scheme to modulate the entanglement between two oscillators separated in space via the squeezing cavity field generated by the optical parametric amplifier instead of injecting the squeezing field directly with the assistance of Coulomb interaction. We show that the Coulomb interaction between the oscillators is the essential reason for the existence of entanglement. Due to the gain of the optical parametric amplifier and the phase of the pump driving the optical parametric amplifier can simultaneously modulate the squeezing cavity field, the radiation pressure interaction between the cavity field and the oscillator is modulated accordingly. We find that there is competing effect between the radiation pressure interaction and the Coulomb interaction for the oscillator which these two interactions act on simultaneously. Therefore, the modulation of entanglement can be achieved with the assistance of Coulomb interaction. The results of numerical simulation show that the present scheme has stronger robustness against the temperature of environment compared with previous schemes in experimentally feasible regimes.
Abstract Parametric down-conversion in a nonlinear crystal is a widely employed technique for generating quadrature squeezed light with multiple modes, which finds applications in quantum metrology, quantum information and communication. Here we study the generation of temporally multimode femtosecond pulsed squeezed light in a synchronously pumped optical parametric oscillator (SPOPO) operating below the oscillation threshold, while considering the presence of non-compensated intracavity group-velocity dispersion. Based on the developed time-domain model of the system, we show that the dispersion results in mode-dependent detuning of the broadband supermodes of the pulsed parametric process from the cavity resonance due to temporal Gouy phase, as well as linear coupling between these supermodes. With perturbation theory up to the second order in the coupling coefficients between modes, we obtained a solution for the amplitudes of multiple supermodes given an arbitrary sub-threshold pump level. The dispersion affects the quantum state of the supermodes by influencing their squeezing level and the rotation of the squeezing ellipse. It also affects the entanglement among the supermodes, leading to reduced suppression of shot noise level as measured in the balanced homodyne detection scheme. Furthermore, our study highlights the potential of SPOPO with group-velocity dispersion as a testbench for experimental investigations of multimode effects in linearly evanescent coupled parametric oscillators.
Abstract A novel and efficient method is proposed for generating mechanical squeezing in a double‐cavity optomechanical system by introducing an optical parametric amplifier (OPA) with pump modulation (PM). The combined effects of periodic amplitude modulation of the driving laser and the OPA enable mechanical squeezing in both the resolved‐sideband and unresolved‐sideband regimes, with significantly enhanced squeezing observed in the resolved‐sideband regime. The individual contributions of the OPA and PM to mechanical squeezing is systematically investigated, with results indicating that PM plays a more dominant role. Additionally, the proposed scheme demonstrates excellent robustness against environmental thermal noise. These findings highlight the potential of this approach for advancing quantum precision measurements and exploring macroscopic quantum phenomena.
A scheme to achieve strong quantum squeezing of a mechanical resonator in a membrane-in-the-middle optomechanical system is developed. To this end, simultaneous linear and nonlinear coupling between the mechanical resonator and the cavity modes is applied. A two-tone driving light field, comprising unequal red-detuned and blue-detuned sidebands, helps in generating a coherent feedback force through the linear coupling with the membrane resonator. Another driving light field with its amplitude modulated at twice the mechanical frequency drives the mechanical parametric amplification through a second-order coupling with the resonator. The combined effect produces strong quantum squeezing of the mechanical state. The proposed scheme is quite robust to excess second-order coupling observed in coherent feedback operations and can suppress the fluctuations in the mechanical quadrature to far below the zero point and achieve strong squeezing (greater than 10 dB) for realistic parameters.