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Optics Express

Comparison of phase quadrature squeezed states generated from degenerate optical parametric amplifiers using PPKTP and PPLN

Zhenju Wan, Jinxia Feng, Yuanji Li, Kuanshou Zhang

Published Feb 23, 2018• 9 citations
Publisher

Abstract

(PPKTP) and periodically poled lithium niobate (PPLN) are compared. A squeezing of 6.8 dB was produced from the DOPA using PPKTP with the phase matching temperature of 34.5 °C. By contrast, a measured squeezing of 4.9 dB was generated using PPLN with the phase matching temperature of 135.2 °C. The degradation of squeezing using a nonlinear crystal with a high phase matching temperature is explained by a theoretical model of DOPAs including the extra phase noise caused by the guided acoustic wave Brillouin scattering within the nonlinear crystal.

DOI
10.1364/oe.26.005531

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(PPKTP) and periodically poled lithium niobate (PPLN) are compared. A squeezing of 6.8 dB was produced from the DOPA using PPKTP with the phase matching temperature of 34.5 °C. By contrast, a measured squeezing of 4.9 dB was generated using PPLN with the phase matching temperature of 135.2 °C. The degradation of squeezing using a nonlinear crystal with a high phase matching temperature is explained by a theoretical model of DOPAs including the extra phase noise caused by the guided acoustic wave Brillouin scattering within the nonlinear crystal.
A squeezed light source requires properties such as high squeezing amplitude, high bandwidth and stability over time, ideally using as few resources, such as laser power, as possible. We compare three nonlinear materials, two of which have not been well characterized for squeezed state production, and also investigate the viability of doubly-resonant optical parametric oscillator cavities in achieving these requirements. A model is produced that provides a new way of looking at the construction of an optical parametric oscillator/optical parametric amplifier setup where second harmonic power is treated as a limited resource. The well-characterized periodically poled potassium titanyl phosphate (PPKTP) is compared in an essentially identical setup to two relatively new materials, periodically poled stoichiometric lithium tantalate (PPSLT) and 1.7% magnesium oxide doped periodically poled stoichiometric lithium niobate (PPSLN). Although from the literature PPSLT and PPSLN present advantages such as a higher damage threshold and a higher nonlinearity, respectively, PPKTP was still found to have the most desirable properties. With PPKTP, 5.8 dB of squeezing below the shot noise limit was achieved. With PPSLT, 5.0 dB of squeezing was observed but the power required to see this squeezing was much higher than expected. A technical problem with the PPSLN limited the observed squeezing to around 1.0 dB. This problem is discussed.
We report on an initial squeezing of 3.3 dB below the shot noise level, generated in bulk, quasi-phase-matched lithium niobate. This squeezing was generated by degenerate parametric amplification, at 1047 nm, of a mode-locked pulse train. We present a detailed comparison of the process performed in both the quasi-phase-matched material and in MgO:LiNbO3,{\mathrm{M}\mathrm{g}\mathrm{O}:\mathrm{L}\mathrm{i}\mathrm{N}\mathrm{b}\mathrm{O}}_{3},MgO:LiNbO3​, which was phase matched using conventional birefringent methods. The single-pass gain measured was 2.5 from MgO:LiNbO3{\mathrm{M}\mathrm{g}\mathrm{O}:\mathrm{L}\mathrm{i}\mathrm{N}\mathrm{b}\mathrm{O}}_{3}MgO:LiNbO3​ and 3.9 from periodically poled lithium niobate (PPLN), although the former was affected by photorefractive damage. We directly recorded 1111%11 of noise reduction in the vacuum using the PPLN parametric amplifier, purely because the detection efficiency was so low in our experiment. The experimental data was fitted to a model which includes the initial squeezing level and the homodyne detector efficiency as free parameters. The observed squeezing agrees well with the a total detection efficiency of just 1616%16 and an initial squeezing level of 3.3 dB (53%) in PPLN.
We report generation of 10.1\pm0.2-dB squeezed light from a broadband periodically poled lithium niobate (PPLN) waveguide optical parametric amplifier (OPA). Based on our previous report where a similar PPLN waveguide shows 8.3-dB squeezing [T. Kashiwazaki et al., Appl. Phys. Lett. 122, 234003 (2023)], we reduce phase fluctuations and overall optical losses in the measurement system. In particular, we introduce a novel phase detection technique that does not require tapping a part of the squeezed light to get a phase locking signal. We use a phase-detection OPA seeded by a tapped probe and pump light before a squeezer OPA. This configuration breaks the conventional trade-off between generating a phase-locking signal with high-signal-to-noise ratio and suppressing degradation of squeezing level caused by optical tapping. With all these improvements, the phase fluctuation angle is reduced from 14 mrad to 9 mrad, and the total optical loss from 12\% to 8\%. Achieving more than 10 dB of squeezing by the broadband waveguide OPA is a significant step towards realization of fault-tolerant ultra-fast universal optical quantum computation.
We report the generation of squeezed light at 1550 nm, as well as the corresponding degradation analyses, from a fiber-based periodically poled lithium niobate (PPLN) waveguide chip. As an optical parametric amplifier (OPA), the highest squeezing level reaches over -3.0 dB. The performance of this on-chip squeezer is analyzed with the help of machine-learning quantum state tomography, to estimate the optical loss and phase noise, as well as the purity of the generated squeezed states at different pump powers. For quantum integrated optical circuits, our results provides a systematic characterization on the quantum light sources in continues variables.
We report detection of 10.1 ± 0.2-dB squeezed light from a broadband periodically poled lithium niobate (PPLN) waveguide optical parametric amplifier (OPA). Based on our previous report, where a similar PPLN waveguide shows 8.3-dB squeezing [T. Kashiwazaki et al ., Appl. Phys. Lett. 122 , 234003 ( 2023 ) 10.1063/5.0144385 ], we reduce phase fluctuations and overall optical losses in the measurement system. In particular, we introduce a phase detection technique that does not require tapping a part of the squeezed light to get a phase locking signal. We use a phase-detection OPA seeded by a tapped probe and pump light before a squeezer OPA. This configuration breaks the conventional trade-off between generating a phase-locking signal with a high signal-to-noise ratio and suppressing the degradation of the squeezing level caused by optical tapping. With all these improvements, the phase fluctuation angle is reduced from 14 mrad to 9 mrad, and the total optical loss from 12% to 8%. Achieving more than 10 dB of squeezing by the broadband waveguide OPA is a significant step towards the realization of fault-tolerant ultra-fast universal optical quantum computation.
We report the generation of long-term stable squeezed vacuum states at 1064 nm using a degenerate optical parametric amplifier (DOPA) with a periodically poled KTiOPO4 crystal (PPKTP). The OPA is pumped by a 532 nm light produced by frequency doubling the fundamental light with a bow-tie enhancement second harmonic generator (SHG). When the DOPA and relative phases are locked using a dither-locking method, the squeezed vacuum states are stably measured over 2 h at 11 MHz. The highly compact and simple squeezed light source is suitable for applications in quantum optics experiments.