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Journal of the Optical Society of America B

Time-domain analysis on the pulsed squeezed vacuum detected with picosecond pulses

Yoshitaka Taguchi, Yasuyuki Ozeki

Published Mar 31, 2020• 15 citations
Publisher

Abstract

The pulsed squeezed state of light is expected to enhance the sensitivity of optical measurements using optical pulses. To achieve a high squeezing level, it is crucial to explore its limiting factors. In this study, we analyze the pulsed squeezed vacuum detected with picosecond pulses to explore two critical factors that limit the achievable squeezing level. First, we investigate the effect of the frequency chirp of local oscillator (LO) pulses and show that there exists an upper bound of the chirp parameter for a given squeezing level. Next, we analyze the effect of temporal matching between the LO pulse and the squeezed vacuum and point out the importance of temporal broadening in nonlinear optical crystals for squeezing.

DOI
10.1364/josab.389039

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The pulsed squeezed state of light is expected to enhance the sensitivity of optical measurements using optical pulses. To achieve a high squeezing level, it is crucial to explore its limiting factors. In this study, we analyze the pulsed squeezed vacuum detected with picosecond pulses to explore two critical factors that limit the achievable squeezing level. First, we investigate the effect of the frequency chirp of local oscillator (LO) pulses and show that there exists an upper bound of the chirp parameter for a given squeezing level. Next, we analyze the effect of temporal matching between the LO pulse and the squeezed vacuum and point out the importance of temporal broadening in nonlinear optical crystals for squeezing.
Squeezed states of light enable enhanced measurement precision by reducing noise below the standard quantum limit. A key application of squeezed light is nonlinear microscopy, where state-of-the-art performance is limited by photodamage and quantum-limited noise. Such microscopes require bright, pulsed light for optimal operation, yet generating and detecting bright pulsed squeezing at high levels remains challenging. In this work, we present an efficient technique to generate high levels of bright picosecond pulsed squeezed light using a χ2χ^2χ2 optical parametric amplification process in a waveguide. We measure −3.2 dB-3.2~\mathrm{dB}−3.2 dB of bright squeezing with optical power compatible with nonlinear microscopy, as well as −3.6 dB-3.6~\mathrm{dB}−3.6 dB of vacuum squeezing. Corrected for losses, these squeezing levels correspond to −15.4−8.7+2.7 dB-15.4^{+2.7}_{-8.7}~\mathrm{dB}−15.4−8.7+2.7​ dB of squeezing generated in the waveguide. The measured level of bright amplitude pulsed squeezing is to our knowledge the highest reported to date, and will contribute to the broader adoption of quantum-enhanced nonlinear microscopy in biological studies.
We experimentally investigate the temporal characteristics of picosecond squeezed pulses generated via an optical parametric amplification in a periodically poled MgO:LiNbO3 waveguide. The noise variances for the various time delays between the squeezed pulse and a local oscillator are measured using a balanced homodyne detector. The measured delay dependence is asymmetric, and this asymmetry indicates that the phase chirping of the squeezed pulse is different from that of the local oscillator pulse. We show that the observed squeezing can be improved by using the pulse shaping of the local oscillator.
A transient noise measurement scheme is described to observe pulsed squeezing generated by means of parametric downconversion of a Q-switched laser. In the usual implementation of balanced-homodyne detection, the vacuumstate noise level is determined by the average local oscillator power. However, if the local oscillator is derived from a pulsed laser, as is the case in our experiments, the associated peak power can easily saturate the detectors along with the subsequent electronics. To overcome this limitation we have implemented a hybrid frequency-time-domain measurement scheme in which the vacuum-state noise level is determined by the peak, instead of the average, local oscillator power, thus avoiding the saturation problem.
In recent years, quantum technology has expanded its reach across a wide range of fields. Pulsed squeezing, in particular, holds significant promise for advancing quantum-enhanced nonlinear microscopy as well as high-speed quantum computing and communication. However, the performance of pulsed squeezing using the widely adopted Ti:sapphire laser has been rarely investigated, especially in the picosecond regime. Here, we report record-level picosecond pulsed squeezing of -4.41 dB generated with a Ti:sapphire laser, together with a method for time-domain phase characterization of picosecond pulsed squeezed light. We anticipate that these results will promote the broader adoption of quantum systems based on the versatile, broadband-tunable Ti:sapphire platform and foster a deeper understanding of pulsed squeezed light.