Pulsed squeezed light is a key resource for many quantum information processing tasks. Among the various methods for generating squeezed light, single-pass parametric amplification has various advantages such as broad bandwidth, compactness, and stability. The challenge in achieving high-level pulsed squeezing has been to improve detection efficiency. We used a spatial light modulator controlled by machine learning to improve the spatial mode matching between the local oscillator and squeezed light. We achieved pulsed squeezing of 5.88 dB generated by optical parametric amplification in a waveguide. To the best of our knowledge, this is the highest obtained pulsed squeezing, and we believe this achievement will lead to more compact and efficient quantum information technology.
Pulsed squeezed light is a key resource for many quantum information processing tasks. Among the various methods for generating squeezed light, single-pass parametric amplification has various advantages such as broad bandwidth, compactness, and stability. The challenge in achieving high-level pulsed squeezing has been to improve detection efficiency. We used a spatial light modulator controlled by machine learning to improve the spatial mode matching between the local oscillator and squeezed light. We achieved pulsed squeezing of 5.88 dB generated by optical parametric amplification in a waveguide. To the best of our knowledge, this is the highest obtained pulsed squeezing, and we believe this achievement will lead to more compact and efficient quantum information technology.
We demonstrate the generation of 12.1±0.2 dB squeezed light from a periodically poled lithium niobate (PPLN) waveguide optical parametric amplifier (OPA). While single-pass OPAs offer squeezed light with THz-order bandwidths, loss from spatial mode mismatch between the squeezed light and the local oscillator (LO) previously capped the squeezing level at $\sim$10 dB [K. Hirota et al., Opt. Express 34, 7958 (2026)]. In this work, we minimize this loss by introducing a machine-learning-optimized spatial light modulator (SLM) in the path of the LO. Specifically, we employed a double-reflection configuration to increase the spatial degrees of freedom, and directly used the measured squeezing level as the optimization's objective function.
Quantum-enhanced measurements using squeezed light provide sensitivities beyond the shot-noise limit and have attracted much attention in many fields such as spectroscopy, gravitational wave detection, and biological imaging. To achieve high squeezing levels, the precise matching of the amplitude and phase between squeezed vacuum and local oscillator (LO) is essential. Still, it is not a simple task, especially when optical pulses are used. For continuous-wave beams, a mode-cleaning cavity or a single-mode waveguide is commonly used to control the spatial profile of the two beams. However, the cavity must be large enough to couple the optical pulses, and the waveguide causes unwanted nonlinearities for intense optical pulses and has a limited variety of materials. This study implemented precise amplitude and phase matching by integrating phase-shift digital holography and spatial light modulator (SLM). Specifically, we used a periodically-poled stoichiometric lithium tantalate (PPSLT) waveguide for optical parametric amplification (OPA). We measured the spatially resolved phase difference and intensity profile of idler light and LO by analyzing their interference movie with phase- shifting digital holography. We performed spatial mode matching by controlling the amplitude and phase of LO using SLM. As a result, we achieved high visibility of 92.9% and observed a squeezing level of -3.61 dB.
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 χ2 optical parametric amplification process in a waveguide. We measure −3.2dB of bright squeezing with optical power compatible with nonlinear microscopy, as well as −3.6dB of vacuum squeezing. Corrected for losses, these squeezing levels correspond to −15.4−8.7+2.7dB 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.
Multimode squeezed light is a key resource for high-dimensional quantum technologies, enhancing metrological sensitivity, boosting communication security, and enabling parallel processing in computation. Its practical potential, however, remains constrained by the inherent single-mode operation of homodyne detection, necessitating post-processing for multimode characterization. Here, we overcome this long-standing challenge by employing multimode optical parametric amplification, enabling loss-tolerant direct detection of squeezing in each mode, which in turn permits mode sorting after amplification. As a result, we demonstrate, for the first time to the best of our knowledge, the real-time monitoring of multimode squeezing. With a spatial light modulator sorting the modes, we simultaneously measure squeezing in nine spatial modes co-propagating within one beam. Although mode sorting and filtering reduce the detection efficiency to less than 0.3%, we observe high-purity squeezing of up to - 7.9 ± 0.6 dB - to the best of our knowledge, the highest squeezing recorded for pulsed light. Furthermore, we demonstrate real-time, loss-tolerant characterization of continuous-variable entanglement and extend it to the detection of cluster states. Similar methods can be applied in the frequency domain, facilitating a crucial capability for scalable quantum technologies.
Multimode squeezed light is an increasingly popular tool in photonic quantum technologies, including sensing, imaging, and computation. Meanwhile, the existing methods of its characterization are technically complicated, and in the best case, deal with a single mode at a time. Here, we demonstrate experimentally how the squeezing can be measured in multiple spatial modes simultaneously, using optical parametric amplification and direct detection followed by modal decomposition based on spatial intensity correlations. We apply this method to a multimode squeezed vacuum generated via high-gain parametric down-conversion. We measure the degrees of squeezing and anti-squeezing for eight strongest spatial modes, obtaining highest squeezing and anti-squeezing values of −5.2±0.2 dB and 8.6±0.3 dB, respectively.
Multimode squeezed light is an increasingly popular tool in photonic quantum technologies, including sensing, imaging, and computation. Meanwhile, the existing methods of its characterization are technically complicated, which reduces the level of squeezing, and mostly deal with a single mode at a time. Here, for the first time, to the best of our knowledge, we employ optical parametric amplification to characterize multiple squeezing eigenmodes simultaneously. We retrieve the shapes and squeezing degrees of all modes at once through direct detection followed by modal decomposition. This method is tolerant to inefficient detection and does not require a local oscillator. For a spectrally and spatially multimode squeezed vacuum, we characterize eight strongest spatial modes, obtaining squeezing and anti-squeezing values of up to −5.2 ± 0.2 dB and 8.6 ± 0.3 dB, respectively, despite the 50% detection loss. This work, being the first exploration of an optical parametric amplifier’s multimode capability for squeezing detection, paves the way for the real-time detection of multimode squeezing.