Light Squeezed to the Limit express
A laser beam is like a taut string: even in complete silence, it trembles almost imperceptibly. This trembling is quantum noise, and it gets in the way of ultra-precise measurements. Physicists have long sought ways to calm the string, and one of them is "squeezing" light: reducing the trembling in one direction while allowing it to increase in another.
In the new work, the researchers took a lithium niobate crystal, a material that can transform light, and passed a laser beam through it. The crystal squeezed the light by 12.1 decibels, meaning it reduced quantum noise by nearly 16 times. This is a record for this type of device. Previously, the problem was that the squeezed beam didn't match the shape of the reference beam it was compared with, causing some light to be lost.
To fix this, the scientists placed a spatial light modulator in the path of the reference beam — a device that can reshape the beam, much like clay changes shape under your hands. The modulator was controlled by a machine learning algorithm: it automatically adjusted the shape to maximize squeezing. The algorithm used a double reflection to gain more flexibility in tuning.
In the end, the beam and the reference signal matched almost perfectly, and light losses dropped. Now the squeezed light can be used in gravitational wave detectors, where every photon counts. It could also be used in quantum computers and communication systems, where noise is the main enemy.
Original abstract
as written by the authors arXiv:2603.02744
We demonstrate the generation of $$12.1 \pm 0.2$$ 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.
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