The “Squeeze Laser”

The level of quantum noise in measurements is bounded from below by the Heisenberg uncertainty principle, but it can be unequally distributed between two noncommuting observables: it can be “squeezed.” Since 2019, all gravitational-wave observatories have been using squeezed light for increasing the astronomical reach. Squeezed laser light is efficiently produced by degenerate parametric down-conversion in a nonlinear crystal located inside an optical resonator. A spontaneously generated initial pair of indistinguishable photons is amplified to a squeezed vacuum state. Overlapped with bright coherent light, the photo-electric measurement shows a sub-Poissonian photon statistics. Squeezed states have ample applications in nonlocal quantum sensing, device-independent quantum key distribution, and quantum computing. Here, we present our continuous-wave 1550-nm “squeeze laser” with a footprint of 80 × 80 cm. The well-defined output beam has an interference contrast of
$\gtrsim 99\%$
with an overlapped 10-mW beam being in an almost perfect TEM00 mode. The interference result shows 13-dB squeezing of the photon shot noise in balanced detection.