In a “squeezed state” of light, the quantum-mechanical uncertainty of a particular parameter is reduced—via nonlinear-optics techniques such as four-wave mixing—by narrowing the uncertainty of the measurement parameter of interest (such as intensity) down at the cost of greater uncertainty in another (such as phase). First proposed in 1981, squeezing has become an increasingly important way to drive ultrasensitive systems below the shot-noise limit. In particular, squeezing recently gained attention as one of the techniques used in a recent round of sensitivity upgrades to the LIGO and Virgo gravitational-wave detectors.

In years ahead, we can expect squeezed light to become more common as a technique leveraged in a new generation of quantum sensors. Ben Lawrie of Oak Ridge National Laboratory, USA, told OPN that there are several reasons for that shift.

“In practice,” said Lawrie, “I’d say what happened between 1980 and today is that the level of squeezing that people have been able to generate in optical systems has slowly walked up.” And meanwhile, he continued, “we’ve reached a point where photonic sensors are increasingly engineered to a point where they’re already sitting at that shot-noise limit—and thus are ready for squeezed-light sources to be integrated with them.”

One such integration is explored in OPN’s two-page tutorial for September 2019. For those who would like to dive deeper, we’ve pulled together some references and resources on squeezed light, particularly in modern quantum sensing applications.

Review article

Selected recent demonstrations

Squeezed light and four-wave mixing: Selected background references