Silicon system produces ‘squeezed light’
CALTECH (US) — A new system constructed on a silicon microchip offers a more useful way to produce the ultraquiet light known as squeezed light.
One of the many counterintuitive and bizarre insights of quantum mechanics is that even in a vacuum—what many of us think of as an empty void—all is not completely still.
Low levels of noise, known as quantum fluctuations, are always present. Always, that is, unless you can pull off a quantum trick. And that’s just what a team led by researchers at the California Institute of Technology (Caltech) has done.
The group engineered the miniature silicon system that produces a type of light that is quieter at certain frequencies—meaning it has fewer quantum fluctuations—than what is usually present in a vacuum.
This “squeezed light” is useful for making precise measurements at lower power levels than are required when using normal light.
Although other research groups previously have produced squeezed light, the new system generates the ultraquiet light in a way that can be more easily adapted to a variety of sensor applications.
“This system should enable a new set of precision microsensors capable of beating standard limits set by quantum mechanics,” says Oskar Painter, a professor of applied physics at Caltech and the senior author on a paper in the journal Nature that describes the system.
“Our experiment brings together, in a tiny microchip package, many aspects of work that has been done in quantum optics and precision measurement over the last 40 years.”
Perfect for electronics
In the past, squeezed light has been made using so-called nonlinear materials, which have unusual optical properties. This latest work marks the first time that squeezed light has been produced using silicon, a standard material.
“We work with a material that’s very plain in terms of its optical properties,” says Amir Safavi-Naeini, a graduate student in Painter’s group and one of three lead authors on the new paper. “We make it special by engineering or punching holes into it, making these mechanical structures that respond to light in a very novel way.
“Of course, silicon is also a material that is technologically very amenable to fabrication and integration, enabling a great many applications in electronics.”
Cancel each other out
In this new system, a waveguide feeds laser light into a cavity created by two tiny silicon beams. Once there, the light bounces back and forth a bit thanks to the engineered holes, which effectively turn the beams into mirrors.
When photons-particles of light-strike the beams, they cause the beams to vibrate. And the particulate nature of the light introduces quantum fluctuations that affect those vibrations.
Typically, such fluctuations mean that in order to get a good reading of a signal, you would have to increase the power of the light to overcome the noise. But by increasing the power you also introduce other problems, such as introducing excess heat into the system.
Ideally, then, any measurements should be made with as low a power as possible. “One way to do that,” says Safavi-Naeini, “is to use light that has less noise.”
And that’s exactly what the new system does; it has been engineered so that the light and beams interact strongly with each other—so strongly, in fact, that the beams impart the quantum fluctuations they experience back on the light.
And, as is the case with the noise-canceling technology used, for example, in some headphones, the fluctuations that shake the beams interfere with the fluctuations of the light.
They effectively cancel each other out, eliminating the noise in the light.
“This is a demonstration of what quantum mechanics really says: light is neither a particle nor a wave; you need both explanations to understand this experiment,” says Safavi-Naeini. “You need the particle nature of light to explain these quantum fluctuations, and you need the wave nature of light to understand this interference.”
The National Science Foundation, the Gordon and Betty Moore Foundation, the Air Force Office of Scientific Research, and the Kavli Nanoscience Institute at Caltech supported the work.
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