Squeezed light produced using silicon micromechanical system

August 7, 2013
Optomechanical device. a, Scanning electron microscope image of a waveguide-coupled zipper optomechanical cavity. b, Left: close-up of the coupling region between one of the cavities and the waveguide. Right: finite-element method (FEM) simulation of the cavity field leaking into the waveguide (log scale). c, Top: FEM simulation showing the in-plane electrical field of the fundamental optical cavity mode. Bottom: FEM simulation of the displacement of the fundamental in-plane differential mode of the structure. The mechanical motion, modifying the gap between the beams, shifts the optical cavity frequency, leading to optomechanical coupling. Credit: (c) Nature, doi: 10.1038/nature12307

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 has engineered a 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 special type of light with fewer fluctuations is known as squeezed light and is useful for making at lower power levels than are required when using normal light. Although other research groups previously have produced squeezed light, the Caltech team's new system, which is miniaturized on a silicon microchip, 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 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 that describes the system; the paper appears in the August 8 issue of the journal Nature. "Our experiment brings together, in a tiny package, many aspects of work that has been done in quantum optics and over the last 40 years."

The history of squeezed light is closely associated with Caltech. More than 30 years ago, Kip Thorne, Caltech's Richard P. Feynman Professor of Theoretical Physics, Emeritus, and physicist Carlton Caves (PhD '79) theorized that squeezed light would enable scientists to build more sensitive detectors that could make more precise measurements. A decade later, Caltech's Jeff Kimble, the William L. Valentine Professor and professor of physics, and his colleagues conducted some of the first experiments using squeezed light. Since then, the LIGO (Laser Interferometer Gravitational-Wave Observatory) Scientific Collaboration has invested heavily in research on squeezed light because of its potential to enhance the sensitivity of gravitational-wave detectors.

In the past, squeezed light has been made using so-called nonlinear materials, which have unusual optical properties. This latest Caltech work marks the first time that 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 (PhD '13), 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."

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 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 , and you need the wave nature of light to understand this interference."

In the experiment, a detector measuring the noise in the light as a function of frequency showed that in a frequency range centered around 28 MHz, the system produces light with less noise than what is present in a vacuum—the standard quantum limit. "But one of the interesting things," Safavi-Naeini adds, "is that by carefully designing our structures, we can actually choose the frequency at which we go below the vacuum." Many signals are specific to a particular frequency range—a certain audio band in the case of acoustic signals, or, in the case of LIGO, a frequency intimately related to the dynamics of astrophysical objects such as circling black holes. Because the optical squeezing occurs near the mechanical resonance frequency where an individual device is most sensitive to external forces, this feature would enable the system studied by the Caltech team to be optimized for targeting specific signals.

"This new way of 'squeezing ' in a silicon micro-device may provide new, significant applications in sensor technology," said Siu Au Lee, program officer at the National Science Foundation, which provided support for the work through the Institute for Quantum Information and Matter, a Physics Frontier Center. "For decades, NSF's Physics Division has been supporting basic research in , precision measurements and nanotechnology that laid the foundation for today's accomplishments."

Explore further: Closing in on Einstein's window to the universe

More information: The paper is titled "Squeezed light from a silicon micromechanical resonator." dx.doi.org/10.1038/nature12307

Related Stories

Closing in on Einstein's window to the universe

August 1, 2013

(Phys.org) —Nearly a century after the world's greatest physicist, Albert Einstein, first predicted the existence of gravitational waves, a global network of gravitational wave observatories has moved a step closer to detecting ...

Squeezed light from single atoms

June 30, 2011

(PhysOrg.com) -- Max Planck Institute of Quantum Optics scientists generate amplitude-squeezed light fields using single atoms trapped inside optical cavities.

Improving measurements by reducing quantum noise

June 27, 2013

If you want to measure something very precisely, such as slight variations of a length, then you are very likely to use light waves. However, many effects, such as variations of gravity, or surface forces, can only be measured ...

Binding together repelling atoms

July 31, 2013

Basic chemistry tells us that a bond between atoms can form if it is energetically more favorable for the atoms to stick together than staying apart. This fundamentally requires an attractive force between the atoms. However, ...

Recommended for you

Probe for nanofibers has atom-scale sensitivity

January 20, 2017

Optical fibers are the backbone of modern communications, shuttling information from A to B through thin glass filaments as pulses of light. They are used extensively in telecommunications, allowing information to travel ...

Magnetic recording with light and no heat on garnet

January 19, 2017

A strong, short light pulse can record data on a magnetic layer of yttrium iron garnet doped with Co-ions. This was discovered by researchers from Radboud University in the Netherlands and Bialystok University in Poland. ...


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Aug 07, 2013
Does anyone have an idea of how many DB of extra gain in sensitivity you get from this squeezed light technique? Only 3 DB or so, or could it be higher?
1 / 5 (3) Aug 07, 2013
"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."

Actually light particle is just wave packet of electromagnetic wave. What which we do not know is - wave of what or what is wavy? Maybe this physical view could help to understand it…
not rated yet Sep 11, 2013
The electromagnetic wave of light travelling at/near the speed of light, when it increases in velocity, the electromagnetic wave gains mass, and when the electromagnetic wave gains mass, it loses velocity, and reverts to an electromagnetic wave. So even energy cannot exceed the speed of light.
Now we need to learn the speed of gravity and what it takes to generate gravity. Perhaps we need to measure the speed of electrons around the nucleus of an atom.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.