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'Squeezed light' on a chip overcomes MEMS quantum limit

Posted: 28 Oct 2013 ?? ?Print Version ?Bookmark and Share

Keywords:DARPA? MEMS sensor? medical biosensor? military system? Heisenberg limit?

Microelectromechanical systems (MEMS) are being used in modern military systems such as gyroscopes for navigation, tiny microphones for lightweight radios, and medical biosensors for assessing the wounded. Such applications benefit from the portability, low power and low cost of MEMS devices. However, they still operate well below their theoretical performance limits due to two obstacles: thermal fluctuations and random quantum fluctuations, a barrier known as the standard quantum limit.

DARPA's Optical Radiation Cooling and Heating in Integrated Devices (ORCHID) programme seeks to overcome the latter obstacle to MEMS device performance. Overcoming the standard quantum limit, or Heisenberg limit, requires delicate engineering of the quantum state of the device. ORCHID is combining micro-optical and mechanical components into a single "optomechanical" device. Paired with novel measurement techniques, these devices can perform beyond the standard quantum limit.

In the latest programme milestone, ORCHID researchers at the California Institute of Technology have reported a method to generate specially-tailored "squeezed light" on a chip. "The Caltech team altered the typical noise properties of light using a deformable optical cavity to generate squeezed light with reduced amplitude fluctuations," said Jamil Abo-Shaeer, the DARPA programme manager who led the ORCHID programme. "The researchers cleverly reduce the amplitude noise of the light at the expense of another parameter (phase) not involved in the measurement. Overall, the total noise in the system is unchanged, it's just redirected away from a parameter researchers need to measure. And unlike previous tabletop demonstrations, this new scheme uses chip-scale, silicon-based technology, giving it the potential for practical use in deployable sensors."

Silicon micromechanical resonator used to generate squeezed light

Figure 1: Silicon micromechanical resonator used to generate squeezed light. Source: Caltech.

Squeezed light has long been a focus for researchers seeking more precise measurements. For example, one thrust of DARPA's Quantum-Assisted Sensing and Readout (QuASAR) programme is optomechanical accelerometers, where squeezed light could play an important role in boosting accelerometer sensitivity. QuASAR researchers at the University of Colorado, as described in a recent paper in Physical Review XStrong Optomechanical Squeezing of Lightproduced squeezed light using an optomechanical architecture consisting of a millimeter-sized silicon-nitride membrane coupled to a Fabry-Perot optical cavity. Other QuASAR thrusts, including magnetic field sensing and time-keeping, could also achieve performance boosts by employing squeezing.

The squeezed light approach is just the latest breakthrough in a programme that quickly transitions basic research to practical applications. Since its launch in 2010, ORCHID has also developed integrated optomechanical devices for low-phase-noise microwave oscillators, which are useful for a variety of DoD applications including secure communication, navigation and surveillance. ORCHID technologies have also benefitted optical signal processing for on-chip light delays, switches, efficient optical wavelength conversion, light storage and high-speed tunable optical filters.

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