Nanomechanical loudspeaker could detect faint electrical signals

January 26, 2012 — The Joint Quantum Institute (JQI), the Neils Bohr Institute in Copenhagen, and Harvard University researchers developed a theoretical method for detecting weak electrical signals, using a nanomechanical "loudspeaker" and laser-based photon signals.

"We envision coupling a nanomechanical membrane to an electrical circuit so that an electrical signal, even if exceedingly faint, will cause the membrane to quiver slightly as a function of the strength of that signal," says JQI physicist Jake Taylor. "We can then bounce photons from a laser off that membrane and read the signal by measuring the modulation of the reflected light as it is shifted by the motion of the membrane. This leads to a change in the wavelength of the light."

If demonstrated through experiment, the work could have a tremendous impact on detection of low-power radio signals, magnetic resonance imaging (MRI), and the developing field of quantum information science.

Figure. The proposed nano mechanical device detecting a signal produced by the quantum-mechanical spin of a group of atoms. The atoms generate a faint radiofrequency signal in a coil (L) connected to microscale wires that form an electrical capacitor. This vibrates the nanomembrane, which in turn affects the resonant frequency of a laser optical cavity. The output is light at frequency that is the sum of the original laser frequency plus the signal from the atoms. SOURCE: Taylor/NIST.

The ability to detect extremely faint electrical signals could improve MRI medical procedures, reducing the size of the superconducting magnets and eliminating the scan tube.

The concept could also be applied in photonics communications, according to Taylor. One popular quantum information system design uses light to transfer information among qubits, entangled particles that will exploit the inherent weirdness of quantum phenomena to perform certain calculations impossible for current computers. The ‘nanospeaker’ could be used to translate low-energy signals from a quantum processor to optical photons, where they can be detected and transmitted from one qubit to another.

According to the team’s calculations, translating the mechanical motion of the "loudspeaker" device into photons will siphon a considerable amount of heat out of the system (from room temperature to 3 kelvin or -270C), reducing noise during signal detection.

The concept is reported at: J. M. Taylor, A. S. Sørensen, C. M. Marcus and E. S. Polzik. Laser cooling and optical detection of excitations in a LC electrical circuit. Phys. Rev. Lett. 107, 273601. Published online Dec. 27, 2011. Access it here:

The JQI is a collaborative venture of the National Institute of Standards and Technology (NIST) and the University of Maryland, College Park.

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