Optical detection of radio waves through a nanomechanical transducer

TLDR: In this article, a room-temperature nanomechanical transducer that couples efficiently to both radio waves and light allows radio-frequency signals to be detected as an optical phase shift with quantum-limited sensitivity.

Abstract: A room-temperature nanomechanical transducer that couples efficiently to both radio waves and light allows radio-frequency signals to be detected as an optical phase shift with quantum-limited sensitivity Many applications, from medical imaging and radio astronomy to navigation and wireless communication, depend on the faithful transmission and detection of weak radio-frequency microwaves Here Eugene Polzik and co-workers demonstrate a completely new capability in this area — the conversion of weak radio waves into laser signals using a nanomechanical oscillator The oscillator, a membrane made from silicon nitride, can couple simultaneously to radio signals and light reflected off its surface and this feature can be used to measure the radio signals as optical phase shifts, with quantum-limited sensitivity Compared to existing detectors, this approach has the advantage of working at room temperature, and the signals produced can be readily transferred into standard optical fibres Low-loss transmission and sensitive recovery of weak radio-frequency and microwave signals is a ubiquitous challenge, crucial in radio astronomy, medical imaging, navigation, and classical and quantum communication Efficient up-conversion of radio-frequency signals to an optical carrier would enable their transmission through optical fibres instead of through copper wires, drastically reducing losses, and would give access to the set of established quantum optical techniques that are routinely used in quantum-limited signal detection Research in cavity optomechanics1,2 has shown that nanomechanical oscillators can couple strongly to either microwave3,4,5 or optical fields6,7 Here we demonstrate a room-temperature optoelectromechanical transducer with both these functionalities, following a recent proposal8 using a high-quality nanomembrane A voltage bias of less than 10 V is sufficient to induce strong coupling4,6,7 between the voltage fluctuations in a radio-frequency resonance circuit and the membrane’s displacement, which is simultaneously coupled to light reflected off its surface The radio-frequency signals are detected as an optical phase shift with quantum-limited sensitivity The corresponding half-wave voltage is in the microvolt range, orders of magnitude less than that of standard optical modulators The noise of the transducer—beyond the measured Johnson noise of the resonant circuit—consists of the quantum noise of light and thermal fluctuations of the membrane, dominating the noise floor in potential applications in radio astronomy and nuclear magnetic imaging Each of these contributions is inferred to be when balanced by choosing an electromechanical cooperativity of with an optical power of 1 mW The noise temperature of the membrane is divided by the cooperativity For the highest observed cooperativity of , this leads to a projected noise temperature of 40 mK and a sensitivity limit of Our approach to all-optical, ultralow-noise detection of classical electronic signals sets the stage for coherent up-conversion of low-frequency quantum signals to the optical domain8,9,10,11