[Paper Review] Detecting Thermal Acoustic Radiation with an Optomechanical Antenna

Robinjeet Singh, Thomas Purdy|arXiv (Cornell University)|Nov 21, 2019

Mechanical and Optical Resonators2 citations

TL;DR

This paper demonstrates that a silicon nitride membrane optomechanical resonator can detect thermal acoustic radiation from a remote macroscopic bath acting as an acoustic blackbody. By decoupling the nanomechanical mode temperature from the local material temperature, the system enables precise thermometry and photoacoustic imaging, offering a pathway to suppress self-heating in quantum optomechanics.

ABSTRACT

Nanomechanical systems are generally embedded in a macroscopic environment where the sources of thermal noise are difficult to pinpoint. We engineer a silicon nitride membrane optomechanical resonator such that its thermal noise is acoustically driven by a spatially well-defined remote macroscopic bath. This bath acts as an acoustic blackbody emitting and absorbing acoustic radiation through the silicon substrate. Our optomechanical system acts as a sensitive detector for the blackbody temperature and for photoacoustic imaging. We demonstrate that the nanomechanical mode temperature is governed by the blackbody temperature and not by the local material temperature of the resonator. Our work presents a route to mitigate self-heating effects in optomechanical thermometry and other quantum optomechanics experiments, as well as acoustic communication in quantum information.

Motivation & Objective

• To isolate and detect thermal acoustic radiation from a remote macroscopic bath in a nanomechanical system.
• To address the challenge of self-heating effects in optomechanical thermometry by decoupling the mechanical mode temperature from the local material temperature.
• To demonstrate that the nanomechanical mode is governed by the blackbody temperature of the acoustic bath rather than the resonator's local temperature.
• To enable applications in quantum optomechanics and acoustic communication by suppressing thermal noise from local sources.

Proposed method

• Engineered a silicon nitride membrane as an optomechanical resonator with tailored acoustic coupling to a remote macroscopic bath.
• Used the silicon substrate as a waveguide for acoustic radiation between the bath and the resonator.
• Treated the remote bath as an acoustic blackbody emitter and absorber of acoustic radiation.
• Employed optical readout to monitor the mechanical mode temperature and correlate it with the blackbody temperature.
• Characterized the system's response to varying bath temperatures to confirm thermal radiation dominance over local heating.
• Validated that the mechanical mode temperature tracks the blackbody temperature rather than the local temperature of the resonator.

Experimental results

Research questions

• RQ1 Can a nanomechanical system detect thermal acoustic radiation from a remote macroscopic bath?
• RQ2 To what extent does the mechanical mode temperature depend on the blackbody temperature of the bath versus the local material temperature?
• RQ3 Can acoustic blackbody radiation be harnessed to suppress self-heating in optomechanical thermometry?
• RQ4 Is the system suitable for photoacoustic imaging and quantum acoustic communication?

Key findings

• The nanomechanical mode temperature is governed by the temperature of the remote acoustic blackbody bath, not by the local temperature of the resonator.
• Thermal noise in the system is primarily driven by acoustic radiation from the remote bath, not by local thermal fluctuations.
• The optomechanical system acts as a sensitive detector for blackbody temperature, enabling precise thermometry.
• The system enables photoacoustic imaging by detecting acoustic radiation emitted from a sample via the blackbody bath.
• Self-heating effects in optomechanical experiments can be mitigated by isolating the mechanical mode from local thermal sources.
• The results open a pathway for acoustic communication in quantum information systems using engineered blackbody radiation.