Abstract
In canonical optomechanical systems, mechanical vibrations are dynamically encoded on an optical probe field, which reciprocally exerts a backaction force. Because of the weak single-photon coupling strength achieved with macroscopic oscillators, most of the existing experiments were conducted with large photon numbers to achieve sizable effects, thereby hiding the original optomechanical nonlinearity. To increase the optomechanical interaction, we make use of subwavelength-sized ultrasensitive suspended nanowires inserted in the mode volume of a fiber-based microcavity. By scanning the nanowire within the cavity mode volume and measuring its impact on the cavity mode, we obtain a map of the 2D optomechanical interaction. Then, by using the toolbox of nanowire-based force-sensing protocols, we explore the backaction of the optomechanical interaction and map the optical force field experienced by the nanowire. These measurements also allow us to demonstrate the possibility to detect variations of the mean intracavity photon number smaller than unity. This implementation should also allow us to enter the promising regime of cavity optomechanics, where a single intracavity photon can displace the oscillator by more than its zero-point fluctuations, which will open novel perspectives in the field.
- Received 17 September 2020
- Revised 13 January 2021
- Accepted 12 February 2021
DOI:https://doi.org/10.1103/PhysRevX.11.021009
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Cavity optomechanics leverages interactions between a light field and vibrations of a macroscopic oscillator to explore the quantum limits of ultrasensitive measurements. The light can actuate the oscillator via optical forces while, reciprocally, the oscillator’s vibrations get encoded on the light field. In this work, we combine an ultrasensitive force sensor—a suspended silicon carbide nanowire—and a small optical microcavity to provide an optomechanical interaction enhanced to a point where the presence of a single photon inside the cavity displaces the oscillator by more than its residual quantum fluctuations at zero temperature.
Historically, most cavity optomechanics experiments have relied on large numbers of photons to produce measurable vibrations in the oscillator. To boost the optomechanical coupling and detect single photons, we turn to a nanowire whose diameter is smaller than the wavelength of the light in the cavity, which, in turn, requires a precise positioning of the nanowire in the cavity standing wave.
By scanning the nanowire in the cavity, we measure and map out the strength and the orientation of the optomechanical interaction at different positions. This mapping provides a novel characterization of the confined optical fields and allows us to properly investigate the subwavelength structure of the light-nanowire interaction, from which we can identify where in the cavity the coupling strength is strongest. Finally, we demonstrate that the nanowire is sensitive enough to detect variations of the mean intracavity photon number by as little as one photon.
This demonstration opens new perspectives in the field of cavity optomechanics at low photon numbers, in particular toward measurements of optical forces arising from vacuum quantum fluctuations.
