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  • entropic forces“Engineered Entropic Forces Allow Ultrastrong Dynamical Backaction”,
    A. Sawadsky, R. A. Harrison, G. I. Harris, W. W. Wasserman, Y. L. Sfendla, W. P. Bowen, and C. G. Baker

    arXiv:2208.05660, August 2022 [pdf]

    When confined within an optical cavity, light can exert strong radiation pressure forces. Combined with dynamical backaction, this enables important processes such as laser cooling, and applications ranging from precision sensors to quantum memories and interfaces. However, the magnitude of radiation pressure forces is constrained by the energy mismatch between photons and phonons. Here, we overcome this barrier using entropic forces arising from the absorption of light. We show that entropic forces can exceed the radiation pressure force by eight orders of magnitude, and demonstrate this using a superfluid helium third-sound resonator. We develop a framework to engineer the dynamical backaction from entropic forces, applying it to achieve phonon lasing with a threshold three orders of magnitude lower than previous work. Our results present a pathway to exploit entropic forces in quantum devices, and to study nonlinear fluid phenomena such as turbulence and solitons.

  • “Scalable nanomechanical logic gate”,Scalable nanomechanical logic gate
    Erick Romero, Nicolas P. Mauranyapin, Timothy M. F. Hirsch, Rachpon Kalra, Christopher G. Baker, Glen I. Harris, Warwick P. Bowen
    arXiv:2206.11661, June 2022 [pdf]


    Nanomechanical computers promise robust, low energy information processing. However, to date, electronics have generally been required to interconnect gates, while no scalable, purely nanomechanical approach to computing has been achieved. Here, we demonstrate a nanomechanical logic gate in a scalable architecture. Our gate uses the bistability of a nonlinear mechanical resonator to define logical states. These states are efficiently coupled into and out of the gate via nanomechanical waveguides, which provide the mechanical equivalent of electrical wires. Crucially, the input and output states share the same spatiotemporal characteristics, so that the output of one gate can serve as the input for the next. Our architecture is CMOS compatible, while realistic miniaturisation could allow both gigahertz frequencies and an energy cost that approaches the fundamental Landauer limit. Together this presents a pathway towards large-scale nanomechanical computers, as well as neuromorphic networks able to simulate computationally hard problems and interacting many-body systems.

  • “Cryogenic and hermetically sealed packaging of photonic chips for optomechanics”,
    W. W. Wasserman, R. A. Harrison, G. I. Harris, A. Sawadsky, Y. Sfendla, W. P. Bowen, C. G. Baker
    Optics Express, vol 30, 30822 (2022).
    main text [pdf] supplementary material [pdf]  arXiv [pdf]


    We demonstrate a hermetically sealed packaging system for integrated photonic devices at cryogenic temperatures with plug-and-play functionality. This approach provides the ability to encapsulate a controlled amount of gas into the optical package allowing helium to be used as a heat-exchange gas to thermalize photonic devices, or condensed into a superfluid covering the device. This packaging system was tested using a silicon-on-insulator slot waveguide resonator which fills with superfluid 4He below the transition temperature. To optimize the fiber-to-chip optical integration 690 tests were performed by thermally cycling optical fibers bonded to various common photonic chip substrates (silicon, silicon oxide and HSQ) with a range of glues (NOA 61, NOA 68, NOA 88, NOA 86H and superglue). This showed that NOA 86H (a UV curing optical adhesive with a latent heat catalyst) provided the best performance under cryogenic conditions for all the substrates tested. The technique is relevant to superfluid optomechanics experiments, as well as quantum photonics and quantum optomechanics applications.

  • Book Chapter: Superfluid SBS“,
    Warwick P. Bowen, Christopher G. Baker, Jack G. E. Harris,
    Part of volume Brillouin Scattering Part 1, Editor(s): Benjamin J. Eggleton, Michael J. Steel, Christopher G. Poulton, Semiconductors and Semimetals, Elsevier, 109, 2022, Pages 193-225, ISBN 9780323989299, DOI: 10.1016/bs.semsem.2022.04.004.    [Author pdf]


    In this chapter, we provide an overview of Brillouin scattering from a quantum fluid, superfluid helium. Its vanishing viscosity at low temperatures, combined with other extreme material properties, provides a choice set of characteristics for Brillouin interactions. We describe the basics of superfluid helium and its optoacoustic interactions, both in bulk and thin films. We provide an overview of the historic contributions Brillouin scattering has made to our understanding of superfluid helium, and cover its new use to control superfluid dynamics and the future applications this may enable, particularly quantum optomechanical technologies such as quantum interfaces, sensors, and memories.
    Keywords: Superfluid helium; Brillouin scattering; Cavity optomechanics; Superfluid films; Third sound; First sound; Electrostriction; Radiation pressure; Fountain pressure

  • Book Chapter: The convergence of cavity optomechanics and Brillouin scattering,
    Mikołaj K. Schmidt, Christopher G. Baker, Raphaël Van Laer,
    Part of volume Brillouin Scattering Part 1, Editor(s): Benjamin J. Eggleton, Michael J. Steel, Christopher G. Poulton, Semiconductors and Semimetals, Elsevier, 109, 2022, Pages 93-131,
    ISBN 9780323989299, DOI: 10.1016/bs.semsem.2022.04.005.


    Cavity optomechanics and Brillouin scattering have historically developed as separate fields of study, focused on distinct optoacoustic interaction effects, and realized in different physical platforms. These gaps are now closing rapidly, as researchers embrace the fundamental similarities between the two fields. Both fields study the three-wave mixing between electromagnetic and acoustic waves. Here, we review this convergence by showing how optoacoustic platforms increasingly blur the traditional distinctions between cavity optomechanics and Brillouin scattering. We discuss how the theoretical formalisms used by the two communities can be directly mapped between each other in both waveguides and cavities.
    Keywords: Optoacoustics; Optomechanical feedback; Brillouin scattering


  • cover-image“Electro-Optomechanical Modulation Instability in a Semiconductor Resonator,”
    Pierre Etienne Allain, Biswarup Guha, Christophe Baker, David Parrain, Aristide Lemaître, Giuseppe Leo, and Ivan Favero,
    Physical Review Letters 126, 243901 (2021).
    main text (pdf) supplementary material (pdf)
    Featured on the cover of PRL


    In semiconductor nano-optomechanical resonators, several forms of light-matter interaction can enrich the canonical radiation pressure coupling of light and mechanical motion and give rise to new dynamical regimes. Here, we observe an electro-optomechanical modulation instability in a gallium arsenide disk resonator. The regime is evidenced by the concomitant formation of regular and dense combs in the radio-frequency and optical spectrums of the resonator associated with a permanent pulsatory dynamics of the mechanical motion and optical intensity. The mutual coupling between light, mechanical oscillations, carriers, and heat, notably through photothermal interactions, stabilizes an extended mechanical comb in the ultrahigh frequency range that can be controlled optically.

  • acoustic-mode-filtering“Tunnelling of transverse acoustic waves on a silicon chip,”
    N. P. Mauranyapin, E. Romero, R. Kalra, G. Harris, C. G. Baker, and W. P. Bowen,
    Physical Review Applied, 15, 5, 054036, May 2021.
    main text (pdf) supplementary material (pdf) arXiv


    Nanomechanical circuits for transverse acoustic waves promise to enable new approaches to computing, precision biochemical sensing, and many other applications. However, progress is hampered by the lack of precise control of the coupling between nanomechanical elements. Here, we demonstrate virtual-phonon coupling between transverse mechanical elements, exploiting tunneling through a zero-mode acoustic barrier. This allows the construction of large-scale nanomechanical circuits on a silicon chip, for which we develop a scalable fabrication technique. As example applications, we build mode-selective acoustic mirrors with controllable reflectivity and demonstrate acoustic spatial-mode filtering. Our work paves the way toward applications such as fully nanomechanical computer processors and distributed nanomechanical sensors, and exploration of the rich landscape of nonlinear nanomechanical dynamics.

  • Superfluid_phononic_crystal“Extreme quantum nonlinearity in superfluid thin-film surface waves,”
    Y. L. Sfendla, C. G. Baker, G. I. Harris, L. Tian, and W. P. Bowen,
    Npj Quantum Information 7, 1 (2021).
    Main text [pdf] Supplementary information [pdf] arXiv [pdf].


    We show that highly confined superfluid films are extremely nonlinear mechanical resonators, offering the prospect to realize a mechanical qubit. Specifically, we consider third-sound surface waves, with nonlinearities introduced by the van der Waals interaction with the substrate. Confining these waves to a disk, we derive analytic expressions for the cubic and quartic nonlinearities and determine the resonance frequency shifts they introduce. We predict single-phonon shifts that are three orders of magnitude larger than in current state-of-the-art nonlinear resonators. Combined with the exquisitely low intrinsic dissipation of superfluid helium and the strongly suppressed acoustic radiation loss in phononic crystal cavities, we predict that this could allow blockade interactions between phonons as well as two-level-system-like behavior. Our work provides a pathway towards extreme mechanical nonlinearities, and towards quantum devices that use mechanical resonators as qubits.

  • Er_doped_double_disks_PRAOptically Tunable Photoluminescence and Up-Conversion Lasing on a Chip,
    C. J. Bekker, C. G. Baker, and W. P. Bowen,
    Physical Review Applied 15, 034022 (2021).
    main text (pdf) arXiv [pdf]
  • Abstract

    The ability to tune the wavelength of light emission on a silicon chip is important for scalable photonic networks, distributed photonic sensor networks, and next generation computer architectures. Here we demonstrate light emission in a chip-scale optomechanical device, with wide tunablity provided by a combination of radiation pressure and photothermal effects. To achieve this, we develop an optically active double-disk optomechanical system through implantation of erbium ions. We observe frequency tuning of photoluminescence in the telecommunications band with a wavelength range of 520 pm, green up-conversion lasing with a threshold of 340±70μW, and optomechanical self-pulsing caused by the interplay of radiation pressure and thermal effects. These results provide a path towards widely tunable micron-scale lasers for photonic networks.


  • “Proposal for a quantum traveling Brillouin resonator,”Superfluid_Brillouin2
    G. I. Harris, A. Sawadsky, Y. L. Sfendla, W. W. Wasserman, W. P. Bowen, and C. G. Baker,
    Optics Express, 28, 15, 22450-22461, Jul 2020
    Main text [(pdf)] – [arXiv (pdf)].
  • Abstract

    Brillouin systems operating in the quantum regime have recently been identified as a valuable tool for quantum information technologies and fundamental science. However, reaching the quantum regime is extraordinarily challenging, owing to the stringent requirements of combining low thermal occupation with low optical and mechanical dissipation, and large coherent phonon-photon interactions. Here, we propose an on-chip liquid based Brillouin system that is predicted to exhibit large phonon-photon coupling with exceptionally low acoustic dissipation. The system is comprised of a silicon-based “slot” waveguide filled with superfluid helium. This type of waveguide supports optical and acoustical traveling waves, strongly confining both fields into a subwavelength-scale mode volume. It serves as the foundation of an on-chip traveling wave Brillouin resonator with an electrostrictive single photon optomechanical coupling rate exceeding 240 kHz. Such devices may enable applications ranging from ultra-sensitive superfluid-based gyroscopes, to non-reciprocal optical circuits. Furthermore, this platform opens up new possibilities to explore quantum fluid dynamics in a strongly interacting condensate.

  • “Strong opticCaptureal coupling through superfluid Brillouin lasing,”
    X. He, G.I. Harris, C.G. Baker, A. Sawadsky, Y.L. Sfendla, Y.P. Sachkou, S. Forstner, and W.P. Bowen,
    Nature Physics (2020).
    main text (pdf) supplementary information (pdf)  readcube [pdf link] [ArXiv 1907.06811 (pdf)].
    See also Nature Photonics News & Views by David Pile:
  • Abstract

    Brillouin scattering has applications ranging from signal processing, sensing and microscopy, to quantum information and fundamental science. Most of these applications rely on the electrostrictive interaction between light and phonons. Here we show that in liquids optically-induced surface deformations can provide an alternative and far stronger interaction. This allows the demonstration of ultralow threshold Brillouin lasing and strong phonon-mediated optical coupling for the first time. This form of strong coupling is a key capability for Brillouin-reconfigurable optical switches and circuits, for photonic quantum interfaces, and to generate synthetic electromagnetic fields. While applicable to liquids quite generally, our demonstration uses superfluid helium. Configured as a Brillouin gyroscope this provides the prospect of measuring superfluid circulation with unprecedented precision, and to explore the rich physics of quantum fluid dynamics, from quantized vorticity to quantum turbulence.


  • Science_fig1“Coherent Vortex Dynamics in a Strongly-Interacting Superfluid on a Silicon Chip,”
    Yauhen P. Sachkou, Christopher G. Baker, Glen I. Harris, Oliver R. Stockdale, Stefan Forstner, Matthew T. Reeves, Xin He, David L. McAuslan, Ashton S. Bradley, Matthew J. Davis, Warwick P. Bowen,
    Science, vol. 366, no. 6472, pp. 1480-1485, Dec 2019.
    main text (pdf) supplementary material (pdf) [ArXiv:1902.04409 (pdf)], Feb. 2019.
  • Abstract

    Two-dimensional superfluidity and quantum turbulence are directly connected to the microscopic dynamics of quantized vortices. However, surface effects have prevented direct observations of coherent vortex dynamics in strongly-interacting two-dimensional systems. Here, we overcome this challenge by confining a two-dimensional droplet of superfluid helium at microscale on the atomically-smooth surface of a silicon chip. An on-chip optical microcavity allows laser-initiation of vortex clusters and nondestructive observation of their decay in a single shot. Coherent dynamics dominate, with thermal vortex diffusion suppressed by six orders-of-magnitude. This establishes a new on-chip platform to study emergent phenomena in strongly-interacting superfluids, test astrophysical dynamics such as those in the superfluid core of neutron stars in the laboratory, and construct quantum technologies such as precision inertial sensors.

  • “Propagation and ImagingCapture3 of Mechanical Waves in a Highly Stressed Single-Mode Acoustic Waveguide,”
    E. Romero, R. Kalra, N. P. Mauranyapin, C. G. Baker, C. Meng, and W. P. Bowen,
    Physical Review Applied, vol. 11, no. 6, Jun. 2019.
    main text (pdf) [arXiv:1902.03750 (pdf)]
  • Abstract

    We demonstrate a single-mode acoustic waveguide that enables robust propagation of mechanical waves. The waveguide is a highly stressed silicon-nitride membrane that supports the propagation of out-of-plane modes. In direct analogy to rectangular microwave waveguides, there exists a band of frequencies over which only the fundamental mode is allowed to propagate, while multiple modes are supported at higher frequencies. We directly image the mode profiles using optical heterodyne vibration measurement, showing good agreement with theory. In the single-mode frequency band, we show low-loss propagation (approximately 1 dB/cm) for an approximately 5-MHz mechanical wave. This design is well suited for acoustic circuits interconnecting elements such as nonlinear resonators or optomechanical devices for signal processing, sensing, or quantum technologies.

  • “Modelling of vorticity, sound and their intervortex_thaction in two-dimensional superfluids,”
    Stefan Forstner, Yauhen Sachkou, Matt Woolley, Glen I. Harris, Xin He, Warwick P. Bowen, Christopher G. Baker,
    New Journal of Physics, vol. 21, p. 053029, May 2019.
    [main text (pdf)] [Arxiv 1901.05167 (pdf)]
  • Abstract

    Vorticity in two-dimensional superfluids is subject to intense research efforts due to its role in quantum turbulence, dissipation and the BKT phase transition. Interaction of sound and vortices is of broad importance in Bose–Einstein condensates and superfluid helium. However, both the modelling of the vortex flow field and of its interaction with sound are complicated hydrodynamic problems, with analytic solutions only available in special cases. In this work, we develop methods to compute both the vortex and sound flow fields in an arbitrary two-dimensional domain. Further, we analyse the dispersive interaction of vortices with sound modes in a two-dimensional superfluid and develop a model that quantifies this interaction for any vortex distribution on any two-dimensional bounded domain, possibly non-simply connected, exploiting analogies with fluid dynamics of an ideal gas and electrostatics. As an example application we use this technique to propose an experiment that should be able to unambiguously detect single circulation quanta in a helium thin film.


  • “Free spectral range electripicturecal tuning of a high quality on-chip microcavity,”
    C. Bekker, C. Baker, R. Kalra, H-H. Cheng, B-B. Li, V. Prakash, W. P. Bowen,
    Opt. Express, vol. 26, pp. 33649–33670, Dec. 2018.
    [main text (pdf)] [Arxiv 1808.01908 (pdf)]
    2018 Raith Micrograph Award 1st place (link)
  • Abstract

    Reconfigurable photonic circuits have applications ranging from next-generation computer architectures to quantum networks, coherent radar and optical metamaterials. Here, we demonstrate an on-chip high quality microcavity with resonances that can be electrically tuned across a full free spectral range (FSR). FSR tuning allows resonance with any source or emitter, or between any number of networked microcavities. We achieve it by integrating nanoelectronic actuation with strong optomechanical interactions that create a highly geometry-dependent effective refractive index. This allows low voltages and sub-nanowatt power consumption. We demonstrate a basic reconfigurable photonic network, bringing the microcavity into resonance with an arbitrary mode of a microtoroidal optical cavity across a telecommunications fibre link. Our results have applications beyond photonic circuits, including widely tuneable integrated lasers, reconfigurable optical filters for telecommunications and astronomy, and on-chip sensor networks.


  • “Injection Cover v1locking of an electro-optomechanical device,”
    C. Bekker, R. Kalra, C. Baker, and W. P. Bowen,
    Optica, vol. 4, pp. 1196-1204, Sept. 2017.
    [main text (pdf)] [Supplementary information (pdf)] [Arxiv 1707.01704 (pdf)]
  • Abstract

    Advances in optomechanics have enabled significant achievements in precision sensing and control of matter, including detection of gravitational waves and cooling of mechanical systems to their quantum ground states. Recently, the inherent nonlinearity in the optomechanical interaction has been harnessed to explore synchronization effects, including the spontaneous locking of an oscillator to a reference injection signal delivered via the optical field. Here, we present, to the best of our knowledge, the first demonstration of a radiation-pressure-driven optomechanical system locking to an inertial drive, with actuation provided by an integrated electrical interface. We use the injection signal to suppress the drift in the optomechanical oscillation frequency, strongly reducing phase noise by over 55 dBc/Hz at 2 Hz offset. We further employ the injection tone to tune the oscillation frequency by more than 2 million times its narrowed linewidth. In addition, we uncover previously unreported synchronization dynamics, enabled by the independence of the inertial drive from the optical drive field. Finally, we show that our approach may enable control of the optomechanical gain competition between different mechanical modes of a single resonator. The electrical interface allows enhanced scalability for future applications involving arrays of injection-locked precision sensors.

  • “Light-Mediated Cascaded Locking ofsynchro_3disks_v6 Multiple Nano-Optomechanical Oscillators,”
    E. Gil-Santos, M. Labousse, C. Baker, A. Goetschy, W. Hease, C. Gomez, A. Lemaître, G. Leo, C. Ciuti, and I. Favero,
    Physical Review Letters, vol. 118, p. 063605, Feb. 2017.
    [main text (pdf)] [Supplementary information (pdf)] [Arxiv 1609.09712 (pdf)]
    Selected as an Editor’s suggestion.
    Selected for the cover of PRL (link).
  • Abstract

    Collective phenomena emerging from nonlinear interactions between multiple oscillators, such as synchronization and frequency locking, find applications in a wide variety of fields. Optomechanical resonators, which are intrinsically nonlinear, combine the scientific assets of mechanical devices with the possibility of long distance controlled interactions enabled by traveling light. Here we demonstrate light-mediated frequency locking of three distant nano-optomechanical oscillators positioned in a cascaded configuration. The oscillators, integrated on a chip along a common coupling waveguide, are optically driven with a single laser and oscillate at gigahertz frequency. Despite an initial mechanical frequency disorder of hundreds of kilohertz, the guided light locks them all with a clear transition in the optical output. The experimental results are described by Langevin equations, paving the way to scalable cascaded optomechanical configurations.

  • “Scalable high-precision tuniDTrU7IdW4AA-Ismng of photonic resonators by resonant cavity-enhanced photoelectrochemical etching,”
    E. Gil-Santos, C. Baker, A. Lemaître, C. Gomez, G. Leo, and I. Favero,
    Nature Communications, vol. 8, p. 14267, Jan. 2017.
    [main text (pdf)] [Supplementary information (pdf)]
    Selected as one of 12 ‘Cool Physics images of 2017’ by Nature editors (link)
    See also related patent WO2016146409 (link) (pdf)
  • Abstract

    Photonic lattices of mutually interacting indistinguishable cavities represent a cornerstone of collective phenomena in optics and could become important in advanced sensing or communication devices. The disorder induced by fabrication technologies has so far hindered the development of such resonant cavity architectures, while post-fabrication tuning methods have been limited by complexity and poor scalability. Here we present a new simple and scalable tuning method for ensembles of microphotonic and nanophotonic resonators, which enables their permanent collective spectral alignment. The method introduces an approach of cavity-enhanced photoelectrochemical etching in a fluid, a resonant process triggered by sub-bandgap light that allows for high selectivity and precision. The technique is presented on a gallium arsenide nanophotonic platform and illustrated by finely tuning one, two and up to five resonators. It opens the way to applications requiring large networks of identical resonators and their spectral referencing to external etalons.


  • “Theoretical CaptureNJPframework for thin film superfluid optomechanics: towards the quantum regime,”
    C. Baker, G. I. Harris, D. L. McAuslan, Y. Sachkou, X. He, and W. P. Bowen,
    New Journal of Physics, vol. 18, p. 123025, Dec. 2016.
    [main text (pdf)]
    [Arxiv 1609.07265 (pdf)]

    Download related Mathematica file for calculation of superfluid third sound mode properties

  • Abstract

    Excitations in superfluid helium represent attractive mechanical degrees of freedom for cavity optomechanics schemes. Here we numerically and analytically investigate the properties of optomechanical resonators formed by thin films of superfluid 4He covering micrometer-scale whispering gallery mode cavities. We predict that through proper optimization of the interaction between film and optical field, large optomechanical coupling rates g0>2π×100 kHz and single photon cooperativities C0>10 are achievable. Our analytical model reveals the unconventional behaviour of these thin films, such as thicker and heavier films exhibiting smaller effective mass and larger zero point motion. The optomechanical system outlined here provides access to unusual regimes such as g0>ΩM and opens the prospect of laser cooling a liquid into its quantum ground state.

  • “Nondestructivefiber Profilometry of Optical Nanofibers,”
    L. S. Madsen, C. Baker, H. Rubinsztein-Dunlop, and W. P. Bowen,
    Nano Letters, vol. 16, p. 7333, Nov. 2016.
    [Arxiv 1606.04064 (pdf)]
  • Abstract

    Single-mode optical nanofibers are a central component of a broad range of applications and emerging technologies. Their fabrication has been extensively studied over the past decade, but imaging of the final submicrometer products has been restricted to destructive or low-precision techniques. Here, we demonstrate an optical scattering-based scanning method that uses a probe nanofiber to locally scatter the evanescent field of a sample nanofibre. The method does not damage the sample nanofiber and is easily implemented by only using the same equipment as in a standard fiber-puller setup. We demonstrate the subnanometer radial resolution at video rates (0.7 nm in 10 ms) on single mode nanofibers, allowing for a complete high-precision profile to be obtained within minutes of fabrication. The method thus enables nondestructive, fast, and precise characterization of optical nanofibers, with applications ranging from optical sensors and cold atom traps to nonlinear optics.

  • “High Thumbnail_OEbandwidth on-chip capacitive tuning of microtoroid resonators,”
    C. Baker, C. Bekker, D. L. McAuslan, E. Sheridan, and W. P. Bowen,
    Optics Express, vol. 24, p. 20400, Sept. 2016.
    [main text (pdf)]
    [Arxiv 1605.07281 (pdf)]
  • Abstract

    We report on the design, fabrication and characterization of silica microtoroid based cavity opto-electromechanical systems (COEMS). Electrodes patterned onto the microtoroid resonators allow for rapid capacitive tuning of the optical whispering gallery mode resonances while maintaining their ultrahigh quality factor, enabling applications such as efficient radio to optical frequency conversion, optical routing and switching applications.

  • “Laser v12_flare3cooling and control of excitations in superfluid helium,”
    G. I. Harris, D. L. McAuslan, E. Sheridan, Y. Sachkou, C. Baker, and W. P. Bowen,
    Nature Physics, vol. 12, pp. 788–793, Aug. 2016.
    [main text (pdf)] [Supplementary information (pdf)] [Arxiv 1506.04542 (pdf)]
    Featured in “Using laser light to cool a quantum liquid” (link).
  • Abstract

    Superfluidity is a quantum state of matter that exists macroscopically in helium at low temperatures. The elementary excitations in superfluid helium have been probed with great success using techniques such as neutron and light scattering. However, measurements of phonon excitations have so far been limited to average thermodynamic properties or the driven response far out of thermal equilibrium. Here, we use cavity optomechanics to probe the thermodynamics of phonon excitations in real time. Furthermore, strong light-matter interactions allow both laser cooling and amplification. This represents a new tool to observe and control superfluid excitations that may provide insight into phonon-phonon interactions, quantized vortices and two-dimensional phenomena such as the Berezinskii-Kosterlitz-Thouless transition. The third sound modes studied here also offer a pathway towards quantum optomechanics with thin superfluid films, including the prospect of femtogram masses, high mechanical quality factors, strong phonon-phonon and phonon-vortex interactions, and self-assembly into complex geometries with sub-nanometre feature size.

  • “MicrophotonicThumbnail Forces from Superfluid Flow,”
    D. McAuslan, G. Harris, C. Baker, Y. Sachkou, X. He, E. Sheridan, and W. Bowen,
    Physical Review X, vol. 6, p. 021012, Apr. 2016.
    [main text (pdf)] [Supplementary information (pdf)]
    [Arxiv 1512.07704 (pdf)]
    Selected for a Focus in Physics “Superfluid Increases Force of Laser Light”, Physics 9, 47, April 2016.
  • Abstract

    In cavity optomechanics, radiation pressure and photothermal forces are widely utilized to cool and control micromechanical motion, with applications ranging from precision sensing and quantum information to fundamental science. Here, we realize an alternative approach to optical forcing based on superfluid flow and evaporation in response to optical heating. We demonstrate optical forcing of the motion of a cryogenic microtoroidal resonator at a level of 1.46 nN, roughly 1 order of magnitude larger than the radiation pressure force. We use this force to feedback cool the motion of a microtoroid mechanical mode to 137 mK. The photoconvective forces we demonstrate here provide a new tool for high bandwidth control of mechanical motion in cryogenic conditions, while the ability to apply forces remotely, combined with the persistence of flow in superfluids, offers the prospect for new applications.

  • “Nano-optomechanicalCaptureIEEE disk resonators operating in liquids for sensing applications,”
    Eduardo Gil-Santos, Christophe Baker, Dac Trung Nguyen, William Hease, Carmen Gomez, Aristide Lemaître, Sara Ducci, Giuseppe Leo, Ivan Favero,
    2016 IEEE 29th International Conference on Micro Electro Mechanical Systems (MEMS), 2016, pp. 238–241.
    [main text (pdf)]
  • Abstract

    We demonstrate that miniature optomechanical disk resonators can operate in liquids as ultrafast and ultrasensitive densimeters, viscometers and mass sensors. We develop numerical and analytical models that describe the fluid-structure interactions at play around these GHz mechanical devices. We test them experimentally by immersing disks of varying dimensions in four distinct liquids of varying density and viscosity. Using optomechanical techniques, we measure the thermomechanical noise spectrum of a disk vibrating in water at 1.3 GHz. The resonator stability measured in liquids, together with the models, allows estimating the limits of detection for mass deposition, and for density and viscosity analysis; beating current technologies by several orders of magnitude.


  • “Highliquid_version11-frequency nano-optomechanical disk resonators in liquids,”
    E. Gil-Santos, C. Baker, D.-T. Nguyen, W. Hease, C. Gomez, A. Lemaitre, S. Ducci, G. Leo, and I. Favero,
    Nature Nanotechnology, vol. 10, pp. 810–816, Sept. 2015.
    [main text (pdf)] [Supplementary information (pdf)] [Arxiv 1503.03472 (pdf)]
    See also News and views in Nature Nanotechnology by Javier Tamayo: doi:10.1038/nnano.2015.200.
  • Abstract

    Nano- and micromechanical resonators are the subject of research that aims to develop ultrasensitive mass sensors for spectrometry, chemical analysis and biomedical diagnosis. Unfortunately, their merits generally diminish in liquids because of an increased dissipation. The development of faster and lighter miniaturized devices would enable improved performances, provided the dissipation was controlled and novel techniques were available to drive and readout their minute displacement. Here we report a nano-optomechanical approach to this problem using miniature semiconductor disks. These devices combine a mechanical motion at high frequencies (gigahertz and above) with an ultralow mass (picograms) and a moderate dissipation in liquids. We show that high-sensitivity optical measurements allow their Brownian vibrations to be resolved directly, even in the most-dissipative liquids. We investigate their interaction with liquids of arbitrary properties, and analyse measurements in light of new models. Nano-optomechanical disks emerge as probes of rheological information of unprecedented sensitivity and speed, which opens up applications in sensing and fundamental science.

  • “OriginCaptureOEOrigin of optical losses in gallium arsenide disk whispering gallery resonators,”
    D. Parrain, C. Baker, G. Wang, B. Guha, E. G. Santos, A. Lemaitre, P. Senellart, G. Leo, S. Ducci, and I. Favero,
    Opt. Express, vol. 23, pp. 19656–19672, Jul 2015.
    [main text (pdf)]
    [Arxiv 1507.04906 (pdf)]
  • Abstract

    Whispering gallery modes in GaAs disk resonators reach half a million of optical quality factor. These high Qs remain still well below the ultimate design limit set by bending losses. Here we investigate the origin of residual optical dissipation in these devices. A Transmission Electron Microscope analysis is combined with an improved Volume Current Method to precisely quantify optical scattering losses by roughness and waviness of the structures, and gauge their importance relative to intrinsic material and radiation losses. The analysis also provides a qualitative description of the surface reconstruction layer, whose optical absorption is then revealed by comparing spectroscopy experiments in air and in different liquids. Other linear and nonlinear optical loss channels in the disks are evaluated likewise. Routes are given to further improve the performances of these miniature GaAs cavities.

  • “Improved CaptureNJP2optomechanical disk resonator sitting on a pedestal mechanical shield,”
    D.-T. Nguyen, W. Hease, C. Baker, E. Gil-Santos, P. Senellart, A. Lemaître, S. Ducci, G. Leo, and I. Favero,
    New Journal of Physics, vol. 17, no. 2, p. 023016, 2015.
    [main text (pdf)]
    [Arxiv 1411.6002 (pdf)]
  • Abstract

    We experimentally demonstrate the controlled enhancement of the mechanical quality factor Q of gallium arsenide disk optomechanical resonators. Disks vibrating at 1.3 GHz with a mechanical shield integrated in their pedestal show a Q improvement by a factor 10–16. The structure is modeled numerically and different modes of vibration are observed, which shed light on the Q enhancement mechanism. An optimized double-disk geometry is presented that promises Q above the million for a large parameter range.

2014 & before

  • “Photoelastic CaptureOEPhotoelasticcoupling in gallium arsenide optomechanical disk resonators,”
    C. Baker, W. Hease, D.-T. Nguyen, A. Andronico, S. Ducci, G. Leo, and I. Favero,
    Optics Express, vol. 22, no. 12, pp. 14072–14086, 2014.
    [main text (pdf)]
    [Arxiv 1403.4269 (pdf)]
  • Abstract

    We analyze the magnitude of the radiation pressure and electrostrictive stresses exerted by light confined inside GaAs semiconductor WGM optomechanical disk resonators, through analytical and numerical means, and find the electrostrictive stress to be of prime importance. We investigate the geometric and photoelastic optomechanical coupling resulting respectively from the deformation of the disk boundary and from the strain-induced refractive index changes in the material, for various mechanical modes of the disks. Photoelastic optomechanical coupling is shown to be a predominant coupling mechanism for certain disk dimensions and mechanical modes, leading to total coupling gom and g0 reaching respectively 3 THz/nm and 4 MHz. Finally, we point towards ways to maximize the photoelastic coupling in GaAs disk resonators, and we provide some upper bounds for its value in various geometries.

  • “On-chip nano-optomechanical whispering gallery resonators”Picture1
    French title: “Résonateurs nano-optomécaniques à mode de galerie sur puce,”
    C. Baker,
    PhD thesis, Université Paris-Diderot – Paris VII, 2013.
    [PhD manuscript (pdf)][Presentation slides (pdf)]
  • Abstract

    This thesis work focuses on the design, fabrication and measurement of Gallium Arsenide (GaAs) nano-optomechanical disk resonators. These disks are both GHz frequency mechanical resonators, and high Q (>10^5) optical whispering gallery mode resonators. By confining optical and mechanical energy on a sub-µm^3 volume, they enable extremely large optomechanical coupling strengths (g0>1 MHz). We present the technological developments which enabled the integration of these resonators with optical coupling waveguides directly on a semiconductor chip, while maintaining state of the art performance. We discuss the different optomechanical coupling mechanisms (radiation pressure, photoelasticity) in GaAs disks, as well as the sources of optical and mechanical dissipation in these resonators. We present as well optomechanical experiments in air and in a cryostat at low temperature, which go from the measurement of Brownian motion and the observation of dynamical back-action, to the first attempts to approach the quantum regime of mechanical displacement. Finally, we present an additional nano-optomechanical development carried out on the silicon nitride (SiN) platform, which lead to the fabrication of high Q on-chip whispering gallery mode resonators. After the study of the optical instability and self-pulsing dynamics of these resonators, we present the first signatures of dissipative optomechanical coupling in these systems.

  • “Ultrahigh CaptureAPLUltra.PNGQ-frequency product for optomechanical disk resonators with a mechanical shield,”
    D. T. Nguyen, C. Baker, W. Hease, S. Sejil, P. Senellart, A. Lemaitre, S. Ducci, G. Leo, and I. Favero,
    Applied Physics Letters, vol. 103, no. 24, p. 241112, 2013.
    [main text (pdf)]
    [Arxiv 1309.4971 (pdf)]
  • Abstract

    We report on optomechanical GaAs disk resonators with ultrahigh quality factor-frequency product Q f. Disks standing on a simple pedestal exhibit GHz mechanical breathing modes attaining a Qxf of 10^13 measured under vacuum at cryogenic temperature. Clamping losses are found to be the dominant source of dissipation. An improved disk resonator geometry integrating a shield within the pedestal is then proposed, and its working principles and performances are investigated by numerical simulations. For dimensions compatible with fabrication constraints, the clamping-loss-limited reaches 10^7–10^9 corresponding to equals 10^16–10^18. This shielded pedestal approach applies to any heterostructure presenting an acoustic mismatch.

  • “OpticalCaptureOE_OISP2 instability and self-pulsing in silicon nitride whispering gallery resonators,”
    C. Baker, S. Stapfner, D. Parrain, S. Ducci, G. Leo, E. Weig, and I. Favero,
    Optics Express
    , vol. 20, no. 27, pp. 29076–29089, 2012.
    [main text (pdf)]

    Download related MATLAB code which reproduces the observed self-pulsing behaviour

  • Abstract

    We report time domain observations of optical instability in high Q silicon nitride whispering gallery disk resonators. At low laser power the transmitted optical power through the disk looks chaotic. At higher power, the optical output settles into a stable self-pulsing regime with periodicity ranging from hundreds of milliseconds to hundreds of seconds. This phenomenon is explained by the interplay between a fast thermo-optic nonlinearity within the disk and a slow thermo-mechanic nonlinearity of the structure. A model for this interplay is developed which provides good agreement with experimental data and points out routes to control this instability.

  • “Damping CaptureAPLDampingof optomechanical disks resonators vibrating in air,”
    D. Parrain, C. Baker, T. Verdier, P. Senellart, A. Lemaitre, S. Ducci, G. Leo, and I. Favero,
    Applied Physics Letters, vol. 100, no. 24, pp. 242105–242105, 2012.
    [main text (pdf)]
    [Arxiv 1206.3032 (pdf)]
  • Abstract

    We report on miniature GaAs disk optomechanical resonators vibrating in air in the radiofrequency range. The flexural modes of the disks are studied by scanning electron microscopy and optical interferometry, and correctly modeled with the elasticity theory for annular plates. The mechanical damping is systematically measured, and confronted with original analytical models for air damping. Formulas are derived that correctly reproduce both the mechanical modes and the damping behavior, and can serve as design tools for optomechanical applications in fluidic environment.

  • “Critical 3disksoptical coupling between a GaAs disk and a nanowaveguide suspended on the chip,”
    C. Baker, C. Belacel, A. Andronico, P. Senellart, A. Lemaitre, E. Galopin, S. Ducci, G. Leo, and I. Favero,
    Applied Physics Letters, vol. 99, p. 151117, 2011.
    [main text (pdf)]
    [Arxiv 1108.0680 (pdf)]
  • Abstract

    We report on an integrated GaAs disk/waveguide system. A millimeter-long waveguide is suspended and tapered on the chip over a length of 25 μm to evanescently couple to high Q optical whispering gallery modes of a GaAs disk. The critical coupling regime is obtained both by varying the disk/guide gap distance and the width of the suspended nanoscale taper. Experimental results are in good agreement with predictions from coupled mode theory.

  • “WavelengthCaptureAPLWavelength-sized GaAs optomechanical resonators with gigahertz frequency,”
    L. Ding, C. Baker, P. Senellart, A. Lemaitre, S. Ducci, G. Leo, and I. Favero,
    Applied Physics Letters, vol. 98, p. 113108, 2011.
    [main text (pdf)]
    [Arxiv 1101.4499 (pdf)]
  • Abstract

    We report on wavelength-sized GaAs optomechanical disk resonators showing ultrastrong optomechanical interaction. We observe optical transduction of a disk mechanical breathing mode with 1.4 GHz frequency and effective mass of ∼2 pg. The measured vacuum optomechanical coupling rate reaches g0=0.8 MHz, with a related differential optomechanical coupling factor gom=485 GHz/nm. The disk Brownian motion is optically resolved with a sensitivity of 10−17 m/√Hz at room temperature and pressure.

  • “HighCapturePRLHigh frequency GaAs nano-optomechanical disk resonator,”
    L. Ding, C. Baker, P. Senellart, A. Lemaitre, S. Ducci, G. Leo, and I. Favero,
    Physical Review Letters, vol. 105, no. 26, p. 263903, 2010.
    [main text (pdf)]
    [Supplementary information (pdf)]
    [Arxiv 1007.3392 (pdf)]
  • Abstract

    Optomechanical coupling between a mechanical oscillator and light trapped in a cavity increases when the coupling takes place in a reduced volume. Here we demonstrate a GaAs semiconductor optomechanical disk system where both optical and mechanical energy can be confined in a subwavelength scale interaction volume. We observe a giant optomechanical coupling rate up to 100  GHz/nm involving picogram mass mechanical modes with a frequency between 100 MHz and 1 GHz. The mechanical modes are singled-out measuring their dispersion as a function of disk geometry. Their Brownian motion is optically resolved with a sensitivity of 10−17  m/√Hz at room temperature and pressure, approaching the quantum limit imprecision.

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