arXiv subjects

Jeff T. Hill

Publications and source records attributed to Jeff T. Hill.

18 recordsLinked to original sources

arXiv2018

Coupling a superconducting quantum circuit to a phononic crystal defect cavity

Connecting nanoscale mechanical resonators to microwave quantum circuits opens new avenues for storing, processing, and transmitting quantum information. In this work, we couple a phononic crystal cavity to a tunable superconducting quantum circuit. By fabricating a one-dimensional periodic pattern in a thin film of lithium niobate and introducing a defect in this artificial lattice, we localize a 6 gigahertz acoustic resonance to a wavelength-scale volume of less than one cubic micron. The strong piezoelectricity of lithium niobate efficiently couples the localized vibrations to the electric field of a widely tunable high-impedance Josephson junction array resonator. We measure a direct phonon-photon coupling rate $g/2π\approx 1.6 \, \mathrm{MHz}$ and a mechanical quality factor $Q_\mathrm{m} \approx 3 \times 10^4$ leading to a cooperativity $C\sim 4$ when the two modes are tuned into resonance. Our work has direct application to engineering hybrid quantum systems for microwave-to-optical conversion as well as emerging architectures for quantum information processing.

quant-ph↗

arXiv2017

A single-mode phononic wire

Photons and electrons transmit information to form complex systems and networks. Phonons on the other hand, the quanta of mechanical motion, are often considered only as carriers of thermal energy. Nonetheless, their flow can also be molded in fabricated nanoscale circuits. We design and experimentally demonstrate wires for phonons that transmit information with little loss or scattering across a chip. By patterning the surface of a silicon chip, we completely eliminate all but one channel of phonon conduction. We observe the emergence of low-loss standing waves in millimeter long phononic wires that we address and cool optically. Coherent transport and strong optical coupling to a phononic wire enables new phononic technologies to manipulate information and energy on a chip.

quant-ph↗

arXiv2017

Engineering phonon leakage in nanomechanical resonators

We propose and experimentally demonstrate a technique for coupling phonons out of an optomechanical crystal cavity. By designing a perturbation that breaks a symmetry in the elastic structure, we selectively induce phonon leakage without affecting the optical properties. It is shown experimentally via cryogenic measurements that the proposed cavity perturbation causes loss of phonons into mechanical waves on the surface of silicon, while leaving photon lifetimes unaffected. This demonstrates that phonon leakage can be engineered in on-chip optomechanical systems. We experimentally observe large fluctuations in leakage rates that we attribute to fabrication disorder and verify this using simulations. Our technique opens the way to engineering more complex on-chip phonon networks utilizing guided mechanical waves to connect quantum systems.

physics.optics↗

arXiv2016

Release-free silicon-on-insulator cavity optomechanics

We demonstrate optically coupled nanomechanical resonators fabricated on silicon-on-insulator. Silicon fin waveguides are used to control the dispersion of mechanical waves and engineer localized resonances by modulation of the fin properties. A photonic crystal cavity is designed to localize laser light near the fin and the mechanical motion is read out and modified by radiation pressure back-action. We expect devices and systems made from similar structures to enable co-integration of signal transduction and processing capabilities via electronic, photonic, and phononic degrees freedom in a single scalable platform.

physics.optics↗

arXiv2016

High-Q photonic resonators and electro-optic coupling using silicon-on-lithium-niobate

Future quantum networks in which superconducting quantum processors are connected via optical links, will require microwave-to-optical photon converters that preserve entanglement. A doubly-resonant electro-optic modulator (EOM) is a promising platform to realize this conversion. Here, we present our progress towards building such a modulator by demonstrating the optically-resonant half of the device. We demonstrate high quality factor ring, disk and photonic crystal resonators using a hybrid silicon-on-lithium-niobate material system. Optical quality factors up to 730,000 are achieved, corresponding to propagation loss of 0.8 dB/cm. We also use the electro-optic effect to modulate the resonance frequency of a photonic crystal cavity, achieving a electro-optic modulation coefficient between 1 and 2 pm/V. In addition to quantum technology, we expect that our results will be useful both in traditional silicon photonics applications and in high-sensitivity acousto-optic devices.

physics.optics↗

arXiv2016

Design of nanobeam photonic crystal resonators for a silicon-on-lithium-niobate platform

We outline the design for a photonic crystal resonator made in a hybrid Silicon/Lithium Niobate material system. Using the index contrast between silicon and lithium niobate, it is possible to guide and confine photonic resonances in a thin film of silicon bonded on top of lithium niobate. Quality factors greater than $10^6$ at optical wavelength scale mode volumes are achievable. We show that patterning electrodes on such a system can yield an electro-optic coupling rate of 0.6 GHz/V (4 pm/V).

physics.optics↗

arXiv2016

Guided acoustic and optical waves in silicon-on-insulator for Brillouin scattering and optomechanics

We numerically study silicon waveguides on silica showing that it is possible to simultaneously guide optical and acoustic waves in the technologically important silicon on insulator (SOI) material system. Thin waveguides, or fins, exhibit geometrically softened mechanical modes at gigahertz frequencies with phase velocities below the Rayleigh velocity in glass, eliminating acoustic radiation losses. We propose slot waveguides on glass with telecom optical frequencies and strong radiation pressure forces resulting in Brillouin gains on the order of 500 and 50,000 1/(Wm) for backward and forward Brillouin scattering, respectively.

physics.optics↗

arXiv2015

Nonlinear radiation pressure dynamics in an optomechanical crystal

Utilizing a silicon nanobeam optomechanical crystal, we investigate the attractor diagram arising from the radiation pressure interaction between a localized optical cavity at $λ= 1552$nm and a mechanical resonance at $ω/2π= 3.72$GHz. At a temperature of $T \approx 10$K, highly nonlinear driving of mechanical motion is observed via continuous wave optical pumping. Introduction of a time-dependent (modulated) optical pump is used to steer the system towards an otherwise inaccessible dynamically stable attractor in which mechanical self-oscillation occurs for an optical pump red-detuned from the cavity resonance. An analytical model incorporating thermo-optic effects due to optical absorption heating is developed, and found to accurately predict the measured device behavior.

physics.optics↗

arXiv2014

Linear and nonlinear capacitive coupling of electro-opto-mechanical photonic crystal cavities

We fabricate and characterize a microscale silicon electro-opto-mechanical system whose mechanical motion is coupled capacitively to an electrical circuit and optically via radiation pressure to a photonic crystal cavity. To achieve large electromechanical interaction strength, we implement an inverse shadow mask fabrication scheme which obtains capacitor gaps as small as 30 nm while maintaining a silicon surface quality necessary for minimizing optical loss. Using the sensitive optical read-out of the photonic crystal cavity, we characterize the linear and nonlinear capacitive coupling to the fundamental 63 MHz in-plane flexural motion of the structure, showing that the large electromechanical coupling in such devices may be suitable for realizing efficient microwave-to-optical signal conversion.

physics.optics↗

arXiv2014

Thermalization properties at mK temperatures of a nanoscale optomechanical resonator with acoustic-bandgap shield

Optical measurements of a nanoscale silicon optomechanical crystal cavity with a mechanical resonance frequency of 3.6GHz are performed at sub-kelvin temperatures. We infer optical-absorption-induced heating and damping of the mechanical resonator from measurements of phonon occupancy and motional sideband asymmetry. At the lowest probe power and lowest fridge temperature (10mK), the localized mechanical resonance is found to couple at a rate of 400Hz (Q=9x10^6) to a thermal bath of temperature 270mK. These measurements indicate that silicon optomechanical crystals cooled to millikelvin temperatures should be suitable for a variety of experiments involving coherent coupling between photons and phonons at the single quanta level.

quant-ph↗

arXiv2014

Two-dimensional phononic-photonic bandgap optomechanical crystal cavity

We present the fabrication and characterization of an artificial crystal structure formed from a thin-film of silicon which has a full phononic bandgap for microwave X-band phonons and a two-dimensional pseudo-bandgap for near-infrared photons. An engineered defect in the crystal structure is used to localize optical and mechanical resonances in the bandgap of the planar crystal. Two-tone optical spectroscopy is used to characterize the cavity system, showing a large vacuum coupling rate of 220kHz between the fundamental optical cavity resonance at 195THz and a co-localized mechanical resonance at 9.3GHz.

physics.optics↗

arXiv2013

Highly efficient coupling from an optical fiber to a nanoscale silicon optomechanical cavity

We demonstrate highly efficient coupling of light from an optical fiber to a silicon photonic crystal optomechanical cavity. The fiber-to-cavity coupling utilizes a compact (L ~ 25 um) intermediate adiabatic coupler. The optical coupling is lithographically controlled, broadband, relatively insensitive to fiber misalignment, and allows for light to be transferred from an optical fiber to, in principle, any photonic chip with refractive index greater than that of the optical fiber. Here we demonstrate single-sided cavity coupling with a total fiber-to-cavity optical power coupling efficiency of 85%.

physics.optics↗

arXiv2013

Squeezing of light via reflection from a silicon micromechanical resonator

We present the measurement of squeezed light generation using an engineered optomechanical system fabricated from a silicon microchip and composed of a micromechanical resonator coupled to a nanophotonic cavity. Laser light is used to measure the fluctuations in the position of the mechanical resonator at a measurement rate comparable to the free dynamics of the mechanical resonator, and greater than its thermal decoherence rate. By approaching the strong continuous measurement regime we observe, through homodyne detection, non-trivial modifications of the reflected light's vacuum fluctuation spectrum. In spite of the mechanical resonator's highly excited thermal state ($10,000$ phonons), we observe squeezing at the level of $4.5 \pm 0.5%$ below that of shot-noise over a few MHz bandwidth around the mechanical resonance frequency of 28 MHz. This squeezing is interpreted as an unambiguous quantum signature of radiation pressure shot-noise.

quant-ph↗

arXiv2012

Laser noise in cavity-optomechanical cooling and thermometry

We review and study the roles of quantum and classical fluctuations in recent cavity-optomechanical experiments which have now reached the quantum regime (mechanical phonon occupancy < 1) using resolved sideband laser cooling. In particular, both the laser noise heating of the mechanical resonator and the form of the optically transduced mechanical spectra, modified by quantum and classical laser noise squashing, are derived under various measurement conditions. Using this theory, we analyze our recent ground-state laser cooling and motional sideband asymmetry experiments with nanoscale optomechanical crystal resonators.

physics.optics↗

arXiv2012

Optimized optomechanical crystal cavity with acoustic radiation shield

We present the design of an optomechanical crystal nanobeam cavity that combines finite-element simulation with numerical optimization, and considers the optomechanical coupling arising from both moving dielectric boundaries and the photo-elastic effect. Applying this methodology results in a nanobeam with an experimentally realized intrinsic optical Q-factor of 1.2x10^6, a mechanical frequency of 5.1GHz, a mechanical Q-factor of 6.8x10^5 (at T=10K), and a zero-point-motion optomechanical coupling rate of g=1.1MHz.

physics.optics↗

arXiv2012

Coherent optical wavelength conversion via cavity-optomechanics

We theoretically propose and experimentally demonstrate coherent wavelength conversion of optical photons using photon-phonon translation in a cavity-optomechanical system. For an engineered silicon optomechanical crystal nanocavity supporting a 4 GHz localized phonon mode, optical signals in a 1.5 MHz bandwidth are coherently converted over a 11.2 THz frequency span between one cavity mode at wavelength 1460 nm and a second cavity mode at 1545 nm with a 93% internal (2% external) peak efficiency. The thermal and quantum limiting noise involved in the conversion process is also analyzed, and in terms of an equivalent photon number signal level are found to correspond to an internal noise level of only 6 and 4x10-3 quanta, respectively.

physics.optics↗

arXiv2011

Measurement of the quantum zero-point motion of a nanomechanical resonator

We present optical sideband spectroscopy measurements of a mesoscopic mechanical oscillator cooled near its quantum ground state. The mechanical oscillator, corresponding to a 3.99GHz acoustic mode of a patterned silicon nanobeam, is coupled via radiation pressure to a pair of co-localized 200THz optical modes. The mechanical mode is cooled close to its quantum ground state from a bath temperature of 18K using radiation pressure back-action stemming from the optical pumping of one of the optical cavity resonances. An optical probe beam, resonant with the second optical cavity resonance, is used to transduce the mechanical motion and determine the phonon occupancy of the mechanical mode. Measurement of the asymmetry between up-converted and down-converted photons of the probe beam yields directly the displacement noise power associated with the quantum zero-point motion of the mechanical oscillator, and provides an absolute calibration of the average phonon occupancy of the mechanical mode.

quant-ph↗

arXiv2011

Laser cooling of a nanomechanical oscillator into its quantum ground state

A patterned Si nanobeam is formed which supports co-localized acoustic and optical resonances that are coupled via radiation pressure. Starting from a bath temperature of T=20K, the 3.68GHz nanomechanical mode is cooled into its quantum mechanical ground state utilizing optical radiation pressure. The mechanical mode displacement fluctuations, imprinted on the transmitted cooling laser beam, indicate that a final phonon mode occupancy of 0.85 +-0.04 is obtained.

quant-ph↗