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We use a reservoir engineering technique based on two-tone driving to generate and stabilize a quantum squeezed state of a micron-scale mechanical oscillator in a microwave optomechanical system. Using an independent backaction evading measurement to directly quantify the squeezing, we observe $4.7\pm0.9$ dB of squeezing below the zero-point level, surpassing the 3 dB limit of standard parametric squeezing techniques. Our measurements also reveal evidence for an additional mechanical parametric effect. The interplay between this effect and the optomechanical interaction enhances the amount of squeezing obtained in the experiment.

Direct detection of gravitational waves is opening a new window onto our universe. Here, we study the sensitivity to continuous-wave strain fields of a kg-scale optomechanical system formed by the acoustic motion of superfluid helium-4 parametrically coupled to a superconducting microwave cavity. This narrowband detection scheme can operate at very high Q-factors, while the resonant frequency is tunable through pressurization of the helium in the 0.1–1.5 kHz range. The detector can therefore be tuned to a variety of astrophysical sources and can remain sensitive to a particular source over a long period of time. For thermal noise limited sensitivity, we find that strain fields on the order of h ~ 10^(-23)/√Hz are detectable. Measuring such strains is possible by implementing state of the art microwave transducer technology. We show that the proposed system can compete with interferometric detectors and potentially surpass the gravitational strain limits set by them for certain pulsar sources within a few months of integration time.

Aided by optical cavities and superconducting circuits, researchers are coaxing ever-larger objects to wiggle, shake, and flex in ways that are distinctly quantum mechanical.

Quantum electromechanical systems offer a unique opportunity to probe quantum noise properties in macroscopic devices, properties that ultimately stem from Heisenberg’s uncertainty relations. A simple example of this behavior is expected to occur in a microwave parametric transducer, where mechanical motion generates motional sidebands corresponding to the up-and-down frequency conversion of microwave photons. Because of quantum vacuum noise, the rates of these processes are expected to be unequal. We measure this fundamental imbalance in a microwave transducer coupled to a radio-frequency mechanical mode, cooled near the ground state of motion. We also discuss the subtle origin of this imbalance: depending on the measurement scheme, the imbalance is most naturally attributed to the quantum fluctuations of either the mechanical mode or of the electromagnetic field.

The ability to transport energy is a fundamental property of the two-dimensional Dirac fermions in graphene. Electronic thermal transport in this system is relatively unexplored and is expected to show unique fundamental properties and to play an important role in future applications of graphene, including opto-electronics, plasmonics, and ultra-sensitive bolometry. Here we present measurements of bipolar, electron-diffusion and electron-phonon thermal conductances, and infer the electronic specific heat, with a minimum value of 10 $k_{\rm{B}}$ ($10^{-22}$ JK$^{-1}$) per square micron. We test the validity of the Wiedemann-Franz law and find the Lorenz number equals $1.32\times(\pi^2/3)(k_{\rm{B}}/e)^2$. The electron-phonon thermal conductance has a temperature power law $T^2$ at high doping levels, and the coupling parameter is consistent with recent theory, indicating its enhancement by impurity scattering. We demonstrate control of the thermal conductance by electrical gating and by suppressing the diffusion channel using superconducting electrodes, which sets the stage for future graphene-based single microwave photon detection.

We investigate the low loss acoustic motion of superfluid $^4$He parametrically coupled to a very low loss, superconducting Nb, TE$_{011}$ microwave resonator, forming a gram-scale, sideband resolved, optomechanical system. We demonstrate the detection of a series of acoustic modes with quality factors as high as $7\cdot 10^6$. At higher temperatures, the lowest dissipation modes are limited by an intrinsic three phonon process. Acoustic quality factors approaching $10^{11}$ may be possible in isotopically purified samples at temperatures below 10 mK. A system of this type may be utilized to study macroscopic quantized motion and as an ultra-sensitive sensor of extremely weak displacements and forces, such as continuous gravity wave sources.

This study focuses on domain wall resistance in Ni_(80) Fe_(20) nanowires containing narrow constrictions down to 15 nm in width. Distinct differences in the magnetoresistance curves were found to depend on the constriction size. Wider constrictions are dominated by the overall anisotropic magnetoresistance of the structure, while constrictions narrower than ∼40 nm exhibit an additional distinct contribution from a domain wall. The effect is negative and typically varies from 1% to 5%.

We have determined the features of a universal energy barrier which mediates the thermal nucleation of quantized vortices. The barrier is deduced from measurements of the intrinsic phase slip critical velocity using both dc flow and single phase slip experiments. It appears that at a given temperature a single curve can predict the outcome of all intrinsic vortex nucleation experiments for flow through small apertures.

Graphene is a material with remarkable electronic properties and exceptional thermal transport properties near room temperature, which have been well examined and understood. However at very low temperatures the thermodynamic and thermal transport properties are much less well explored and somewhat surprisingly, is expected to exhibit extreme thermal isolation. Here we demonstrate an ultra-sensitive, wide-bandwidth measurement scheme to probe the thermal transport and thermodynamic properties of the electron gas of graphene. We employ Johnson noise thermometry at microwave frequency to sensitively measure the temperature of the electron gas with resolution of $4 mK/\sqrt{Hz}$ and a bandwidth of 80 MHz. We have measured the electron-phonon coupling from 2-30 K at a charge density of $2\cdot 10^{11} cm^{-2}$. Utilizing bolometric mixing, we have sensed temperature oscillations with period of 430 ps and have determined the heat capacity of the electron gas to be $2\cdot 10^{-21} J/(K\cdot \mu m^2)$ at 5 K which is consistent with that of a two dimensional, Dirac electron gas. These measurements suggest that graphene-based devices together with wide bandwidth noise thermometry can generate substantial advances in the areas of ultra-sensitive bolometry, calorimetry, microwave and terahertz photo-detection, and bolometric mixing for applications in areas such as observational astronomy and quantum information and measurement., Comment: 8 pages, 4 figures

When performing continuous measurements of position with sensitivity approaching quantum mechanical limits, one must confront the fundamental effects of detector back-action. Back-action forces are responsible for the ultimate limit on continuous position detection, can also be harnessed to cool the observed structure, and are expected to generate quantum entanglement. Back-action can also be evaded, allowing measurements with sensitivities that exceed the standard quantum limit, and potentially allowing for the generation of quantum squeezed states. We realize a device based on the parametric coupling between an ultra-low dissipation nanomechanical resonator and a microwave resonator. Here we demonstrate back-action evading (BAE) detection of a single quadrature of motion with sensitivity 4 times the quantum zero-point motion, back-action cooling of the mechanical resonator to n = 12 quanta, and a parametric mechanical pre-amplification effect which is harnessed to achieve position resolution a factor 1.3 times quantum zero-point motion., 19 pages (double-spaced) including 4 figures and references

We have observed that at temperatures below 200 mK quantized vortices are created by a new process which is not described by the thermal activation theory of vortex nucleation. The critical flow velocity in a submicron orifice has been determined using two techniques. Down to about 200 mK the critical velocities rise linearly with falling temperature. Below this temperature the critical velocity stops rising and becomes almost temperature independent, indicating that a new process, possible quantum tunneling, dominates the phase-slip nucleation.

In a recent Letter, Gaidarzhy et al. [1] claim to have observed evidence for "quantized displacements" of a high-order mode of a nanomechanical oscillator. We contend that the methods employed by the authors are unsuitable in principle to observe such states for any harmonic mode.

Nanoelectromechanical structures are starting to approach the ultimate quantum mechanical limits for detecting and exciting motion at the nanoscale. Nonclassical states of a mechanical resonator are also on the horizon.

We analyse the quantum dynamics of a micromechanical resonator capacitively coupled to a Cooper box. With appropriate quantum state control of the Cooper box, the resonator can be driven into a superposition of spatially separated states. The Cooper box can also be used to probe the environmentally-induced decoherence of the resonator superposition state., Comment: 4 pages, 3 figures

We have developed the superfluid analog of the superconducting rf SQUID. Such a device is a quantum mechanically based, absolute gyroscope and has been used to sense the rotation of the Earth. Our device is fabricated using silicon processing techniques and forms a planer sensing loop of superfluid helium which couples to the applied rotation. A much more sensitive superfluid gyroscope based on the principle’s demonstrated with this device, might ultimately be used to detect the precession of our local inertial frame with respect to the fixed stars by the gravitomagnetic field of the rotating Earth. We compare the superfluid gyroscope against two other experiments aimed at detecting this general relativistic effect.

We measure both the linear and nonlinear coupling between transverse modes in a nanomechanical resonator. The nonlinear coupling is due to the displacement dependent tension of the resonator and leads to a frequency shift (“pulling”) of each mode proportional to the square of the orthogonal mode's displacement amplitude. The linear coupling is apparent as an avoided crossing of the resonant frequencies that occurs when one electrostatically tunes the modes into degeneracy via a nearby DC gate. We consider the possibility that the linear coupling results from an electrostatic interaction and find that this effect can only partially explain the magnitude of the observed coupling. By measuring the coupled amplitudes magnetomotively at various angles to the applied field, we find that as the modes are tuned through the degeneracy point, they remain linearly polarized, while their planes of vibration rotate by 90°.

We have developed an apparatus which is the superfluid analog of the RF SQUID and exhibits the characteristics “staircase” response. This device is of the type demonstrated by O. Avenel and E. Varoquaux. The superfluid Helmholtz resonator is constructed from Silicon using microfabrication techniques and has an internal volume of only 5.0 mm3. The staircase pattern can be reliably reproduced in each new cell constructed by this technique. This device can, in principle, be used to detect absolute rotation. Numerical calculations of the flow field for our particular geometry predict sufficient sensitivity to detect the rotation of the Earth with s/n∼100. An ongoing search is being performed to observe the rotation effects.

An array of 1126 identical microapertures is used as the hydrodynamic inductance in a superfluid3He Helmholtz resonator. Each aperture is 0.27 micron square, fabricated by e-beam lithography in a 0.1 micron thick SiN membrane. These dimensions are not too much larger than the superfluid coherence length and therefore, particularly at higher temperatures, an aperture might be though of as a Josephson weak link (in the sense of a Dayem bridge). The superfluid3He critical mass current, Ic, through this array has been measured over a wide range of temperatures. The results indicate that the critical current has a Ginzburg-Landau form of Ic=Ico(1-T/Tc)3/2. This temperature dependence is consistent with phase slippage (not necessarily involving vortices), at the pair breaking velocity, as the critical mechanism.

We present preliminary measurements of the intrinsic critical velocity for vortex production due to flow through a submicron aperture at temperatures from 1.65K toT λ−T=3×10−3 K and fluid drive pressures (Josephson frequencies) from 0.5mPa (f j=35Hz) to 250mPa (f j=17kHz). The critical velocity is probed using a constant pressure drive technique which maintains a constant phase slip nucleation rate for several minutes. The measured critical velocity qualitatively agrees with a model of thermally activated vortex half rings.