8,989 research outputs found
Ultrasensitive and Wide-Bandwidth Thermal Measurements of Graphene at Low Temperatures
Graphene is a material with remarkable electronic properties[1] and exceptional thermal transport
properties near room temperature, which have been well examined and understood[2, 3].
However at very low temperatures the thermodynamic and thermal transport properties are much
less well explored[4, 5] 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 4mK/√Hz and a bandwidth of 80 MHz. We have measured the
electron-phonon coupling from 2-30 K at a charge density of 2 •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 • 10^(-21)J/(K •µm^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[6], calorimetry[7], microwave and terahertz photo-detection[8],
and bolometric mixing for applications in areas such as observational astronomy[9] and quantum
information and measurement[10]
Superfluid Optomechanics: Coupling of a Superfluid to a Superconducting Condensate
We investigate the low loss acoustic motion of superfluid He
parametrically coupled to a very low loss, superconducting Nb, TE
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 . At higher temperatures, the lowest
dissipation modes are limited by an intrinsic three phonon process. Acoustic
quality factors approaching 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
Ultra-high Q Acoustic Resonance in Superfluid 4He
We report the measurement of the acoustic quality factor of a gram-scale,
kilo-hertz frequency superfluid resonator, detected through the parametric
coupling to a superconducting niobium microwave cavity. For temperature between
400mK and 50mK, we observe a temperature dependence of the quality
factor, consistent with a 3-phonon dissipation mechanism. We observe Q factors
up to , consistent with the dissipation due to dilute He
impurities, and expect that significant further improvements are possible.
These experiments are relevant to exploring quantum behavior and decoherence of
massive macroscopic objects, the laboratory detection of continuous wave
gravitational waves from pulsars, and the probing of possible limits to
physical length scales.Comment: 5 pages, 2 figure
Mesoscopic Mechanical Resonators as Quantum Non-Inertial Reference Frames
An atom attached to a micrometer-scale wire that is vibrating at a frequency
of 100 MHz and with displacement amplitude 1 nm experiences an acceleration
magnitude 10^9 ms^-2, approaching the surface gravity of a neutron star. As one
application of such extreme non-inertial forces in a mesoscopic setting, we
consider a model two-path atom interferometer with one path consisting of the
100 MHz vibrating wire atom guide. The vibrating wire guide serves as a
non-inertial reference frame and induces an in principle measurable phase shift
in the wave function of an atom traversing the wire frame. We furthermore
consider the effect on the two-path atom wave interference when the vibrating
wire is modeled as a quantum object, hence functioning as a quantum
non-inertial reference frame. We outline a possible realization of the
vibrating wire, atom interferometer using a superfluid helium quantum
interference setup.Comment: Published versio
Spring constant and damping constant tuning of nanomechanical resonators using a single-electron transistor
By fabricating a single-electron transistor onto a mechanical system in a high magnetic field, it is shown that one can manipulate both the mechanical spring constant and damping constant by adjusting a potential of a nearby gate electrode. The spring constant effect is shown to be usable to control the resonant frequency of silicon-based nanomechanical resonators, while an additional damping constant effect is relevant for the resonators built upon carbon nanotube or similar molecular-sized materials. This could prove to be a very convenient scheme to actively control the response of nanomechanical systems for a variety of applications including radio-frequency signal processing, ultrasensitive force detection, and fundamental physics explorations
Measurement of energy eigenstates by a slow detector
We propose a method for a weak continuous measurement of the energy
eigenstates of a fast quantum system by means of a "slow" detector. Such a
detector is only sensitive to slowly-changing variables, e. g. energy, while
its back-action can be limited solely to decoherence of the eigenstate
superpositions. We apply this scheme to the problem of detection of quantum
jumps between energy eigenstates in a harmonic oscillator.Comment: 4 page
Phonon scattering mechanisms in suspended nanostructures from 4 to 40 K
We have developed specially designed semiconductor devices for the measurement of thermal conductance in suspended nanostructures. By means of a novel subtractive comparison, we are able to deduce the phonon thermal conductance of individual nanoscale beams of different geometry and dopant profiles. The separate roles of important phonon scattering mechanisms are analyzed and a quantitative estimation of their respective scattering rates is obtained using the Callaway model. Diffuse surface scattering proves to be particularly important in the temperature range from 4 to 40 K. The rates of other scattering mechanisms, arising from phonon-phonon, phonon-electron, and phonon-point defect interactions, also appear to be significantly higher in nanostructures than in bulk samples
Comment on "Evidence for Quantized Displacement in Macroscopic Nanomechanical Oscillators"
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
Effect of the Strawberry Genotype, Cultivation and Processing on the Fra a 1 Allergen Content
Birch pollen allergic patients show cross-reactivity to vegetables and fruits, including
strawberries (Fragaria × ananassa). The objective of this study was to quantify the level of the
Fra a 1 protein, a Bet v 1-homologous protein in strawberry fruits by a newly developed ELISA,
and determine the effect of genotype, cultivation and food processing on the allergen amount.
An indirect competitive ELISA using a specific polyclonal anti-Fra a 1.02 antibody was established
and revealed high variability in Fra a 1 levels within 20 different genotypes ranging from 0.67
to 3.97 μg/g fresh weight. Mature fruits of red-, white- and yellow-fruited strawberry cultivars
showed similar Fra a 1 concentrations. Compared to fresh strawberries, oven and solar-dried
fruits contained slightly lower levels due to thermal treatment during processing. SDS-PAGE and
Western blot analysis demonstrated degradation of recombinant Fra a 1.02 after prolonged (>10 min)
thermal treatment at 99 â—¦ C. In conclusion, the genotype strongly determined the Fra a 1 quantity
in strawberries and the color of the mature fruits does not relate to the amount of the PR10-protein.
Cultivation conditions (organic and conventional farming) do not affect the Fra a 1 level, and seasonal
effects were minor
Quantum-measurement backaction from a Bose-Einstein condensate coupled to a mechanical oscillator
We study theoretically the dynamics of a hybrid optomechanical system consisting of a macroscopic mechanical membrane magnetically coupled to a spinor Bose-Einstein condensate via a nanomagnet attached at the membrane center. We demonstrate that this coupling permits us to monitor indirectly the center-of-mass position of the membrane via measurements of the spin of the condensed atoms. These measurements normally induce a significant backaction on the membrane motion, which we quantify for the cases of thermal and coherent initial states of the membrane. We discuss the possibility of measuring this quantum backaction via repeated measurements. We also investigate the potential to generate nonclassical states of the membrane, in particular Schrödinger-cat states, via such repeated measurements
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