1,675 research outputs found
Universal quantum fluctuations of a cavity mode driven by a Josephson junction
We analyze the quantum dynamics of a superconducting cavity coupled to a
voltage biased Josephson junction. The cavity is strongly excited at resonances
where the voltage energy lost by a Cooper pair traversing the circuit is a
multiple of the cavity photon energy. We find that the resonances are
accompanied by substantial squeezing of the quantum fluctuations of the cavity
over a broad range of parameters and are able to identify regimes where the
fluctuations in the system take on universal values.Comment: 5 pages, 4 figure
Dissipation due to tunneling two-level systems in gold nanomechanical resonators
We present measurements of the dissipation and frequency shift in
nanomechanical gold resonators at temperatures down to 10 mK. The resonators
were fabricated as doubly-clamped beams above a GaAs substrate and actuated
magnetomotively. Measurements on beams with frequencies 7.95 MHz and 3.87 MHz
revealed that from 30 mK to 500 mK the dissipation increases with temperature
as , with saturation occurring at higher temperatures. The relative
frequency shift of the resonators increases logarithmically with temperature up
to at least 400 mK. Similarities with the behavior of bulk amorphous solids
suggest that the dissipation in our resonators is dominated by two-level
systems
Changes with Time in the Availability of Soil Applied Zinc to Navy Beans and in the Chemical Extraction of Zinc from Soils
The effect of the incubation of zinc (Zn) applied to the soil on Zn uptake and the Zn concentrations in chemical extractants was studied. In a glasshouse experiment using a Zn-deficient gravelly sandy loam, the effect of recently applied Zn was compared with that of Zn incubated with the soil for 15 days at 40°C on growth and Zn uptake by navy beans (Phaseolus vulgaris cv. Gallaroy). At the second harvest (33 days after sowing), the dry weight of shoots of recently applied Zn was consistently higher than that of incubated Zn, except at the highest rate of 1 µg Zn g-1 soil, where yields were similar. Comparisons of the slope of the linear regressions of Zn uptake as a function of rate of application showed that incubated Zn was approximately 80% as effective as recently applied Zn. A laboratory experiment measured the decrease in Zn concentration in HCl, EDTA, DTPA, and dilute CaCl2 with incubation for up to 8 days at 40°C in four contrasting soils from Western Australia and Queensland. An addition of 2.5 µg Zn g-1 soil increased the concentration of Zn in all extractants at all times of incubation compared with the untreated soil. The recovery of the added Zn was generally highest with HCl and lowest with 0.002 M CaCl2 and decreased exponentially in all extractants with increasing time of incubation in all soils. The order of the rate of decrease in Zn concentration for all extractants was krasnozem \u3e gravelly sandy loam \u3e sand \u3e sandy clay loam. The model, Y = CtB, where C and B are constants, was used to describe the relationship between the recovery of added Zn and time of incubation
Dynamical instabilities of a resonator driven by a superconducting single-electron transistor
We investigate the dynamical instabilities of a resonator coupled to a
superconducting single-electron transistor (SSET) tuned to the Josephson
quasiparticle (JQP) resonance. Starting from the quantum master equation of the
system, we use a standard semiclassical approximation to derive a closed set of
mean field equations which describe the average dynamics of the resonator and
SSET charge. Using amplitude and phase coordinates for the resonator and
assuming that the amplitude changes much more slowly than the phase, we explore
the instabilities which arise in the resonator dynamics as a function of
coupling to the SSET, detuning from the JQP resonance and the resonator
frequency. We find that the locations (in parameter space) and sizes of the
limit cycle states predicted by the mean field equations agree well with
numerical solutions of the full master equation for sufficiently weak
SSET-resonator coupling. The mean field equations also give a good qualitative
description of the set of dynamical transitions in the resonator state that
occur as the coupling is progressively increased.Comment: 23 pages, 6 Figures, Accepted for NJ
Nonlinear modal coupling in a high-stress doubly-clamped nanomechanical resonator
We present results from a study of the nonlinear intermodal coupling between
different flexural vibrational modes of a single high-stress, doubly-clamped
silicon nitride nanomechanical beam. The measurements were carried out at 100
mK and the beam was actuated using the magnetomotive technique. We observed the
nonlinear behavior of the modes individually and also measured the coupling
between them by driving the beam at multiple frequencies. We demonstrate that
the different modes of the resonator are coupled to each other by the
displacement induced tension in the beam, which also leads to the well known
Duffing nonlinearity in doubly-clamped beams.Comment: 15 pages, 7 figure
Measuring mechanical motion with a single spin
We study theoretically the measurement of a mechanical oscillator using a
single two level system as a detector. In a recent experiment, we used a single
electronic spin associated with a nitrogen vacancy center in diamond to probe
the thermal motion of a magnetized cantilever at room temperature {Kolkowitz et
al., Science 335, 1603 (2012)}. Here, we present a detailed analysis of the
sensitivity limits of this technique, as well as the possibility to measure the
zero point motion of the oscillator. Further, we discuss the issue of
measurement backaction in sequential measurements and find that although
backaction heating can occur, it does not prohibit the detection of zero point
motion. Throughout the paper we focus on the experimental implementation of a
nitrogen vacancy center coupled to a magnetic cantilever; however, our results
are applicable to a wide class of spin-oscillator systems. Implications for
preparation of nonclassical states of a mechanical oscillator are also
discussed.Comment: 17 pages, 6 figure
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