3,458 research outputs found
Quantum gears: a simple mechanical system in the quantum regime
Abstract. The quantum mechanics of a simple mechanical system is considered. A group of gears can serve as a model for several different systems such as an artifically constructed nanomechanical device or a group of ring molecules. It is shown that the classical motion of the gears in which the angular velocities are locked together does not correspond to
Generation of Squeezed States of Nanomechanical Resonators by Reservoir Engineering
An experimental demonstration of a non-classical state of a nanomechanical
resonator is still an outstanding task. In this paper we show how the resonator
can be cooled and driven into a squeezed state by a bichromatic microwave
coupling to a charge qubit. The stationary oscillator state exhibits a reduced
noise in one of the quadrature components by a factor of 0.5 - 0.2. These
values are obtained for a 100 MHz resonator with a Q-value of 10 to 10
and for support temperatures of T 25 mK. We show that the coupling to
the charge qubit can also be used to detect the squeezed state via measurements
of the excited state population. Furthermore, by extending this measurement
procedure a complete quantum state tomography of the resonator state can be
performed. This provides a universal tool to detect a large variety of
different states and to prove the quantum nature of a nanomechanical
oscillator.Comment: 13 pages,9 figure
Entanglement and decoherence of a micromechanical resonator via coupling to a Cooper box
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 figure
Nonlinear response of a driven vibrating nanobeam in the quantum regime
We analytically investigate the nonlinear response of a damped doubly clamped
nanomechanical beam under static longitudinal compression which is excited to
transverse vibrations. Starting from a continuous elasticity model for the
beam, we consider the dynamics of the beam close to the Euler buckling
instability. There, the fundamental transverse mode dominates and a quantum
mechanical time-dependent effective single particle Hamiltonian for its
amplitude can be derived. In addition, we include the influence of a
dissipative Ohmic or super-Ohmic environment. In the rotating frame, a
Markovian master equation is derived which includes also the effect of the
time-dependent driving in a non-trivial way. The quasienergies of the pure
system show multiple avoided level crossings corresponding to multiphonon
transitions in the resonator. Around the resonances, the master equation is
solved analytically using Van Vleck perturbation theory. Their lineshapes are
calculated resulting in simple expressions. We find the general solution for
the multiple multiphonon resonances and, most interestingly, a bath-induced
transition from a resonant to an antiresonant behavior of the nonlinear
response.Comment: 25 pages, 5 figures, submitted to NJ
Optimal generation of Fock states in a weakly nonlinear oscillator
We apply optimal control theory to determine the shortest time in which an
energy eigenstate of a weakly anharmonic oscillator can be created under the
practical constraint of linear driving. We show that the optimal pulses are
beatings of mostly the transition frequencies for the transitions up to the
desired state and the next leakage level. The time of a shortest possible pulse
for a given nonlinearity scale with the nonlinearity parameter delta as a power
law of alpha with alpha=-0.73 +/-0.029. This is a qualitative improvement
relative to the value alpha=1 suggested by a simple Landau-Zener argument.Comment: 10 pages, 6 figure
Theory of superconductor-insulator transition in single Josephson junctions
A non-band theory is developed to describe the superconductor-insulator (SI)
transtition in resistively shunted, single Josephson junctions. The
characteristic is formulated by a Landauer-like formula and evaluated by the
path-integral transfer-matrix method. The result is consistent with the recent
experiments at around 80 . However, the insulator phase shrinks with
decreasing temperature indicating that the single Josephson junction becomes
all superconducting at absolute zero temperature, as long as dissipation is
present.Comment: 4 pages, 3 figure
2018 Ottawa consensus statement : Selection and recruitment to the healthcare professions
Acknowledgments: The authors thank Tom Kinirons and Sarah Stott of Work Psychology Group for supporting the consensus group discussions and workshops, and in preparing the final manuscript. We also gratefully acknowledge Professor Lambert Schuwirth for his helpful comments on an earlier draft of this paperPeer reviewedPostprin
Cooling and squeezing the fluctuations of a nanomechanical beam by indirect quantum feedback control
We study cooling and squeezing the fluctuations of a nanomechanical beam
using quantum feedback control. In our model, the nanomechanical beam is
coupled to a transmission line resonator via a superconducting quantum
interference device (SQUID). The leakage of the electromagnetic field from the
transmission line resonator is measured using homodyne detection. This measured
signal is then used to design a quantum-feedback-control signal to drive the
electromagnetic field in the transmission line resonator. Although the control
is imposed on the transmission line resonator, this quantum-feedback-control
signal indirectly affects the thermal motion of the nanomechanical beam via the
inductive beam-resonator coupling, making it possible to cool and squeeze the
fluctuations of the beam, allowing it to approach the standard quantum limit.Comment: 14 pages, 9 figure
Quantum theory of electromechanical noise and momentum transfer statistics
A quantum mechanical theory is developed for the statistics of momentum
transferred to the lattice by conduction electrons. Results for the
electromechanical noise power in the semiclassical diffusive transport regime
agree with a recent theory based on the Boltzmann-Langevin equation. All
moments of the transferred momentum are calculated for a single-channel
conductor with a localized scatterer, and compared with the known statistics of
transmitted charge.Comment: 10 pages, 2 figure
A Mechanical Mass Sensor with Yoctogram Resolution
Nanoelectromechanical systems (NEMS) have generated considerable interest as
inertial mass sensors. NEMS resonators have been used to weigh cells,
biomolecules, and gas molecules, creating many new possibilities for biological
and chemical analysis [1-4]. Recently, NEMS-based mass sensors have been
employed as a new tool in surface science in order to study e.g. the phase
transitions or the diffusion of adsorbed atoms on nanoscale objects [5-7]. A
key point in all these experiments is the ability to resolve small masses. Here
we report on mass sensing experiments with a resolution of 1.7 yg (1 yg =
10^-24 g), which corresponds to the mass of one proton, or one hydrogen atom.
The resonator is made of a ~150 nm long carbon nanotube resonator vibrating at
nearly 2 GHz. The unprecedented level of sensitivity allows us to detect
adsorption events of naphthalene molecules (C10H8) and to measure the binding
energy of a Xe atom on the nanotube surface (131 meV). These ultrasensitive
nanotube resonators offer new opportunities for mass spectrometry,
magnetometry, and adsorption experiments.Comment: submitted version of the manuscrip
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