6,880 research outputs found
Mechanically probing coherent tunnelling in a double quantum dot
We study theoretically the interaction between the charge dynamics of a
few-electron double quantum dot and a capacitively-coupled AFM cantilever, a
setup realized in several recent experiments. We demonstrate that the
dot-induced frequency shift and damping of the cantilever can be used as a
sensitive probe of coherent inter-dot tunnelling, and that these effects can be
used to quantitatively extract both the magnitude of the coherent interdot
tunneling and (in some cases) the value of the double-dot T_1 time. We also
show how the adiabatic modulation of the double-dot eigenstates by the
cantilever motion leads to new effects compared to the single-dot case.Comment: 6 pages, 2 figure
Generation and detection of NOON states in superconducting circuits
NOON states, states between two modes of light of the form
allow for super-resolution interformetry. We
show how NOON states can be efficiently produced in circuit quntum
electrodynamics using superconducting phase qubits and resonators. We propose a
protocol where only one interaction between the two modes is required, creating
all the necessary entanglement at the start of the procedure. This protocol
makes active use of the first three states of the phase qubits. Additionally,
we show how to efficiently verify the success of such an experiment, even for
large NOON states, using randomly sampled measurements and semidefinite
programming techniques.Comment: 15 pages and 3 figure
Electron-phonon coupling and longitudinal mechanical-mode cooling in a metallic nanowire
We investigate electron-phonon coupling in a narrow suspended metallic wire,
in which the phonon modes are restricted to one dimension but the electrons
behave three-dimensionally. Explicit theoretical results related to the known
bulk properties are derived. We find out that longitudinal vibration modes can
be cooled by electronic tunnel refrigeration far below the bath temperature
provided the mechanical quality factors of the modes are sufficiently high. The
obtained results apply to feasible experimental configurations.Comment: 4+ pages, 3 figure
Parametric resonances in electrostatically interacting carbon nanotube arrays
We study, numerically and analytically, a model of a one-dimensional array of
carbon nanotube resonators in a two-terminal configuration. The system is
brought into resonance upon application of an AC-signal superimposed on a
DC-bias voltage. When the tubes in the array are close to each other,
electrostatic interactions between tubes become important for the array
dynamics. We show that both transverse and longitudinal parametric resonances
can be excited in addition to primary resonances. The intertube electrostatic
interactions couple modes in orthogonal directions and affect the mode
stability.Comment: 11 pages, 12 figures, RevTeX
Tablet computers in assessing performance in a high stakes exam : opinion matters
The authors would like to thank Dr Craig brown, University of Aberdeen for assistance with data analysis.Peer reviewedPublisher PD
Mixing with the radiofrequency single-electron transistor
By configuring a radio-frequency single-electron transistor as a mixer, we
demonstrate a unique implementation of this device, that achieves good charge
sensitivity with large bandwidth about a tunable center frequency. In our
implementation we achieve a measurement bandwidth of 16 MHz, with a tunable
center frequency from 0 to 1.2 GHz, demonstrated with the transistor operating
at 300 mK. Ultimately this device is limited in center frequency by the RC time
of the transistor's center island, which for our device is ~ 1.6 GHz, close to
the measured value. The measurement bandwidth is determined by the quality
factor of the readout tank circuit.Comment: Submitted to APL september 200
Nonlinear modal interactions in clamped-clamped mechanical resonators
A theoretical and experimental investigation is presented on the intermodal
coupling between the flexural vibration modes of a single clamped-clamped beam.
Nonlinear coupling allows an arbitrary flexural mode to be used as a
self-detector for the amplitude of another mode, presenting a method to measure
the energy stored in a specific resonance mode. Experimentally observed complex
nonlinear dynamics of the coupled modes are quantitatively captured by a model
which couples the modes via the beam extension; the same mechanism is
responsible for the well-known Duffing nonlinearity in clamped-clamped beams.Comment: 5 pages, 3 figure
Quantum Effects in the Mechanical Properties of Suspended Nanomechanical Systems
We explore the quantum aspects of an elastic bar supported at both ends and
subject to compression. If strain rather than stress is held fixed, the system
remains stable beyond the buckling instability, supporting two potential
minima. The classical equilibrium transverse displacement is analogous to a
Ginsburg-Landau order parameter, with strain playing the role of temperature.
We calculate the quantum fluctuations about the classical value as a function
of strain. Excitation energies and quantum fluctuation amplitudes are compared
for silicon beams and carbon nanotubes.Comment: RevTeX4. 5 pages, 3 eps figures. Submitted to Physical Review Letter
Hot electrons in low-dimensional phonon systems
A simple bulk model of electron-phonon coupling in metals has been
surprisingly successful in explaining experiments on metal films that actually
involve surface- or other low-dimensional phonons. However, by an exact
application of this standard model to a semi-infinite substrate with a free
surface, making use of the actual vibrational modes of the substrate, we show
that such agreement is fortuitous, and that the model actually predicts a
low-temperature crossover from the familiar T^5 temperature dependence to a
stronger T^6 log T scaling. Comparison with existing experiments suggests a
widespread breakdown of the standard model of electron-phonon thermalization in
metals
Noise-enabled precision measurements of a Duffing nanomechanical resonator
We report quantitative experimental measurements of the nonlinear response of
a radiofrequency mechanical resonator, with very high quality factor, driven by
a large swept-frequency force. We directly measure the noise-free transition
dynamics between the two basins of attraction that appear in the nonlinear
regime, and find good agreement with those predicted by the one-dimensional
Duffing equation of motion. We then measure the response of the transition
rates to controlled levels of white noise, and extract the activation energy
from each basin. The measurements of the noise-induced transitions allow us to
obtain precise values for the critical frequencies, the natural resonance
frequency, and the cubic nonlinear parameter in the Duffing oscillator, with
direct applications to high sensitivity parametric sensors based on these
resonators.Comment: 5 pages, 5 figure
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