555 research outputs found
Dynamics of a nanomechanical resonator coupled to a superconducting single-electron transistor
We present an analysis of the dynamics of a nanomechanical resonator coupled
to a superconducting single electron transistor (SSET) in the vicinity of the
Josephson quasiparticle (JQP) and double Josephson quasiparticle (DJQP)
resonances. For weak coupling and wide separation of dynamical timescales, we
find that for either superconducting resonance the dynamics of the resonator is
given by a Fokker-Planck equation, i.e., the SSET behaves effectively as an
equilibrium heat bath, characterised by an effective temperature, which also
damps the resonator and renormalizes its frequency. Depending on the gate and
drain-source voltage bias points with respect to the superconducting resonance,
the SSET can also give rise to an instability in the mechanical resonator
marked by negative damping and temperature within the appropriate Fokker-Planck
equation. Furthermore, sufficiently close to a resonance, we find that the
Fokker-Planck description breaks down. We also point out that there is a close
analogy between coupling a nanomechanical resonator to a SSET in the vicinity
of the JQP resonance and Doppler cooling of atoms by means of lasers
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
Observation and interpretation of motional sideband asymmetry in a quantum electro-mechanical device
Quantum electro-mechanical systems offer a unique opportunity to probe
quantum noise properties in macroscopic devices, properties which ultimately
stem from the Heisenberg Uncertainty Principle. A simple example of this 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. Due to 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
Introduction to Quantum Noise, Measurement and Amplification
The topic of quantum noise has become extremely timely due to the rise of
quantum information physics and the resulting interchange of ideas between the
condensed matter and AMO/quantum optics communities. This review gives a
pedagogical introduction to the physics of quantum noise and its connections to
quantum measurement and quantum amplification. After introducing quantum noise
spectra and methods for their detection, we describe the basics of weak
continuous measurements. Particular attention is given to treating the standard
quantum limit on linear amplifiers and position detectors using a general
linear-response framework. We show how this approach relates to the standard
Haus-Caves quantum limit for a bosonic amplifier known in quantum optics, and
illustrate its application for the case of electrical circuits, including
mesoscopic detectors and resonant cavity detectors.Comment: Substantial improvements over initial version; include supplemental
appendices
Optomechanical circuits for nanomechanical continuous variable quantum state processing
We propose and analyze a nanomechanical architecture where light is used to
perform linear quantum operations on a set of many vibrational modes. Suitable
amplitude modulation of a single laser beam is shown to generate squeezing,
entanglement, and state-transfer between modes that are selected according to
their mechanical oscillation frequency. Current optomechanical devices based on
photonic crystals may provide a platform for realizing this scheme.Comment: 11 pages, 5 figure
Quantum squeezing of motion in a mechanical resonator
As a result of the quantum, wave-like nature of the physical world, a
harmonic oscillator can never be completely at rest. Even in the quantum ground
state, its position will always have fluctuations, called the zero-point
motion. Although the zero-point fluctuations are unavoidable, they can be
manipulated. In this work, using microwave frequency radiation pressure, we
both prepare a micron-scale mechanical system in a state near the quantum
ground state and then manipulate its thermal fluctuations to produce a
stationary, quadrature-squeezed state. We deduce that the variance of one
motional quadrature is 0.80 times the zero-point level, or 1 dB of
sub-zero-point squeezing. This work is relevant to the quantum engineering of
states of matter at large length scales, the study of decoherence of large
quantum systems, and for the realization of ultra-sensitive sensing of force
and motion
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