4,458 research outputs found
Brillouin Cooling
We analyze how to exploit Brillouin scattering for the purpose of cooling
opto-mechanical devices and present a quantum-mechanical theory for Brillouin
cooling. Our analysis shows that significant cooling ratios can be obtained
with standard experimental parameters. A further improvement of cooling
efficiency is possible by increasing the dissipation of the optical anti-Stokes
resonance.Comment: 4 pages 3 figure
Quantum Cloning of Binary Coherent States - Optimal Transformations and Practical Limits
The notions of qubits and coherent states correspond to different physical
systems and are described by specific formalisms. Qubits are associated with a
two-dimensional Hilbert space and can be illustrated on the Bloch sphere. In
contrast, the underlying Hilbert space of coherent states is
infinite-dimensional and the states are typically represented in phase space.
For the particular case of binary coherent state alphabets these otherwise
distinct formalisms can equally be applied. We capitalize this formal
connection to analyse the properties of optimally cloned binary coherent
states. Several practical and near-optimal cloning schemes are discussed and
the associated fidelities are compared to the performance of the optimal
cloner.Comment: 12 pages, 12 figure
Exploiting the nonlinear impact dynamics of a single-electron shuttle for highly regular current transport
The nanomechanical single-electron shuttle is a resonant system in which a
suspended metallic island oscillates between and impacts at two electrodes.
This setup holds promise for one-by-one electron transport and the
establishment of an absolute current standard. While the charge transported per
oscillation by the nanoscale island will be quantized in the Coulomb blockade
regime, the frequency of such a shuttle depends sensitively on many parameters,
leading to drift and noise. Instead of considering the nonlinearities
introduced by the impact events as a nuisance, here we propose to exploit the
resulting nonlinear dynamics to realize a highly precise oscillation frequency
via synchronization of the shuttle self-oscillations to an external signal.Comment: 5 pages, 4 figure
Decoherence induced by an interacting spin environment in the transition from integrability to chaos
We investigate the decoherence properties of a central system composed of two
spins 1/2 in contact with a spin bath. The dynamical regime of the bath ranges
from a fully integrable integrable limit to complete chaoticity. We show that
the dynamical regime of the bath determines the efficiency of the decoherence
process. For perturbative regimes, the integrable limit provides stronger
decoherence, while in the strong coupling regime the chaotic limit becomes more
efficient. We also show that the decoherence time behaves in a similar way. On
the contrary, the rate of decay of magnitudes like linear entropy or fidelity
does not depend on the dynamical regime of the bath. We interpret the latter
results as due to a comparable complexity of the Hamiltonian for both the
integrable and the fully chaotic limits.Comment: Submitted to Phys. Rev.
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
TIRS Cryocooler: Spacecraft Integration and Test and Early Flight Data
The Thermal Infrared Sensor (TIRS) is an instrument on Landsat 8, launched in February 2013. The focal plane is cooled by a two-stage Ball Aerospace Stirling cycle cryocooler, with a coldfinger operating at 40K. This paper describes events during the spacecraft integration and test program, and results from early orbit operation of the cryocooler
Electrothermal flow in Dielectrophoresis of Single-Walled Carbon Nanotubes
We theoretically investigate the impact of the electrothermal flow on the
dielectrophoretic separation of single-walled carbon nanotubes (SWNT). The
electrothermal flow is observed to control the motions of semiconducting SWNTs
in a sizeable domain near the electrodes under typical experimental conditions,
therefore helping the dielectrophoretic force to attract semiconducting SWNTs
in a broader range. Moreover, with the increase of the surfactant
concentration, the electrothermal flow is enhanced, and with the change of
frequency, the pattern of the electrothermal flow changes. It is shown that
under some typical experimental conditions of dielectrophoresis separation of
SWNTs, the electrothermal flow is a dominating factor in determining the motion
of SWNTs.Comment: 5 pages, 4 figures, Submitted to PR
Gradient Ascent Pulse Engineering with Feedback
Efficient approaches to quantum control and feedback are essential for quantum technologies, from sensing to quantum computation. Pure control tasks have been successfully solved using optimization techniques, including methods like gradient-ascent pulse engineering (GRAPE) , relying on a differentiable model of the quantum dynamics. For feedback tasks, such methods are not directly applicable, since the aim is to discover strategies conditioned on measurement outcomes. There, model-free reinforcement learning (RL) has recently proven a powerful new ansatz. What is missing is a way to combine the best of both approaches for scenarios that go beyond weak measurements. In this work, we introduce feedback-GRAPE, which borrows concepts from model-free RL to incorporate the response to strong stochastic (discrete or continuous) measurements, while still performing direct gradient ascent through the quantum dynamics. We illustrate its power on a Jaynes-Cummings model with feedback, where it yields interpretable feedback strategies for state preparation and stabilization in the presence of noise. This approach could be employed for discovering strategies in a wide range of feedback tasks, from calibration of multi-qubit devices to linear-optics quantum computation strategies, quantum-enhanced sensing with adaptive measurements, and quantum error correction
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