36,722 research outputs found
Nanoelectromechanics of shuttle devices
A single-electron tunneling (SET) device with a nanoscale central island that
can move with respect to the bulk source- and drain electrodes allows for a
nanoelectromechanical (NEM) coupling between the electrical current through the
device and mechanical vibrations of the island. Although an electromechanical
"shuttle" instability and the associated phenomenon of single-electron
shuttling were predicted more than 15 years ago, both theoretical and
experimental studies of NEM-SET structures are still carried out. New
functionalities based on quantum coherence, Coulomb correlations and coherent
electron-spin dynamics are of particular current interest. In this article we
present a short review of recent activities in this area.Comment: 23 pages, 26 figure
Robust amplification of Santha-Vazirani sources with three devices
We demonstrate that amplification of arbitrarily weak randomness is possible
using quantum resources. We present a randomness amplification protocol that
involves Bell experiments. We find a Bell inequality which can amplify
arbitrarily weak randomness and give a detailed analysis of the protocol
involving it. Our analysis includes finding a sufficient violation of Bell
inequality as a function of the initial quality of randomness. It has a very
important property that for any quality the required violation is strictly
lower than possible to obtain using quantum resources. Among other things, it
means that the protocol takes a finite amount of time to amplify arbitrarily
weak randomness.Comment: published versio
Chaos and Correspondence in Classical and Quantum Hamiltonian Ratchets: A Heisenberg Approach
Previous work [Gong and Brumer, Phys. Rev. Lett., 97, 240602 (2006)]
motivates this study as to how asymmetry-driven quantum ratchet effects can
persist despite a corresponding fully chaotic classical phase space. A simple
perspective of ratchet dynamics, based on the Heisenberg picture, is
introduced. We show that ratchet effects are in principle of common origin in
classical and quantum mechanics, though full chaos suppresses these effects in
the former but not necessarily the latter. The relationship between ratchet
effects and coherent dynamical control is noted.Comment: 21 pages, 7 figures, to appear in Phys. Rev.
Weak values in a classical theory with an epistemic restriction
Weak measurement of a quantum system followed by postselection based on a
subsequent strong measurement gives rise to a quantity called the weak value: a
complex number for which the interpretation has long been debated. We analyse
the procedure of weak measurement and postselection, and the interpretation of
the associated weak value, using a theory of classical mechanics supplemented
by an epistemic restriction that is known to be operationally equivalent to a
subtheory of quantum mechanics. Both the real and imaginary components of the
weak value appear as phase space displacements in the postselected expectation
values of the measurement device's position and momentum distributions, and we
recover the same displacements as in the quantum case by studying the
corresponding evolution in the classical theory. By using this analogous
classical theory, we gain insight into the appearance of the weak value as a
result of the statistical effects of post selection, and this provides us with
an operational interpretation of the weak value, both its real and imaginary
parts. We find that the imaginary part of the weak value is a measure of how
much postselection biases the mean phase space distribution for a given amount
of measurement disturbance. All such biases proportional to the imaginary part
of the weak value vanish in the limit where disturbance due to measurement goes
to zero. Our analysis also offers intuitive insight into how measurement
disturbance can be minimised and the limits of weak measurement.Comment: 9 pages, 2 figures, comments welcome; v2 added some references; v3
published versio
Electronic spin working mechanically
A single-electron tunneling (SET) device with a nanoscale central island that
can move with respect to the bulk source- and drain electrodes allows for a
nanoelectromechanical (NEM) coupling between the electrical current through the
device and mechanical vibrations of the island. Although an electromechanical
"shuttle" instability and the associated phenomenon of single-electron
shuttling were predicted more than 15 years ago, both theoretical and
experimental studies of NEM-SET structures are still carried out. New
functionalities based on quantum coherence, Coulomb correlations and coherent
electron-spin dynamics are of particular current interest. In this article we
present a short review of recent activities in this area.Comment: 17 pages, 11 figures. arXiv admin note: substantial text overlap with
arXiv:1303.074
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