2,119 research outputs found
Controlled Dephasing of Electrons by Non-Gaussian Shot Noise
In a 'controlled dephasing' experiment [1-3], an interferometer loses its
coherence due to entanglement with a controlled quantum system ('which path'
detector). In experiments that were conducted thus far in mesoscopic systems
only partial dephasing was achieved. This was due to weak interactions between
many detector electrons and the interfering electron, resulting in a Gaussian
phase randomizing process [4-10]. Here, we report the opposite extreme: a
complete destruction of the interference via strong phase randomization only by
a few electrons in the detector. The realization was based on interfering edge
channels (in the integer quantum Hall effect regime, filling factor 2) in a
Mach-Zehnder electronic interferometer, with an inner edge channel serving as a
detector. Unexpectedly, the visibility quenched in a periodic lobe-type form as
the detector current increased; namely, it periodically decreased as the
detector current, and thus the detector's efficiency, increased. Moreover, the
visibility had a V-shape dependence on the partitioning of the detector
current, and not the expected dependence on the second moment of the shot
noise, T(1-T), with T the partitioning. We ascribe these unexpected features to
the strong detector-interferometer coupling, allowing only 1-3 electrons in the
detector to fully dephase the interfering electron. Consequently, in this work
we explored the non-Gaussian nature of noise [11], namely, the direct effect of
the shot noise full counting statistics [12-15].Comment: 14 pages, 4 figure
Mesoscopic Spin-Boson Models of Trapped Ions
Trapped ions arranged in Coulomb crystals provide us with the elements to
study the physics of a single spin coupled to a boson bath. In this work we
show that optical forces allow us to realize a variety of spin-boson models,
depending on the crystal geometry and the laser configuration. We study in
detail the Ohmic case, which can be implemented by illuminating a single ion
with a travelling wave. The mesoscopic character of the phonon bath in trapped
ions induces new effects like the appearance of quantum revivals in the spin
evolution.Comment: 4.4 pages, 5 figure
Fermionic Mach-Zehnder interferometer subject to a quantum bath
We study fermions in a Mach-Zehnder interferometer, subject to a
quantum-mechanical environment leading to inelastic scattering, decoherence,
renormalization effects, and time-dependent conductance fluctuations. Both the
loss of interference contrast as well as the shot noise are calculated, using
equations of motion and leading order perturbation theory. The full dependence
of the shot-noise correction on setup parameters, voltage, temperature and the
bath spectrum is presented. We find an interesting contribution due to
correlations between the fluctuating renormalized phase shift and the output
current, discuss the limiting behaviours at low and high voltages, and compare
with simpler models of dephasing.Comment: 5 pages, 3 figure
Dimensional Crossover of the Dephasing Time in Disordered Mesoscopic Rings: From Diffusive through Ergodic to 0D Behavior
We analyze dephasing by electron interactions in a small disordered quasi-one
dimensional (1D) ring weakly coupled to leads, where we recently predicted a
crossover for the dephasing time \tPh(T) from diffusive or ergodic 1D
(\tPh^{-1} \propto T^{2/3}, T^{1}) to behavior (\tPh^{-1} \propto
T^{2}) as drops below the Thouless energy \ETh. We provide a detailed
derivation of our results, based on an influence functional for quantum Nyquist
noise, and calculate all leading and subleading terms of the dephasing time in
the three regimes. Explicitly taking into account the Pauli blocking of the
Fermi sea in the metal allows us to describe the regime on equal footing
as the others. The crossover to , predicted by Sivan, Imry and Aronov for
3D systems, has so far eluded experimental observation. We will show that for
T \ll \ETh, dephasing governs not only the -dependence for the smooth
part of the magnetoconductivity but also for the amplitude of the
Altshuler-Aronov-Spivak oscillations, which result only from electron paths
winding around the ring. This observation can be exploited to filter out and
eliminate contributions to dephasing from trajectories which do not wind around
the ring, which may tend to mask the behavior. Thus, the ring geometry
holds promise of finally observing the crossover to experimentally.Comment: in "Perspectives of Mesoscopic Physics - Dedicated to Yoseph Imry's
70th Birthday", edited by Amnon Aharony and Ora Entin-Wohlman (World
Scientific, 2010), chap. 20, p. 371-396, ISBN-13 978-981-4299-43-
Einleitung: Subjekthaftigkeit, Digitalität, Fiktion und Alltagswirklichkeit
Welche Ansätze und welche Perspektiven finden sich in der gegenwärtigen Forschung zum Subjekt und den daran gekoppelten Praktiken, Formen, Kulturen und Ordnungen? Welche Aspekte des Digitalen gilt es in dieser Hinsicht präzise zu bestimmen und wie genau passen die Kategorien des Subjekts und des Digitalen zusammen? Die Einleitung wirft einen Blick auf wesentliche Positionen der gegenwärtigen Subjektforschung, fragt nach dem Beitrag, den die Literaturwissenschaft dabei erbringen kann und stellt knapp die Aufsätze dieses Sammelbandes vor
Explaining Sad People's Memory Advantage for Faces.
Sad people recognize faces more accurately than happy people (Hills et al., 2011). We devised four hypotheses for this finding that are tested between in the current study. The four hypotheses are: (1) sad people engage in more expert processing associated with face processing; (2) sad people are motivated to be more accurate than happy people in an attempt to repair their mood; (3) sad people have a defocused attentional strategy that allows more information about a face to be encoded; and (4) sad people scan more of the face than happy people leading to more facial features to be encoded. In Experiment 1, we found that dysphoria (sad mood often associated with depression) was not correlated with the face-inversion effect (a measure of expert processing) nor with response times but was correlated with defocused attention and recognition accuracy. Experiment 2 established that dysphoric participants detected changes made to more facial features than happy participants. In Experiment 3, using eye-tracking we found that sad-induced participants sampled more of the face whilst avoiding the eyes. Experiment 4 showed that sad-induced people demonstrated a smaller own-ethnicity bias. These results indicate that sad people show different attentional allocation to faces than happy and neutral people
Spin Relaxation in a Quantum Dot due to Nyquist Noise
We calculate electron and nuclear spin relaxation rates in a quantum dot due
to the combined action of Nyquist noise and electron-nuclei hyperfine or
spin-orbit interactions. The relaxation rate is linear in the resistance of the
gate circuit and, in the case of spin-orbit interaction, it depends essentially
on the orientations of both the static magnetic field and the fluctuating
electric field, as well as on the ratio between Rashba and Dresselhaus
interaction constants. We provide numerical estimates of the relaxation rate
for typical system parameters, compare our results with other, previously
discussed mechanisms, and show that the Nyquist mechanism can have an
appreciable effect for experimentally relevant systems.Comment: v2: New discussion of arbitrary gate setups (1 new figure), more
Comments on experiments; 6 pages, 4 figure
Dynamical multistability in high-finesse micromechanical optical cavities
We analyze the nonlinear dynamics of a high-finesse optical cavity in which
one mirror is mounted on a flexible mechanical element. We find that this
system is governed by an array of dynamical attractors, which arise from
phase-locking between the mechanical oscillations of the mirror and the ringing
of the light intensity in the cavity. We describe an analytical approximation
to map out the diagram of attractors in parameter space, derive the slow
amplitude dynamics of the system, including thermally activated hopping between
different attractors, and suggest a scheme for exploiting the dynamical
multistability in the measurement of small displacements.Comment: 5 pages, 4 figure
Disruption of the three-body gravitational systems: Lifetime statistics
We investigate statistics of the decay process in the equal-mass three-body
problem with randomized initial conditions. Contrary to earlier expectations of
similarity with "radioactive decay", the lifetime distributions obtained in our
numerical experiments turn out to be heavy-tailed, i.e. the tails are not
exponential, but algebraic. The computed power-law index for the differential
distribution is within the narrow range, approximately from -1.7 to -1.4,
depending on the virial coefficient. Possible applications of our results to
studies of the dynamics of triple stars known to be at the edge of disruption
are considered.Comment: 13 pages, 2 tables, 3 figure
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