821 research outputs found
Observing quantum state diffusion by heterodyne detection of fluorescence
A qubit can relax by fluorescence, which prompts the release of a photon into
its electromagnetic environment. By counting the emitted photons, discrete
quantum jumps of the qubit state can be observed. The succession of states
occupied by the qubit in a single experiment, its quantum trajectory, depends
in fact on the kind of detector. How are the quantum trajectories modified if
one measures continuously the amplitude of the fluorescence field instead?
Using a superconducting parametric amplifier, we have performed heterodyne
detection of the fluorescence of a superconducting qubit. For each realization
of the measurement record, we can reconstruct a different quantum trajectory
for the qubit. The observed evolution obeys quantum state diffusion, which is
characteristic of quantum measurements subject to zero point fluctuations.
Independent projective measurements of the qubit at various times provide a
quantitative validation of the reconstructed trajectories. By exploring the
statistics of quantum trajectories, we demonstrate that the qubit states span a
deterministic surface in the Bloch sphere at each time in the evolution.
Additionally, we show that when monitoring fluorescence, coherent
superpositions are generated during the decay from excited to ground state.
Counterintuitively, measuring light emitted during relaxation can give rise to
trajectories with increased excitation probability.Comment: Supplementary material can be found in the ancillary sectio
Using Spontaneous Emission of a Qubit as a Resource for Feedback Control
Persistent control of a transmon qubit is performed by a feedback protocol
based on continuous heterodyne measurement of its fluorescence. By driving the
qubit and cavity with microwave signals whose amplitudes depend linearly on the
instantaneous values of the quadratures of the measured fluorescence field, we
show that it is possible to stabilize permanently the qubit in any targeted
state. Using a Josephson mixer as a phase-preserving amplifier, it was possible
to reach a total measurement efficiency =35%, leading to a maximum of 59%
of excitation and 44% of coherence for the stabilized states. The experiment
demonstrates multiple-input multiple-output analog Markovian feedback in the
quantum regime.Comment: Supplementary material can be found as an ancillary objec
Widely tunable, non-degenerate three-wave mixing microwave device operating near the quantum limit
We present the first experimental realization of a widely frequency tunable,
non-degenerate three-wave mixing device for quantum signals at GHz frequency.
It is based on a new superconducting building-block consisting of a ring of
four Josephson junctions shunted by a cross of four linear inductances. The
phase configuration of the ring remains unique over a wide range of magnetic
fluxes threading the loop. It is thus possible to vary the inductance of the
ring with flux while retaining a strong, dissipation-free, and noiseless
non-linearity. The device has been operated in amplifier mode and its noise
performance has been evaluated by using the noise spectrum emitted by a voltage
biased tunnel junction at finite frequency as a test signal. The unprecedented
accuracy with which the crossover between zero-point-fluctuations and shot
noise has been measured provides an upper-bound for the noise and dissipation
intrinsic to the device.Comment: Accepted for Physical Review Letters. Supplementary material can be
found in the source packag
Neutrino oscillations and the effect of the finite lifetime of the neutrino source
We consider a neutrino source at rest and discuss a condition for the
existence of neutrino oscillations which derives from the finite lifetime
of the neutrino source particle. This condition is present if the
neutrino source is a free particle such that its wave function is
non-stationary. For a Gaussian wave function and with some simplifying
assumptions, we study the modification of the usual oscillation probability
stemming from . In the present accelerator experiments the effect of
can be neglected. We discuss some experimental situations where the
source lifetime becomes relevant in the oscillation formula.Comment: 13 pages latex file with 2 figure
Coherence of neutrino flavor mixing in quantum field theory
In the simplistic quantum mechanical picture of flavor mixing, conditions on
the maximum size and minimum coherence time of the source and detector regions
for the observation of interference---as well as the very viability of the
approach---can only be argued in an ad hoc way from principles external to the
formalism itself. To examine these conditions in a more fundamental way, the
quantum field theoretical -matrix approach is employed in this paper,
without the unrealistic assumption of microscopic stationarity. The fully
normalized, time-dependent neutrino flavor mixing event rates presented here
automatically reveal the coherence conditions in a natural, self-contained, and
physically unambiguous way, while quantitatively describing the transition to
their failure.Comment: 12 pages, submitted to Phys. Rev.
Observing a quantum Maxwell demon at work
This is the author accepted manuscript. The final version is available from National Academy of Sciences via the DOI in this record.In apparent contradiction to the laws of thermodynamics, Maxwell’s
demon is able to cyclically extract work from a system in contact
with a thermal bath exploiting the information about its microstate.
The resolution of this paradox required the insight that an intimate
relationship exists between information and thermodynamics. Here,
we realize a Maxwell demon experiment that tracks the state of each
constituent both in the classical and quantum regimes. The demon
is a microwave cavity that encodes quantum information about a superconducting
qubit and converts information into work by powering
up a propagating microwave pulse by stimulated emission. Thanks
to the high level of control of superconducting circuits, we directly
measure the extracted work and quantify the entropy remaining in
the demon’s memory. This experiment provides an enlightening illustration
of the interplay of thermodynamics with quantum information.This work was supported by the
ANR under the grants 12-JCJC-TIQS and 13-JCJC-INCAL, by
Ville de Paris through the grant Qumotel of the Emergence program
and by the COST network MP1209 "Thermodynamics in the
quantum regime". J.A. acknowledges support from EPSRC, grant
EP/M009165/1, and the Royal Societ
GPCR-OKB: the G protein coupled receptor oligomer knowledge base
Rapid expansion of available data about G Protein Coupled Receptor (GPCR) dimers/oligomers over the past few years requires an effective system to organize this information electronically. Based on an ontology derived from a community dialog involving colleagues using experimental and computational methodologies, we developed the GPCR-Oligomerization Knowledge Base (GPCR-OKB). GPCR-OKB is a system that supports browsing and searching for GPCR oligomer data. Such data were manually derived from the literature. While focused on GPCR oligomers, GPCR-OKB is seamlessly connected to GPCRDB, facilitating the correlation of information about GPCR protomers and oligomers
Behavioral assessment of emotional and motivational appraisal during visual processing of emotional scenes depending on spatial frequencies
a b s t r a c t Previous studies performed on visual processing of emotional stimuli have revealed preference for a specific type of visual spatial frequencies (high spatial frequency, HSF; low spatial frequency, LSF) according to task demands. The majority of studies used a face and focused on the appraisal of the emotional state of others. The present behavioral study investigates the relative role of spatial frequencies on processing emotional natural scenes during two explicit cognitive appraisal tasks, one emotional, based on the selfemotional experience and one motivational, based on the tendency to action. Our results suggest that HSF information was the most relevant to rapidly identify the self-emotional experience (unpleasant, pleasant, and neutral) while LSF was required to rapidly identify the tendency to action (avoidance, approach, and no action). The tendency to action based on LSF analysis showed a priority for unpleasant stimuli whereas the identification of emotional experience based on HSF analysis showed a priority for pleasant stimuli. The present study confirms the interest of considering both emotional and motivational characteristics of visual stimuli
conversion in nuclei within the CMSSM seesaw: universality versus non-universality
In this paper we study conversion in nuclei within the context of the
Constrained Minimal Supersymmetric Standard Model, enlarged by three right
handed neutrinos and their supersymmetric partners, and where the neutrino
masses are generated via a seesaw mechanism. Two different scenarios with
either universal or non-universal soft supersymmetry breaking Higgs masses at
the gauge coupling unification scale are considered. In the first part we
present a complete one-loop computation of the conversion rate for this process
that includes the photon-, -boson, and Higgs-boson penguins, as well as box
diagrams, and compare their size in the two considered scenarios. Then, in
these two scenarios we analyse the relevance of the various parameters on the
conversion rates, particularly emphasising the role played by the heavy
neutrino masses, , and especially . In the case of
hierachical heavy neutrinos, an extremely high sensitivity of the rates to
is indeed found. The last part of this work is devoted to the
study of the interesting loss of correlation between the conversion and
rates that occurs in the non-universal scenario. In the case
of large and light Higgs boson an enhanced ratio of the
to rates, with respect to the universal case is
found, and this could be tested with the future experimental sensitivities.Comment: 48 pages, 15 figures. Minor typos corrected and some references adde
, and the neutrino mass hierarchy at a double baseline Li/B -Beam
We consider a -Beam facility where Li and B ions are
accelerated at , accumulated in a 10 Km storage ring and let
decay, so as to produce intense and beams. These beams
illuminate two iron detectors located at Km and
Km, respectively. The physics potential of this setup is analysed in full
detail as a function of the flux. We find that, for the highest flux ( ion decays per year per baseline), the sensitivity to
reaches ; the sign of
the atmospheric mass difference can be identified, regardless of the true
hierarchy, for ; and, CP-violation
can be discovered in 70% of the -parameter space for , having some sensitivity to CP-violation down to
for .Comment: 35 pages, 20 figures. Minor changes, matches the published versio
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