33,924 research outputs found
All-optical non-demolition measurement of single-hole spin in a quantum-dot molecule
We propose an all-optical scheme to perform a non-demolition measurement of a
single hole spin localized in a quantum-dot molecule. The latter is embedded in
a microcavity and driven by two lasers. This allows to induce Raman transitions
which entangle the spin state with the polarization of the emitted photons. We
find that the measurement can be completed with high fidelity on a timescale of
100 ps, shorter than the typical T2. Furthermore, we show that the scheme can
be used to induce and observe spin oscillations without the need of
time-dependent magnetic fields
Entanglement properties in the Inhomogeneous Tavis-Cummings model
In this work we study the properties of the atomic entanglement in the
eigenstates spectrum of the inhomogeneous Tavis-Cummings Model. The
inhomogeneity is present in the coupling among the atoms with quantum
electromagnetic field. We calculate analytical expressions for the concurrence
and we found that this exhibits a strong dependence on the inhomogeneity.Comment: 5 pages, 5 figure
Universal Quantum Computation with Continuous-Variable Cluster States
We describe a generalization of the cluster-state model of quantum
computation to continuous-variable systems, along with a proposal for an
optical implementation using squeezed-light sources, linear optics, and
homodyne detection. For universal quantum computation, a nonlinear element is
required. This can be satisfied by adding to the toolbox any single-mode
non-Gaussian measurement, while the initial cluster state itself remains
Gaussian. Homodyne detection alone suffices to perform an arbitrary multi-mode
Gaussian transformation via the cluster state. We also propose an experiment to
demonstrate cluster-based error reduction when implementing Gaussian
operations.Comment: 4 pages, no figure
F(750), We Miss You as a Bound State of 6 Top and 6 Antitop Quarks, Multiple Point Principle
We review our speculation, that in the pure Standard Model the exchange of
Higgses, including also the ones "eaten by and Z", and of gluons
together make a bound state of 6 top plus 6 anti top quarks bind so strongly
that its mass gets down to about 1/3 of the mass of the collective mass 12
of the 12 constituent quarks. The true importance of this speculated
bound state is that it makes it possible to uphold, even inside the Standard
Mode, our proposal for what is really a new law of nature saying that there are
several phases of empty space, vacua, all having very small energy densities
(of the order of the present energy density in the universe). The reason
suggested for believing in this new law called the "Multiple (Criticality)
Point Principle" is, that estimating the mass of the speculated bound state
using the "Multiple Point Principle" leads to two consistent mass-values; and
they even agree with a crude bag-model like estimate of the mass of this bound
state. Very, unfortunately, the statistical fluctuation so popular last year,
when interpreted as the digamma resonance F(750), turned out not to be a real
resonance, because our estimated bound state mass is just around the mass of
750 GeV.Comment: 25 pages, 11 figures, Corfu Summer Institute 2016 "School and
Workshops on Elementary Particle Physics and Gravity", 31 August - 23
September, 2016, Corfu, Greec
One qubit almost completely reveals the dynamics of two
From the time dependence of states of one of them, the dynamics of two
interacting qubits is determined to be one of two possibilities that differ
only by a change of signs of parameters in the Hamiltonian. The only exception
is a simple particular case where several parameters in the Hamiltonian are
zero and one of the remaining nonzero parameters has no effect on the time
dependence of states of the one qubit. The mean values that describe the
initial state of the other qubit and of the correlations between the two qubits
also are generally determined to within a change of signs by the time
dependence of states of the one qubit, but with many more exceptions. An
example demonstrates all the results. Feedback in the equations of motion that
allows time dependence in a subsystem to determine the dynamics of the larger
system can occur in both classical and quantum mechanics. The role of quantum
mechanics here is just to identify qubits as the simplest objects to consider
and specify the form that equations of motion for two interacting qubits can
take.Comment: 6 pages with new and updated materia
Extreme AO Observations of Two Triple Asteroid Systems with SPHERE
We present the discovery of a new satellite of asteroid (130) Elektra -
S/2014 (130) 1 - in differential imaging and in integral field spectroscopy
data over multiple epochs obtained with SPHERE/VLT. This new (second) moonlet
of Elektra is about 2 km across, on an eccentric orbit and about 500 km away
from the primary. For a comparative study, we also observed another triple
asteroid system (93) Minerva. For both systems, component-resolved reflectance
spectra of the satellites and primary were obtained simultaneously. No
significant spectral difference was observed between the satellites and the
primary for either triple system. We find that the moonlets in both systems are
more likely to have been created by sub-disruptive impacts as opposed to having
been captured.Comment: 8 pages, 4 figures, 1 table, accepted to be published in the
Astrophysical Journal Letter
Loss Tolerant Optical Qubits
We present a linear optics quantum computation scheme that employs a new
encoding approach that incrementally adds qubits and is tolerant to photon loss
errors. The scheme employs a circuit model but uses techniques from cluster
state computation and achieves comparable resource usage. To illustrate our
techniques we describe a quantum memory which is fault tolerant to photon loss
Optimizing photon indistinguishability in the emission from incoherently-excited semiconductor quantum dots
Most optical quantum devices require deterministic single-photon emitters.
Schemes so far demonstrated in the solid state imply an energy relaxation which
tends to spoil the coherent nature of the time evolution, and with it the
photon indistinguishability. We focus our theoretical investigation on
semiconductor quantum dots embedded in microcavities. Simple and general
relations are identified between the photon indistinguishability and the
collection efficiency. The identification of the key parameters and of their
interplay provides clear indications for the device optimization
Revivals of Coherence in Chaotic Atom-Optics Billiards
We investigate the coherence properties of thermal atoms confined in optical
dipole traps where the underlying classical dynamics is chaotic. A perturbative
expression derived for the coherence of the echo scheme of [Andersen et. al.,
Phys. Rev. Lett. 90, 023001 (2003)] shows it is a function of the survival
probability or fidelity of eigenstates of the motion of the atoms in the trap.
The echo coherence and the survival probability display "system specific"
features, even when the underlying classical dynamics is chaotic. In
particular, partial revivals in the echo signal and the survival probability
are found for a small shift of the potential. Next, a "semi-classical"
expression for the averaged echo signal is presented and used to calculate the
echo signal for atoms in a light sheet wedge billiard. Revivals in the echo
coherence are found in this system, indicating they may be a generic feature of
dipole traps
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