1,111 research outputs found
Uncollapsing the wavefunction by undoing quantum measurements
We review and expand on recent advances in theory and experiments concerning
the problem of wavefunction uncollapse: Given an unknown state that has been
disturbed by a generalized measurement, restore the state to its initial
configuration. We describe how this is probabilistically possible with a
subsequent measurement that involves erasing the information extracted about
the state in the first measurement. The general theory of abstract measurements
is discussed, focusing on quantum information aspects of the problem, in
addition to investigating a variety of specific physical situations and
explicit measurement strategies. Several systems are considered in detail: the
quantum double dot charge qubit measured by a quantum point contact (with and
without Hamiltonian dynamics), the superconducting phase qubit monitored by a
SQUID detector, and an arbitrary number of entangled charge qubits.
Furthermore, uncollapse strategies for the quantum dot electron spin qubit, and
the optical polarization qubit are also reviewed. For each of these systems the
physics of the continuous measurement process, the strategy required to ideally
uncollapse the wavefunction, as well as the statistical features associated
with the measurement is discussed. We also summarize the recent experimental
realization of two of these systems, the phase qubit and the polarization
qubit.Comment: 19 pages, 4 figure
Methods for detection and characterization of signals in noisy data with the Hilbert-Huang Transform
The Hilbert-Huang Transform is a novel, adaptive approach to time series
analysis that does not make assumptions about the data form. Its adaptive,
local character allows the decomposition of non-stationary signals with
hightime-frequency resolution but also renders it susceptible to degradation
from noise. We show that complementing the HHT with techniques such as
zero-phase filtering, kernel density estimation and Fourier analysis allows it
to be used effectively to detect and characterize signals with low signal to
noise ratio.Comment: submitted to PRD, 10 pages, 9 figures in colo
Undoing a weak quantum measurement of a solid-state qubit
We propose an experiment which demonstrates the undoing of a weak continuous
measurement of a solid-state qubit, so that any unknown initial state is fully
restored. The undoing procedure has only a finite probability of success
because of the non-unitary nature of quantum measurement, though it is
accompanied by a clear experimental indication of whether or not the undoing
has been successful. The probability of success decreases with increasing
strength of the measurement, reaching zero for a traditional projective
measurement. Measurement undoing (``quantum un-demolition'') may be interpreted
as a kind of a quantum eraser, in which the information obtained from the first
measurement is erased by the second measurement, which is an essential part of
the undoing procedure. The experiment can be realized using quantum dot
(charge) or superconducting (phase) qubits.Comment: 5 page
Qubit feedback and control with kicked quantum nondemolition measurements: A quantum Bayesian analysis
The informational approach to continuous quantum measurement is derived from
POVM formalism for a mesoscopic scattering detector measuring a charge qubit.
Quantum Bayesian equations for the qubit density matrix are derived, and cast
into the form of a stochastic conformal map. Measurement statistics are derived
for kicked quantum nondemolition measurements, combined with conditional
unitary operations. These results are applied to derive a feedback protocol to
produce an arbitrary pure state after a weak measurement, as well as to
investigate how an initially mixed state becomes purified with and without
feedback.Comment: 13 pages, 3 figure
Ninja data analysis with a detection pipeline based on the Hilbert-Huang Transform
The Ninja data analysis challenge allowed the study of the sensitivity of
data analysis pipelines to binary black hole numerical relativity waveforms in
simulated Gaussian noise at the design level of the LIGO observatory and the
VIRGO observatory. We analyzed NINJA data with a pipeline based on the Hilbert
Huang Transform, utilizing a detection stage and a characterization stage:
detection is performed by triggering on excess instantaneous power,
characterization is performed by displaying the kernel density enhanced (KD)
time-frequency trace of the signal. Using the simulated data based on the two
LIGO detectors, we were able to detect 77 signals out of 126 above SNR 5 in
coincidence, with 43 missed events characterized by signal to noise ratio SNR
less than 10. Characterization of the detected signals revealed the merger part
of the waveform in high time and frequency resolution, free from time-frequency
uncertainty. We estimated the timelag of the signals between the detectors
based on the optimal overlap of the individual KD time-frequency maps, yielding
estimates accurate within a fraction of a millisecond for half of the events. A
coherent addition of the data sets according to the estimated timelag
eventually was used in a characterization of the event.Comment: Accepted for publication in CQG, special issue NRDA proceedings 200
Lithium in strong magnetic fields
The electronic structure of the lithium atom in a strong magnetic field 0 <=
gamma <= 10 is investigated. Our computational approach is a full configuration
interaction method based on a set of anisotropic Gaussian orbitals that is
nonlinearly optimized for each field strength. Accurate results for the total
energies and one-electron ionization energies for the ground and several
excited states for each of the symmetries ^20^+, ^2(-1)^+, ^4(-1)^+, ^4(-1)^-,
^2(-2)^+, ^4(-2)^+, are presented. The behaviour of these energies
as a function of the field strength is discussed and classified. Transition
wave lengths for linear and circular polarized transitions are presented as
well.Comment: 12 pages, 13 figures, accepted for publication in Phys. Rev.
Evidence of hybridization between Galatella villosa and G. linosyris, and a taxonomic reappraisal of the hybrid G. xsubvillosa
At the westernmost distribution of the steppe herbaceous plant, Galatella villosa, in Hungary, Serbia and Ukraine, we recently observed intermediate specimens between this species and its close relative, G. linosyris. We were able to demonstrate the hybrid origin of these individuals by sequencing the biparentally inherited nuclear ribosomal internal transcribed spacer (nrITS) region and checking additive polymorphism in the hybrids. In addition, examination of the maternally inherited plastid regions (trnH-psbA and trnL-trnF intergenic spacers) revealed that G. villosa is likely to be the maternal parent in the Hungarian and Ukrainian populations and G. linosyris in the Serbian population. The intermediate forms produced only sterile seeds. The alleged hybrid between the above two species has already been described as G. xsubvillosa based on a very brief diagnosis. Still, the analysis of the morphological characters using linear discriminant analyses clearly separated the holotype of G. xsubvillosa from individuals of G. linosyris x G. villosa. The latter appeared to be morphologically intermediate between populations of G. villosa and G. linosyris. Contrary to the originally stated hybrid origin of the type plants of G. xsubvillosa, morphological evidence indicates the involvement of G. divaricata not G. linosyris. The hybrid G. linosyris x G. villosa is thus described here, as a new nothospecies G. xfeketegaborii. This study highlights the power of easily available molecular phylogenetic tools for demonstrating the hybrid origin of plants and illustrates how additive polymorphism can be distinguished from other types of intraindividual polymorphism in nuclear DNA sequences.Peer reviewe
Sparkling extreme-ultraviolet bright dots observed with Hi-C
Observing the Sun at high time and spatial scales is a step toward understanding the finest and fundamental scales of heating events in the solar corona. The high-resolution coronal (Hi-C) instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 2012 July 11 that exhibits several interesting features in the EUV line at 193 Å. One of them is the existence of short, small brightenings "sparkling" at the edge of the active region; we call these EUV bright dots (EBDs). Individual EBDs have a characteristic duration of 25 s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength; however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA, which suggests a temperature between 0.5 and 1.5 MK. Based on their frequency in the Hi-C time series, we define four different categories of EBDs: single peak, double peak, long duration, and bursty. Based on a potential field extrapolation from an SDO/HMI magnetogram, the EBDs appear at the footpoints of large-scale, trans-equatorial coronal loops. The Hi-C observations provide the first evidence of small-scale EUV heating events at the base of these coronal loops, which have a free magnetic energy of the order of 1026 erg. © 2014. The American Astronomical Society. All rights reserved
Golden gaskets: variations on the Sierpi\'nski sieve
We consider the iterated function systems (IFSs) that consist of three
general similitudes in the plane with centres at three non-collinear points,
and with a common contraction factor \la\in(0,1).
As is well known, for \la=1/2 the invariant set, \S_\la, is a fractal
called the Sierpi\'nski sieve, and for \la<1/2 it is also a fractal. Our goal
is to study \S_\la for this IFS for 1/2<\la<2/3, i.e., when there are
"overlaps" in \S_\la as well as "holes". In this introductory paper we show
that despite the overlaps (i.e., the Open Set Condition breaking down
completely), the attractor can still be a totally self-similar fractal,
although this happens only for a very special family of algebraic \la's
(so-called "multinacci numbers"). We evaluate \dim_H(\S_\la) for these
special values by showing that \S_\la is essentially the attractor for an
infinite IFS which does satisfy the Open Set Condition. We also show that the
set of points in the attractor with a unique ``address'' is self-similar, and
compute its dimension.
For ``non-multinacci'' values of \la we show that if \la is close to 2/3,
then \S_\la has a nonempty interior and that if \la<1/\sqrt{3} then \S_\la$
has zero Lebesgue measure. Finally we discuss higher-dimensional analogues of
the model in question.Comment: 27 pages, 10 figure
Horizon Problem Remediation via Deformed Phase Space
We investigate the effects of a special kind of dynamical deformation between
the momenta of the scalar field of the Brans-Dicke theory and the scale factor
of the FRW metric. This special choice of deformation includes linearly a
deformation parameter. We trace the deformation footprints in the cosmological
equations of motion when the BD coupling parameter goes to infinity. One class
of the solutions gives a constant scale factor in the late time that confirms
the previous result obtained via another approach in the literature. This
effect can be interpreted as a quantum gravity footprint in the coarse grained
explanation. The another class of the solutions removes the big bang
singularity, and the accelerating expansion region has an infinite temporal
range which overcomes the horizon problem. After this epoch, there is a
graceful exiting by which the universe enters in the radiation dominated era.Comment: 13 pages, 2 figures, to appear in GER
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