6,470 research outputs found
Pauli problem for a spin of arbitrary length: A simple method to determine its wave function
The problem of determining a pure state vector from measurements is investigated for a quantum spin of arbitrary length. Generically, only a finite number of wave functions is compatible with the intensities of the spin components in two different spatial directions, measured by a Stern-Gerlach apparatus. The remaining ambiguity can be resolved by one additional well-defined measurement. This method combines efficiency with simplicity: only a small number of quantities have to be measured and the experimental setup is elementary. Other approaches to determine state vectors from measurements, also known as the ââPauli problem,ââ are reviewed for both spin and particle systems
Determining a quantum state by means of a single apparatus
The unknown state \hrho of a quantum system S is determined by letting it
interact with an auxiliary system A, the initial state of which is known. A
one-to-one mapping can thus be realized between the density matrix \hrho and
the probabilities of occurrence of the eigenvalues of a single and factorized
observable of S+A, so that \hrho can be determined by repeated measurements
using a single apparatus. If S and A are spins, it suffices to measure
simultaneously their -components after a controlled interaction. The most
robust setups are determined in this case, for an initially pure or a
completely disordered state of A. They involve an Ising or anisotropic
Heisenberg coupling and an external field.Comment: 5 pages revte
Target Mass Monitoring and Instrumentation in the Daya Bay Antineutrino Detectors
The Daya Bay experiment measures sin^2 2{\theta}_13 using functionally
identical antineutrino detectors located at distances of 300 to 2000 meters
from the Daya Bay nuclear power complex. Each detector consists of three nested
fluid volumes surrounded by photomultiplier tubes. These volumes are coupled to
overflow tanks on top of the detector to allow for thermal expansion of the
liquid. Antineutrinos are detected through the inverse beta decay reaction on
the proton-rich scintillator target. A precise and continuous measurement of
the detector's central target mass is achieved by monitoring the the fluid
level in the overflow tanks with cameras and ultrasonic and capacitive sensors.
In addition, the monitoring system records detector temperature and levelness
at multiple positions. This monitoring information allows the precise
determination of the detectors' effective number of target protons during data
taking. We present the design, calibration, installation and in-situ tests of
the Daya Bay real-time antineutrino detector monitoring sensors and readout
electronics.Comment: 22 pages, 20 figures; accepted by JINST. Changes in v2: minor
revisions to incorporate editorial feedback from JINS
Collisional shifts in optical-lattice atom clocks
We theoretically study the effects of elastic collisions on the determination
of frequency standards via Ramsey fringe spectroscopy in optical-lattice atom
clocks. Interparticle interactions of bosonic atoms in multiply-occupied
lattice sites can cause a linear frequency shift, as well as generate
asymmetric Ramsey fringe patterns and reduce fringe visibility due to
interparticle entanglement. We propose a method of reducing these collisional
effects in an optical lattice by introducing a phase difference of
between the Ramsey driving fields in adjacent sites. This configuration
suppresses site to site hopping due to interference of two tunneling pathways,
without degrading fringe visibility. Consequently, the probability of double
occupancy is reduced, leading to cancellation of collisional shifts.Comment: 15 pages, 11 figure
BATSE Gamma-Ray Burst Line Search: V. Probability of Detecting a Line in a Burst
The physical importance of the apparent discrepancy between the detections by
pre-BATSE missions of absorption lines in gamma-ray burst spectra and the
absence of a BATSE line detection necessitates a statistical analysis of this
discrepancy. This analysis requires a calculation of the probability that a
line, if present, will be detected in a given burst. However, the connection
between the detectability of a line in a spectrum and in a burst requires a
model for the occurrence of a line within a burst. We have developed the
necessary weighting for the line detection probability for each spectrum
spanning the burst. The resulting calculations require a description of each
spectrum in the BATSE database. With these tools we identify the bursts in
which lines are most likely to be detected. Also, by assuming a small frequency
with which lines occur, we calculate the approximate number of BATSE bursts in
which lines of various types could be detected. Lines similar to the Ginga
detections can be detected in relatively few BATSE bursts; for example, in only
~20 bursts are lines similar to the GB 880205 pair of lines detectable. Ginga
reported lines at ~20 and ~40 keV whereas the low energy cutoff of the BATSE
spectra is typically above 20 keV; hence BATSE's sensitivity to lines is less
than that of Ginga below 40 keV, and greater above. Therefore the probability
that the GB 880205 lines would be detected in a Ginga burst rather than a BATSE
burst is ~0.2. Finally, we adopted a more appropriate test of the significance
of a line feature.Comment: 20 pages, AASTeX 4.0, 5 figures, Ap.J. in pres
Evolution of the Low-Energy Photon Spectra in Gamma-Ray Bursts
We report evidence that the asymptotic low-energy power law slope alpha
(below the spectral break) of BATSE gamma-ray burst photon spectra evolves with
time rather than remaining constant. We find a high degree of positive
correlation exists between the time-resolved spectral break energy E_pk and
alpha. In samples of 18 "hard-to-soft" and 12 "tracking" pulses, evolution of
alpha was found to correlate with that of the spectral break energy E_pk at the
99.7% and 98% confidence levels respectively. We also find that in the flux
rise phase of "hard-to-soft" pulses, the mean value of alpha is often positive
and in some bursts the maximum value of alpha is consistent with a value > +1.
BATSE burst 3B 910927, for example, has a alpha_max equal to 1.6 +/- 0.3. These
findings challenge GRB spectral models in which alpha must be negative of
remain constant.Comment: 12 pages (including 6 figures), accepted to Ap
Spectral Hardness Decay with Respect to Fluence in BATSE Gamma-Ray Bursts
We have analyzed the evolution of the spectral hardness parameter Epk as a
function of fluence in gamma-ray bursts. We fit 41 pulses within 26 bursts with
the trend reported by Liang & Kargatis (1996) which found that Epk decays
exponentially with respect to photon fluence. We also fit these pulses with a
slight modification of this trend, where Epk decays linearly with energy
fluence. In both cases, we found the set of 41 pulses to be consistent with the
trend. For the latter trend, which we believe to be more physical, the
distribution of the decay constant is roughly log-normal, with a mean of 1.75
+/- 0.07 and a FWHM of 1.0 +/- 0.1. Regarding an earlier reported invariance in
the decay constant among different pulses in a single burst, we found
probabilities of 0.49 to 0.84 (depending on the test used) that such invariance
would occur by coincidence, most likely due to the narrow distribution of decay
constant values among pulses.Comment: 17 pages, 7 figure pages, 2 table pages, submitted to The
Astrophysical Journa
Influence of the Earth on the background and the sensitivity of the GRM and ECLAIRs instruments aboard the Chinese-French mission SVOM
SVOM (Space-based multi-band astronomical Variable Object Monitor) is a
future Chinese-French satellite mission which is dedicated to Gamma-Ray Burst
(GRB) studies. Its anti-solar pointing strategy makes the Earth cross the field
of view of its payload every orbit. In this paper, we present the variations of
the gamma-ray background of the two high energy instruments aboard SVOM, the
Gamma-Ray Monitor (GRM) and ECLAIRs, as a function of the Earth position. We
conclude with an estimate of the Earth influence on their sensitivity and their
GRB detection capability.Comment: 24 pages, 15 figures, accepted for publication in Experimental
Astronom
Selective excitation of metastable atomic states by femto- and attosecond laser pulses
The possibility of achieving highly selective excitation of low metastable
states of hydrogen and helium atoms by using short laser pulses with reasonable
parameters is demonstrated theoretically. Interactions of atoms with the laser
field are studied by solving the close-coupling equations without
discretization. The parameters of laser pulses are calculated using different
kinds of optimization procedures. For the excitation durations of hundreds of
femtoseconds direct optimization of the parameters of one and two laser pulses
with Gaussian envelopes is used to introduce a number of simple schemes of
selective excitation. To treat the case of shorter excitation durations,
optimal control theory is used and the calculated optimal fields are
approximated by sequences of pulses with reasonable shapes. A new way to
achieve selective excitation of metastable atomic states by using sequences of
attosecond pulses is introduced.Comment: To be published in Phys. Rev. A, 10 pages, 3 figure
Observing GRBs with EXIST
We describe the Energetic X-ray Imaging Survey Telescope EXIST, designed to carry out a sensitive all-sky survey in the 10 keV â 600 keV band. The primary goal of EXIST is to find black holes in the local and distant universe. EXIST also traces cosmic star formation via gamma-ray bursts and gamma-ray lines from radioactive elements ejected by supernovae and novae
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