5,722 research outputs found
Magnetic Trapping of Cold Bromine Atoms
Magnetic trapping of bromine atoms at temperatures in the milliKelvin regime
is demonstrated for the first time. The atoms are produced by photodissociation
of Br molecules in a molecular beam. The lab-frame velocity of Br atoms is
controlled by the wavelength and polarization of the photodissociation laser.
Careful selection of the wavelength results in one of the pair of atoms having
sufficient velocity to exactly cancel that of the parent molecule, and it
remains stationary in the lab frame. A trap is formed at the null point between
two opposing neodymium permanent magnets. Dissociation of molecules at the
field minimum results in the slowest fraction of photofragments remaining
trapped. After the ballistic escape of the fastest atoms, the trapped slow
atoms are only lost by elastic collisions with the chamber background gas. The
measured loss rate is consistent with estimates of the total cross section for
only those collisions transferring sufficient kinetic energy to overcome the
trapping potential
Adaptive homodyne measurement of optical phase
We present an experimental demonstration of the power of real-time feedback
in quantum metrology, confirming a theoretical prediction by Wiseman regarding
the superior performance of an adaptive homodyne technique for single-shot
measurement of optical phase. For phase measurements performed on weak coherent
states with no prior knowledge of the signal phase, we show that the variance
of adaptive homodyne estimation approaches closer to the fundamental quantum
uncertainty limit than any previously demonstrated technique. Our results
underscore the importance of real-time feedback for reaching quantum
performance limits in coherent telecommunication, precision measurement and
information processing.Comment: RevTex4, color PDF figures (separate files), submitted to PR
Semiclassical theory of cavity-assisted atom cooling
We present a systematic semiclassical model for the simulation of the
dynamics of a single two-level atom strongly coupled to a driven high-finesse
optical cavity. From the Fokker-Planck equation of the combined atom-field
Wigner function we derive stochastic differential equations for the atomic
motion and the cavity field. The corresponding noise sources exhibit strong
correlations between the atomic momentum fluctuations and the noise in the
phase quadrature of the cavity field. The model provides an effective tool to
investigate localisation effects as well as cooling and trapping times. In
addition, we can continuously study the transition from a few photon quantum
field to the classical limit of a large coherent field amplitude.Comment: 10 pages, 8 figure
Tomography of an optomechanical oscillator via parametrically amplified position measurement
We propose a protocol for quantum state tomography of nonclassical states in
optomechanical systems. Using a parametric drive, the procedure overcomes the
challenges of weak optomechanical coupling, poor detection efficiency, and
thermal noise to enable high efficiency homodyne measurement. Our analysis is
based on the analytic description of the generalized measurement that is
performed when optomechanical position measurement competes with thermal noise
and a parametric drive. The proposed experimental procedure is numerically
simulated in realistic parameter regimes, which allows us to show that
tomographic reconstruction of otherwise unverifiable nonclassical states is
made possible.Comment: 37 pages, 5 figures, comments welcome. Published versio
Evolution and CNO yields of Z=10^-5 stars and possible effects on CEMP production
Our main goals are to get a deeper insight into the evolution and final fates
of intermediate-mass, extremely metal-poor (EMP) stars. We also aim to
investigate their C, N, and O yields. Using the Monash University Stellar
Evolution code we computed and analysed the evolution of stars of metallicity Z
= 10^-5 and masses between 4 and 9 M_sun, from their main sequence until the
late thermally pulsing (super) asymptotic giant branch, TP-(S)AGB phase. Our
model stars experience a strong C, N, and O envelope enrichment either due to
the second dredge-up, the dredge-out phenomenon, or the third dredge-up early
during the TP-(S)AGB phase. Their late evolution is therefore similar to that
of higher metallicity objects. When using a standard prescription for the mass
loss rates during the TP-(S)AGB phase, the computed stars lose most of their
envelopes before their cores reach the Chandrasekhar mass, so our standard
models do not predict the occurrence of SNI1/2 for Z = 10^-5 stars. However, we
find that the reduction of only one order of magnitude in the mass-loss rates,
which are particularly uncertain at this metallicity, would prevent the
complete ejection of the envelope, allowing the stars to either explode as an
SNI1/2 or become an electron-capture SN. Our calculations stop due to an
instability near the base of the convective envelope that hampers further
convergence and leaves remnant envelope masses between 0.25 M_sun for our 4
M_sun model and 1.5 M_sun for our 9 M_sun model. We present two sets of C, N,
and O yields derived from our full calculations and computed under two
different assumptions, namely, that the instability causes a practically
instant loss of the remnant envelope or that the stars recover and proceed with
further thermal pulses. Our results have implications for the early chemical
evolution of the Universe.Comment: 12 pages, 13 figures, accepted for publication in A&
Quantum control on entangled bipartite qubits
Ising interaction between qubits could produce distortion in entangled pairs
generated for engineering purposes (as in quantum computation) in presence of
parasite magnetic fields, destroying or altering the expected behavior of
process in which is projected to be used. Quantum control could be used to
correct that situation in several ways. Sometimes the user should be make some
measurement upon the system to decide which is the best control scheme; other
posibility is try to reconstruct the system using similar procedures without
perturbate it. In the complete pictures both schemes are present. We will work
first with pure systems studying advantages of different procedures. After, we
will extend these operations when time of distortion is uncertain, generating a
mixed state, which needs to be corrected by suposing the most probably time of
distortion.Comment: 10 pages, 5 figure
Sensitivity optimization in quantum parameter estimation
We present a general framework for sensitivity optimization in quantum
parameter estimation schemes based on continuous (indirect) observation of a
dynamical system. As an illustrative example, we analyze the canonical scenario
of monitoring the position of a free mass or harmonic oscillator to detect weak
classical forces. We show that our framework allows the consideration of
sensitivity scheduling as well as estimation strategies for non-stationary
signals, leading us to propose corresponding generalizations of the Standard
Quantum Limit for force detection.Comment: 15 pages, RevTe
Two-dimensional Nanolithography Using Atom Interferometry
We propose a novel scheme for the lithography of arbitrary, two-dimensional
nanostructures via matter-wave interference. The required quantum control is
provided by a pi/2-pi-pi/2 atom interferometer with an integrated atom lens
system. The lens system is developed such that it allows simultaneous control
over atomic wave-packet spatial extent, trajectory, and phase signature. We
demonstrate arbitrary pattern formations with two-dimensional 87Rb wavepackets
through numerical simulations of the scheme in a practical parameter space.
Prospects for experimental realizations of the lithography scheme are also
discussed.Comment: 36 pages, 4 figure
A Systematic Review of the Role of Penile Rehabilitation in Prostate Cancer Patients Receiving Radiotherapy and Androgen Deprivation Therapy
© 2018 Introduction/Background: Treatment-induced erectile dysfunction (ED) is a common side effect of radiotherapy and androgen deprivation therapy (ADT) that impacts on patient quality of life. Penile rehabilitation interventions including pharmacologic and physical therapies aim to reduce the impact of ED. Despite The National Institute for Health and Care Excellence guidelines recommending access to ED services, penile rehabilitation is not widely discussed or implemented. This systematic review aimed to appraise the evidence base for penile rehabilitation and identify evidence-based recommendations for practice. Methods: A systematic review of the evidence base was undertaken using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The Scopus and Medline (EBSCO) databases were searched for articles relevant to penile rehabilitation interventions for prostate radiotherapy patients. Study quality was graded using the Oxford Levels of Evidence and the Scottish Intercollegiate Guidelines Network. Results: This study identified 19 articles on penile rehabilitation in prostate radiotherapy patients, consisting of eight randomized controlled trials, three systematic reviews, and eight case studies. Findings confirmed the value of early use of phosphodiesterase type 5 inhibitors. Discussion: Despite the range of available physical and pharmaceutical interventions, relevant research focussed solely on the use of phosphodiesterase type 5 inhibitors. Themes from the reviewed articles indicated that timing of intervention was important with early on-going dosage most useful. There was also an identified need for ongoing prophylactic use during ADT. Evidence, in general, was of low quality and based on quantitative data only. Conclusion: Additional research into the wider range of penile rehabilitation interventions is urgently required to ensure patients have access to those therapies that are most appropriate for them. A paradigm shift toward qualitative research in the field of penile rehabilitation for prostate cancer patients treated with radiotherapy and ADT may be of value in future studies
- …