275 research outputs found
Distinguishability of hyperentangled Bell state by linear evolution and local projective measurement
Measuring an entangled state of two particles is crucial to many quantum
communication protocols. Yet Bell state distinguishability using a finite
apparatus obeying linear evolution and local measurement is theoretically
limited. We extend known bounds for Bell-state distinguishability in one and
two variables to the general case of entanglement in two-state variables.
We show that at most classes out of hyper-Bell states can be
distinguished with one copy of the input state. With two copies, complete
distinguishability is possible. We present optimal schemes in each case.Comment: 5 pages, 2 figure
Obtaining Self-similar Scalings in Focusing Flows
The surface structure of converging thin fluid films displays self-similar
behavior, as was shown in the work by Diez et al [Q. Appl. Math 210, 155,
1990]. Extracting the related similarity scaling exponents from either
numerical or experimental data is non-trivial. Here we provide two such
methods. We apply them to experimental and numerical data on converging fluid
films driven by both surface tension and gravitational forcing. In the limit of
pure gravitational driving, we recover Diez' semi-analytic result, but our
methods also allow us to explore the entire regime of mixed capillary and
gravitational driving, up to entirely surface tension driven flows. We find
scaling forms of smoothly varying exponents up to surprisingly small Bond
numbers. Our experimental results are in reasonable agreement with our
numerical simulations, which confirm theoretically obtained relations between
the scaling exponents.Comment: 11 pages, 11 figures, accepted for Phys Rev
p-wave Feshbach molecules
We have produced and detected molecules using a p-wave Feshbach resonance
between 40K atoms. We have measured the binding energy and lifetime for these
molecules and we find that the binding energy scales approximately linearly
with magnetic field near the resonance. The lifetime of bound p-wave molecules
is measured to be 1.0 +/- 0.1 ms and 2.3 +/- 0.2 ms for the m_l = +/- 1 and m_l
= 0 angular momentum projections, respectively. At magnetic fields above the
resonance, we detect quasi-bound molecules whose lifetime is set by the
tunneling rate through the centrifugal barrier
Interactions between cardiac activity and conscious somatosensory perception
Fluctuations in the heart's activity can modulate the access of external stimuli to consciousness. The link between perceptual awareness and cardiac signals has been investigated mainly in the visual and auditory domain. Here, we investigated whether the phase of the cardiac cycle and the prestimulus heart rate influence conscious somatosensory perception. We also tested how conscious detection of somatosensory stimuli affects the heart rate. Electrocardiograms (ECG) of 33 healthy volunteers were recorded while applying near‐threshold electrical pulses at a fixed intensity to the left index finger. Conscious detection was not uniformly distributed across the cardiac cycle but significantly higher in diastole than in systole. We found no evidence that the heart rate before a stimulus influenced its detection, but hits (correctly detected somatosensory stimuli) led to a more pronounced cardiac deceleration than misses. Our findings demonstrate interactions between cardiac activity and conscious somatosensory perception, which highlights the importance of internal bodily states for sensory processing beyond the auditory and visual domain
Guided Quasicontinuous Atom Laser
We report the first realization of a guided quasicontinuous atom laser by rf
outcoupling a Bose-Einstein condensate from a hybrid optomagnetic trap into a
horizontal atomic waveguide. This configuration allows us to cancel the
acceleration due to gravity and keep the de Broglie wavelength constant at 0.5
m during 0.1 s of propagation. We also show that our configuration,
equivalent to pigtailing an optical fiber to a (photon) semiconductor laser,
ensures an intrinsically good transverse mode matching.Comment: version published in Phys. Rev. Lett. 97, 200402 (2006
The potential energy of a K Fermi gas in the BCS-BEC crossover
We present a measurement of the potential energy of an ultracold trapped gas
of K atoms in the BCS-BEC crossover and investigate the temperature
dependence of this energy at a wide Feshbach resonance, where the gas is in the
unitarity limit. In particular, we study the ratio of the potential energy in
the region of the unitarity limit to that of a non-interacting gas, and in the
T=0 limit we extract the universal many-body parameter . We find ; this value is consistent with previous measurements
using Li atoms and also with recent theory and Monte Carlo calculations.
This result demonstrates the universality of ultracold Fermi gases in the
strongly interacting regime
- …