2,435,910 research outputs found
Continuous measurement feedback control of a Bose-Einstein condensate using phase contrast imaging
We consider the theory of feedback control of a Bose-Einstein condensate
(BEC) confined in a harmonic trap under a continuous measurement constructed
via non-destructive imaging. A filtering theory approach is used to derive a
stochastic master equation (SME) for the system from a general Hamiltonian
based upon system-bath coupling. Numerical solutions for this SME in the limit
of a single atom show that the final steady state energy is dependent upon the
measurement strength, the ratio of photon kinetic energy to atomic kinetic
energy, and the feedback strength. Simulations indicate that for a weak
measurement strength, feedback can be used to overcome heating introduced by
the scattering of light, thereby allowing the atom to be driven towards the
ground state.Comment: 4 figures, 11 page
Can Recent Charge Fluctuations Be a Reliable signal for a QGP at RHIC?
The recent papers of Jeon and Koch [1] and Asakawa, Heinz, and Muller [2]
argue that the event by event fluctuations of the ratio of the positively
charged and negatively charged pions provide a distinct signal for a QGP at
RHIC/LHC due to differences in those from the QGP phase and the Hadron Gas
Phase.In this paper we point out that aside from the questionability of the
many assumptions in the treatment used,even following their approach there are
other effects not considered, e.g. color charge fluctuations, which could
significantly or even completely wash out the proposed signal.Therefore lack of
observation of these charge fluctuation signals cannot lead one to conclude
that a QGP is not formed at RHIC. A general discussion of experimental
requirements for observation of such signals(if they exist),annd how to
interpret them is included.Comment: 9 pages and 2 Fig
Gauge/Gravity Duality and Some Applications
We discuss the AdS/CFT correspondence in which space-time emerges from an
interacting theory of D-branes and open strings. These ideas have a historical
continuity with QCD which is an interacting theory of quarks and gluons. In
particular we review the classic case of D3 branes and the non-conformal D1
brane system. We outline by some illustrative examples the calculations that
are enabled in a strongly coupled gauge theory by correspondence with dynamical
horizons in semi-classical gravity in one higher dimension. We also discuss
implications of the gauge-fluid/gravity correspondence for the information
paradox of black hole physics.Comment: 19 pages, 2 figures, Contribution to "Conference in Honor of Murray
Gell-Mann's 80th Birthday
Reanalysis of the spectrum of the z=10 galaxy
In a recent paper Pello et al. reported observations of a faint galaxy,
gravitationally lensed by the galaxy cluster Abell 1835. Deep J-band
spectroscopy revealed a weak emission line near 1.34 microns, detected in two
spectra with different central wavelengths. The line was interpreted as
Lyman-alpha at redshift z=10.0. This interpretation is supported by the
broad-band photometric spectral energy distribution, and by the location of the
galaxy close to the lens critical line for this redshift. We have reanalysed
the two spectra, just released from the data archive. Our analysis includes
allowance for wavelength shifts due to transverse drift of the object in the
slit. We do not detect a significant emission line at the reported location, or
nearby, at either grating setting, nor in the combined spectrum. We provide a
possible explanation for the reported detection as due to spurious positive
flux introduced in the sky-subtraction stage as a result of variable hot
pixels. We provide our final reduced 2D frame, and corresponding error array.Comment: 4 pages, 1 figure. To appear in A&A Letters. Added possible
explanation for reported emission line as due to variable hot pixel
Class of bipartite quantum states satisfying the original Bell inequality
In a general setting, we introduce a new bipartite state property sufficient
for the validity of the perfect correlation form of the original Bell
inequality for any three bounded quantum observables. A bipartite quantum state
with this property does not necessarily exhibit perfect correlations. The class
of bipartite states specified by this property includes both separable and
nonseparable states. We prove analytically that, for any dimension d>2, every
Werner state, separable or nonseparable, belongs to this class.Comment: 6 pages, v.2: one reference added, the statement on Werner states
essentially extended; v.3: details of proofs inserte
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