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