665 research outputs found

### Probing BEC phase fluctuations with atomic quantum dots

We consider the dephasing of two internal states |0> and |1> of a trapped
impurity atom, a so-called atomic quantum dot (AQD), where only state |1>
couples to a Bose-Einstein condensate (BEC). A direct relation between the
dephasing of the internal states of the AQD and the temporal phase fluctuations
of the BEC is established. Based on this relation we suggest a scheme to probe
BEC phase fluctuations nondestructively via dephasing measurements of the AQD.
In particular, the scheme allows to trace the dependence of the phase
fluctuations on the trapping geometry of the BEC.Comment: 11 pages, 3 figure

### Depletion of molecular gas by an accretion outburst in a protoplanetary disk

We investigate new and archival 3-5 $\mu$m high resolution ($\sim3$ km
s$^{-1}$) spectroscopy of molecular gas in the inner disk of the young
solar-mass star EX Lupi, taken during and after the strong accretion outburst
of 2008. The data were obtained using the CRIRES spectrometer at the ESO Very
Large Telescope in 2008 and 2014. In 2008, emission lines from CO, H$_{2}$O,
and OH were detected with broad profiles tracing gas near and within the
corotation radius (0.02-0.3 AU). In 2014, the spectra display marked
differences. The CO lines, while still detected, are much weaker, and the
H$_{2}$O and OH lines have disappeared altogether. At 3 $\mu$m a veiled stellar
photospheric spectrum is observed. Our analysis finds that the molecular gas
mass in the inner disk has decreased by an order of magnitude since the
outburst, matching a similar decrease in the accretion rate onto the star. We
discuss these findings in the context of a rapid depletion of material
accumulated beyond the disk corotation radius during quiescent periods, as
proposed by models of episodic accretion in EXor type young stars.Comment: 6 pages, 4 figures, 1 table, accepted for publication in the
Astrophysical Journal Letter

### Exploiting boundary states of imperfect spin chains for high-fidelity state transfer

We study transfer of a quantum state through XX spin chains with static
imperfections. We combine the two standard approaches for state transfer based
on (i) modulated couplings between neighboring spins throughout the spin chain
and (ii) weak coupling of the outermost spins to an unmodulated spin chain. The
combined approach allows us to design spin chains with modulated couplings and
localized boundary states, permitting high-fidelity state transfer in the
presence of random static imperfections of the couplings. The modulated
couplings are explicitly obtained from an exact algorithm using the close
relation between tridiagonal matrices and orthogonal polynomials [Linear
Algebr. Appl. 21, 245 (1978)]. The implemented algorithm and a graphical user
interface for constructing spin chains with boundary states (spinGUIn) are
provided as Supplemental Material.Comment: 7 pages, 3 figures + spinGUIn description and Matlab files
iepsolve.m, spinGUIn.fig, spinGUIn.

### Analytical Approximations for the Collapse of an Empty Spherical Bubble

The Rayleigh equation 3/2 R'+RR"+p/rho=0 with initial conditions R(0)=Rmax,
R'(0)=0 models the collapse of an empty spherical bubble of radius R(T) in an
ideal, infinite liquid with far-field pressure p and density rho. The solution
for r=R/Rmax as a function of time t=T/Tcollapse, where R(Tcollapse)=0, is
independent of Rmax, p, and rho. While no closed-form expression for r(t) is
known we find that s(t)=(1-t^2)^(2/5) approximates r(t) with an error below 1%.
A systematic development in orders of t^2 further yields the
0.001%-approximation r*(t)=s(t)[1-a Li(2.21,t^2)], where a=-0.01832099 is a
constant and Li is the polylogarithm. The usefulness of these approximations is
demonstrated by comparison to high-precision cavitation data obtained in
microgravity.Comment: 5 pages, 2 figure

### Breathing oscillations of a trapped impurity in a Bose gas

Motivated by a recent experiment [J. Catani et al., arXiv:1106.0828v1
preprint, 2011], we study breathing oscillations in the width of a harmonically
trapped impurity interacting with a separately trapped Bose gas. We provide an
intuitive physical picture of such dynamics at zero temperature, using a
time-dependent variational approach. In the Gross-Pitaevskii regime we obtain
breathing oscillations whose amplitudes are suppressed by self trapping, due to
interactions with the Bose gas. Introducing phonons in the Bose gas leads to
the damping of breathing oscillations and non-Markovian dynamics of the width
of the impurity, the degree of which can be engineered through controllable
parameters. Our results reproduce the main features of the impurity dynamics
observed by Catani et al. despite experimental thermal effects, and are
supported by simulations of the system in the Gross-Pitaevskii regime.
Moreover, we predict novel effects at lower temperatures due to self-trapping
and the inhomogeneity of the trapped Bose gas.Comment: 7 pages, 3 figure

### Probing the radial temperature structure of protoplanetary disks with Herschel/HIFI

Herschel/HIFI spectroscopic observations of CO J=10-9, CO J=16-15 and [CII]
towards HD 100546 are presented. The objective is to resolve the velocity
profile of the lines to address the emitting region of the transitions and
directly probe the distribution of warm gas in the disk. The spectra reveal
double-peaked CO line profiles centered on the systemic velocity, consistent
with a disk origin. The J=16-15 line profile is broader than that of the J=10-9
line, which in turn is broader than those of lower J transitions (6-5, 3-2,
observed with APEX), thus showing a clear temperature gradient of the gas with
radius. A power-law flat disk model is used to fit the CO line profiles and the
CO rotational ladder simultaneously, yielding a temperature of T_0=1100 \pm 350
K (at r_0 = 13 AU) and an index of q=0.85 \pm 0.1 for the temperature radial
gradient. This indicates that the gas has a steeper radial temperature gradient
than the dust (mean q_{dust} ~ 0.5), providing further proof of the thermal
decoupling of gas and dust at the disk heights where the CO lines form. The
[CII] line profile shows a strong single-peaked profile red-shifted by 0.5 km
s-1 compared to the systemic velocity. We conclude that the bulk of the [CII]
emission has a non-disk origin (e.g., remnant envelope or diffuse cloud).Comment: Accepted for publication in ApJ

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