6,791 research outputs found
Efficient orthogonal control of tunnel couplings in a quantum dot array
Electrostatically-defined semiconductor quantum dot arrays offer a promising
platform for quantum computation and quantum simulation. However, crosstalk of
gate voltages to dot potentials and inter-dot tunnel couplings complicates the
tuning of the device parameters. To date, crosstalk to the dot potentials is
routinely and efficiently compensated using so-called virtual gates, which are
specific linear combinations of physical gate voltages. However, due to
exponential dependence of tunnel couplings on gate voltages, crosstalk to the
tunnel barriers is currently compensated through a slow iterative process. In
this work, we show that the crosstalk on tunnel barriers can be efficiently
characterized and compensated for, using the fact that the same exponential
dependence applies to all gates. We demonstrate efficient calibration of
crosstalk in a quadruple quantum dot array and define a set of virtual barrier
gates, with which we show orthogonal control of all inter-dot tunnel couplings.
Our method marks a key step forward in the scalability of the tuning process of
large-scale quantum dot arrays.Comment: 8 pages, 7 figure
The Origin of C IV Absorption Systems at Redshifts z<1---Discovery of Extended C IV Envelopes Around Galaxies
(Abridged) We report the discovery of extended CIV gaseous envelopes around
galaxies of a wide range of luminosity and morphological type. First, we show
that CIV absorption systems are strongly clustered around galaxies on velocity
scales of v < 250 km/s and impact parameter scales of rho < 100 h^{-1} kpc but
not on larger velocity or impact parameter scales. Next, adopting measurements
of galaxy properties presented in previous papers, we examine how properties of
the CIV absorption systems depend on properties of the galaxies. On the basis
of 14 galaxy and absorber pairs and 36 galaxies that do not produce
corresponding CIV absorption lines to within sensitive upper limits, we find
that: (1) Galaxies of a range of morphological type and luminosity appear to
possess extended CIV gaseous envelopes of radius R ~ 100 h^{-1} kpc, with
abrupt boundaries between the CIV absorbing and non-absorbing regions. (2) The
extent of CIV-absorbing gas around galaxies scales with galaxy B-band
luminosity as R \propto L_B^{0.5 +/- 0.1} but does not depend strongly on
galaxy surface brightness, redshift, or morphological type. And (3) the
covering factor of CIV clouds within ~ 100 h^{-1} kpc of galaxies is nearly
unity, but there is a large scatter in the mean number of clouds encountered
along the line of sight. The most significant implication of the study is that
galaxies of a wide range of luminosity and morphological type are surrounded by
chemically enriched gas that extends for at least ~ 100 h^{-1} kpc. We consider
various scenarios that may have produced metals at large galactic distance and
conclude that accreting satellites are most likely to be responsible for
chemically enriched gas at large galactic distances to regular looking
galaxies.Comment: 19 pages, 3 figures, to appear in ApJ, July 20 200
Near-IR studies of recurrent nova V745 Scorpii during its 2014 outburst
The recurrent nova (RN) V745 Scorpii underwent its third known outburst on
2014 February 6. Infrared monitoring of the eruption on an almost daily basis,
starting from 1.3d after discovery, shows the emergence of a powerful blast
wave generated by the high velocity nova ejecta exceeding 4000 kms
plowing into its surrounding environment. The temperature of the shocked gas is
raised to a high value exceeding 10K immediately after outburst
commencement. The energetics of the outburst clearly surpass those of similar
symbiotic systems like RS Oph and V407 Cyg which have giant secondaries. The
shock does not show a free-expansion stage but rather shows a decelerative
Sedov-Taylor phase from the beginning. Such strong shockfronts are known to be
sites for ray generation. V745 Sco is the latest nova, apart from five
other known novae, to show ray emission. It may be an important
testbed to resolve the crucial question whether all novae are generically
ray emitters by virtue of having a circumbinary reservoir of material
that is shocked by the ejecta rather than ray generation being
restricted to only symbiotic systems with a shocked red giant (RG) wind. The
lack of a free-expansion stage favors V745 Sco to have a density enhancement
around the white dwarf (WD), above that contributed by a RG wind. Our analysis
also suggests that the WD in V745 Sco is very massive and a potential
progenitor for a future SN Ia explosion.Comment: To appear in ApJ (Letters
The Gaseous Extent of Galaxies and the Origin of \lya Absorption Systems. III. Hubble Space Telescope Imaging of \lya-Absorbing Galaxies at z < 1
We present initial results of a program to obtain and analyze HST WFPC2
images of galaxies identified in an imaging and spectroscopic survey of faint
galaxies in fields of HST spectroscopic target QSOs. We measure properties of
87 galaxies, of which 33 are associated with corresponding \lya absorption
systems and 24 do not produce corresponding \lya absorption lines to within
sensitive upper limits. Considering only galaxy and absorber pairs that are
likely to be physically associated and excluding galaxy and absorber pairs
within 3000 \kms of the background QSOs leaves 26 galaxy and absorber pairs and
seven galaxies that do not produce corresponding \lya absorption lines to
within sensitive upper limits. Redshifts of the galaxy and absorber pairs range
from 0.0750 to 0.8912 with a median of 0.3718, and impact parameter separations
of the galaxy and absorber pairs range from 12.4 to kpc with a
median of kpc. The primary result of the analysis is that the
amount of gas encountered along the line of sight depends on the galaxy impact
parameter and B-band luminosity but does not depend strongly on the galaxy
average surface brightness, disk-to-bulge ratio, or redshift. This result
confirms and improves upon the anti-correlation between \lya absorption
equivalent width and galaxy impact parameter found previously by Lanzetta et
al. (1995). There is no evidence that galaxy interactions play an important
role in distributing tenuous gas around galaxies in most cases. Galaxies might
account for all \lya absorption systems with \AA, but this depends on
the unknown luminosity function and gaseous cross sections of low-luminosity
galaxies as well as on the uncertainties of the observed number density of \lya
absorption systems.Comment: Minor changes. Figure 1 stays intact and is available at
ftp://ftp.ess.sunysb.edu/pub/lanzetta/wfpc
Critical behavior of the 3-state Potts model on Sierpinski carpet
We study the critical behavior of the 3-state Potts model, where the spins
are located at the centers of the occupied squares of the deterministic
Sierpinski carpet. A finite-size scaling analysis is performed from Monte Carlo
simulations, for a Hausdorff dimension . The phase
transition is shown to be a second order one. The maxima of the susceptibility
of the order parameter follow a power law in a very reliable way, which enables
us to calculate the ratio of the exponents . We find that the
scaling corrections affect the behavior of most of the thermodynamical
quantities. However, the sequence of intersection points extracted from the
Binder's cumulant provides bounds for the critical temperature. We are able to
give the bounds for the exponent as well as for the ratio of the
exponents , which are compatible with the results calculated from
the hyperscaling relation.Comment: 13 pages, 4 figure
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