965 research outputs found
Scheme for direct measurement of a general two-qubit Hamiltonian
The construction of two-qubit gates appropriate for universal quantum
computation is of enormous importance to quantum information processing.
Building such gates is dependent on accurate knowledge of the interaction
dynamics between two qubit systems. This letter will present a systematic
method for reconstructing the full two-qubit interaction Hamiltonian through
experimental measures of concurrence. This not only gives a convenient method
for constructing two qubit quantum gates, but can also be used to
experimentally determine various Hamiltonian parameters in physical systems. We
show explicitly how this method can be employed to determine the first and
second order spin-orbit corrections to the exchange coupling in quantum dots.Comment: 4 Pages, 1 Figur
Quantum information transport to multiple receivers
The importance of transporting quantum information and entanglement with high
fidelity cannot be overemphasized. We present a scheme based on adiabatic
passage that allows for transportation of a qubit, operator measurements and
entanglement, using a 1-D array of quantum sites with a single sender (Alice)
and multiple receivers (Bobs). Alice need not know which Bob is the receiver,
and if several Bobs try to receive the signal, they obtain a superposition
state which can be used to realize two-qubit operator measurements for the
generation of maximally entangled states.Comment: Modified in view of referee's comments, new author added, natural
scheme for operator measurements identified, hence W state preparation
replaced with GHZ state preparation via operator measurements. 4 pages, 3
figure
Bowen ratio estimates of evapotranspiration for stands on the Virgin River in Southern Nevada
A Bowen ratio energy balance was conducted over a Tamarix ramosissima (saltcedar) stand growing in a riparian corridor along the Virgin River in southern Nevada. Measurements in two separate years were compared and contrasted on the basis of changes in growing conditions. In 1994, a drought year, record high temperatures, dry winds, and a falling water table caused partial wilt of outer smaller twigs in the canopy of many trees in the stand around the Bowen tower. Subsequently, evapotranspiration (ET) estimates declined dramatically over a 60âday period (11 mm dâ1 todâ1). In 1995, the Virgin River at the Bowen tower area changed its course, hydrologically isolating the Tamarix stand in the vicinity of the tower. In 1996, a 25% canopy loss was visually estimated for the Tamarix growing in the area of the tower. Higher soil temperatures relative to air temperatures were recorded in 1996 in response to this loss in canopy. With a more open canopy, thermally induced turbulence was observed in 1996. On day 160 of 1996, a 28°C rise over a 9âhour period was correlated with increased wind speeds of greater than 4 m sâ1. Subsequently, higher ET estimates were made in 1996 compared to 1994 (145 cm versus 75 cm). However, the energy balance was dominated by advection in 1996, with latent energy flux exceeding net radiation 65% of the measurement days compared to only 11% in 1994. We believe this advection was on a scale of the floodplain (hundreds of meters) as opposed to regional advection, since the majority of wind (90%) was in a NâS direction along the course of the river, and that a more open canopy allowed the horizontal transfer of energy into the Tamarix stand at the Bowen tower. Our results suggest that Tamarix has the potential to be both a low water user and a high water user, depending on moisture availability, canopy development, and atmospheric demand, and that advection can dominate energy balances and ET in aridland riparian zones such as the Virgin River
2009 Sub-Librarians Meeting: History Detective: Researching the BSI Archival Histories
The Sub-Librarians, members of the Criterion Bar, and local Sherlockians met at Blackie\u27s in Chicago on Sunday, July 12th at 12:00pm. Marsha Pollak, Sub-Librarians, and Allan Devitt of The Criterion Bar Association welcomed the group. The traditional toasts were made: Lomax by Valli Hoski; Sherlock Holmes by Bob Coghill; Hill Barton by George Scheetz; Baron Gruner by Marsha Pollak; and Kitty Winter by Gayle L. Puhl. The featured speaker was Jon L. Lellenberg, presenting History Detective: Researching the BSI Archival Histories.
Lellenberg has written numerous volumes on the history of the Baker Street Irregulars, and presented on his detective work and some of his most interesting discoveries from the BSI\u27s origins and early decades.
View full text of speech.
Local arrangements thanks to Susan Diamond and Allan Devitt of the Criterion Bar Association of Chicago
Asymmetric quantum error correction via code conversion
In many physical systems it is expected that environmental decoherence will
exhibit an asymmetry between dephasing and relaxation that may result in qubits
experiencing discrete phase errors more frequently than discrete bit errors. In
the presence of such an error asymmetry, an appropriately asymmetric quantum
code - that is, a code that can correct more phase errors than bit errors -
will be more efficient than a traditional, symmetric quantum code. Here we
construct fault tolerant circuits to convert between an asymmetric subsystem
code and a symmetric subsystem code. We show that, for a moderate error
asymmetry, the failure rate of a logical circuit can be reduced by using a
combined symmetric asymmetric system and that doing so does not preclude
universality.Comment: 5 pages, 8 figures, presentation revised, figures and references
adde
Physics-based mathematical models for quantum devices via experimental system identification
We consider the task of intrinsic control system identification for quantum
devices. The problem of experimental determination of subspace confinement is
considered, and simple general strategies for full Hamiltonian identification
and decoherence characterization of a controlled two-level system are
presented.Comment: 15 pages, 8 figures, published in proceedings of workshop on
Physics-based mathematical models of low-dimensional semi-conductor
nanostructures (18-23 November, 2007, Banff International Research Station,
Alberta, Canada
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