11,207 research outputs found
Antenna pointing compensation based on precision optical measurement techniques
The pointing control loops of the Deep Space Network 70 meter antennas extend only to the Intermediate Reference Structure (IRS). Thus, distortion of the structure forward of the IRS due to unpredictable environmental loads can result in uncompensated boresight shifts which degrade blind pointing accuracy. A system is described which can provide real time bias commands to the pointing control system to compensate for environmental effects on blind pointing performance. The bias commands are computed in real time based on optical ranging measurements of the structure from the IRS to a number of selected points on the primary and secondary reflectors
Indeterminate-length quantum coding
The quantum analogues of classical variable-length codes are
indeterminate-length quantum codes, in which codewords may exist in
superpositions of different lengths. This paper explores some of their
properties. The length observable for such codes is governed by a quantum
version of the Kraft-McMillan inequality. Indeterminate-length quantum codes
also provide an alternate approach to quantum data compression.Comment: 32 page
Remote State Preparation
Quantum teleportation uses prior entanglement and forward classical
communication to transmit one instance of an unknown quantum state. Remote
state preparation (RSP) has the same goal, but the sender knows classically
what state is to be transmitted. We show that the asymptotic classical
communication cost of RSP is one bit per qubit - half that of teleportation -
and becomes even less when transmitting part of a known entangled state. We
explore the tradeoff between entanglement and classical communication required
for RSP, and discuss RSP capacities of general quantum channels.Comment: 4 pages including 1 epsf figure; v3 has an additional author and
discusses relation to work of Devetak and Berger (quant-ph/0102123); v4
improves low-entanglement protocols without back communication to perform as
well as low-entanglement protocols with back communication; v5 (journal
version) has a few small change
Quantum channels with a finite memory
In this paper we study quantum communication channels with correlated noise
effects, i.e., quantum channels with memory. We derive a model for correlated
noise channels that includes a channel memory state. We examine the case where
the memory is finite, and derive bounds on the classical and quantum
capacities. For the entanglement-assisted and unassisted classical capacities
it is shown that these bounds are attainable for certain classes of channel.
Also, we show that the structure of any finite memory state is unimportant in
the asymptotic limit, and specifically, for a perfect finite-memory channel
where no nformation is lost to the environment, achieving the upper bound
implies that the channel is asymptotically noiseless.Comment: 7 Pages, RevTex, Jrnl versio
The quantum capacity is properly defined without encodings
We show that no source encoding is needed in the definition of the capacity
of a quantum channel for carrying quantum information. This allows us to use
the coherent information maximized over all sources and and block sizes, but
not encodings, to bound the quantum capacity. We perform an explicit
calculation of this maximum coherent information for the quantum erasure
channel and apply the bound in order find the erasure channel's capacity
without relying on an unproven assumption as in an earlier paper.Comment: 19 pages revtex with two eps figures. Submitted to Phys. Rev. A.
Replaced with revised and simplified version, and improved references, etc.
Why can't the last line of the comments field end with a period using this
web submission form
Alternative Buffer-Layers for the Growth of SrBi2Ta2O9 on Silicon
In this work we investigate the influence of the use of YSZ and CeO2/YSZ as
insulators for Metal- Ferroelectric-Insulator-Semiconductor (MFIS) structures
made with SrBi2Ta2O9 (SBT). We show that by using YSZ only the a-axis oriented
Pyrochlore phase could be obtained. On the other hand the use of a CeO2/YSZ
double-buffer layer gave a c-axis oriented SBT with no amorphous SiO2 inter-
diffusion layer. The characteristics of MFIS diodes were greatly improved by
the use of the double buffer. Using the same deposition conditions the memory
window could be increased from 0.3 V to 0.9 V. From the piezoelectric response,
nano-meter scale ferroelectric domains could be clearly identified in SBT thin
films.Comment: 5 pages, 9 figures, 13 refernece
Synchronized single electron emission from dynamical quantum dots
We study synchronized quantized charge pumping through several dynamical
quantum dots (QDs) driven by a single time modulated gate signal. We show that
the main obstacle for synchronization being the lack of uniformity can be
overcome by operating the QDs in the decay cascade regime. We discuss the
mechanism responsible for lifting the stringent uniformity requirements. This
enhanced functionality of dynamical QDs might find applications in
nanoelectronics and quantum metrology.Comment: 4 pages, 3 figures, submitted to AP
Generalized remote state preparation: Trading cbits, qubits and ebits in quantum communication
We consider the problem of communicating quantum states by simultaneously
making use of a noiseless classical channel, a noiseless quantum channel and
shared entanglement. We specifically study the version of the problem in which
the sender is given knowledge of the state to be communicated. In this setting,
a trade-off arises between the three resources, some portions of which have
been investigated previously in the contexts of the quantum-classical trade-off
in data compression, remote state preparation and superdense coding of quantum
states, each of which amounts to allowing just two out of these three
resources. We present a formula for the triple resource trade-off that reduces
its calculation to evaluating the data compression trade-off formula. In the
process, we also construct protocols achieving all the optimal points. These
turn out to be achievable by trade-off coding and suitable time-sharing between
optimal protocols for cases involving two resources out of the three mentioned
above.Comment: 15 pages, 2 figures, 1 tabl
Moist turbulent Rayleigh-Benard convection with Neumann and Dirichlet boundary conditions
Turbulent Rayleigh-Benard convection with phase changes in an extended layer
between two parallel impermeable planes is studied by means of
three-dimensional direct numerical simulations for Rayleigh numbers between
10^4 and 1.5\times 10^7 and for Prandtl number Pr=0.7. Two different sets of
boundary conditions of temperature and total water content are compared:
imposed constant amplitudes which translate into Dirichlet boundary conditions
for the scalar field fluctuations about the quiescent diffusive equilibrium and
constant imposed flux boundary conditions that result in Neumann boundary
conditions. Moist turbulent convection is in the conditionally unstable regime
throughout this study for which unsaturated air parcels are stably and
saturated air parcels unstably stratified. A direct comparison of both sets of
boundary conditions with the same parameters requires to start the turbulence
simulations out of differently saturated equilibrium states. Similar to dry
Rayleigh-Benard convection the differences in the turbulent velocity
fluctuations, the cloud cover and the convective buoyancy flux decrease across
the layer with increasing Rayleigh number. At the highest Rayleigh numbers the
system is found in a two-layer regime, a dry cloudless and stably stratified
layer with low turbulence level below a fully saturated and cloudy turbulent
one which equals classical Rayleigh-Benard convection layer. Both are separated
by a strong inversion that gets increasingly narrower for growing Rayleigh
number.Comment: 19 pages, 13 Postscript figures, Figures 10,11,12,13, in reduced
qualit
Fast high-efficiency integrated waveguide photodetectors using novel hybrid vertical/butt coupling geometry
We report a novel coupling geometry for integrated waveguide photodetectors−a hybrid vertical coupling/butt coupling scheme that allows the integration of fast, efficient, photodetectors with conventional double heterostructure waveguides. It can be employed to yield a planar, or pseudo-planar, surface that supports further levels of integration. The approach is demonstrated with a 25-µm-long p-i-n detector integrated with an InP/InGaAsP/InP waveguide, which displays a high (~90%) efficiency and large (~15 GHz) bandwidth. This is the fastest high-efficiency integrated waveguide photodetector reported to date
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