3,454 research outputs found
Accumulator for shaft encoder
Digital accumulator relies almost entirely on integrated circuitry to process the data derived from the outputs of gyro shaft encoder. After the read command is given, the output register collects and stores the data that are on the set output terminals of the up-down counters
Sediment Denitrification In The Gulf Of Mexico Zone Of Hypoxia
The largest zone of anthropogenic bottom water hypoxia in the Western Hemisphere occurs seasonally in the northern Gulf of Mexico between the Mississippi River delta and the coast of eastern Texas. This zone of hypoxia reaches its greatest extent in the summer months and is a consequence of seasonal stratification of the water column combined with the decomposition of organic matter derived from accelerated rates of primary production. This enhanced productivity is driven primarily by the input of inorganic nitrogen from the Mississippi River. There are 3 likely sinks for fixed nitrogen within this zone of hypoxia: sequestration in the sediment, dispersion and dilution into the Gulf of Mexico, and denitrification. We assessed potential denitrification rates at 7 stations in the zone of hypoxia during the summer of 1999. Those data are compared with bottom water nitrate, ammonium and dissolved oxygen (DO) concentrations. No denitrification was observed in the water column. Denitrification potential rates in the surface sediments were unexpectedly low and ranged between 39.8 and 108.1 mumol m(-1) h(-1). The highest rates were observed at stations with bottom water DO concentrations between 1 and 3 mg l(-1). Denitrification activity was significantly lower at stations where DO was lower than 1 mg l(-1) or higher than 3 mg l(-1). Nutrient data for these stations demonstrate that as anoxia is approached, the dominant species of nitrogen shifts from nitrate to ammonium. The shift in nitrogen species suggests competition between microbial populations in the sediment community. The lower denitrification rates at stations with bottom water DO l(-1) may be due to nitrate limitation or an increase in the competitive advantage of microorganisms capable of dissimilatory nitrate reduction to ammonium (DNRA). Suppression of denitrification at low DO by any mechanism will increase the residence time of bioavailable nitrogen. This trend could act as a positive feedback mechanism in the formation of hypoxic bottom waters
Optimizing the discrete time quantum walk using a SU(2) coin
We present a generalized version of the discrete time quantum walk, using the
SU(2) operation as the quantum coin. By varying the coin parameters, the
quantum walk can be optimized for maximum variance subject to the functional
form and the probability distribution in the position
space can be biased. We also discuss the variation in measurement entropy with
the variation of the parameters in the SU(2) coin. Exploiting this we show how
quantum walk can be optimized for improving mixing time in an -cycle and for
quantum walk search.Comment: 6 pages, 6 figure
Discrimination of unitary transformations in the Deutsch-Jozsa algorithm
We describe a general framework for regarding oracle-assisted quantum
algorithms as tools for discriminating between unitary transformations. We
apply this to the Deutsch-Jozsa problem and derive all possible quantum
algorithms which solve the problem with certainty using oracle unitaries in a
particular form. We also use this to show that any quantum algorithm that
solves the Deutsch-Jozsa problem starting with a quantum system in a particular
class of initial, thermal equilibrium-based states of the type encountered in
solution state NMR can only succeed with greater probability than a classical
algorithm when the problem size exceeds Comment: 7 pages, 1 figur
Architectures for a quantum random access memory
A random access memory, or RAM, is a device that, when interrogated, returns
the content of a memory location in a memory array. A quantum RAM, or qRAM,
allows one to access superpositions of memory sites, which may contain either
quantum or classical information. RAMs and qRAMs with n-bit addresses can
access 2^n memory sites. Any design for a RAM or qRAM then requires O(2^n)
two-bit logic gates. At first sight this requirement might seem to make large
scale quantum versions of such devices impractical, due to the difficulty of
constructing and operating coherent devices with large numbers of quantum logic
gates. Here we analyze two different RAM architectures (the conventional fanout
and the "bucket brigade") and propose some proof-of-principle implementations
which show that in principle only O(n) two-qubit physical interactions need
take place during each qRAM call. That is, although a qRAM needs O(2^n) quantum
logic gates, only O(n) need to be activated during a memory call. The resulting
decrease in resources could give rise to the construction of large qRAMs that
could operate without the need for extensive quantum error correction.Comment: 10 pages, 7 figures. Updated version includes the answers to the
Refere
Quantum search by measurement
We propose a quantum algorithm for solving combinatorial search problems that
uses only a sequence of measurements. The algorithm is similar in spirit to
quantum computation by adiabatic evolution, in that the goal is to remain in
the ground state of a time-varying Hamiltonian. Indeed, we show that the
running times of the two algorithms are closely related. We also show how to
achieve the quadratic speedup for Grover's unstructured search problem with
only two measurements. Finally, we discuss some similarities and differences
between the adiabatic and measurement algorithms.Comment: 8 pages, 2 figure
Experimental Implementation of Discrete Time Quantum Random Walk on an NMR Quantum Information Processor
We present an experimental implementation of the coined discrete time quantum
walk on a square using a three qubit liquid state nuclear magnetic resonance
(NMR) quantum information processor (QIP). Contrary to its classical
counterpart, we observe complete interference after certain steps and a
periodicity in the evolution. Complete state tomography has been performed for
each of the eight steps making a full period. The results have extremely high
fidelity with the expected states and show clearly the effects of quantum
interference in the walk. We also show and discuss the importance of choosing a
molecule with a natural Hamiltonian well suited to NMR QIP by implementing the
same algorithm on a second molecule. Finally, we show experimentally that
decoherence after each step makes the statistics of the quantum walk tend to
that of the classical random walk.Comment: revtex4, 8 pages, 6 figures, submitted to PR
Disordered quantum walk-induced localization of a Bose-Einstein condensate
We present an approach to induce localization of a Bose-Einstein condensate
in a one-dimensional lattice under the influence of unitary quantum walk
evolution using disordered quantum coin operation. We introduce a discrete-time
quantum walk model in which the interference effect is modified to diffuse or
strongly localize the probability distribution of the particle by assigning a
different set of coin parameters picked randomly for each step of the walk,
respectively. Spatial localization of the particle/state is explained by
comparing the variance of the probability distribution of the quantum walk in
position space using disordered coin operation to that of the walk using an
identical coin operation for each step. Due to the high degree of control over
quantum coin operation and most of the system parameters, ultracold atoms in an
optical lattice offer opportunities to implement a disordered quantum walk that
is unitary and induces localization. Here we present a scheme to use a
Bose-Einstein condensate that can be evolved to the superposition of its
internal states in an optical lattice and control the dynamics of atoms to
observe localization. This approach can be adopted to any other physical system
in which controlled disordered quantum walk can be implemented.Comment: 6 pages, 4 figures, published versio
Generic quantum walk using a coin-embedded shift operator
The study of quantum walk processes has been widely divided into two standard
variants, the discrete-time quantum walk (DTQW) and the continuous-time quantum
walk (CTQW). The connection between the two variants has been established by
considering the limiting value of the coin operation parameter in the DTQW, and
the coin degree of freedom was shown to be unnecessary [26]. But the coin
degree of freedom is an additional resource which can be exploited to control
the dynamics of the QW process. In this paper we present a generic quantum walk
model using a quantum coin-embedded unitary shift operation . The
standard version of the DTQW and the CTQW can be conveniently retrieved from
this generic model, retaining the features of the coin degree of freedom in
both variants.Comment: 5 pages, 1 figure, Publishe
Quantumness of noisy quantum walks: a comparison between measurement-induced disturbance and quantum discord
Noisy quantum walks are studied from the perspective of comparing their
quantumness as defined by two popular measures, measurement-induced disturbance
(MID) and quantum discord (QD). While the former has an operational definition,
unlike the latter, it also tends to overestimate non-classicality because of a
lack of optimization over local measurements. Applied to quantum walks, we find
that MID, while acting as a loose upper bound on QD, still tends to reflect
correctly the trends in the behavior of the latter. However, there are regimes
where its behavior is not indicative of non-classicality: in particular, we
find an instance where MID increases with the application of noise, where we
expect a reduction of quantumness.Comment: 5 pages with 4 figures, Published Versio
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