3,089 research outputs found
Hamiltonian and measuring time for analog quantum search
We derive in this study a Hamiltonian to solve with certainty the analog
quantum search problem analogue to the Grover algorithm. The general form of
the initial state is considered. Since the evaluation of the measuring time for
finding the marked state by probability of unity is crucially important in the
problem, especially when the Bohr frequency is high, we then give the exact
formula as a function of all given parameters for the measuring time.Comment: 5 page
Measuring Energy, Estimating Hamiltonians, and the Time-Energy Uncertainty Relation
Suppose that the Hamiltonian acting on a quantum system is unknown and one
wants to determine what is the Hamiltonian. We show that in general this
requires a time which obeys the uncertainty relation where is a measure of how accurately the unknown
Hamiltonian must be estimated. We then apply this result to the problem of
measuring the energy of an unknown quantum state. It has been previously shown
that if the Hamiltonian is known, then the energy can in principle be measured
in an arbitrarily short time. On the other hand we show that if the Hamiltonian
is not known then an energy measurement necessarily takes a minimum time
which obeys the uncertainty relation
where is the precision of the energy measurement. Several examples
are studied to address the question of whether it is possible to saturate these
uncertainty relations. Their interpretation is discussed in detail.Comment: 12pages, revised version with small correction
Preparing ground states of quantum many-body systems on a quantum computer
Preparing the ground state of a system of interacting classical particles is
an NP-hard problem. Thus, there is in general no better algorithm to solve this
problem than exhaustively going through all N configurations of the system to
determine the one with lowest energy, requiring a running time proportional to
N. A quantum computer, if it could be built, could solve this problem in time
sqrt(N). Here, we present a powerful extension of this result to the case of
interacting quantum particles, demonstrating that a quantum computer can
prepare the ground state of a quantum system as efficiently as it does for
classical systems.Comment: 7 pages, 1 figur
A Quantum Random Walk Search Algorithm
Quantum random walks on graphs have been shown to display many interesting
properties, including exponentially fast hitting times when compared with their
classical counterparts. However, it is still unclear how to use these novel
properties to gain an algorithmic speed-up over classical algorithms. In this
paper, we present a quantum search algorithm based on the quantum random walk
architecture that provides such a speed-up. It will be shown that this
algorithm performs an oracle search on a database of items with
calls to the oracle, yielding a speed-up similar to other quantum
search algorithms. It appears that the quantum random walk formulation has
considerable flexibility, presenting interesting opportunities for development
of other, possibly novel quantum algorithms.Comment: 13 pages, 3 figure
A Hybrid Quantum Encoding Algorithm of Vector Quantization for Image Compression
Many classical encoding algorithms of Vector Quantization (VQ) of image
compression that can obtain global optimal solution have computational
complexity O(N). A pure quantum VQ encoding algorithm with probability of
success near 100% has been proposed, that performs operations 45sqrt(N) times
approximately. In this paper, a hybrid quantum VQ encoding algorithm between
classical method and quantum algorithm is presented. The number of its
operations is less than sqrt(N) for most images, and it is more efficient than
the pure quantum algorithm.
Key Words: Vector Quantization, Grover's Algorithm, Image Compression,
Quantum AlgorithmComment: Modify on June 21. 10pages, 3 figure
Quantum Algorithm for Molecular Properties and Geometry Optimization
It is known that quantum computers, if available, would allow an exponential
decrease in the computational cost of quantum simulations. We extend this
result to show that the computation of molecular properties (energy
derivatives) could also be sped up using quantum computers. We provide a
quantum algorithm for the numerical evaluation of molecular properties, whose
time cost is a constant multiple of the time needed to compute the molecular
energy, regardless of the size of the system. Molecular properties computed
with the proposed approach could also be used for the optimization of molecular
geometries or other properties. For that purpose, we discuss the benefits of
quantum techniques for Newton's method and Householder methods. Finally, global
minima for the proposed optimizations can be found using the quantum basin
hopper algorithm, which offers an additional quadratic reduction in cost over
classical multi-start techniques.Comment: 6 page
New Samarium and Neodymium based admixed ferromagnets with near zero net magnetization and tunable exchange bias field
Rare earth based intermetallics, SmScGe and NdScGe, are shown to exhibit near
zero net magnetization with substitutions of 6 to 9 atomic percent of Nd and 25
atomic percent of Gd, respectively. The notion of magnetic compensation in them
is also elucidated by the crossover of zero magnetization axis at low magnetic
fields (less than 103 Oe) and field-induced reversal in the orientation of the
magnetic moments of the dissimilar rare earth ions at higher magnetic fields.
These magnetically ordered materials with no net magnetization and appreciable
conduction electron polarization display an attribute of an exchange bias
field, which can be tuned. The attractively high magnetic ordering temperatures
of about 270 K, underscore the importance of these materials for potential
applications in spintronics.Comment: 6 page text + 5 figure
Effectiveness of BaTiO3 dielectric patches on YBa2Cu3O7 thin films for MEM switches
A micro-electro-mechanical (MEM) switch built on a superconducting microstrip filter will be utilized to investigate BaTiO3 dielectric patches for functional switching points of contact. Actuation voltage resulting from the MEM switch provokes static friction between the bridge membrane and BaTiO3 insulation layer. The dielectric patch crystal structure and roughness affect the ability of repetitively switching cycles and lifetime. A series of experiments have been performed using different deposition methods and RF magnetron sputtering was found to be the best deposition process for the BaTiO3 layer. The effect examination of surface morphology will be presented using characterization techniques as x-ray diffraction, SEM and AFM for an optimum switching device. The thin film is made of YBa2Cu3O7 deposited on LaAlO3 substrate by pulsed laser deposition. For this work, the dielectric material sputtering pressure is set at 9.5x10-6 Torr. The argon gas is released through a mass-flow controller to purge the system prior to deposition. RF power is 85 W at a distance of 9 cm. The behavior of Au membranes built on ultimate BaTiO3 patches will be shown as part of the results. These novel surface patterns will in turn be used in modelling other RF MEM switch devices such as distributed-satellite communication system operating at cryogenic temperatures
Quantum Search with Two-atom Collisions in Cavity QED
We propose a scheme to implement two-qubit Grover's quantum search algorithm
using Cavity Quantum Electrodynamics. Circular Rydberg atoms are used as
quantum bits (qubits). They interact with the electromagnetic field of a
non-resonant cavity . The quantum gate dynamics is provided by a
cavity-assisted collision, robust against decoherence processes. We present the
detailed procedure and analyze the experimental feasibility.Comment: 4 pages, 2 figure
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