1,086 research outputs found
Quantum Energies of Interfaces
We present a method for computing the one-loop, renormalized quantum energies
of symmetrical interfaces of arbitrary dimension and codimension using
elementary scattering data. Internal consistency requires finite-energy sum
rules relating phase shifts to bound state energies.Comment: 8 pages, 1 figure, minor changes, Phys. Rev. Lett., in prin
Gravitational Force and the Cardiovascular System
Cardiovascular responses to changes in gravitational force are considered. Man is ideally suited to his 1-g environment. Although cardiovascular adjustments are required to accommodate to postural changes and exercise, these are fully accomplished for short periods (min). More challenging stresses are those of short-term microgravity (h) and long-term microgravity (days) and of gravitational forces greater than that of Earth. The latter can be simulated in the laboratory and quantitative studies can be conducted
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
Adiabatic quantum computation and quantum phase transitions
We analyze the ground state entanglement in a quantum adiabatic evolution
algorithm designed to solve the NP-complete Exact Cover problem. The entropy of
entanglement seems to obey linear and universal scaling at the point where the
mass gap becomes small, suggesting that the system passes near a quantum phase
transition. Such a large scaling of entanglement suggests that the effective
connectivity of the system diverges as the number of qubits goes to infinity
and that this algorithm cannot be efficiently simulated by classical means. On
the other hand, entanglement in Grover's algorithm is bounded by a constant.Comment: 5 pages, 4 figures, accepted for publication in PR
Casimir Effects in Renormalizable Quantum Field Theories
We review the framework we and our collaborators have developed for the study
of one-loop quantum corrections to extended field configurations in
renormalizable quantum field theories. We work in the continuum, transforming
the standard Casimir sum over modes into a sum over bound states and an
integral over scattering states weighted by the density of states. We express
the density of states in terms of phase shifts, allowing us to extract
divergences by identifying Born approximations to the phase shifts with low
order Feynman diagrams. Once isolated in Feynman diagrams, the divergences are
canceled against standard counterterms. Thus regulated, the Casimir sum is
highly convergent and amenable to numerical computation. Our methods have
numerous applications to the theory of solitons, membranes, and quantum field
theories in strong external fields or subject to boundary conditions.Comment: 27 pp., 11 EPS figures, LaTeX using ijmpa1.sty; email correspondence
to R.L. Jaffe ; based on talks presented by the authors at
the 5th workshop `QFTEX', Leipzig, September 200
Energy and Efficiency of Adiabatic Quantum Search Algorithms
We present the results of a detailed analysis of a general, unstructured
adiabatic quantum search of a data base of items. In particular we examine
the effects on the computation time of adding energy to the system. We find
that by increasing the lowest eigenvalue of the time dependent Hamiltonian {\it
temporarily} to a maximum of , it is possible to do the
calculation in constant time. This leads us to derive the general theorem which
provides the adiabatic analogue of the bound of conventional quantum
searches. The result suggests that the action associated with the oracle term
in the time dependent Hamiltonian is a direct measure of the resources required
by the adiabatic quantum search.Comment: 6 pages, Revtex, 1 figure. Theorem modified, references and comments
added, sections introduced, typos corrected. Version to appear in J. Phys.
Fermion Production in the Background of Minkowski Space Classical Solutions in Spontaneously Broken Gauge Theory
We investigate fermion production in the background of Minkowski space
solutions to the equations of motion of gauge theory spontaneously
broken via the Higgs mechanism. First, we attempt to evaluate the topological
charge of the solutions. We find that for solutions is not well-defined
as an integral over all space-time. Solutions can profitably be characterized
by the (integer-valued) change in Higgs winding number . We show
that solutions which dissipate at early and late times and which have nonzero
must have at least the sphaleron energy. We show that if we couple
a quantized massive chiral fermion to a classical background given by a
solution, the number of fermions produced is , and is not related
to .Comment: Version to be published. Argument showing that the topological charge
of solutions is undefined has been strengthened and clarified. Conclusions
unchange
Effective Hamiltonian approach to adiabatic approximation in open systems
The adiabatic approximation in open systems is formulated through the
effective Hamiltonian approach. By introducing an ancilla, we embed the open
system dynamics into a non-Hermitian quantum dynamics of a composite system,
the adiabatic evolution of the open system is then defined as the adiabatic
dynamics of the composite system. Validity and invalidity conditions for this
approximation are established and discussed. A High-order adiabatic
approximation for open systems is introduced. As an example, the adiabatic
condition for an open spin- particle in time-dependent magnetic
fields is analyzed.Comment: 6 pages, 2 figure
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
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