1,828 research outputs found
Perturbative Gadgets at Arbitrary Orders
Adiabatic quantum algorithms are often most easily formulated using many-body
interactions. However, experimentally available interactions are generally
two-body. In 2004, Kempe, Kitaev, and Regev introduced perturbative gadgets, by
which arbitrary three-body effective interactions can be obtained using
Hamiltonians consisting only of two-body interactions. These three-body
effective interactions arise from the third order in perturbation theory. Since
their introduction, perturbative gadgets have become a standard tool in the
theory of quantum computation. Here we construct generalized gadgets so that
one can directly obtain arbitrary k-body effective interactions from two-body
Hamiltonians. These effective interactions arise from the kth order in
perturbation theory.Comment: Corrected an error: U dagger vs. U invers
Optical mode crossings and the low temperature anomalies of SrTiO3
Optical mode crossing is not a plausible explanation for the new broad
Brillouin doublet nor for the strong acoustic anomalies observed at low
temperatures in SrTiO3. Data presented to support that explanation are also
inconclusive.Comment: This is a comment to a paper from J.F. Scott (same ZFP volume
HD2D is a Regulator of Abscisic Acid Responses in Arabidopsis
Histone deacetylases have important roles in development and stress response in plants. To further investigate their function, the HD2D gene, of the plant specific HD2 family, was studied. An hd2d-1 mutant and two HD2D overexpression lines were used in this study. Germination was delayed in hd2d-1 and HD2D overexpression seeds only in the presence of ABA. HD2D was found to positively regulate the expression of members of the ABA-response pathway (ABI1, ABI5, and RD29A) leading to increased resistance to drought and salinity treatments. Furthermore, HD2D expression delayed flowering by positively regulating FLC expression. Using bimolecular fluorescence complementation, the HD2D protein was found to interact with the ABA pathway members ABI1, ABI2, and ABI5. Taken together, the results of this study suggest that HD2D is a regulator of ABA responses in Arabidopsis. By expanding the knowledge of plant stress response, this research will help lead to long-term improvements of drought tolerance
Experimental study of ultracold neutron production in pressurized superfluid helium
We have investigated experimentally the pressure dependence of the production
of ultracold neutrons (UCN) in superfluid helium in the range from saturated
vapor pressure to 20bar. A neutron velocity selector allowed the separation of
underlying single-phonon and multiphonon pro- cesses by varying the incident
cold neutron (CN) wavelength in the range from 3.5 to 10{\AA}. The predicted
pressure dependence of UCN production derived from inelastic neutron scattering
data was confirmed for the single-phonon excitation. For multiphonon based UCN
production we found no significant dependence on pressure whereas calculations
from inelastic neutron scattering data predict an increase of 43(6)% at 20bar
relative to saturated vapor pressure. From our data we conclude that applying
pressure to superfluid helium does not increase the overall UCN production rate
at a typical CN guide.Comment: 18 pages, 8 figures Version accepted for publication in PR
Three and Four-Body Interactions in Spin-Based Quantum Computers
In the effort to design and to construct a quantum computer, several leading
proposals make use of spin-based qubits. These designs generally assume that
spins undergo pairwise interactions. We point out that, when several spins are
engaged mutually in pairwise interactions, the quantitative strengths of the
interactions can change and qualitatively new terms can arise in the
Hamiltonian, including four-body interactions. In parameter regimes of
experimental interest, these coherent effects are large enough to interfere
with computation, and may require new error correction or avoidance techniques.Comment: 5 pages incl. 4 figures. To appear in Phys. Rev. Lett. For an
expanded version including detailed calculations see
http://xxx.lanl.gov/abs/cond-mat/030201
A new perturbative approach to the adiabatic approximation
A new and intuitive perturbative approach to time-dependent quantum mechanics
problems is presented, which is useful in situations where the evolution of the
Hamiltonian is slow. The state of a system which starts in an instantaneous
eigenstate of the initial Hamiltonian is written as a power series which has a
straightforward diagrammatic representation. Each term of the series
corresponds to a sequence of "adiabatic" evolutions, during which the system
remains in an instantaneous eigenstate of the Hamiltonian, punctuated by
transitions from one state to another. The first term of this series is the
standard adiabatic evolution, the next is the well-known first correction to
it, and subsequent terms can be written down essentially by inspection.
Although the final result is perhaps not terribly surprising, it seems to be
not widely known, and the interpretation is new, as far as we know. Application
of the method to the adiabatic approximation is given, and some discussion of
the validity of this approximation is presented.Comment: 9 pages. Added references, discussion of previous results, expanded
upon discussion of main result and application of i
Quantum games via search algorithms
We build new quantum games, similar to the spin flip game, where as a novelty
the players perform measurements on a quantum system associated to a continuous
time search algorithm. The measurements collapse the wave function into one of
the two possible states. These games are characterized by a continuous space of
strategies and the selection of a particular strategy is determined by the
moments when the players measure.Comment: 4 pages, 3 figure
Grover's algorithm on a Feynman computer
We present an implementation of Grover's algorithm in the framework of
Feynman's cursor model of a quantum computer. The cursor degrees of freedom act
as a quantum clocking mechanism, and allow Grover's algorithm to be performed
using a single, time-independent Hamiltonian. We examine issues of locality and
resource usage in implementing such a Hamiltonian. In the familiar language of
Heisenberg spin-spin coupling, the clocking mechanism appears as an excitation
of a basically linear chain of spins, with occasional controlled jumps that
allow for motion on a planar graph: in this sense our model implements the idea
of "timing" a quantum algorithm using a continuous-time random walk. In this
context we examine some consequences of the entanglement between the states of
the input/output register and the states of the quantum clock
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