784 research outputs found
Berry's phase in noncommutative spaces
We introduce the perturbative aspects of noncommutative quantum mechanics.
Then we study the Berry's phase in the framework of noncommutative quantum
mechanics. The results show deviations from the usual quantum mechanics which
depend on the parameter of space/space noncommtativity.Comment: 7 pages, no figur
Heisenberg quantization for the systems of identical particles and the Pauli exclusion principle in noncommutative spaces
We study the Heisenberg quantization for the systems of identical particles
in noncommtative spaces. We get fermions and bosons as a special cases of our
argument, in the same way as commutative case and therefore we conclude that
the Pauli exclusion principle is also valid in noncommutative spaces.Comment: 8 pages, 1 figur
Activation of sperm motility in the euryhaline tilapia Sarotherodon melanotheron heudelotii (Dumeril, 1859) acclimatized to fresh, sea and hypersaline waters
The effects of osmolality and ions were examined on motility of sperm from males of Sarotherodon melanotheron heudelotii acclimatized in tanks at salinities set at 0, 35 and 70 g L-1. The range of osmolality that enabled sperm activation, shifted and broadened as the maintenance salinity of broodfish increased. The requirement of extracellular Ca2+ for activation of sperm motility increased when the maintenance salinity of broodfish was higher
Dynamics of continuous-time quantum walks in restricted geometries
We study quantum transport on finite discrete structures and we model the
process by means of continuous-time quantum walks. A direct and effective
comparison between quantum and classical walks can be attained based on the
average displacement of the walker as a function of time. Indeed, a fast growth
of the average displacement can be advantageously exploited to build up
efficient search algorithms. By means of analytical and numerical
investigations, we show that the finiteness and the inhomogeneity of the
substrate jointly weaken the quantum walk performance. We further highlight the
interplay between the quantum-walk dynamics and the underlying topology by
studying the temporal evolution of the transfer probability distribution and
the lower bound of long time averages.Comment: 25 pages, 13 figure
Orders of magnitude increased accuracy for quantum many-body problems on quantum computers via an exact transcorrelated method
Transcorrelated methods provide an efficient way of partially transferring the description of electronic correlations from the ground-state wave function directly into the underlying Hamiltonian. In particular, Dobrautz et al. [Phys. Rev. B 99, 075119 (2019)2469-995010.1103/PhysRevB.99.075119] have demonstrated that the use of momentum-space representation, combined with a nonunitary similarity transformation, results in a Hubbard Hamiltonian that possesses a significantly more "compact"ground-state wave function, dominated by a single Slater determinant. This compactness/single-reference character greatly facilitates electronic structure calculations. As a consequence, however, the Hamiltonian becomes non-Hermitian, posing problems for quantum algorithms based on the variational principle. We overcome these limitations with the Ansatz-based quantum imaginary-time evolution algorithm and apply the transcorrelated method in the context of digital quantum computing. We demonstrate that this approach enables up to four orders of magnitude more accurate and compact solutions in various instances of the Hubbard model at intermediate interaction strength (U/t=4), enabling the use of shallower quantum circuits for wave-function Ans\ue4tzes. In addition, we propose a more efficient implementation of the quantum imaginary-time evolution algorithm in quantum circuits that is tailored to non-Hermitian problems. To validate our approach, we perform hardware experiments on the ibmq_lima quantum computer. Our work paves the way for the use of exact transcorrelated methods for the simulations of ab initio systems on quantum computers
Ab Initio Transcorrelated Method enabling accurate Quantum Chemistry on near-term Quantum Hardware
Quantum computing is emerging as a new computational paradigm with the
potential to transform several research fields, including quantum chemistry.
However, current hardware limitations (including limited coherence times, gate
infidelities, and limited connectivity) hamper the straightforward
implementation of most quantum algorithms and call for more noise-resilient
solutions. In quantum chemistry, the limited number of available qubits and
gate operations is particularly restrictive since, for each molecular orbital,
one needs, in general, two qubits. In this study, we propose an explicitly
correlated Ansatz based on the transcorrelated (TC) approach, which transfers
-- without any approximation -- correlation from the wavefunction directly into
the Hamiltonian, thus reducing the number of resources needed to achieve
accurate results with noisy, near-term quantum devices. In particular, we show
that the exact transcorrelated approach not only allows for more shallow
circuits but also improves the convergence towards the so-called basis set
limit, providing energies within chemical accuracy to experiment with smaller
basis sets and, therefore, fewer qubits. We demonstrate our method by computing
bond lengths, dissociation energies, and vibrational frequencies close to
experimental results for the hydrogen dimer and lithium hydride using just 4
and 6 qubits, respectively. Conventional methods require at least ten times
more qubits for the same accuracy
Ensemble density-functional theory for ab-initio molecular dynamics of metals and finite-temperature insulators
A new method is presented for performing first-principles molecular-dynamics
simulations of systems with variable occupancies. We adopt a matrix
representation for the one-particle statistical operator Gamma, to introduce a
``projected'' free energy functional G that depends on the Kohn-Sham orbitals
only and that is invariant under their unitary transformations. The Liouville
equation [ Gamma , H ] = 0 is always satisfied, guaranteeing a very efficient
and stable variational minimization algorithm that can be extended to
non-conventional entropic formulations or fictitious thermal distributions.Comment: 5 pages, two-column style with 2 postscript figures embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#nm_meta
CP Violation in SUSY
Supersymmetry exhibts new sources of CP violation. We discuss the
implications of these new contributions to CP violation both in the K and B
physics. We show that CP violation puts severe constraints on low energy SUSY,
but it represents also a promising ground to look for signals of new physics.Comment: 10 pages, 2 figures. Invited talk by A. Masiero at Ferrara 2000, CP
violation physic
Binary systems of neutral mesons in Quantum Field Theory
Quasi-degenerate binary systems of neutral mesons of the kaon type are
investigated in Quantum Field Theory (QFT). General constraints cast by
analyticity and discrete symmetries P, C, CP, TCP on the propagator (and on its
spectral function) are deduced. Its poles are the physical masses; this
unambiguously defines the propagating eigenstates. It is diagonalized and its
spectrum thoroughly investigated. The role of ``spurious'' states, of zero norm
at the poles, is emphasized, in particular for unitarity and for the
realization of TCP symmetry. The K_L-K_S mass splitting triggers a tiny
difference between their CP violating parameters \epsilon_L and \epsilon_S,
without any violation of TCP. A constant mass matrix like used in Quantum
Mechanics (QM) can only be introduced in a linear approximation to the inverse
propagator, which respects its analyticity and positivity properties; it is
however unable to faithfully describe all features of neutral mesons as we
determine them in QFT, nor to provide any sensible parameterization of eventual
effects of TCP violation. The suitable way to diagonalize the propagator makes
use of a bi-orthogonal basis; it is inequivalent to a bi-unitary transformation
(unless the propagator is normal, which cannot occur here). Problems linked
with the existence of different ``in'' and ``out'' eigenstates are smoothed
out. We study phenomenological consequences of the differences between the QFT
and QM treatments. The non-vanishing of semi-leptonic asymmetry \delta_S -
\delta_L does not signal, unlike usually claimed, TCP violation, while A_TCP
keeps vanishing when TCP is realized. We provide expressions invariant by the
rephasing of K0 and K0bar.Comment: 44 pages, 2 figures. Version to appear in Int. J. Mod. Phys.
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