29 research outputs found
Quantum revival patterns from classical phase-space trajectories
A general semiclassical method in phase space based on the final value
representation of the Wigner function is considered that bypasses caustics and
the need to root-search for classical trajectories. We demonstrate its
potential by applying the method to the Kerr Hamiltonian, for which the exact
quantum evolution is punctuated by a sequence of intricate revival patterns.
The structure of such revival patterns, lying far beyond the Ehrenfest time, is
semiclassically reproduced and revealed as a consequence of constructive and
destructive interferences of classical trajectories.Comment: 7 pages, 6 figure
Principle of majorization: Application to random quantum circuits
We test the principle of majorization [J. I. Latorre and M. A. Martín-Delgado, Phys. Rev. A 66, 022305 (2002)] in random circuits. Three classes of circuits were considered: (i) universal, (ii) classically simulatable, and (iii) neither universal nor classically simulatable. The studied families are: {CNOT, H, T}, {CNOT, H, NOT}, {CNOT, H, S} (Clifford), matchgates, and IQP (instantaneous quantum polynomial-time). We verified that all the families of circuits satisfy on average the principle of decreasing majorization. In most cases the asymptotic state (number of gates → ∞) behaves like a random vector. However, clear differences appear in the fluctuations of the Lorenz curves associated to asymptotic states. The fluctuations of the Lorenz curves discriminate between universal and non-universal classes of random quantum circuits, and they also detect the complexity of some non-universal but not classically efficiently simulatable quantum random circuits. We conclude that majorization can be used as a indicator of complexity of quantum dynamics, as an alternative to, e.g., entanglement spectrum and out-of-time-order correlators (OTOCs).Fil: Vallejos, Raúl O.. Centro Brasileiro de Pesquisas Físicas; BrasilFil: De Melo, Fernando. Centro Brasileiro de Pesquisas Físicas; BrasilFil: Carlo, Gabriel Gustavo. Comisión Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones No Nucleares. Gerencia Física (CAC). Departamento de Física de la Materia Condensada; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Entangling power of baker's map: Role of symmetries
The quantum baker map possesses two symmetries: a canonical "spatial"
symmetry, and a time-reversal symmetry. We show that, even when these features
are taken into account, the asymptotic entangling power of the baker's map does
not always agree with the predictions of random matrix theory. We have verified
that the dimension of the Hilbert space is the crucial parameter which
determines whether the entangling properties of the baker are universal or not.
For power-of-two dimensions, i.e., qubit systems, an anomalous entangling power
is observed; otherwise the behavior of the baker is consistent with random
matrix theories. We also derive a general formula that relates the asymptotic
entangling power of an arbitrary unitary with properties of its reduced
eigenvectors.Comment: 5 page
Resultados del tratamiento kinésico precoz y oportuno en un niño con Parálisis Facial
Paciente de 12 años, de sexo masculino, con diagnóstico médico de parálisis facial derecha, que ingresa al Servicio Universitario de Kinesiología de la Facultad de Medicina de la UNNE. Al inicio del tratamiento, el paciente presenta: alteración de la fascie con una marcada hipotonía de la hemicara afectada y una leve hipertonía en el lado contralateral. Se realizaron nueve sesiones de tratamiento kinésico basado en electroestimulación muscular selectiva indirecta con corriente exponencial y rectangular, asociada a ejercicios de reeducación muscular y masoterapia. Mediante esta técnica se logra mantener el trofismo muscular; una vez que el paciente recupera las funciones musculares, posteriormente desarrolla simetría y sincronía en la realización de los gestos de la mímica.El paciente logra su recuperación total en un corto considerado breve, sin ninguna complicación derivada de la utilización de electroestimulación
On the classical-quantum correspondence for the scattering dwell time
Using results from the theory of dynamical systems, we derive a general
expression for the classical average scattering dwell time, tau_av. Remarkably,
tau_av depends only on a ratio of phase space volumes. We further show that,
for a wide class of systems, the average classical dwell time is not in
correspondence with the energy average of the quantum Wigner time delay.Comment: 5 pages, 1 figur
Statistical bounds on the dynamical production of entanglement
We present a random-matrix analysis of the entangling power of a unitary
operator as a function of the number of times it is iterated. We consider
unitaries belonging to the circular ensembles of random matrices (CUE or COE)
applied to random (real or complex) non-entangled states. We verify numerically
that the average entangling power is a monotonic decreasing function of time.
The same behavior is observed for the "operator entanglement" --an alternative
measure of the entangling strength of a unitary. On the analytical side we
calculate the CUE operator entanglement and asymptotic values for the
entangling power. We also provide a theoretical explanation of the time
dependence in the CUE cases.Comment: preprint format, 14 pages, 2 figure
WKB Propagation of Gaussian Wavepackets
We analyze the semiclassical evolution of Gaussian wavepackets in chaotic
systems. We prove that after some short time a Gaussian wavepacket becomes a
primitive WKB state. From then on, the state can be propagated using the
standard TDWKB scheme. Complex trajectories are not necessary to account for
the long-time propagation. The Wigner function of the evolving state develops
the structure of a classical filament plus quantum oscillations, with phase and
amplitude being determined by geometric properties of a classical manifold.Comment: 4 pages, 4 figures; significant improvement
On the semiclassical theory for universal transmission fluctuations in chaotic systems: the importance of unitarity
The standard semiclassical calculation of transmission correlation functions
for chaotic systems is severely influenced by unitarity problems. We show that
unitarity alone imposes a set of relationships between cross sections
correlation functions which go beyond the diagonal approximation. When these
relationships are properly used to supplement the semiclassical scheme we
obtain transmission correlation functions in full agreement with the exact
statistical theory and the experiment. Our approach also provides a novel
prediction for the transmission correlations in the case where time reversal
symmetry is present