790 research outputs found
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
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Shocks and PDRs in an intermediate mass star forming globule: the case of IC1396N
The dark globule IC1396N is a typical example of a star formation process induced by radiation driven implosion due to the strong UV field from a nearby O6 star. The IRAS source embedded in the globule and its associated molecular outflow have been observed with the Long Wavelength Spectrometer (LWS) on ISO revealing an extremely rich spectrum including: CO rotational lines from J=14-13 up to J=28-27, rotational lines from ortho-H2O, OH lines involving the first four rotational levels of both ladders, atomic (OI 63μm, OI 145μm) and ionic (CII 157μm, OIII 52μm, OIII 88μm) lines. A complex picture arises, where an externally illuminated PDR coexists with strong C-shocks within IC1396N and whose origin is not clear
The Poincare-Birkhoff theorem in Quantum Mechanics
Quantum manifestations of the dynamics around resonant tori in perturbed
Hamiltonian systems, dictated by the Poincar\'e--Birkhoff theorem, are shown to
exist. They are embedded in the interactions involving states which differ in a
number of quanta equal to the order of the classical resonance. Moreover, the
associated classical phase space structures are mimicked in the
quasiprobability density functions and their zeros.Comment: 5 pages, 3 figures, Full resolution figures available at
http://www.df.uba.ar/users/wisniaki/publications.htm
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ISO observations of M8, the Lagoon nebula
In this paper, IRAS, ISO, and molecular line observations of the M8 and M8E sources in the Lagoon Nebula are reported
Multifractal eigenstates of quantum chaos and the Thue-Morse sequence
We analyze certain eigenstates of the quantum baker's map and demonstrate,
using the Walsh-Hadamard transform, the emergence of the ubiquitous Thue-Morse
sequence, a simple sequence that is at the border between quasi-periodicity and
chaos, and hence is a good paradigm for quantum chaotic states. We show a
family of states that are also simply related to Thue-Morse sequence, and are
strongly scarred by short periodic orbits and their homoclinic excursions. We
give approximate expressions for these states and provide evidence that these
and other generic states are multifractal.Comment: Substantially modified from the original, worth a second download. To
appear in Phys. Rev. E as a Rapid Communicatio
Quantum Process Tomography of the Quantum Fourier Transform
The results of quantum process tomography on a three-qubit nuclear magnetic
resonance quantum information processor are presented, and shown to be
consistent with a detailed model of the system-plus-apparatus used for the
experiments. The quantum operation studied was the quantum Fourier transform,
which is important in several quantum algorithms and poses a rigorous test for
the precision of our recently-developed strongly modulating control fields. The
results were analyzed in an attempt to decompose the implementation errors into
coherent (overall systematic), incoherent (microscopically deterministic), and
decoherent (microscopically random) components. This analysis yielded a
superoperator consisting of a unitary part that was strongly correlated with
the theoretically expected unitary superoperator of the quantum Fourier
transform, an overall attenuation consistent with decoherence, and a residual
portion that was not completely positive - although complete positivity is
required for any quantum operation. By comparison with the results of computer
simulations, the lack of complete positivity was shown to be largely a
consequence of the incoherent errors during the quantum process tomography
procedure. These simulations further showed that coherent, incoherent, and
decoherent errors can often be identified by their distinctive effects on the
spectrum of the overall superoperator. The gate fidelity of the experimentally
determined superoperator was 0.64, while the correlation coefficient between
experimentally determined superoperator and the simulated superoperator was
0.79; most of the discrepancies with the simulations could be explained by the
cummulative effect of small errors in the single qubit gates.Comment: 26 pages, 17 figures, four tables; in press, Journal of Chemical
Physic
Probing the quantum phase transition in the Dicke model through mechanical vibrations
This paper is concerned with quantum dynamics of a system coupled to a
critical reservoir. In this context, we employ the Dicke model which is known
to exhibit a super radiant quantum phase transition (QPT) and we allow one of
the mirrors to move under a linear restoring force. The electromagnetic field
couples to the movable mirror though radiation pressure just like in typical
optomechanical setups. We show that, in the thermodynamical limit, the
super-radiant phase induces a classical driving force on the mirror without
causing decoherence.Comment: 6 pages, 3 figures, final versio
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