2,775 research outputs found
Enhancement of Geometric Phase by Frustration of Decoherence: A Parrondo like Effect
Geometric phase plays an important role in evolution of pure or mixed quantum
states. However, when a system undergoes decoherence the development of
geometric phase may be inhibited. Here, we show that when a quantum system
interacts with two competing environments there can be enhancement of geometric
phase. This effect is akin to Parrondo like effect on the geometric phase which
results from quantum frustration of decoherence. Our result suggests that the
mechanism of two competing decoherence can be useful in fault-tolerant
holonomic quantum computation.Comment: 5 pages, 3 figures, Published versio
Resources required for exact remote state preparation
It has been shown [M.-Y. Ye, Y.-S. Zhang, and G.-C. Guo, Phys. Rev. A 69,
022310 (2004)] that it is possible to perform exactly faithful remote state
preparation using finite classical communication and any entangled state with
maximal Schmidt number. Here we give an explicit procedure for performing this
remote state preparation. We show that the classical communication required for
this scheme is close to optimal for remote state preparation schemes of this
type. In addition we prove that it is necessary that the resource state have
maximal Schmidt number.Comment: 7 pages, 1 figur
Dynamics of two atoms coupled to a cavity field
We investigate the interaction of two two-level atoms with a single mode
cavity field. One of the atoms is exactly at resonance with the field, while
the other is well far from resonance and hence is treated in the dispersive
limit. We find that the presence of the non-resonant atom produces a shift in
the Rabi frequency of the resonant atom, as if it was detuned from the field.
We focus on the discussion of the evolution of the state purity of each atom.Comment: LaTex, 2 figure
Fluctuation, time-correlation function and geometric Phase
We establish a fluctuation-correlation theorem by relating the quantum
fluctuations in the generator of the parameter change to the time integral of
the quantum correlation function between the projection operator and force
operator of the ``fast'' system. By taking a cue from linear response theory we
relate the quantum fluctuation in the generator to the generalised
susceptibility. Relation between the open-path geometric phase, diagonal
elements of the quantum metric tensor and the force-force correlation function
is provided and the classical limit of the fluctuation-correlation theorem is
also discussed.Comment: Latex, 12 pages, no figures, submitted to J. Phys. A: Math & Ge
Geometric Phases for Mixed States during Cyclic Evolutions
The geometric phases of cyclic evolutions for mixed states are discussed in
the framework of unitary evolution. A canonical one-form is defined whose line
integral gives the geometric phase which is gauge invariant. It reduces to the
Aharonov and Anandan phase in the pure state case. Our definition is consistent
with the phase shift in the proposed experiment [Phys. Rev. Lett. \textbf{85},
2845 (2000)] for a cyclic evolution if the unitary transformation satisfies the
parallel transport condition. A comprehensive geometric interpretation is also
given. It shows that the geometric phases for mixed states share the same
geometric sense with the pure states.Comment: 9 pages, 1 figur
Entrapment of magnetic micro-crystals for on-chip electron spin resonance studies
On-chip Electron Spin Resonance (ESR) of magnetic molecules requires the
ability to precisely position nanosized samples in antinodes of the
electro-magnetic field for maximal magnetic interaction. A method is developed
to entrap micro-crystals containing spins in a well defined location on a
substrate's surface. Traditional cavity ESR measurements are then performed on
a mesoscopic crystal at 34 GHz. Polycrystalline diluted Cr spins were
entrapped as well and measured while approaching the lower limit of the ESR
sensitivity. This method suggests the feasibility of on-chip ESR measurements
at dilution refrigerator temperatures by enabling the positioning of samples
atop an on-chip superconducting cavity.Comment: to appear in Journal of Applied Physic
Quark Mixings in and Suppression of
The quark mixing matrix is studied in depth on the basis of
superstring inspired model with global flavor symmetries.
The sizable mixings between right-handed down-type quark and colored
Higgs field potentially occur but no such mixings in up-type quark
sector. In the model the hierarchical pattern of is understood
systematically. It is shown that due to large - mixings is
naturally suppressed compared to . It is pointed out that the observed
suppression of is in favor of the presence of gauge symmetry
but not in accord with generic SU(5) GUT.Comment: 10pages with no figure, Latex fil
Unification of SU(2)xU(1) Using a Generalized Covariant Derivative and U(3)
A generalization of the Yang-Mills covariant derivative, that uses both
vector and scalar fields and transforms as a 4-vector contracted with Dirac
matrices, is used to simplify and unify the Glashow-Weinberg-Salam model. Since
SU(3) assigns the wrong hypercharge to the Higgs boson, it is necessary to use
a special representation of U(3) to obtain all the correct quantum numbers. A
surplus gauge scalar boson emerges in the process, but it uncouples from all
other particles.Comment: 12 pages, no figures. To be published in Int. J. Mod. Phys.
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