892 research outputs found
The Role of Temperature in the occurrence of some Zeno Phenomena
Temperature can be responsible for strengthening effective couplings between
quantum states, determining a hierarchy of interactions, and making it possible
to establish such dynamical regimes known as Zeno dynamics, wherein a strong
coupling can hinder the effects of a weak one. The relevant physical mechanisms
which connect the structure of a thermal state with the appearance of special
dynamical regimes are analyzed in depth
Genuine Tripartite Entanglement in a Spin-Star Network at Thermal Equilibrium
In a recent paper [M. Huber {\it et al}, Phys. Rev. Lett. {\bf 104}, 210501
(2010)] new criteria to find out the presence of multipartite entanglement have
been given. We exploit these tools in order to study thermal entanglement in a
spin-star network made of three peripheral spins interacting with a central
one. Genuine tripartite entanglement is found in a wide range of the relevant
parameters. A comparison between predictions based on the new criteria and on
the tripartite negativity is also given.Comment: 8 pages, 13 figure
Sensitivity of Measurement-Based Purification Processes to Inner Interactions
The sensitivity of a repeated measurement-based purification scheme to
additional undesired couplings is analyzed, focusing on the very simple and
archetypical system consisting of two two-level systems interacting with a
repeatedly measured one. Several regimes are considered and in the strong
coupling (i.e., when the coupling constant of the undesired interaction is very
large) the occurrence of a quantum Zeno effect is proven to dramatically
jeopardize the efficiency of the purification process.Comment: 12 pages, 6 figure
Oscillations of the purity in the repeated-measurement-based generation of quantum states
Repeated observations of a quantum system interacting with another one can
drive the latter toward a particular quantum state, irrespectively of its
initial condition, because of an {\em effective non-unitary evolution}. If the
target state is a pure one, the degree of purity of the system approaches
unity, even when the initial condition of the system is a mixed state. In this
paper we study the behavior of the purity from the initial value to the final
one, that is unity. Depending on the parameters, after a finite number of
measurements, the purity exhibits oscillations, that brings about a lower
purity than that of the initial state, which is a point to be taken care of in
concrete applications.Comment: 5 pages, 3 figure
Geometric phase accumulation-based effects in the quantum dynamics of an anisotropically trapped ion
New physical effects in the dynamics of an ion confined in an anisotropic
two-dimensional Paul trap are reported. The link between the occurrence of such
manifestations and the accumulation of geometric phase stemming from the
intrinsic or controlled lack of symmetry in the trap is brought to light. The
possibility of observing in laboratory these anisotropy-based phenomena is
briefly discussed.Comment: 10 pages. Acta Physica Hungarica B 200
Revealing non-classical behaviours in the oscillatory motion of a trapped ion
The possibility of revealing non-classical behaviours in the dynamics of a
trapped ion via measurements of the mean value of suitable operators is
reported. In particular we focus on the manifestation known as `` Parity
Effect\rq\rq which may be observed \emph{directly measuring} the expectation
value of an appropriate correlation operator. The experimental feasibility of
our proposal is discussed.Comment: 5 pages, 2 figure
Synchronizing Quantum Harmonic Oscillators through Two-Level Systems
Two oscillators coupled to a two-level system which in turn is coupled to an
infinite number of oscillators (reservoir) are considered, bringing to light
the occurrence of synchronization. A detailed analysis clarifies the physical
mechanism that forces the system to oscillate at a single frequency with a
predictable and tunable phase difference. Finally, the scheme is generalized to
the case of oscillators and two-level systems.Comment: 9 pages, 3 figure
Zeno Dynamics and High-Temperature Master Equations Beyond Secular Approximation
Complete positivity of a class of maps generated by master equations derived
beyond the secular approximation is discussed. The connection between such
class of evolutions and physical properties of the system is analyzed in depth.
It is also shown that under suitable hypotheses a Zeno dynamics can be induced
because of the high temperature of the bath.Comment: 9 pages, 2 figure
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