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ABSTRACT: The Stimulated Raman adiabatic passage (STIRAP) in three-state systems in the presence of quantum noise is considered. A comparison
is made between different models, one based on a phenomenological introduction of decays, one traceable back to a microscopic
description of the system-environment interaction. Effects related, to off-resonance in the coupling between the involved
states are considered.
Optics and Spectroscopy 05/2012; 111(4):589-592. · 0.61 Impact Factor
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ABSTRACT: A new approach for reconstructing the vibrational quantum state of a trapped ion is proposed. The method rests upon the current
ability of manipulating the trapped ion state and on the possibility of effectively measuring the scalar product of the two
vibrational cofactors of a vibronic entangled state. The experimental feasibility of the method is briefly discussed.
Keywordstrapped ions–coherences–measurement
PACS03.65.Ta–32.80.Pj–42.50.Ct–42.50.Hz
Acta Physica Hungarica B) Quantum Electronics 04/2012; 20(1):109-112.
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ABSTRACT: We discuss the partitioning of the Hilbert space of a quantum system induced
by the interaction with another system at thermal equilibrium, showing that the
higher the temperature the more effective is the formation of Zeno subspaces.
We show that our analysis keeps its validity even in the case of interaction
with a bosonic reservoir, provided appropriate limitations of the relevant
bandwidth.
06/2011;
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ABSTRACT: We analyze the effect of a dissipative bosonic environment on the
Landau-Zener-Stuckelberg-Majorana (LZSM) level crossing model by using a
microscopic approach to derive the relevant master equation. For an environment
at zero temperature and weak dissipation our microscopic approach confirms the
independence of the survival probability on the decay rate that has been
predicted earlier by the simple phenomenological LZSM model. For strong decay
the microscopic approach predicts a notable increase of the survival
probability, which signals dynamical decoupling of the initial state. Unlike
the phenomenological model our approach makes it possible to study the
dependence of the system dynamics on the temperature of the environment. In the
limit of very high temperature we find that the dynamics is characterized by a
very strong dynamical decoupling of the initial state - temperature-induced
quantum Zeno effect.
06/2011;
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ABSTRACT: The presence of a continuous measurement quantum Zeno effect in a stimulated Raman adiabatic passage is studied, exploring in detail a sort of self-competition of the damping, which drives the system toward a loss of population and, at the same time, realizes the conditions for optimizing the adiabatic passage.
Physica Scripta 02/2011; 2011(T143):014019. · 1.20 Impact Factor
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ABSTRACT: We exploit a microscopically derived master equation for the study of STIRAP in the presence of decay from the auxiliary level toward the initial and final state, and compare our results with the predictions obtained from a phenomenological model previously used [P. A. Ivanov, N. V. Vitanov, and K. Bergmann, Phys. Rev. A 72, 053412 (2005)]. It is shown that our approach predicts a much higher efficiency. The effects of temperature are also taken into account, proving that in b-STIRAP thermal pumping can increase the efficiency of the population transfer. Comment: 10 pages, 7 figures
08/2010;
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ABSTRACT: A master equation approach to the study of environmental effects in the adiabatic population transfer in three-state systems is presented. A systematic comparison with the non-Hermitian Hamiltonian approach [N. V. Vitanov and S. Stenholm, Phys. Rev. A {\bf 56}, 1463 (1997)] shows that in the weak coupling limit the two treatments lead to essentially the same results. Instead, in the strong damping limit the predictions are quite different: in particular the counterintuitive sequences in the STIRAP scheme turn out to be much more efficient than expected before. This point is explained in terms of quantum Zeno dynamics. Comment: 11 pages, 4 figures
03/2010;
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ABSTRACT: We provide a microscopic derivation for the non-Markovian master equation for an atom-cavity system with cavity losses and show that they can induce population trapping in the atomic excited state, when the environment outside the cavity has a non-flat spectrum. Our results apply to hybrid solid state systems and can turn out to be helpful to find the most appropriate description of leakage in the recent developments of cavity quantum electrodynamics.
06/2008;
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ABSTRACT: Decoherence is believed to deteriorate the ability of a purification scheme that is based on the idea of driving a system to a pure state by repeatedly measuring another system in interaction with the former and hinder for a pure state to be extracted asymptotically. Nevertheless, we find a way out of this difficulty by deriving an analytic expression of the reduced density matrix for a two-qubit system immersed in a bath. It is shown that we can still extract a pure state if the environment brings about only dephasing effects. In addition, for a dissipative environment, there is a possibility of obtaining a dominant pure state when we perform a finite number of measurements.
Physical Review A 04/2008; 77(4):042114. · 2.88 Impact Factor
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ABSTRACT: 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 figures
Physical Review A 04/2008; 77(4):042109. · 2.88 Impact Factor
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ABSTRACT: In population trapping the occupation of a decaying quantum level keeps a constant non-zero value. We show that an atom-cavity system interacting with an environment characterized by a non-flat spectrum, in the non-Markovian limit, exhibits such a behavior, effectively realizing the preservation of nonclassical states against dissipation. Our results allow to understand the role of cavity losses in hybrid solid state systems and pave the way to the proper description of leakage in the recently developed cavity quantum electrodynamic systems.
11/2007;
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ABSTRACT: A quantum system put in interaction with another one that is repeatedly measured is subject to a non-unitary dynamics, through which it is possible to extract subspaces. This key idea has been exploited to propose schemes aimed at the generation of pure quantum states (purification). All such schemes have so far been considered in the ideal situations of isolated systems. In this paper, we analyze the influence of non-negligible interactions with environment during the extraction process, with the scope of investigating the possibility of purifying the state of a system in spite of the sources of dissipation. A general framework is presented and a paradigmatic example consisting of two interacting spins immersed in a bosonic bath is studied. The effectiveness of the purification scheme is discussed in terms of purity for different values of the relevant parameters and in connection with the bath temperature. Comment: 10 pages, 3 figures
Physical Review A 10/2007; 76(4):042110. · 2.88 Impact Factor
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ABSTRACT: A microscopic derivation of the master equation for the
Jaynes-Cummings model with cavity losses is given, taking into account the
terms in the dissipator which vary with frequencies of the order of the vacuum
Rabi frequency. Our approach allows to single out physical contexts wherein the
usual phenomenological dissipator turns out to be fully justified and
constitutes an extension of our previous analysis [Scala M. {\em et al.} 2007
Phys. Rev. A {\bf 75}, 013811], where a microscopic derivation was given in the
framework of the Rotating Wave Approximation.
09/2007;
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ABSTRACT: In this paper we provide a microscopic derivation of the master equation for the Jaynes-Cummings model with cavity losses. We single out both the differences with the phenomenological master equation used in the literature and the approximations under which the phenomenological model correctly describes the dynamics of the atom-cavity system. Some examples wherein the phenomenological and the microscopic master equations give rise to different predictions are discussed in detail.
11/2006;
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ABSTRACT: The so-called Lindblad equation, a typical master equation describing the dissipative quantum dynamics, is shown to be solvable for finite-level systems in a compact form without resort to writing it down as a set of equations among matrix elements. The solution is then naturally given in an operator form, known as the Kraus representation. Following a few simple examples, the general applicability of the method is clarified.
07/2006;
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ABSTRACT: A quantum system interacting with a repeatedly measured one undergoes a nonunitary time evolution pushing it into some specific
subspaces. We deeply investigate the origin of the relevant selection rule, bringing to the light its connection with the
survival probability related with the two-system interaction. The possibility of inducing an effective dynamics in the distilled
subspace just during the distillation process is demonstrated.
Optics and Spectroscopy 08/2005; 99(3):438-442. · 0.61 Impact Factor
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ABSTRACT: A quantum system in interaction with a repeatedly measured one undergoes a nonunitary time evolution and is pushed into a subspace substantially determined by the two-system coupling. The possibility of suitably modifying such an evolution through quantum Zeno dynamics (i.e., the generalized quantum Zeno effect) addressing the system toward an a priori decided target subspace is illustrated. Applications and their possible realizations in the context of trapped ions are also discussed.
Phys. Rev. A. 03/2005; 71(3).
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ABSTRACT: 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 2005
09/2004;
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ABSTRACT: In the spirit of Quantum Non-Demolition Measurements, we show that exploiting suitable vibronic couplings and repeatedly measuring the atomic population of a confined ion, it is possible to distill center of mass vibrational states with well defined square of angular momentum or, alternatively, angular momentum projection Schr\"odinger cat states. Comment: 7 pages
05/2004;
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ABSTRACT: A new systematic strategy for steering the distillation process for a quantum system, that utilizes the so-called "pulsed" and "continuous" measurements on another quantum system in interaction with the former, is proposed. The distillation process characterized by the specific interaction between the two systems and the "pulsed" measurements is shown to be controllable through the "continuous" measurements, i.e., the quantum Zeno dynamics, providing an effective recipe to prefix the target.
05/2004;
