A. Napoli

Università degli Studi di Palermo, Palermo, Sicily, Italy

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Publications (81)101.97 Total impact

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    ABSTRACT: By quickly modifying the shape of the effective potential of a double SQUID flux qubit from a single-well to a double-well condition, we experimentally observe an anomalous behavior, namely, an alternation of resonance peaks, in the probability to find the qubit in a given flux state. The occurrence of Landau-Zener transitions as well as resonant tunneling between degenerate levels in the two wells may be invoked to partially justify the experimental results. A quantum simulation of the time evolution of the system indeed suggests that the observed anomalous behavior can be imputable to quantum coherence effects. The interplay among all these mechanisms has a practical implication for quantum computing purposes, giving a direct measurement of the limits on the sweeping rates possible for a correct manipulation of the qubit state by means of fast flux pulses, avoiding transitions to noncomputational states.
    Physical Review B 04/2014; 89:134506. · 3.66 Impact Factor
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    ABSTRACT: A stationary physical system satisfies peculiar balance conditions involving mean values of appropriate observables. In this paper we show how to deduce such quantitative links, named balance equations, demonstrating as well their usefulness in bringing to light physical properties of the system without solving the Schrodinger equation. The knowledge of such properties in the case of Rabi Hamiltonian is exploit to provide arguments to make easier the variational engineering of the ground state of this model.
    Journal of Russian Laser Research 02/2014; 35(1). · 0.71 Impact Factor
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    ABSTRACT: We report the experimental observation of resonance peaks in the characteristics of a double SQUID flux qubit, obtained by quickly modifying the potential shape from single well to double well cases at a base temperature of 30mK, for different sweeping rates and potential tiltings. Theoretical analysis and numerical simulations explain the result in term of a quantum phenomenon due to the interplay of Landau-Zener transitions, resonant tunneling between degenerate levels in the two wells, and coherent states evolution. This interesting mechanism has a practical implication for quantum computing purposes, giving a direct measurement of the limits on the sweeping rates possible for a correct manipulation of the qubit state by means of fast flux pulses, avoiding transitions to non-computational states.
    10/2013;
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    ABSTRACT: Employing the stochastic wave function method, we study quantum features of stochastic entropy production in nonequilibrium processes of open systems. It is demonstrated that continuous measurements on the environment introduce an additional, nonthermal contribution to the entropy flux, which is shown to be a direct consequence of quantum fluctuations. These features lead to a quantum definition of single trajectory entropy contributions, which accounts for the difference between classical and quantum trajectories and results in a quantum correction to the standard form of the integral fluctuation theorem.
    Physical Review A 10/2013; 88:042111. · 3.04 Impact Factor
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    ABSTRACT: A microscopic master equation describing the dynamics of two qubits coupled via a nonlinear mediator is constructed supposing that the two qubits, as well as the nonlinear mode, interact, each with its own independent bosonic bath. Generally speaking the master equation derived in this way represents a more appropriate tool for studying the dynamics of open quantum systems. Indeed we show that it is more complex than the phenomenological master equation, constructed simply adding ad hoc dissipative terms.
    Journal of Engineering Mathematics 10/2013; · 1.08 Impact Factor
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    ABSTRACT: Exploiting previous results on Markovian dynamics and fluctuation theorems, we study the consequences of memory effects on single realizations of nonequilibrium processes within an open system approach. The entropy production along single trajectories for forward and backward processes is obtained with the help of a recently proposed classical-like non-Markovian stochastic unravelling, which is demonstrated to lead to a correction of the standard entropic fluctuation theorem. This correction is interpreted as resulting from the interplay between the information extracted from the system through measurements and the flow of information from the environment to the open system: Due to memory effects single realizations of a dynamical process are no longer independent, and their correlations fundamentally affect the behavior of entropy fluctuations.
    Physical Review E 03/2013; 87:032113. · 2.31 Impact Factor
  • R. Migliore, A. Messina, A. Napoli
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    ABSTRACT: We prove that a mesoscopic Josephson junction, irradiated with a quantum superposition of two 180o{180^o}-out of phase optical coherent states, exhibits an experimentally observable sensitivity to the quantum coherences of the field state. PACS. 73.23.-b Mesoscopic systems–74.50.+r Proximity effects, weak links, tunneling phenomena, and Josephson effects–42.50.Dv Nonclassical field states; squeezed, antibunched, and sub-Poissonian states; operational definitions of the phase of the field; phase measurements
    Physics of Condensed Matter 04/2012; 13(3):585-588. · 1.28 Impact Factor
  • R.migliore, A.messina, A.napoli
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    ABSTRACT: We show that the quantum nature of a mesoscopic Josephson junction may be exploited for detecting low-intensity electromagnetic quantized fields. In particular we prove that intensity and phase of single-mode quantized coherent field may be reconstructed measuring amplitude and quantum noise of the first quantum Shapiro step occurring in the I-V characteristic of the ultrasmall Josephson junction.
    International Journal of Modern Physics B 01/2012; 14(25n27). · 0.46 Impact Factor
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    ABSTRACT: We analyse an entangling protocol to generate tripartite Greenberger–Horne–Zeilinger (GHZ) states in a system consisting of three superconducting qubits with pairwise coupling. The dynamics of the open quantum system is investigated by taking into account the interaction of each qubit with an independent bosonic bath with an ohmic spectral structure. To this end, a microscopic master equation is constructed and exactly solved. We find that the protocol discussed here is stable against decoherence and dissipation due to the presence of the external baths.
    Journal of Physics B Atomic Molecular and Optical Physics 01/2012; 45(6). · 2.03 Impact Factor
  • B. Leggio, A. Napoli, A. Messina
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    ABSTRACT: We show that a two-atom Bose–Hubbard model exhibits three different phases in the behavior of thermal entanglement in its parameter space. These phases are demonstrated to be traceable back to the existence of level crossings in the ground state of the same system. Significant similarities between the behaviors of thermal entanglement and heat capacity in the parameter space are brought to light thus allowing to interpret the occurrence and the meaning of all these three phases.
    Physics Letters A 01/2012; 376:339. · 1.63 Impact Factor
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    B. Leggio, A. Napoli, A. Messina
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    ABSTRACT: We show that a two-atoms Bose-Hubbard model exhibits three different phases in the behavior of thermal entanglement in its parameter space. These phases are demonstrated to be traceable back to the existence of quantum phase transitions in the same system. Significant similarities between the behaviors of thermal entanglement and heat capacity in the parameter space are brought to light thus allowing to interpret the occurrence and the meaning of all these three phases.
    07/2011;
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    ABSTRACT: A simple two-qubit model showing Quantum Phase Transitions as a consequence of ground state level crossings is studied in detail. Using the Concurrence of the system as an entanglement measure and heat capacity as a marker of thermodynamical properties, an analytical expression giving the latter in terms of the former is obtained. A protocol allowing an experimental measure of entanglement is then presented and compared with a related proposal recently reported by Wie\'sniak, Vedral and Brukner
    Journal of Russian Laser Research 07/2011; 32(4):362. · 0.71 Impact Factor
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    ABSTRACT: The dynamics of an open quantum system, consisting of three superconducting qubits interacting with independent reservoirs, is investigated to elucidate the effects of the environment on a unitary generation scheme of W states (Migliore R et al 2006 Phys. Rev. B 74 104503). To this end a microscopic master equation is constructed and its exact resolution predicts the generation of a Werner-like state instead of the W state. A comparison between our model and a more intuitive phenomenological model is also considered, in order to find the limits of the latter approach in the case of structured reservoirs.
    Journal of Physics B Atomic Molecular and Optical Physics 03/2011; 44(7):075503. · 2.03 Impact Factor
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    ABSTRACT: In this paper, we review some results concerning the dissipative dynamics of two coupled qubits interacting with independent reservoirs. In particular, we focus on the role of counter-rotating terms in the qubit-qubit coupling, showing that their presence is the origin of stationary entanglement, which also turns out to be robust with respect to temperature. We also discuss the performances of different non-Markovian approaches in the description of the qubit-qubit dynamics, by considering a simplified exactly solvable Hamiltonian model.
    Optics and Spectroscopy 01/2011; 111(4):553-557. · 0.56 Impact Factor
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    ABSTRACT: We investigate the dynamics of a central spin that is coupled to a bath of spins through a non-uniform distribution of coupling constants. Simple analytical arguments based on master equation techniques as well as numerical simulations of the full von Neumann equation of the total system show that the short-time damping and decoherence behaviour of the central spin can be modelled accurately through an effective Hamiltonian involving a single effective coupling constant. The reduced short-time dynamics of the central spin is thus reproduced by an analytically solvable effective Hamiltonian model.
    Physica Scripta 09/2010; 2010(T140):014021. · 1.03 Impact Factor
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    ABSTRACT: In the framework of the dissipative dynamics of coupled qubits interacting with independent reservoirs, a comparison between non-Markovian master equation techniques and an exact solution is presented here. We study various regimes in order to find the limits of validity of the Nakajima–Zwanzig and the time-convolutionless master equations in the description of the entanglement dynamics. A comparison between the performances of the concurrence and the negativity as entanglement measures for the system under study is also presented.
    Physica Scripta 09/2010; 2010(T140):014042. · 1.03 Impact Factor
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    ABSTRACT: A high-fidelity scheme to generate N-photon generalized binomial states (NGBSs) in a single-mode high-Q cavity is proposed. A method to construct superpositions of exact orthogonal NGBSs is also provided. It is then shown that these states, for any value of N, may be used for a realization of a controlled-NOT gate, based on the dispersive interaction between the cavity field and a control two-level atom. The possible implementation of the schemes is finally discussed.
    Physics Letters A 03/2010; · 1.63 Impact Factor
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    ABSTRACT: We investigate the entanglement evolution of two qubits interacting with a common environment trough an Heisenberg XX mechanism. We reveal the possibility of realizing the phenomenon of entanglement sudden death as well as the entanglement sudden birth acting on the environment. Such analysis is of maximal interest at the light of the large applications that spin systems have in quantum information theory.
    10/2009;
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    ABSTRACT: The reduced dynamics of two interacting qubits coupled to two independent bosonic baths is investigated. The one-excitation dynamics is derived and compared with that based on the resolution of appropriate non-Markovian master equations. The Nakajima-Zwanzig and the time-convolutionless projection operator techniques are exploited to provide a description of the non-Markovian features of the dynamics of the two-qubits system. The validity of such approximate methods and their range of validity in correspondence to different choices of the parameters describing the system are brought to light. Comment: 6 pages, 3 figures. Submitted to PRA
    Physical Review A 07/2009; · 3.04 Impact Factor
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    ABSTRACT: The dynamics of two interacting spins coupled to separate bosonic baths is studied. An analytical solution in Born approximation for arbitrary spectral density functions of the bosonic environments is found. It is shown that in the non-Markovian cases concurrence "lives" longer or reaches greater values. Comment: 13 pages
    Journal of Physics A Mathematical and Theoretical 06/2009; · 1.77 Impact Factor

Publication Stats

283 Citations
101.97 Total Impact Points

Institutions

  • 1998–2014
    • Università degli Studi di Palermo
      • Dipartimento di Fisica e Chimica
      Palermo, Sicily, Italy
  • 2008
    • Polytechnic University of Timisoara
      Freidorf, Timiş, Romania
  • 2004–2005
    • Sapienza University of Rome
      • Department of Basic and Applied Sciences for Engineering
      Roma, Latium, Italy