Person:
Relaño Pérez, Armando

First Name

Armando

Last Name

Relaño Pérez

URI

https://hdl.handle.net/20.500.14352/75045

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Estructura de la Materia, Física Térmica y Electrónica

Area

Física Aplicada

Identifiers

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Now showing 1 - 10 of 12

Excited state quantum phase transitions and chaos in the Dicke model
(Meeting on Beauty in Physics - Theory and Experiment in Honor of Francesco Lachello on the Occasion of his 70th Birthday, 2012) Pérez Fernández, P.; Relaño Pérez, Armando; Cejnar, P.; Arias, J. M.; Dukelsky, J.; García Ramos, J. E.
In this contribution, the critical behavior of excited state quantum phase transitions (ESQPT's) and its relation to order and chaos in the Dicke model are studied. This model is non-integrable. For comparison, the same problem is studied for the Jaynes-Cummings model which is, somehow, the integrable version of the Dicke model. The existence of an ESQPT is confirmed in both cases. However, in the Dicke model the signatures of criticality in excited states are blurred by the onset of quantum chaos. It is concluded that the order-to-chaos transition just below the critical energy gives us a chance to study the impact of chaotic dynamics on the signatures of ESQPTs.
Decoherence and quantum quench: their relationship with excited state quantum phase transitions
(Beauty in physics: theory and experiment: in honor of Francesco Lachello on the occasion of his 70th birthday, 2012) García Ramos, J. E.; Arias, J. M.; Cejnar, P.; Dukelsky, J.; Pérez Fernández, P.; Relaño Pérez, Armando
We study the similarities and differences between the phenomena of Quantum Decoherence and Quantum Quench in presence of an Excited State Quantum Phase Transition (ESQPT). We analyze, on one hand, the decoherence induced on a single qubit by the interaction with a two-level boson system with critical internal dynamics and, on the other, we treat the quantum relaxation process that follows an abrupt quench in the control parameter of the system Hamiltonian. We explore how the Quantum Decoherence and the quantum relaxation process are affected by the presence of an ESQPT. We conclude that the dynamics of the qubit or the quantum relaxation process change dramatically when the system passes through a continuous ESQPT.
Decoherence due to an excited-state quantum phase transition in a two-level boson model
(Physical Review A, 2009) Relaño Pérez, Armando; Pérez Fernández, P.; Arias, J. M.; Dukelsky, J.; García Ramos, J. E.
The decoherence induced on a single qubit by its interaction with the environment is studied. The environment is modeled as a scalar two-level boson system that can go through either first-order or continuous-excited-state quantum phase transitions, depending on the values of the control parameters. A mean-field method based on the Tamm-Damkoff approximation is worked out in order to understand the observed behavior of the decoherence. Only the continuous-excited-state phase transition produces a noticeable effect in the decoherence of the qubit. This is maximal when the system-environment coupling brings the environment to the critical point for the continuous phase transition. In this situation, the decoherence factor (or the fidelity) goes to zero with a finite-size scaling power law.
Stringent numerical test of the Poisson distribution for finite quantum integrable Hamiltonians
(Physical Review E, 2004) Relaño Pérez, Armando; Dukelsky, J.; Gómez Gómez, José María; Retamosa Granado, Joaquín
Using a class of exactly solvable models based on the pairing interaction, we show that it is possible to construct integrable Hamiltonians with a Wigner distribution of nearest-neighbor level spacings. However, these Hamiltonians involve many-body interactions and the addition of a small integrable perturbation very quickly leads the system to a Poisson distribution. Besides this exceptional case, we show that the accumulated distribution of an ensemble of random integrable two-body pairing Hamiltonians is in perfect agreement with the Poisson limit. These numerical results for quantum integrable Hamiltonians provide a further empirical confirmation of the work of Berry and Tabor in the semiclassical limit.
Decoherence induced by an interacting spin environment in the transition from integrability to chaos
(Physical Review E, 2007) Relaño Pérez, Armando; Dukelsky, J.; Molina, R. A.
We investigate the decoherence properties of a central system composed of two spins 1/2 in contact with a spin bath. The dynamical regime of the bath ranges from a fully integrable limit to complete chaoticity. We show that the dynamical regime of the bath determines the efficiency of the decoherence process. For perturbative regimes, the integrable limit provides stronger decoherence, while in the strong coupling regime the chaotic limit becomes more efficient. We also show that the decoherence time behaves in a similar way. On the contrary, the rate of decay of magnitudes like linear entropy or fidelity does not depend on the dynamical regime of the bath. We interpret the latter results as due to a comparable complexity of the Hamiltonian for both the integrable and the fully chaotic limits.
Excited-state phase transition and onset of chaos in quantum optical models
(Physical Review E, 2011) Pérez Fernández, P.; Relaño Pérez, Armando; Arias, J. M.; Cejnar, P.; Dukelsky, J.; García Ramos, J. E.
We study the critical behavior of excited states and its relation to order and chaos in the Jaynes-Cummings and Dicke models of quantum optics. We show that both models exhibit a chain of excited-state quantum phase transitions demarcating the upper edge of the superradiant phase. For the Dicke model, the signatures of criticality in excited states are blurred by the onset of quantum chaos. We show that the emergence of quantum chaos is caused by the precursors of the excited-state quantum phase transition.
Connection between decoherence and excited state quantum phase transitions
(La Rabida 2009: International Scientific Meeting on Nuclear Physics: Basic Concepts in Nuclear Physics: Theory, Experiments, And Applications, 2010) Pérez Fernández, P.; Relaño Pérez, Armando; Arias, J. M.; Dukelsky, J.; García Ramos, J. E.; Caballero, J. A.; Alonso, C. E.; Andrés, M. V.; García Ramos, J. E.; Pérez Bernal, F.
In this work we explore the relationship between an excited state quantum phase transition (ESQPT) and the phenomenon of quantum decoherence. For this purpose, we study how the decoherence is affected by the presence of a continuous ESQPT in the environment. This one is modeled as a two level boson system described by a Lipkin Hamiltonian. We will show that the decoherence of the system is maximal when the environment undergoes a continuous ESQPT.
Decoherence as a signature of an excited-state quantum phase transition
(Physical Review A, 2008) Relaño Pérez, Armando; Arias, J. M.; Dukelsky, J.; García Ramos, J. E.; Pérez Fernández, P.
We analyze the decoherence induced on a single qubit by the interaction with a two-level boson system with critical internal dynamics. We explore how the decoherence process is affected by the presence of quantum phase transitions in the environment. We conclude that the dynamics of the qubit changes dramatically when the environment passes through a continuous excited state quantum phase transition. If the system-environment coupling energy equals the energy at which the environment has a critical behavior, the decoherence induced on the qubit is maximal and the fidelity tends to zero with finite size scaling obeying a power law.
Quantum phase transitions of atom-molecule Bose mixtures in a double-well potential
(Physical review E, 2014) Relaño Pérez, Armando; Dukelsky, J.; Pérez Fernández, P.; Arias, J. M.
The ground state and spectral properties of Bose gases in double-well potentials are studied in two different scenarios: (i) an interacting atomic Bose gas, and (ii) a mixture of an atomic gas interacting with diatomic molecules. A ground state second-order quantum phase transition is observed in both scenarios. For large attractive values of the atom-atom interaction, the ground state is degenerate. For repulsive and small attractive interaction, the ground state is not degenerate and is well approximated by a boson coherent state. Both systems depict an excited state quantum phase transition. In both cases, a critical energy separates a region in which all the energy levels are degenerate in pairs, from another region in which there are no degeneracies. For the atomic system, the critical point displays a singularity in the density of states, whereas this behavior is largely smoothed for the mixed atom-molecule system.
Quantum quench influenced by an excited-state phase transition
(Physical Review A, 2011) Pérez Fernández, P.; Cejnar, P.; Arias, J. M.; Dukelsky, J.; García Ramos, J. E.; Relaño Pérez, Armando
We analyze excited-state quantum phase transitions (ESQPTs) in three schematic (integrable and nonintegrable) models describing a single-mode bosonic field coupled to a collection of atoms. It is shown that the presence of the ESQPT in these models affects the quantum relaxation processes following an abrupt quench in the control parameter. Clear-cut evidence of the ESQPT effects is presented in integrable models, while in a nonintegrable model the evidence is blurred due to chaotic behavior of the system in the region around the critical energy.