The Experts below are selected from a list of 25110 Experts worldwide ranked by ideXlab platform

Adrian Tanasa - One of the best experts on this subject based on the ideXlab platform.

Paola Verrucchi - One of the best experts on this subject based on the ideXlab platform.

  • Open Quantum Systems and the Parametric Representation: From Entanglement to Berry’s Phase
    International Journal of Theoretical Physics, 2014
    Co-Authors: Dario Calvani, Alessandro Cuccoli, Nikitas I. Gidopoulos, Paola Verrucchi
    Abstract:

    Open quantum systems (OQS) are usually treated, in particular in the realm of quantum information theory and quantum computation, in terms of reduced density matrices, which provide a definition of the state of the principal system via the partial trace operation over the environment. This approach is a powerful tool to investigate relevant features of the open system evolution, especially when the physical situation allows for Markovian-like approximation schemes. On the other hand, the density matrix formulation and the subsequent approximation schemes induce an uncontrollable loss of information about the environmental structure, preventing some phenomena to be properly described. In this work we propose an alternative description of OQS, based on a Parametric Representation of the environment, as obtained in terms of generalized coherent states. The Representation is used to describe a prototypical composite system, made of a spin- $\frac{1}{2}$ (the principal system) and a spin- S (the environment), interacting via a Heisenberg Hamiltonian. The resulting description shows that the emergence of a geometric (Berry) phase for a spin in an external magnetic field does follow from the fact that the true physical set up, of which the “spin in a field” is just a semiclassical-like Parametric Representation, is that of a quantum composite system in an entangled state. In fact, the Von Neumann entropy of the spin- $\frac{1}{2}$ , which is finite due to the existence of the environment (the spin- S ), turns out to be the binary entropy of the normalized Berry’s phase.

  • Parametric Representation of open quantum systems and cross over from quantum to classical environment
    Proceedings of the National Academy of Sciences of the United States of America, 2013
    Co-Authors: Dario Calvani, Alessandro Cuccoli, Nikitas I. Gidopoulos, Paola Verrucchi
    Abstract:

    Abstract The behavior of most physical systems is affected by their natural surroundings. A quantum system with an environment is referred to as open, and its study varies according to the classical or quantum description adopted for the environment. We propose an approach to open quantum systems that allows us to follow the cross-over from quantum to classical environments; to achieve this, we devise an exact Parametric Representation of the principal system, based on generalized coherent states for the environment. The method is applied to the Heisenberg star with frustration, where the quantum character of the environment varies with the couplings entering the Hamiltonian H. We find that when the star is in an eigenstate of H, the central spin behaves as if it were in an effective magnetic field, pointing in the direction set by the environmental coherent-state angle variables , and broadened according to their quantum probability distribution. Such distribution is independent of φ, whereas as a function of θ is seen to get narrower as the quantum character of the environment is reduced, collapsing into a Dirac-δ function in the classical limit. In such limit, because φ is left undetermined, the Von Neumann entropy of the central spin remains finite; in fact, it is equal to the entanglement of the original fully quantum model, a result that establishes a relation between this latter quantity and the Berry phase characterizing the dynamics of the central spin in the effective magnetic field.

Vincent Rivasseau - One of the best experts on this subject based on the ideXlab platform.

Dario Calvani - One of the best experts on this subject based on the ideXlab platform.

  • Open Quantum Systems and the Parametric Representation: From Entanglement to Berry’s Phase
    International Journal of Theoretical Physics, 2014
    Co-Authors: Dario Calvani, Alessandro Cuccoli, Nikitas I. Gidopoulos, Paola Verrucchi
    Abstract:

    Open quantum systems (OQS) are usually treated, in particular in the realm of quantum information theory and quantum computation, in terms of reduced density matrices, which provide a definition of the state of the principal system via the partial trace operation over the environment. This approach is a powerful tool to investigate relevant features of the open system evolution, especially when the physical situation allows for Markovian-like approximation schemes. On the other hand, the density matrix formulation and the subsequent approximation schemes induce an uncontrollable loss of information about the environmental structure, preventing some phenomena to be properly described. In this work we propose an alternative description of OQS, based on a Parametric Representation of the environment, as obtained in terms of generalized coherent states. The Representation is used to describe a prototypical composite system, made of a spin- $\frac{1}{2}$ (the principal system) and a spin- S (the environment), interacting via a Heisenberg Hamiltonian. The resulting description shows that the emergence of a geometric (Berry) phase for a spin in an external magnetic field does follow from the fact that the true physical set up, of which the “spin in a field” is just a semiclassical-like Parametric Representation, is that of a quantum composite system in an entangled state. In fact, the Von Neumann entropy of the spin- $\frac{1}{2}$ , which is finite due to the existence of the environment (the spin- S ), turns out to be the binary entropy of the normalized Berry’s phase.

  • Parametric Representation of open quantum systems and cross over from quantum to classical environment
    Proceedings of the National Academy of Sciences of the United States of America, 2013
    Co-Authors: Dario Calvani, Alessandro Cuccoli, Nikitas I. Gidopoulos, Paola Verrucchi
    Abstract:

    Abstract The behavior of most physical systems is affected by their natural surroundings. A quantum system with an environment is referred to as open, and its study varies according to the classical or quantum description adopted for the environment. We propose an approach to open quantum systems that allows us to follow the cross-over from quantum to classical environments; to achieve this, we devise an exact Parametric Representation of the principal system, based on generalized coherent states for the environment. The method is applied to the Heisenberg star with frustration, where the quantum character of the environment varies with the couplings entering the Hamiltonian H. We find that when the star is in an eigenstate of H, the central spin behaves as if it were in an effective magnetic field, pointing in the direction set by the environmental coherent-state angle variables , and broadened according to their quantum probability distribution. Such distribution is independent of φ, whereas as a function of θ is seen to get narrower as the quantum character of the environment is reduced, collapsing into a Dirac-δ function in the classical limit. In such limit, because φ is left undetermined, the Von Neumann entropy of the central spin remains finite; in fact, it is equal to the entanglement of the original fully quantum model, a result that establishes a relation between this latter quantity and the Berry phase characterizing the dynamics of the central spin in the effective magnetic field.

Pradip Sircar - One of the best experts on this subject based on the ideXlab platform.

  • A Novel AFM Signal Model for Parametric Representation of Speech Phonemes
    Circuits Systems and Signal Processing, 2019
    Co-Authors: Mohan Bansal, Pradip Sircar
    Abstract:

    A new multicomponent multitone amplitude and frequency-modulated signal model for Parametric modelling of speech phoneme (voiced and unvoiced) is presented in this paper. As the speech signal is a multicomponent non-stationary signal, the Fourier–Bessel expansion is used to separate all individual components from the multicomponent speech signal. The parameter estimation is done by analysing the amplitude envelope (AE) and instantaneous frequency (IF) of the signal component separately. The AE and IF functions for separated components are extracted by using the discrete energy separation algorithm. The amplitude-modulated signal parameters and the amplitude of the signal are estimated by analysing the AE function, whereas the frequency-modulated signal parameters and the carrier frequency of the signal are estimated by analysing the IF function. This technique is found to be quite efficient for accurate parameter estimation of the speech phoneme. As an illustration of model-based speech processing, the proposed model is used for various speech signal processing applications.

  • Parametric Representation of speech employing multi-component AFM signal model
    International Journal of Speech Technology, 2015
    Co-Authors: Avinash Shrikant Hood, Ram Bilas Pachori, Varuna Kumar Reddy, Pradip Sircar
    Abstract:

    In this paper, we have proposed Parametric Representation of speech signals employing a novel multi-component amplitude and frequency modulated (AFM) sinusoidal signal model. The Fourier–Bessel (FB) series expansion is used to separate the multi-component speech signal into a set of mono-component signals. It has been shown that the first component or low-frequency component can be modeled with one set of parameters for the complete signal length. For other components of the speech which is a non-stationary signal, segmentation is required in order to apply the AFM signal model. We have proposed modeling of the second and third (and higher) components based on the AFM model with time-varying parameters. Thus, the signal is to be modeled in segments by selecting suitable length where the AFM signal model is admissible. The Itakura–Saito distance and root mean square log-spectral measure have been applied to determine distortion between the actual and modeled speech signals. Simulation results demonstrate the suitability of the AFM signal model for speech signal Representation.

  • fast communication eeg signal analysis using fb expansion and second order linear tvar process
    Signal Processing, 2008
    Co-Authors: Ram Bilas Pachori, Pradip Sircar
    Abstract:

    In this paper, we propose a second-order linear time-varying autoregressive (TVAR) process for Parametric Representation of the electroencephalogram (EEG) signals. The coefficients of the Fourier-Bessel (FB) series expansion have been used to constitute a feature vector for segmentation of the EEG signal. Our approach is novel in the sense that by selecting an appropriate data length, we find a simple model for Parametric Representation of the EEG signals. The complete method for estimation of model parameters is presented in this work.