Thermal Bath

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Junichi Yokoyama - One of the best experts on this subject based on the ideXlab platform.

  • langevin description of gauged scalar fields in a Thermal Bath
    Physical Review D, 2014
    Co-Authors: Yuhei Miyamoto, Hayato Motohashi, Teruaki Suyama, Junichi Yokoyama
    Abstract:

    We study the dynamics of the oscillating gauged scalar field in a Thermal Bath. A Langevin-type equation of motion of the scalar field, which contains both dissipation and fluctuation terms, is derived by using the real-time finite-temperature effective action approach. The existence of the quantum fluctuation-dissipation relation between the nonlocal dissipation term and the Gaussian stochastic noise terms is verified. We find that the noise variables are anticorrelated at equal time. The dissipation rate for each mode is also studied, which turns out to depend on the wave number.

  • fate of oscillating scalar fields in a Thermal Bath and their cosmological implications
    Physical Review D, 2004
    Co-Authors: Junichi Yokoyama
    Abstract:

    Relaxation process of a coherent scalar field oscillation in the Thermal Bath is investigated using nonequilibrium quantum field theory. The Langevin-type equation of motion is obtained which has a memory term and both additive and multiplicative noise terms. The dissipation rate of the oscillating scalar field is calculated for various interactions such as Yukawa coupling, three-body scalar interaction, and biquadratic interaction. When the background temperature is larger than the oscillation frequency, the dissipation rate arising from the interactions with fermions is suppressed due to the Pauli-blocking, while it is enhanced for interactions with bosons due to the induced effect. In both cases, we find that the microphysical detailed-balance relation drives the oscillating field to a Thermal equilibrium state. That is, for low-momentum modes, the classical fluctuation-dissipation theorem holds and they relax to a state the equipartition law is satisfied, while higher-momentum modes reach the state the number density of each quanta consists of the Thermal boson distribution function and zero-point vacuum contribution. The temperature-dependent dissipation rates obtained here are applied to the late reheating phase of inflationary universe. It is found that in some cases the reheat temperature may take a somewhat different value from the conventional estimates, and inmore » an extreme case the inflaton can dissipate its energy without linear interactions that leads to its decay. Furthermore the evaporation rate of the Affleck-Dine field at the onset of its oscillation is calculated.« less

Hartmut Neven - One of the best experts on this subject based on the ideXlab platform.

  • artificial quantum Thermal Bath engineering temperature for a many body quantum system
    Physical Review A, 2016
    Co-Authors: Alireza Shabani, Hartmut Neven
    Abstract:

    Temperature determines the relative probability of observing a physical system in an energy state when that system is energetically in equilibrium with its environment. In this paper, we present a theory for engineering the temperature of a quantum system different from its ambient temperature. We define criteria for an engineered quantum Bath that, when coupled to a quantum system with Hamiltonian $H$, drives the system to the equilibrium state $\frac{e^{-H/T}}{{{\rm{Tr}}}(e^{-H/T})}$ with a tunable parameter $T$. This is basically an analog counterpart of the digital quantum metropolis algorithm. For a system of superconducting qubits, we propose a circuit-QED approximate realization of such an engineered Thermal Bath consisting of driven lossy resonators. Our proposal opens the path to simulate thermodynamical properties of many-body quantum systems of size not accessible to classical simulations. Also we discuss how an artificial Thermal Bath can serve as a temperature knob for a hybrid quantum-Thermal annealer.

  • artificial quantum Thermal Bath engineering temperature for a many body quantum system
    Physical Review A, 2016
    Co-Authors: Alireza Shabani, Hartmut Neven
    Abstract:

    Temperature determines the relative probability of observing a physical system in an energy state when that system is energetically in equilibrium with its environment. In this paper we present a theory for engineering the temperature of a quantum system different from its ambient temperature. We define criteria for an engineered quantum Bath that, when coupled to a quantum system with Hamiltonian $H$, drives the system to the equilibrium state $\frac{{e}^{\ensuremath{-}H/T}}{\mathrm{Tr}({e}^{\ensuremath{-}H/T})}$ with a tunable parameter $T$. This is basically an analog counterpart of the digital quantum metropolis algorithm. For a system of superconducting qubits, we propose a circuit-QED approximate realization of such an engineered Thermal Bath consisting of driven lossy resonators. Our proposal opens the path to simulate thermodynamical properties of many-body quantum systems of size not accessible to classical simulations. Also we discuss how an artificial Thermal Bath can serve as a temperature knob for a hybrid quantum-Thermal annealer.

Bibhas Ranjan Majhi - One of the best experts on this subject based on the ideXlab platform.

  • radiative process of two entangled uniformly accelerated atoms in a Thermal Bath a possible case of anti unruh event
    Journal of High Energy Physics, 2021
    Co-Authors: Subhajit Barman, Bibhas Ranjan Majhi
    Abstract:

    We study the radiative process of two entangled two-level atoms uniformly accelerated in a Thermal Bath, coupled to a massless scalar field. First, by using the positive frequency Wightman function from the Minkowski modes with a Rindler transformation we provide the transition probabilities for the transitions from maximally entangled symmetric and anti-symmetric Bell states to the collective excited or ground state in (1 + 1) and (1 + 3) dimensions. We observe a possible case of anti-Unruh-like event in these transition probabilities, though the (1+1) and (1+3) dimensional results are not completely equivalent. We infer that Thermal Bath plays a major role in the occurrence of the anti-Unruh-like effect, as it is also present in the transition probabilities corresponding to a single detector in this case. Second, we have considered the Green’s functions in terms of the Rindler modes with the vacuum of Unruh modes for estimating the same. Here the anti-Unruh effect appears only for the transition from the anti-symmetric state to the collective excited or ground state. It is noticed that here the (1 + 1) and (1 + 3) dimensional results are equivalent, and for a single detector, we do not observe any anti-Unruh effect. This suggests that the entanglement between the states of the atoms is the main cause for the observed anti-Unruh effect in this case. In going through the investigation, we find that the transition probability for a single detector case is symmetric under the interchange between the Thermal Bath’s temperature and the Unruh temperature for Rindler mode analysis; whereas this is not the case for Minkowski mode. We further comment on whether this observation may shed light on the analogy between an accelerated observer and a real Thermal Bath. An elaborate investigation for the classifications of our observed anti-Unruh effects, i.e., either weak or strong anti-Unruh effect, is also thoroughly demonstrated.

  • radiative process of two entangled uniformly accelerated atoms in a Thermal Bath a possible case of anti unruh event
    arXiv: General Relativity and Quantum Cosmology, 2021
    Co-Authors: Subhajit Barman, Bibhas Ranjan Majhi
    Abstract:

    We study the radiative process of two entangled two-level atoms uniformly accelerated in a Thermal Bath, coupled to a massless scalar field. First, using the positive frequency Wightman function from the Minkowski modes with a Rindler transformation we provide the transition probabilities for the transitions from maximally entangled symmetric and anti-symmetric Bell states to the collective excited state in $(1+1)$ and $(1+3)$ dimensions. We observe a possible case of \emph{anti-Unruh-like} event in these transition probabilities, though the $(1+1)$ and $(1+3)$ dimensional results are not completely equivalent. We infer that Thermal Bath plays a major role in the occurrence of the anti-Unruh-like effect, as it is also present in the transition probabilities corresponding to a single detector in this case. Second, we have considered the Green's functions in terms of the Rindler modes with the vacuum of Unruh modes for estimating the same. Here the anti-Unruh effect appears only for the transition from the anti-symmetric state to the collective excited state. It is noticed that here the $(1+1)$ and $(1+3)$ dimensional results are equivalent, and for a single detector, we do not observe any anti-Unruh effect. This suggests that the entanglement between the states of the atoms is the main cause for the observed anti-Unruh effect in this case. In going through the investigation, we find that the transition probability for a single detector case is symmetric under the interchange between the Thermal Bath's temperature and the Unruh temperature for Rindler mode analysis; whereas this is not the case for Minkowski mode. We further comment on whether this observation may shed light on the analogy between an accelerated observer and a real Thermal Bath. An elaborate investigation for the classifications of our observed anti-Unruh effects is also thoroughly demonstrated.

  • how robust is the indistinguishability between quantum fluctuation seen from noninertial frame and real Thermal Bath
    Physical Review D, 2019
    Co-Authors: Chandramouli Chowdhury, Susmita Das, Surojit Dalui, Bibhas Ranjan Majhi
    Abstract:

    We re-advocated the conjecture of indistinguishability between the quantum fluctuation observed from a Rindler frame and a real Thermal Bath, for the case of a free massless scalar field. To clarify the robustness and how far such is admissible, in this paper, we investigate the issue from two different non-inertial observers' perspective. A detailed analysis is being done to find the observable quantities as measured by two non-inertial observers (one is Rindler and another is uniformly rotating) on the real Thermal Bath and Rindler frame in Minkowski spacetime. More precisely, we compare Thermal-Rindler with Rindler-Rindler and Thermal-rotating with Rindler-rotating situations. In the first model it is observed that although some of the observables are equivalent, all the components of renormalised stress-tensor are not the same. In the later model, we again find that this equivalence is not totally guaranteed. Therefore we argue that the indistinguishability between the real Thermal Bath and the Rindler frame may not be totally true.

Sanved Kolekar - One of the best experts on this subject based on the ideXlab platform.

  • indistinguishability of Thermal and quantum fluctuations
    Classical and Quantum Gravity, 2015
    Co-Authors: Sanved Kolekar, T Padmanabhan
    Abstract:

    The existence of Davies–Unruh temperature in a uniformly accelerated frame shows that quantum fluctuations of the inertial vacuum state appears as Thermal fluctuations in the accelerated frame. Hence thermodynamic experiments cannot distinguish between phenomena occurring in a Thermal Bath of temperature T in the inertial frame from those in a frame accelerating through inertial vacuum with the acceleration . We show that this indisguishability between quantum fluctuations and Thermal fluctuations goes far beyond the fluctuations in the vacuum state. We show by an exact calculation, that the reduced density matrix for a uniformly accelerated observer when the quantum field is in a Thermal state of temperature , is symmetric between acceleration temperature and the Thermal Bath temperature . Thus Thermal phenomena cannot distinguish whether (i) one is accelerating with through a Bath of temperature or (ii) accelerating with through a Bath of temperature T. This shows that Thermal and quantum fluctuations in an accelerated frame affect the observer in a symmetric manner. The implications are discussed.

  • uniformly accelerated observer in a Thermal Bath
    Physical Review D, 2014
    Co-Authors: Sanved Kolekar
    Abstract:

    We investigate the quantum field aspects in flat spacetime for a uniformly accelerated observer moving in a Thermal Bath. In particular, we obtain an exact closed expression of the reduced density matrix for a uniformly accelerated observer with acceleration $a=2\ensuremath{\pi}T$ when the state of the quantum field is a Thermal Bath at temperature ${T}^{\ensuremath{'}}$. We find that the density matrix has a simple form with an effective partition function $Z$ being a product, $Z={Z}_{T}{Z}_{{T}^{\ensuremath{'}}}$, of two Thermal partition functions corresponding to temperatures $T$ and ${T}^{\ensuremath{'}}$ and hence is not Thermal, even when $T={T}^{\ensuremath{'}}$. We show that, even though the partition function has a product structure, the two Thermal Baths are, in fact, interacting systems; although in the high frequency limit ${\ensuremath{\omega}}_{k}\ensuremath{\gg}T$ and ${\ensuremath{\omega}}_{k}\ensuremath{\gg}{T}^{\ensuremath{'}}$, the interactions are found to become subdominant. We further demonstrate that the resulting spectrum of the Rindler particles can be interpreted in terms of spontaneous and stimulated emission due to the background Thermal Bath. The density matrix is also found to be symmetric in the acceleration temperature $T$ and the Thermal Bath temperature ${T}^{\ensuremath{'}}$ indicating that thermodynamic experiments alone cannot distinguish between the Thermal effects due to $T$ and those due to ${T}^{\ensuremath{'}}$. The entanglement entropy associated with the reduced density matrix (with the background contribution of the Davies-Unruh Bath removed) is shown to satisfy, in the ${\ensuremath{\omega}}_{k}\ensuremath{\gg}{T}^{\ensuremath{'}}$ limit, a first law of thermodynamics relation of the form $T\ensuremath{\delta}S=\ensuremath{\delta}E$, where $\ensuremath{\delta}E$ is the difference in the energies corresponding to the reduced density matrix and the background Davies-Unruh Bath. The implications are discussed.

  • indistinguishability of Thermal and quantum fluctuations
    arXiv: General Relativity and Quantum Cosmology, 2013
    Co-Authors: Sanved Kolekar, T Padmanabhan
    Abstract:

    The existence of Davies-Unruh temperature in a uniformly accelerated frame shows that quantum fluctuations of the inertial vacuum state appears as Thermal fluctuations in the accelerated frame. Hence thermodynamic experiments cannot distinguish between phenomena occurring in a Thermal Bath of temperature T in the inertial frame from those in a frame accelerating through inertial vacuum with the acceleration $a=2\pi T$. We show that this indisguishability between quantum fluctuations and Thermal fluctuations goes far beyond the fluctuations in the vacuum state. We show by an exact calculation, that the reduced density matrix for a uniformly accelerated observer when the quantum field is in a Thermal state of temperature $T^\prime$ is symmetric between acceleration temperature $T = a/(2\pi)$ and the Thermal Bath temperature $T^\prime$. Thus Thermal phenomena cannot distinguish whether (i) one is accelerating with $a = 2\pi T$ through a Bath of temperature $T^\prime$ or (ii) accelerating with $a=2\pi T^\prime$ through a Bath of temperature T. This shows that Thermal and quantum fluctuations in an accelerated frame affect the observer in a symmetric manner. The implications are discussed.

Hichem Dammak - One of the best experts on this subject based on the ideXlab platform.

  • on the use of quantum Thermal Bath in unimolecular fragmentation simulation
    Journal of Physical Chemistry A, 2019
    Co-Authors: Riccardo Spezia, Hichem Dammak
    Abstract:

    In the present work, we have investigated the possibility of using the quantum Thermal Bath (QTB) method in molecular simulations of unimolecular dissociation processes. Notably, QTB is used in introducing nuclear quantum effects with a computational time, which is basically the same as in Newtonian simulations. At this end, we have considered the model fragmentation of CH4 for which an analytical function is present in the literature. Moreover, based on the same model, a microcanonical algorithm, which monitors the zero-point energy of products and eventually modifies trajectories, was recently proposed. We have thus compared classical and quantum rate constants with these different models. QTB seems to correctly reproduce some quantum features, in particular the difference between classical and quantum activation energies, making it a promising method to study, with molecular simulations, unimolecular fragmentation of much complex systems. The role of a QTB thermostat in rotational degrees of freedom is also analyzed and discussed.

  • Zero-Point Energy Leakage in Quantum Thermal Bath Molecular Dynamics Simulations
    Journal of Chemical Theory and Computation, 2016
    Co-Authors: Fabien Brieuc, Hichem Dammak, Yael Bronstein, Philippe Depondt, Fabio Finocchi, Marc Hayoun
    Abstract:

    The quantum Thermal Bath (QTB) has been presented as an alternative to path-integral-based methods to introduce nuclear quantum effects in molecular dynamics simulations. The method has proved to be efficient, yielding accurate results for various systems. However, the QTB method is prone to zero-point energy leakage (ZPEL) in highly anharmonic systems. This is a well-known problem in methods based on classical trajectories where part of the energy of the high-frequency modes is transferred to the low-frequency modes leading to a wrong energy distribution. In some cases, the ZPEL can have dramatic consequences on the properties of the system. Thus, we investigate the ZPEL by testing the QTB method on selected systems with increasing complexity in order to study the conditions and the parameters that influence the leakage. We also analyze the consequences of the ZPEL on the structural and vibrational properties of the system. We find that the leakage is particularly dependent on the damping coefficient and that increasing its value can reduce and, in some cases, completely remove the ZPEL. When using sufficiently high values for the damping coefficient, the expected energy distribution among the vibrational modes is ensured. In this case, the QTB method gives very encouraging results. In particular, the structural properties are well-reproduced. The dynamical properties should be regarded with caution although valuable information can still be extracted from the vibrational spectrum, even for large values of the damping term.

  • Quantum Thermal Bath for molecular dynamics simulation
    Physical Review Letters, 2009
    Co-Authors: Hichem Dammak, Yann Chalopin, Marine Laroche, Marc Hayoun, Jean-jacques Greffet
    Abstract:

    Molecular dynamics (MD) is a numerical simulation technique based on classical mechanics. It has been taken for granted that its use is limited to a large temperature regime where classical statistics is valid. To overcome this limitation, the authors introduce in a universal way a quantum Thermal Bath that accounts for quantum statistics while using standard MD. The efficiency of the new technique is illustrated by reproducing several experimental data at low temperatures in a regime where quantum statistical effects cannot be neglected.