Simulation of dynamical properties of normal and superfluid helium.
Akira Nakayama,Nancy Makri +1 more
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This simulation demonstrates that the peak enhancement observed in the neutron scattering experiments below the transition temperature arises exclusively from particle exchange, illuminating the role of Bose-statistical effects on the dynamics of the quantum liquid.Abstract:
The formation of a superfluid when 4He is cooled below the characteristic lambda transition temperature is accompanied by intricate quantum mechanical phenomena, including the emergence of a Bose condensate. A combination of path integral and semiclassical techniques is used to calculate the single-particle velocity autocorrelation function across the normal-to-superfluid transition. We find that the inclusion of particle exchange alters qualitatively the shape of the correlation function below the characteristic transition temperature but has no noticeable effect on the dynamics in the normal phase. The incoherent structure factor extracted from the velocity autocorrelation function is in very good agreement with neutron scattering data, reproducing the width, height, frequency shift, and asymmetry of the curves, as well as the observed increase in peak height characteristic of the superfluid phase. Our simulation demonstrates that the peak enhancement observed in the neutron scattering experiments below the transition temperature arises exclusively from particle exchange, illuminating the role of Bose-statistical effects on the dynamics of the quantum liquid.read more
Citations
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Direct Monte Carlo evaluation of real-time quantum correlation functions using single-step propagators
Jeb Kegerreis,Nancy Makri +1 more
TL;DR: In this paper, real-time correlation functions can be expressed as integrals of smooth functions, and thus can be efficiently evaluated by Monte Carlo methods, allowing direct calculation of correlation functions at intermediate temperatures over short to intermediate time lengths.
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Non-Markovian trajectories involving future in semi-classical path integral expression
TL;DR: In this paper, a quantum system coupled to a harmonic bath is derived based on the stationary phase condition and it is discovered that the system path is non-Markovian, i.e. the equation of motion for the system is an integro-differential equation that involves all times.
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Small Matrix Quantum-Classical Path Integral.
Sohang Kundu,Nancy Makri +1 more
TL;DR: In this article , a small matrix decomposition (SMatQCPI) was developed to eliminate the tensor storage requirements of the iterative QCPI algorithm, which reduced the computational cost to that of a single step.
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Microscopic self dynamics in liquids: Connections between the Gaussian approximation and the asymptotic impulsive regime
TL;DR: In this article, a power series of the inverse momentum transfer is used to measure the difference between the exact single-particle response function and the well-known impulsive approximation.
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Properties of condensed matter from fundamental physical constants
TL;DR: The lower bound of kinematic viscosity represents the global minimum on the phase diagram as mentioned in this paper , and this result answers the long-standing question considered by Purcell and Weisskopf, namely why viscous fluids never fall below a certain value.
References
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Bose-Einstein condensation
TL;DR: The Bose-Einstein condensation (BEC) phenomenon was first introduced by Bose as discussed by the authors, who derived the Planck law for black-body radiation by treating the photons as a gas of identical particles.
BookDOI
Theory Of Quantum Liquids
TL;DR: In this article, the two-fluid model is used to model elementary excitement in He II and the response to a transverse probe is described as a superfluid flow.
Journal ArticleDOI
The theory of quantum liquids
TL;DR: In this paper, the two-fluid model is used to describe the behavior of a superfluid in response to a transverse probe in a two-fluid model.
Journal ArticleDOI
Path integrals in the theory of condensed helium
TL;DR: In this paper, the authors introduce a picture of a boson superfluid and show how superfluidity and Bose condensation manifest themselves, showing the excellent agreement between simulations and experimental measurements on liquid and solid helium for such quantities as pair correlations, the superfluid density, the energy, and the momentum distribution.
Journal ArticleDOI
Bose-Einstein condensation in the alkali gases: Some fundamental concepts
TL;DR: In this paper, the authors present a tutorial review of some ideas that are basic to our current understanding of Bose-Einstein condensation in the dilute atomic alkali gases, with special emphasis on the case of two or more coexisting hyperfine species.
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