scholarly journals Universal single-frequency oscillations in a quantum impurity system after a local quench

2015 ◽  
Vol 92 (15) ◽  
Author(s):  
Abolfazl Bayat ◽  
Sougato Bose ◽  
Henrik Johannesson ◽  
Pasquale Sodano
Keyword(s):  
Single Frequency ◽  
Quantum Impurity ◽  
Impurity System

Nonlinear entangled quantum dynamics in many-body systems with strong electron correlation

2017 ◽  
Vol 31 (10) ◽  
pp. 1742009 ◽  
Author(s):  
Jongbae Hong
Keyword(s):  
Electron Correlation ◽  
Quantum Dynamics ◽  
Entangled State ◽  
Tunneling Conductance ◽  
Strong Electron Correlation ◽  
Strong Electron ◽  
Zero Bias ◽  
Highly Nonlinear ◽  
Quantum Impurity ◽  
Impurity System

A quantum impurity system out of equilibrium comprises two metallic reservoirs with different chemical potentials and one mediating spin impurity between them. We study the highly nonlinear tunneling conductance of this system, and clarify that three coherent peaks, one zero-bias peak and two side peaks, naturally appear in the tunneling conductance. We use the Liouvillian approach, in which a complete set of basis operators is available, and construct a Liouville matrix to obtain Green’s function at the mediating site. We show that the two coherent side peaks are the outcome of steady-state nonequilibrium combined with strong electron correlation at the mediating site. Tunneling in the quantum impurity system out of equilibrium is performed by an entangled state which is a linear combination of two Kondo singlets formed by the spin at the mediating site and the coherent spins in each reservoir. The fluctuation by incoherent spins is also included. The spectral weights and positions of the three coherent peaks are analytically discussed via atomic limit analysis. Our theoretical results well fit experimental data obtained for quantum point contacts with symmetric and asymmetric Kondo couplings.

scholarly journals Impact of Parallel Computing on Study of Time Evolution of a Quantum Impurity System in Response to a Quench

2020 ◽  
Vol 36 (1) ◽  
Author(s):  
Nghiem Thi Minh Hoa ◽  
Dang The Hung ◽  
Luong Minh Tuan ◽  
Duong Xuan Nui ◽  
Nguyen Duc Trung Kien
Keyword(s):  
Parallel Computing ◽  
Spectral Function ◽  
Time Evolution ◽  
Degrees Of Freedom ◽  
Time Dependent ◽  
Arbitrary System ◽  
Time Resolved ◽  
Quantum Impurity ◽  
Impurity System ◽  
Near Future

In an arbitrary system subjected to a quench, or an external field that varies the system parameters, the degrees of freedom increases double in comparison to that of an isolated system. In this study, we consider the quantum impurity system subjected to a quench, and measure the corresponding time-evolution of the spectral function, which is originated from the time-resolved photoemission spectroscopy. Due to the large number of degrees of freedom, the expression of the time-dependent spectral function is twice much more complicated than that of the time-independent spectral function, and therefore the calculation is extremely time consuming. In this paper, we estimate the scale of time consumption of such calculation in comparison to that of time-independent calculation, and present our solution to the problem by using parallel computing as implementing both MPI and OpenMP to the calculation. We also discuss the possibility to exploit parallel computing with GPU in the near future, and the preliminary results of time-dependent spectral function.

Calculation-and-experimental estimation of the role of the frequency ratio in changing the endurance at two-frequency deformation modes

2019 ◽  
Vol 85 (1(I)) ◽  
pp. 64-71 ◽  
Author(s):  
M. M. Gadenin
Keyword(s):  
High Frequency ◽  
Experimental Studies ◽  
Low Frequency ◽  
Reduction Factor ◽  
Single Frequency ◽  
Cyclic Loads ◽  
Small Ratio ◽  
Harmonic Components ◽  
Deformation Modes

The cycle configuration at two-frequency loading regimes depends on the number of parameters including the absolute values of the frequencies and amplitudes of the low-frequency and high-frequency loads added during this mode, the ratio of their frequencies and amplitudes, as well as the phase shift between these harmonic components, the latter having a significant effect only with a small ratio of frequencies. Presence of such two-frequency regimes or service loading conditions for parts of machines and structures schematized by them can significantly reduce their endurance. Using the results of experimental studies of changes in the endurance of a two-frequency loading of specimens of cyclically stable, cyclically softened and cyclically hardened steels under rigid conditions we have shown that decrease in the endurance under the aforementioned conditions depends on the ratio of frequencies and amplitudes of operation low-frequency low-cycle and high-frequency vibration stresses, and, moreover, the higher the level of the ratios of amplitudes and frequencies of those stacked harmonic processes of loading the greater the effect. It is shown that estimation of such a decrease in the endurance compared to a single frequency loading equal in the total stress (strains) amplitudes can be carried out using an exponential expression coupling those endurances through a parameter (reduction factor) containing the ratio of frequencies and amplitudes of operation cyclic loads and characteristic of the material. The reduction is illustrated by a set of calculation-experimental curves on the corresponding diagrams for each of the considered types of materials and compared with the experimental data.

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