Time-Reversal Symmetry and Arrow of Time in Quantum Mechanics of Open Systems

It is one of the most important and long-standing issues of physics to derive the irreversibility out of a time-reversal symmetric equation of motion. The present paper considers the breaking of the time-reversal symmetry in open quantum systems and the emergence of an arrow of time. We claim that the time-reversal symmetric Schr\"{o}dinger equation can have eigenstates that break the time-reversal symmetry if the system is open in the sense that it has at least a countably infinite number of states. Such eigenstates, namely the resonant and anti-resonant states, have complex eigenvalues. We show that, although these states are often called "unphysical," they observe the probability conservation in a particular way. We also comment that the seemingly Hermitian Hamiltonian is non-Hermitian in the functional space of the resonant and anti-resonant states, and hence there is no contradiction in the fact that it has complex eigenvalues. We finally show how the existence of the states that break the time-reversal symmetry affects the quantum dynamics. The dynamics that starts from a time-reversal symmetric initial state is dominated by the resonant states for $t>0$; this explains the phenomenon of the arrow of time, in which the decay excels the growth. The time-reversal symmetry holds in that the dynamics ending at a time-reversal symmetric final state is dominated by the anti-resonant states for $t<0$.Comment: 14 pages, 4 figures, published in Entropy Journal Special Issue "Coherence in Open Quantum Systems

Universal electric current of interacting resonant-level models with asymmetric interactions: An extension of the Landauer formula

We study the electron transport in open quantum-dot systems described by the interacting resonant-level models with Coulomb interactions. We consider the situation in which the quantum dot is connected to the left and right leads asymmetrically. We exactly construct many-electron scattering eigenstates for the two-lead system, where two-body bound states appear as a consequence of one-body resonances and the Coulomb interactions. By using an extension of the Landauer formula, we calculate the average electric current for the system under bias voltages in the first order of the interaction parameters. Through a renormalization-group technique, we arrive at the universal electric current, where we observe the suppression of the electric current for large bias voltages, i.e., negative differential conductance. We find that the suppressed electric current is restored by the asymmetry of the system parameters.Comment: 27 pages, 3 figure

Tunable Bound States in Continuum by Optical Frequency

We demonstrate the existence of tunable bound-states in continuum (BIC) in a 1-dimensional quantum wire with two impurities induced by an intense monochromatic radiation field. We found that there is a new type of BIC due to the Fano interference between two optical transition channels, in addition to the ordinary BIC due to a geometrical interference between electron wave functions emitted by impurities. In both cases the BIC can be achieved by tuning the frequency of the radiation field.Comment: 5 figure

Wave function propagation in a two-dimensional paramagnetic semiconductor from an impurity

We simulated modifications to a model of a two-dimensional paramagnetic semiconductor called the half-BHZ model, also known as the QWZ model, and simulated a modified full BHZ model, where a time reversal pair is introduced. Our modifications to the models include adding single and multiple impurities connected to the lattices or as a connection between the time-reversal pairs. We employed the Julia programming language to show how to speed up calculations for time evolutions. By simulating the time evolutions, we could observe the differences in the effects of these modifications. Our simulations showed the presence of scattering behavior associated with the infinite QWZ model topological states. Moreover, we observed scattering and absorption behavior related to the parameters and placements of impurities and Hamiltonian imaginary component's symmetry or anti-symmetry. These tools and early results lay the foundations for developing electronic devices that use the models' unique scattering and absorption behaviors and explore more complex and physically accurate modifications to the models