Polaron dynamics of Bloch–Zener oscillations in an extended Holstein model

Recent developments in qubit engineering make circuit quantum electrodynamics devices promising candidates for the study of Bloch oscillations (BOs) and Landau–Zener (LZ) transitions. In this work, a hybrid circuit chain with alternating site energies under external electric fields is employed to study Bloch–Zener oscillations (BZOs), i.e. coherent superpositions of BOs and LZ transitions. We couple each of the tunable qubits in the chain to dispersionless optical phonons and build an extended Holstein polaron model with the purpose of investigating vibronic effects in the BZOs. We employ an extension of the Davydov ansatz in combination with the Dirac–Frenkel time-dependent variational principle to simulate the dynamics of the qubit chain under the influence of high-frequency quantum harmonic oscillators. Band gaps emerge due to energy differences in site energies at alternating qubit sites, and are shown to play key roles in tuning band structures and time periodic reconstructions of the wave patterns. In the absence of qubit–phonon interactions, the qubits undergo either standard BZOs or breathing modes, depending on whether the initial wave packet is formed by a broad or narrow Gaussian wave packet, respectively. The BZOs can get localized in space if the band gaps are sufficiently large. In the presence of qubit–phonon coupling, the periodic behavior of BZOs can be washed out and undergo dynamic localization. The influence of an ohmic bath on the dynamics of BZOs is investigated by means of a Markovian master equation approach. Finally, we calculate the von Neumann entropy as a measure of the entanglement between qubits and phonons.

Regime of small number of photons in the cavity for a singleemitter laser

The model of a single-emitter laser generating in the regime of small number of photons in the cavity mode is theoretically investigated. Based on a system of equations for different moments of the field operators the analytical expressions for mean photon number and photon number variance are obtained. Using the master equation approach the differential equation for the phase-averaged quasi-probability Q is derived. For some limiting cases the exact solutions of this equation are found.

Modeling Neuronal Systems as an Open Quantum System

We propose a physical model for neurons to describe how neurons interact with one another through the surrounding materials of neuronal cell bodies. We model the neuronal cell surroundings, include the dendrites, the axons and the synapses, as well as the surrounding glial cells, as a continuous distribution of oscillating modes inspired from the electric circuital picture of neuronal action potential. By analyzing the dynamics of this neuronal model by using the master equation approach of open quantum systems, we investigated the collective behavior of neurons. After applying stimulations to the neuronal system, the neuron collective state is activated and shows the action potential behavior. We find that this model can generate random neuron–neuron interactions and is appropriate for describing the process of information transmission in the neuronal system, which may pave a potential route toward understanding the dynamics of nervous system.

Suppression of shot noise in a spin–orbit coupled quantum dot

We study theoretically the transport properties of electrons in a quantum dot system with spin–orbit coupling. By using the quantum master equation approach, the shot noise and skewness of the transport electrons are calculated. We obtain super-Poisson noise behaviour by investigating the full counting statistics of the transport system. We discover super-Poisson behaviour is more obvious with the spin polarization increasing. More importantly, we discover the suppression of shot noise induced by spin–orbit coupling. The value of shot noise is gradually decreasing when spin–orbit coupling strength increases.

Theoretical Study on Proton Diffusivity in Y-Doped BaZrO3 with Realistic Dopant Configurations

We theoretically revisit the proton diffusivity in yttrium-doped barium zirconate (Y-doped BaZrO₃) with realistic dopant configurations under processing conditions. In a recent study employing the replica exchange Monte Carlo method, the equilibrium Y configurations at typical sintering temperatures were shown to deviate from the random configuration assumed in earlier theoretical studies. In the present study, we took this observation into account and evaluated the effect of the Y configuration on the proton diffusivity. Using the master equation approach based on local diffusion barriers calculated from first principles, the proton diffusivities under realistic Y configurations were estimated to be higher than those in the random configuration. This is explained by the fact that realistic Y configurations have fewer trap sites with deep potential wells compared to the random configuration due to the isolation trend of Y dopants. In addition, the effects of proton-proton interaction and the abundance of preferential conduction pathways are discussed; it is found that both are relatively minor factors compared to the trap site effect in determining the dependence of the proton diffusivity on the Y configurations.<br>