Influence Of Dephasing Research Articles

One-shot coherence distillation in superconducting circuit systems

Distilling quantum coherence is important for optimizing the performance of quantum technologies, however, it cannot always be accomplished with certainty. Then, the probabilistic distillation of quantum coherence has been developed and successfully implemented in experiments. We introduce a proposal to realize the one-shot coherence distillation in the superconducting circuit system. The target maximally coherent state can be extracted from a single copy of the prepared state by using appropriate incoherent operations and a finite error tolerance is allowed. It is easy to implement our scheme in the experiment that only a superconducting qubit is required to be the auxiliary system. To demonstrate the feasibility of our scheme, we numerically simulate the distillation process under the influence of dephasing (according to the typical experimental parameters). We find that the distillation rate of the coherence resource can be well achieved with the current experimental technique.

Two-photon induced ultrafast coherence decay of highly excited states in single molecules

Coherence is a key aspect of a large variety of processes, ranging from the coherent delocalisation of excitation energy, which is important for energy transfer in supramolecular nanostructures, to coherence between electronic states of a single quantum system, which is essential for quantum optical applications. Coherent control schemes exploit this quantum mechanical property by actively manipulating the outcome of dynamical processes. Moreover, this technique allows measuring dynamical processes under the influence of dephasing. However, going beyond the ensemble averaged situation, i.e. working on the level of single quantum systems, is highly challenging for quantum systems embedded in a solid matrix at elevated temperature. Since interactions between the quantum system and its specific local environment are a priori unknown, this requires a reliable approach to retrieve the relevant parameters governing the ultrafast coherent dynamics. Here, we present measurements of the ultrafast coherence decay of two-photon accessible excited states in single organic molecules embedded in a disordered environment at room temperature. We combine this experimental approach with a quantum dynamics identification procedure, which yields a minimum three-level model to describe the obtained data with very good agreement. In particular, we are able to retrieve the ultrafast (coherent) excited state dynamics in single molecules and demonstrate its sensitivity to the local nanoenvironment from molecule to molecule. This work provides a robust approach to measure and analyse ultrafast quantum dynamics in complex nanosystems.

Influence of dephasing and B/N doping on valley Seebeck effect in zigzag graphene nanoribbons

We investigate the dephasing effect and atomic doping effect of random substitutional boron (B) or nitrogen (N) on the valley Seebeck effect in zigzag graphene nanoribbons (ZGNRs) using the tight-binding model calculations. When thermal gradient applied in the device made of ZGNRs is around several hundreds K, dephasing effect can only reduce the magnitude of pure valley current without generating electric current associated with the valley Seebeck effect. In the presence of B/N dopants, valley-polarized current occurs in ZGNRs. It is found that the generated valley polarized current is linearly dependent on the temperature gradient (ΔT) when the temperature of one lead is fixed and shows nonlinear dependence on temperature of a particular lead when ΔT is fixed. By calculating the phase diagrams such as (ΔT,p) with p the doping concentration, we find that the valley polarization can be tuned in a wide range from zero up to 0.72, indicating that it can be well controlled by B/N doping concentration. Finally, the noise power of valley Seebeck effect is also studied providing important information on the fluctuation of valley polarized current.

Influence of Dephasing and Geometrical Parameters on Quantum Correction to DC Conductance of Cylindrical Nanowires

Calculations of the quantum correction to the DC conductance of a cylindrical nanowire due to the quantum interference are presented. The real space Cooperon equation is solved for cylindrical geometry. Using this approach, it is shown that the quantum correction to the conductance in the weak localisation regime depends not only on the dephasing processes but also on geometrical parameters of the nanowire.

Thermoelectric transport of mesoscopic conductors coupled to voltage and thermal probes

We investigate basic properties of the thermopower (Seebeck coefficient) of phase-coherent conductors under the influence of dephasing and inelastic processes. Transport across the system is caused by a voltage bias or a thermal gradient applied between two terminals. Inelastic scattering is modeled with the aid of an additional probe acting as an ideal potentiometer and thermometer. We find that inelastic scattering reduces the conductor's thermopower and, more unexpectedly, generates a magnetic-field asymmetry in the Seebeck coefficient. The latter effect is shown to be a higher-order effect in the Sommerfeld expansion. We discuss our result using two illustrative examples. First, we consider a generic mesoscopic system described within random matrix theory and demonstrate that thermopower fluctuations disappear quickly as the number of probe modes increases. Second, the asymmetry is explicitly calculated in the quantum limit of a ballistic microjunction. We find that asymmetric scattering strongly enhances the effect and discuss its dependence on temperature and Fermi energy.

Rabi oscillations in semiconductor quantum dots revisited: Influence of LO-phonon collisions

Coherence properties of semiconductor quantum dots are of central importance for a variety of applications. Previous studies of decoherence in these systems mainly focused on the interaction with LA phonons, only giving rise to dephasing. In contrast, the interaction with LO phonons additionally causes carrier scattering. To show the importance of the combined influence of dephasing and carrier scattering, we revisit the case of Rabi oscillations in semiconductor quantum dots using a quantum-kinetic treatment of the carrier-LO-phonon interaction.

Geometry and dynamics of quantum state diffusion

Riemannian metric on real 2n-dimensional space associated with the equation governing complex diffusion of pure states of an open quantum system is introduced and studied. Examples of a qubit under the influence of dephasing and thermal environments are used to show that the curvature of the diffusion metric is a good indicator of the properties of the environment-dominated evolution and its stability.

Decoherence in elastic and polaronic transport via discrete quantum states

Abstract In this work we study the effect of decoherence on elastic and polaronic transport via discrete quantum states. Calculations are performed with the help of a nonperturbative computational scheme, based on Green’s function theory within the framework of polaron transformation (GFT-PT), where the many-body electron-phonon interaction problem is mapped exactly into a single-electron multi-channel scattering problem. In particular, the influence of dephasing and relaxation processes on the shape of the electrical current and shot noise curves is discussed in detail under linear and nonlinear transport conditions.