Nonadiabatic particle and energy pump at strong system-reservoir coupling

Abstract

We study the dynamics of electron and energy currents in a nonadiabatic pump. The pump is a quantum dot nanojunction with time-varying gate potential and tunnel couplings to the leads. The leads are unbiased and maintained at the same temperature and chemical potential. We find that synchronized variations of the gate and tunnel couplings can pump electrons and energy from the left to the right lead. Inspired by quantum heat engines, we devise a four-stroke operating protocol that can optimally pump energy and hence, we investigate energy transfer and the coefficient of performance of the device. We compare our device to a two-stroke pump and find that the latter's lower performance is due to the bi-directional flow of energy currents resulting in low net energy currents. The performance of our four-stroke pump can be improved, up to a point, by increasing the net energy carried by the pumped electrons through energy charging via the gate potential. This is achieved by increasing the durations of energy charging and discharging strokes in the pump's protocol. However, despite the large energy output for long charging and discharging strokes, the energy required to maintain the strokes become large too resulting in a stagnant pump performance. Our pump operates effectively only in the strong lead coupling regime and becomes a dud in the weak coupling regime due to the net output energy flowing in the reverse direction. We use nonequilibirum Green's functions techniques to calculate the currents and capture the effects of strong lead-channel coupling exactly while simultaneously incorporating three time-varying parameters. Results from our work could aid in the design of high-performance quantum pumps.

Emission rate of electron transport through a quantum point contact

“…The above results show that when the QPC is close to pinchoff, the correlations between electrons are restricted between two successively emitted electrons, which occurs at the timescale shorter than T. This makes the emission process can be described within the renewal theory and hence all the emission rate λn with n ⩾ 2 can be described by the same emission rate λg(t) via equation (40). On the timescale shorter than T, the emission rate λg(t) exhibits a zero-dip around t = 0, indicating a strong correlation due to the Pauli exclusion principle.…”

“…These results demonstrate that the electron emission can exhibit rich behaviors emerging purely from the Fermi statistics, which can be effectively manipulated by the time-dependent driving voltage. Although we concentrate on a single-channel QPC in this paper, our approach can also be generalized to study the electron emission in other nano-structures subjected to strong time-dependent driving voltage [31][32][33][34][35][36][37][38][39][40][41].…”