  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.
