Adiabatic Quantum Motors

When parameters are varied periodically, charge can be pumped through a mesoscopic conductor without applied bias. Here, we consider the inverse effect in which a transport current drives a periodic variation of an adiabatic degree of freedom. This provides a general operating principle for adiabatic quantum motors which we discuss here in general terms. We relate the work performed per cycle on the motor degree of freedom to characteristics of the underlying quantum pump and discuss the motors’ efficiency. Quantum motors based on chaotic quantum dots operate solely due to quantum interference, and motors based on Thouless pumps have ideal efficiency.

Figure 1

Generic adiabatic quantum motors building on (a) a quantum pump based on a chaotic quantum dot and (b) a Thouless pump. When a voltage is applied to the pump, the current “turns the wheel” and makes the phase angle $\theta$ wind.

Figure 2

Efficiency of the Thouless motor vs Fermi energy for $L=0.75\mu \mathrm{m}$ and $v={10}^5\mathrm{m}/\mathrm{s}$. From top to bottom, the curves correspond to dissipative loads $\gamma /\hslash =1/2\pi$, 0.5, 1. The motor has ideal efficiency ($\eta =1$) when the Fermi energy lies in the gap $|E_F|<\Delta$, and the length is taken to infinity. The inset shows the cycle frequency for a current-biased Thouless motor vs Fermi energy.