Quantum stochastic resonance in an a.c.-driven single-electron quantum dot

In stochastic resonance, the combination of a weak signal with noise leads to its amplification and optimization(1). This phenomenon has been observed in several systems in contexts ranging from palaeoclimatology, biology, medicine, sociology and economics to physics(1-9). In all these cases, the systems were either operating in the presence of thermal noise or were exposed to external classical noise sources. For quantummechanical systems, it has been theoretically predicted that intrinsic fluctuations lead to stochastic resonance as well, a phenomenon referred to as quantum stochastic resonance(1,)(10)(,11), but this has not been reported experimentally so far. Here we demonstrate tunnelling-controlled quantum stochastic resonance in the a.c.-driven charging and discharging of single electrons on a quantum dot. By analysing the counting statistics(12-16), we demonstrate that synchronization between the sequential tunnelling processes and a periodic driving signal passes through an optimum, irrespective of whether the external frequency or the internal tunnel coupling is tuned.