Environmental effects on a single electron box

Lafarge et al. (Zeitschrift für Physik B 85 (1991) 327) have measured the average junction charge in a single electron box. Their results are in agreement with theoretical predictions at temperatures T above 100 mK but not at lower T values. We explain the lower T experimental results by incorporating quantum charge fluctuations due to the environment by use of a quantum Langevin equation model. It is shown that, at T = 0, the sawtooth shape of the junction charge, as predicted by existing theories, is rounded off by the quantum fluctuation effects. At finite temperature, the theory is compared with the experiments of Lafarge et al., nd a good fit is obtained at all the relevant temperatures.