Tunable decoherence in the vicinity of a normal metal-superconducting junction - art. no. 035315

The decoherence rate of a quantum dot coupled to a fluctuating environment described by a normal-metal-superconductor junction is considered. The dens ity-density correlator at low frequencies constitutes a kernel which enters the calculation of the phase coherence time. The density fluctuations are connected to the finite-frequency current-current correlations in the point contact via the continuity equation. Below and above the gap, at zero temp erature the density correlator contains spatial oscillations at half of the Fermi wavelength on the normal side. As the bias crosses the superconducti ng gap, the opening of scattering channels enhances the decoherence rate dr amatically, suggesting the possibility of tuning the decoherence rate in a controllable manner.