A quantum pumping mechanism that produces dc current or voltage in response to a cyclic deformation of the confining potential in an open quantum dot is reported. The voltage produced at zero current bias is sinusoidal in the phase difference between the two ac voltages deforming the potential and shows random fluctuations in amplitude and direction with small changes in external parameters such as magnetic field. The amplitude of the pumping response increases linearly with the frequency of the deformation. Dependencies of pumping on the strength of the deformations, temperature, and breaking of time-reversal symmetry were also investigated.

Shape-averaged magnetoconductance (weak localization) is used for the first time to obtain the electron phase coherence time t f in open ballistic GaAs quantum dots.Values for t f in the range of temperature T from 0.335 to 4 K are found to be independent of dot area, and are not consistent with the t f µ -T 2 behavior expected for isolated dots. Surprisingly, t f T ( ) agrees quantitatively with the predicted dephasing time for disordered two-dimensional electron systems.Decoherence is the process by which the quantum mechanical properties of a microscopic system are transformed into the familiar classical behavior seen in macroscopic objects. Mesoscopic electronic systems, which exhibit strong coherent quantum mechanical effects such as weak localization and universal conductance fluctuations (UCF), are ideal for investigations of decoherence. The key quantity in these phenomena is the phase coherence time, t f , which determines the energy and length scales at which quantum behavior is seen. Considerable theoretical [1-4] and experimental [5-9] study has been directed toward understanding the mechanisms responsible for the loss of phase coherence (dephasing) and their dependence on temperature, dimensionality, and disorder.Most studies of dephasing in mesoscopic systems have focused on disordered 1Dand 2D conductors, where the dimensional crossover for quantum corrections to transport and interactions responsible for dephasing occurs when the sample width exceeds the phase

A technique borrowed from biology, rapid cryofixation/freeze fracture, has been adapted for the study of liquid–solid interfaces. This technique allows high-resolution imaging of the interfaces between water and substrates with varying degrees of hydrophobicity. The interface between gas-saturated water and hydrophobic surfaces is covered with a network of 100 nm scale features similar to those previously reported, while degassed water produces smooth interfaces. We thus confirm that the features are indeed nanobubbles which form spontaneously from dissolved gas in the liquid. The interface of gas-saturated water and a hydrophilic surface, while showing no evidence of nanobubbles, is not as smooth as the degassed interface.