Dephasing in Low Dimensional Disordered Conductors
We are currently fabricating quasi-one-dimensional wires of different materials and measuring the electron dephasing time at dilution refrigerator temperatures. We aim to understand the mechanism of dephasing at low temperatures, which constitutes an important unresolved issue in condensed matter physics.
The dephasing time of a material characterizes how long on average quasiparticles maintain their phase information. Loss of this phase information, or decoherence, is caused by inelastic scattering or spin-flip events, which randomize the phase of the particle. The dephasing time is important because
- it sets the length-scale on which coherent physics can be observed
- The most significant obstacle to building a quantum computer in the solid state is decoherence. It is therefore important to understand the origin of decoherence so that ultimately it may be reduced or controlled.
- recent experiments measuring the dephasing time find a significant disagreement between the theory of disordered conductors and experiment.
One way to obtain the dephasing time is to perform a magnetoresistance measurement, i.e. measure resistance R as a function of perpendicular magnetic field H. The decoherence time can be extracted from the magnetoresistance data using the theory of weak localization, which gives the dependence of R(H) on the dephasing time.
Some recent experiments have found that the roughly dephasing time becomes roughly temperature independent at low temperatures. This contradicts Fermi Liquid Theory according to which quasiparticles should remain coherent for an arbitrary long time in the low temperature limit. Similar saturation has been found independently in other materials and also for two dimensional systems.
For more information contact Dominik Zumbuhl (dzumbuhl@harvard.edu)