NIRT: Nanoscale Quantum Systems: Excitations and Control

Rutgers University New Brunswick, New Brunswick NJ

Investigators

Abstract

This proposal was received in response to the Nanoscale Science and Engineering Initiative, NSF-01-157, Nanoscale Interdisciplinary Research Teams (NIRT). The award is funded jointly by the NSF Divisions of Materials Research, Mathematical Sciences and Physics. The design, development and control of nanoscale electronics raises many challenging questions, particularly in the area of quantum systems far from equilibrium. Such mesoscopic devices are often weakly coupled to their environment, so that equilibration is difficult. Common issues are shared by diverse problems including quantum dots, driven Josephson junctions and finite-size quantum glasses. There now exist controllable quantum systems far from equilibrium that are accessible to both theory and experiment. In this research, a team of theorists from Rutgers, Princeton and NEC will address global issues in this area through a series of specific studies, using the conceptual links between nonequilibrium spin systems and disordered interacting electrons. It is emphasized that nonequilibrium sources of electron decoherence must be better understood in order to optimize performance of nanoscale circuitry, especially that which involves quantum dynamics. The problem of nonequilibrium quantum dynamics can be approached using localization theory. The dynamics of a quantum glass can be described by particle motion in a random potential on a high-dimensional sphere. Such systems display diffusive behavior not expected from a localization perspective. This discrepancy will be reconciled. Charge transport in a low-density disordered insulator displays slow relaxation, indicative of the system's inability to find its ground-state. Its complex free energy is due to competition between Coulomb interactions and a random potential. Taking an approach analogous to that in spin glasses, the team will identify and solve a model describing the localization-delocalization transition in an isolated electronic system. Sources of electron dephasing must be better understood in order to control phase coherence. This issue is crucial for the construction of quantum circuitry; even if each element is designed optimally, there is the possibility of collective dephasing. A related problem is the identification of a single qubit where decoherence is minimized. A spin liquid with a doubly degenerate ground-state and a gap may be an attractive candidate, since its absence of long-range order effectively decouples it from the external environment. %%% This proposal was received in response to the Nanoscale Science and Engineering Initiative, NSF-01-157, Nanoscale Interdisciplinary Research Teams (NIRT). The award is funded jointly by the NSF Divisions of Materials Research, Mathematical Sciences and Physics. This complementary team of theorists from Rutgers, Princeton and NEC will combine their talents to study fundamental issues relating to quantum electron dynamics at the nanoscale. As electrical circuitry approaches the nanoscale these issues become more critical, particularly as they relate to problems of phase coherence in nanodevices and its possible application in quantum computers. ***