Quantum Phenomena in Complex Systems

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9616749 Garg This grant consists of a theoretical study of quantum phenomena in complex systems. The specific projects include (1) macroscopic quantum tunneling or resonance in ferro and antiferromagnetic particles of size 50-75 A, domain walls in magnetic wires and in SQUIDs (Superconducting Quantum Interference Devices) and (2) decoherence effects in quantum computers. The PI has earlier proposed that nuclear spin dissipation is critical to understanding both the coherence effects as well as tunneling in magnetic particles. This grant continues further exploration of possible dissipation sources and their consequences in the experiments. Quantum computers are devices which aim to exploit the linearity of the superposition principle to achieve computational parallelism. The operation of these computers, however, requires strict coherence between all their elements. Using the techniques developed in the first project, it may be possible to analyze whether an interaction with environment is too deleterious for the desirable properties of a quantum computer. %%% This is a mid career PI who has emerged as an acknowledged expert on applications of quantum mechanics to complex systems, in particular on the effect of environment on quantum phenomena. The proposed research has both fundamental and somewhat more applied aspects. In the first category, he is proposing to study quantum phenomena that are commonly seen at the microscopic level, but rarely at the macroscopic level, because they are masked by environmental noise. Specifically, he is proposing to study these quantum effects in small magnetic particles and narrow wires, where the chances for experimental observation are believed to be highest. In the second category he proposes to consider the limitations of recently proposed quantum computers as they are influenced by the environment. This influence is widely accepted as being detrimental to the operation of quantum computers, but the current under standing in the field is largely qualitative. The PI proposes to make quantitative assessments of its severity using methods developed in the course of studying macroscopic quantum phenomena.