Quantum Phenomena in Complex Systems

9616749加尔格这项拨款包括对复杂系统中量子现象的理论研究。具体项目包括(1)大小为50-75A的铁氧体和反铁磁性粒子中的宏观量子隧道或共振，磁线和超导量子干涉器件(SQUID)中的磁畴壁，以及(2)量子计算机中的退相干效应。PI早些时候提出，核自旋耗散对于理解磁性粒子中的相干效应和隧道效应都是至关重要的。这笔赠款继续进一步探索可能的耗散源及其在实验中的后果。量子计算机是一种旨在利用叠加原理的线性来实现计算并行的设备。然而，这些计算机的操作需要它们所有元素之间的严格一致性。使用第一个项目中开发的技术，可能会分析与环境的相互作用是否过于有害，不利于量子计算机的理想特性。%这是一名职业生涯中期的PI，他已经成为量子力学在复杂系统中的应用，特别是环境对量子现象的影响方面的公认专家。拟议的研究既有基础性的方面，也有一定程度上更实用的方面。在第一类中，他提议研究在微观层面上常见但在宏观层面上很少看到的量子现象，因为它们被环境噪声掩盖了。具体地说，他提议在微小的磁性粒子和窄导线中研究这些量子效应，在这些地方，实验观察的机会被认为是最高的。在第二类中，他建议考虑最近提出的量子计算机的局限性，因为它们受到环境的影响。这种影响被广泛接受为对量子计算机的运行不利，但目前该领域的理解在很大程度上是定性的。PI建议使用在研究宏观量子现象过程中开发的方法对其严重性进行定量评估。

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.