Quantum Phenomena in Complex Systems

9616749 Garg该资助包括复杂系统中量子现象的理论研究。 具体项目包括：（1）尺寸为50-75 A的铁磁和反铁磁粒子中的宏观量子隧穿或共振，磁线和SQUID（超导量子干涉器件）中的畴壁;（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相干效应以及磁性粒子中的隧穿都至关重要。 这项资助继续进一步探索可能的耗散源及其在实验中的后果。 量子计算机是旨在利用叠加原理的线性来实现计算并行性的设备。 然而，这些计算机的操作要求其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，可以分析与环境的相互作用是否对量子计算机的理想性能过于有害。 这是一个职业生涯中期的PI，他已经成为量子力学在复杂系统中应用的公认专家，特别是环境对量子现象的影响。 拟议中的研究既有基本的，也有更多的应用方面。在第一类中，他建议研究在微观水平上常见但很少在宏观水平上看到的量子现象，因为它们被环境噪声所掩盖。具体来说，他建议在小磁性粒子和窄导线中研究这些量子效应，据信实验观察的机会最高。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。这种影响被广泛认为对量子计算机的运行是有害的，但目前在该领域的理解主要是定性的。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.