Suppressing decoherence in solid-state quantum information processing

量子物理学描述亚原子粒子，它们之间的相互作用，以及与外部影响（如光）的相互作用。量子计算是一项潜在的突破性技术，它将量子物理定律应用于计算任务，需要对量子粒子状态进行前所未有的控制，以便执行在任何传统计算机上都不可能实现的算法。例如，这种计算机可以提供无与伦比的安全通信标准和有效的数据库搜索。然而，在实践中，量子计算机仅限于实验室和少量的计算元素。执行15的因数分解（使用7个元素的寄存器）是最先进的。虽然，乍一看，这似乎不是一个特别令人印象深刻的壮举（传统计算机现在已经分解了200位数字），但更仔细地检查构建单个量子处理器固有的问题，更不用说寄存器了，揭示了这是一个多么大的突破。传统的计算机通过存储和处理以二进制位形式编码的信息来执行任务，这些二进制位的值为1或0（对应于逻辑上的真或假）。量子计算机以类似的方式（量子比特或量子位）对信息进行编码。量子位与它们的经典对口物相比有两个重要的优势：它们不仅可以以1或0的形式存在，还可以作为两者的组合（称为叠加）存在——由于一种被称为纠缠的特性（即量子位可以相互通信），量子位的寄存器可以在每个元素之间共享信息。正是这两个特性导致了量子算法的更高效率。不幸的是，叠加和纠缠使量子态极其脆弱。由于与处理器周围的材料接触，它们所保存的信息很快就会丢失，从而导致操作错误。这是一个被称为退相干的过程。任何大型量子计算机都必须克服这一基本限制。因此，我计划研究的目的是更好地理解信息是如何从量子计算机的计算元素中丢失的，并提出防止这种退相干的方法。

Quantum physics describes sub-atomic particles, their interactions with each other, and with external influences such as light. Quantum computation is a potentially ground-breaking technology which applies the laws of quantum physics to computational tasks, requiring an unprecedented level of control over the states of quantum particles, in order to perform algorithms that are impossible on any conventional computer. For example, such computers could provide an unmatched standard of secure communications and efficient database searches.However, in practise, quantum computers are confined to the laboratory and to small numbers of computational elements. Performing the factorisation of 15 (using a register of 7 elements) is state of the art. Although, at first glance, this does not seem a particularly impressive feat (conventional computers have now factorised a 200-digit number), closer examination of the problems inherent in building even a single quantum processor, never mind a register, reveals what a breakthrough this is.Conventional computers perform tasks by storing and processing information encoded in the form of binary bits which take a value of either 1 or 0 (corresponding to logical true or false). Quantum computers encode information in an analogous way (in quantum bits or qubits ). Qubits hold two important advantages over their classical counterparts: they may exist not only as 1 or 0 but as a combination of the two (known as a superposition) - and a register of qubits can share information out between each element due to a property known as entanglement (i.e. the qubits can talk to one another). It is these two properties that lead to the higher efficiency of quantum algorithms. Unfortunately, superposition and entanglement make quantum states extremely fragile. The information they hold is lost very quickly due to contact with the surrounding material of the processor, leading to errors in operation. This is a process known as decoherence. For any large scale quantum computer to be built this fundamental limitation must be overcome.The aim of my planned research is therefore to provide a better understanding of how information is lost from the computational elements of a quantum computer and to propose methods for protecting against such decoherence.