Closing the gap on the third way of computation.

最近，我们逐渐意识到，我们对信息的概念与我们所信仰的科学定律紧密相连。这种联系的一个原因是，计算机实际上是一种物理实验。这可以理解为以下几点。虽然用于构建计算机的电路按照众所周知的规则运行，但这些规则可能会导致复杂的行为，因此计算电路网络将如何演变可能对应于耗时的数学问题。通过制造计算机，我们实际上扭转了这个问题--我们建立了电路网络，观察它们的演变，然后利用观察结果给出我们用纸和笔很难解决的问题的答案。然而，事实证明，有许多问题即使是现在的计算机也不能有效地解决。其中有一个非常重要的例子：计算符合量子物理定律的系统的演化是极其困难的。量子物理学这个术语指的是我们认为描述宇宙基本运作的定律。这些定律对于描述原子和光子(光子是光的基本‘粒子’)等小物体的行为特别重要。事实上，很难计算出遵守量子物理定律的物体的演化，这就引出了一个问题：我们能扭转这个问题吗？如果我们可以观察量子系统，有没有传统计算机难以解决的数学问题？这个问题的答案似乎是肯定的--有一些非常重要的问题，所谓的量子计算机比使用传统计算的最著名的方法更容易解决。事实上，量子物理不仅使我们能够建造更好的计算机，还使我们能够以非常不同的方式进行交流。事实证明，量子物理定律允许我们以一种非常特殊的方式隐藏信息，从而使我们能够以前所未有的方式执行各种形式的密码术(秘密通信)。量子密码学的基本形式已经可以商业化。尽管有这样的希望，但要获得具有足够控制的量子系统，使我们能够建立成熟的量子信息处理设备，仍然是非常具有挑战性的。尽管从根本上讲，量子物理被认为对几乎所有材料的行为都负有责任，但成熟的量子系统往往非常小，容易受到周围环境的干扰。该研究项目旨在找出这种噪音对我们处理量子信息的能力有什么影响。特别是，我们将致力于了解现实中的不完美是否仍然允许第三种形式的计算--一种比传统计算更好的计算，尽管没有理想的量子计算机那么强大。这样的第三种计算形式，如果它存在的话，在现实生活中可能更容易构建。如果它不存在，那么这将意味着要么现有的量子计算机方案可以容忍更高的缺陷，要么我们可能会在传统计算机上比之前想象的更好地模拟复杂的量子系统。所有这些可能性都会产生很大的影响，但要想受益，我们首先需要确定哪一种是实际情况！该研究项目希望开始在这一极其重要但极具挑战性的问题上取得系统性进展。

In recent times we have come to realise that our concept of information is deeply connected to the scientific laws that we believe in. One reason for this connection is that a computer is in fact a form of physical experiment. This can be understood as follows. While the electrical circuits that are used to build computers behave according to well understood rules, these rules can lead to complex behaviour, and so calculating how networks of circuits will evolve can correspond to time-consuming mathematical problems. By building computers we actually turn this problem around - we build networks of circuits, observe their evolution, and then use the observations to give answers to problems that we would have found difficult using a pen and paper.However, it turns out that there are many problems that even current computers cannot solve efficiently. Among them there is one very important example: it is extremely difficult to compute the evolution of systems obeying the laws of quantum physics. The term quantum physics refers to the laws that we believe describe the fundamental workings of the universe. These laws are particularly important for describing the behaviour of small objects such as atoms and photons (photons are elementary 'particles' of light). The fact that it is difficult to calculate the evolution of objects obeying the laws of quantum physics leads to the question: can we turn this problem around? If we can observe quantum systems, are there mathematical problems that we can solve that conventional computers find difficult? The answer to this question appears to be yes - there are some very important problems that so called quantum computers find much easier to solve than the best known methods using conventional computation. In fact, quantum physics can not only enable us to build better computers, it also enables us to communicate in very different ways. It turns out that the laws of quantum physics allow us to hide information in a very special way, and hence enable us to perform forms of cryptography (secret communication) in ways that have never been previously possible. Elementary forms of quantum cryptography are already commercially available.Despite such promise, it is still very challenging to obtain quantum systems with sufficient control to allow us to build full-blown quantum information processing devices. Although at a fundamental level quantum physics is believed to be responsible for the behaviour of almost all materials, full-blown quantum systems tend to be very small and susceptible to disturbances from their surroundings. The research project intends to find out what effect this noise has on our ability to process quantum information. In particular we will aim to understand whether realistic imperfections can still allow a third form of computation - one that is better than conventional computational, albeit not as powerful as an idealised quantum computer. Such a third form of computation, if it exists, may be significantly easier to build in real life. If it does not exist, then that would mean that either existing quantum computer proposals can tolerate much higher imperfections, or that we may simulate complex quantum systems on conventional computers much better than previously thought. All these possibilities are would have high impact, but to benefit we first need to determine which one is actually the case! The research project hopes to start making systematic progress on this extremely significant but extremely challenging problem.