Closing the gap on the third way of computation.

近年来，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密切相关。这种联系的一个原因是，计算机实际上是一种物理实验。这可以理解如下。虽然用于构建计算机的电路按照众所周知的规则运行，但这些规则可能导致复杂的行为，因此计算电路网络将如何演变可能对应耗时的数学问题。通过制造计算机，我们实际上扭转了这个问题——我们构建电路网络，观察它们的演变，然后利用这些观察结果来回答我们用笔和纸很难解决的问题。然而，事实证明，即使是现在的计算机也不能有效地解决许多问题。其中有一个非常重要的例子：计算遵循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”）等小物体的行为尤为重要。很难计算出遵循量子物理定律的物体的演化，这一事实引出了一个问题：我们能否扭转这个问题？如果我们能观察到量子系统，是否存在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，所谓的量子计算机发现比使用传统计算的最知名方法更容易解决。事实上，量子物理学不仅能让我们制造更好的计算机，还能让我们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密码学（秘密通信）。量子密码学的基本形式已经商业化。尽管有这样的前景，获得具有足够控制的量子系统以允许我们构建成熟的量子信息处理设备仍然是非常具有挑战性的。尽管在基本层面上，量子物理学被认为对几乎所有材料的行为负责，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，我们将致力于理解现实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，尽管不如理想的量子计算机那么强大。这种第三种形式的计算，如果存在的话，在现实生活中可能会容易得多。如果它不存在，那就意味着要么现有的量子计算机方案可以容忍更高的缺陷，要么我们可以在传统计算机上模拟复杂的量子系统，比以前想象的要好得多。所有这些可能性都会产生很大的影响，但为了从中受益，我们首先需要确定哪一种情况才是真正的情况！该研究项目希望在这个极其重要但极具挑战性的问题上开始取得系统进展。

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.