A practical quantum simulator: simulating molecular vibrations with photons

物理模型的计算机模拟已经成为科学和工程中的重要工具。例如，一款新车的空气动力学和底盘完整性将在早在生产开始之前就在一个计算机化模型上进行完全模拟，而生物学家将使用一个简化的计算机模型来模拟蛋白质折叠所涉及的动力学。在这两种情况下，要模拟的模型的物理基础是熟悉的经典世界的物理基础，处理的信息也是如此。相比之下，在微观尺度上研究系统的化学家(量子化学家)必须将量子物理纳入他们的物理模型。但这些模型遇到了在经典计算机上模拟即使是中等大小的量子系统的困难。任何系统的可能配置的数量都随着其自由度的增加而指数增长，就像一排硬币的正面/反面配置的数量随着每增加一枚硬币而成倍增加一样。由于量子系统可以同时存在于其所有构型中，其演化太大，无法用经典计算机模拟。因此，经典计算机的量子力学模型必然是有限的，而更多的竞争模型从根本上难以处理经典模拟。然而，科学家们越来越需要了解量子物理的作用，例如在生物分子中。著名物理学家、诺贝尔奖获得者理查德·费曼在1982年的一次开创性演讲中认识到了这个问题。他还提出了一个解决方案。费曼建议用一个可控制的量子系统来模拟人们想要研究的量子系统的模型。这一巧妙概念的最终实现是一个数字量子模拟器，从理论上讲，它可以被编程来模拟任何量子系统。制造这种设备是日益密集的国际努力或竞争的焦点。这一努力可能是长期的，因为事实证明，隔离、数字化和相干控制大型量子系统是非常具有挑战性的，因为它们倾向于与环境耦合，在这里解码，并以经典的方式运行。毕竟，我们周围看到的世界是经典的，而不是量子的。因此，通往超越经典计算机能力的量子模拟器的道路似乎是漫长而艰难的，这是从事量子信息科学工作的科学家的最终目标。这一奖学金提出了一条通往大规模量子模拟的智能路线，该路线本质上是可扩展的，可以用可制造的技术来实现。该项目旨在以超过传统计算机能力的规模模拟量子物理模型。这是可能的，因为已经确定了分子量子振动行为的已建立模型和可制造光学芯片中的光子描述之间的映射。通过将单个光子的系综注入到多功能光学芯片中，可以跟踪大分子的演化。研究的方向是通过一系列微扰来改进分子数学模型，这些微扰在松散的条件下通过光子之间弱相互作用的形式与光路相匹配。单光子强相互作用的困难是光量子计算机面临的主要挑战。然而，开发建立弱相互作用层的连续几代设备允许在越来越定制和精确的分子模型上进行有趣和复杂的模拟。随着这些设备的进步，它们将开发更多的计算能力，例如计算涉及化学转变的因素和生物分子的特征属性。

Computer simulations of physical models have become a vital tool in science and engineering. For example, the aerodynamics and chassis integrity for a new car design will be fully simulated on a computerised model, long before production begins, while biologists will use a simplified computer model to simulate the dynamics involved in protein folding. In both of these cases, the physics underlying the model to be simulated is that of the familiar, classical world, as is the information that is processed. In contrast, chemists working with systems at the microscopic scale (quantum chemists) must incorporate quantum physics into their physical models. But these models come up against the intractability of simulating even modestly sized quantum systems on classical computers.The number of possible configurations of any system grows exponentially with its degrees of freedom, just like the number of heads/tails configurations of a row of coins doubles with each additional coin. Since a quantum system can exist simultaneously across all of its configurations, its evolution is too large to be simulated with a classical computer. Therefore, quantum mechanical models for classical computers are necessarily limited while more compete models are fundamentally intractable to classical simulation. Yet increasingly, scientists need to understand the role of quantum physics, for example in biological molecules.The famous physicist and Nobel Laureate, Richard Feynman, identified this problem in a seminal lecture in 1982. He also proposed a solution. Feynman suggested using one controllable quantum system to simulate the model for the quantum system one wishes to study. The ultimate realisation of this ingenious concept is a digital quantum simulator that theoretically can be programmed to simulate any quantum system. Building this device is the focus of an increasingly intensive international effort, or competition. This effort is likely to be long term since isolating, digitising, and coherently controlling large quantum systems has proved to be highly challenging, due to their inclination to couple to the environment, decohere, and behave classically. After all, the world we see around us is classical, not quantum. Therefore, the road to a quantum simulator that surpasses the capabilities of classical computers seems, long and difficult, and is an ultimate goal to scientists working in quantum information science.This fellowship proposes a smart route to large-scale quantum simulations that is intrinsically scalable, and can be implemented with manufacturable technologies. The project aims to simulate quantum physical models at a scale that surpasses the capabilities of conventional computers. This is possible because a mapping has been identified between an established model for the quantum vibrational behaviour of molecules, which cannot be simulated with a conventional computer, and the description of photons in manufacturable optical chips. By injecting ensembles of single photons into a versatile optical chip, the evolution of a large molecule can be tracked.The direction of the research is to then make improvements to the molecular mathematical model with a series of perturbations, which, in loose terms, are matched by perturbations to the optical circuits in the form of weak interactions between the photons. The difficulty in getting single photons to strongly interact is the main challenge for optical quantum computers. However, developing successive generations of devices that build up layers of weak interactions allows interesting and complex simulations to be performed on an increasingly tailored and accurate molecular model. As these devices progress, they will develop additional computational capabilities, such as the calculation of factors involved in chemical transitions and characteristic properties of biotic molecules.