1. 主题：PRL：新加坡科学家提出“声子计算机”

目前人们使用的计算机都是使用电子来携带信息，理论上的光子计算机是使用光子。现在，新加坡的物理学家们提出了一种新型的“声子计算机”，将利用声子携带的热来完成各种操作。

新加坡国立大学（NUS）的Baowen Li教授和同事Lei Wang在最新的《物理评论快报》（Physical Review Letters，PRL）上发表文章，论证了怎样制造未来的声子计算机中使用的热逻辑门。逻辑门是计算机中的基本单元。在电子逻辑门中，电压表示输入输出；而在热逻辑门中，温度表示输入输出。

在他们的模型中，使用格振动来管理热。当两个终端的振动谱相重叠，热将能够很容易地在终端中传递，这代表了“开启”状态；当两个终端的振动谱不相重叠，几乎没有热量的传递，代表了“关闭”状态。终端表面粒子之间振动谱的匹配和不匹配产生的“负积分热阻”使这两种状态十分稳定，使热逻辑门成为可能。

他们在文中还论证了怎样把这些热晶体管结合起来制成如信号转发器等各种热逻辑门。信号转发器把热输入转为“是”或“否”的数字化。他们还基于同样的热晶体管模型设计了与门、非门和或门。

尽管这篇文章只是在理论上论证了热逻辑门的可行性，但是Wang和Li相信用纳米技术来实现这个系统并不遥远。因为另一种热装置——固态热整流器——在2006年就已经被发明。

Li说：“我们的声子计算机的优点是无需消耗大量的电能。我们可以使用大自然或者其它电器中的冗余热量来驱动它。”

作者： fishwoodok 2007-11-06 17:28:13 引用此发言

2. 回复：PRL：新加坡科学家提出“声子计算机”

'Phononic Computer' Could Process Information with Heat

By Lisa Zyga

A thermal transistor controls heat flow. Heat passes between terminals S and D for the “on” state, and little or no heat passes between S and D for the “off” state. G is the control terminal. Image credit: Wang and Li.

Most computers today use electrons to carry information, while theoretical optical computers use photons. Recently, physicists from Singapore have proposed a third type of computer: a “phononic computer,” which would use heat, carried by phonons, to perform operations similar to its electronic counterpart.

“Heat is very abundant and very often it is regarded as useless and harmful for information processing,” Professor Baowen Li of the National University of Singapore told PhysOrg.com. “The merit of our paper is that we demonstrate that, in addition to the existing electrons and photons, the phonons can also perform a similar function. This provides an alternative way for information processing. Moreover, the heat can be harnessed to use.”

Li and co-author Lei Wang from the NUS have demonstrated how to make thermal logic gates for possible use in future phononic computers, with their results published in a recent issue of Physical Review Letters.

Logic gates, one of the basic elements of computers, perform an operation on one or more logic inputs to produce a single logic output. In electronic logic gates, the inputs and outputs are represented by different voltages. However, in a thermal logic gate, the inputs and outputs are represented by different temperatures.

The key element of the logic gate is the thermal transistor (which was invented by Li’s group last year), which works similar to how a field-effect transistor controls electric current. The thermal transistor is composed of two terminals that are weakly coupled, plus a third control terminal.

“Like all other theoretical modeling, we use heat bath to produce heat, which is a kind of random atomic or molecular motion,” Li explained. “To conduct heat, you don't need too much external power. Any temperature difference will lead to heat conduction.”

In the researchers’ model, heat is conducted by lattice vibration. When the vibration spectra of the two terminals are combined, their overlap determines the heat current. For example, when the two spectra overlap, the heat can easily travel between the terminals, representing the “on” state. When the vibration spectra do not overlap, very little heat (or no heat) passes through, representing the “off” state. The “negative differential thermal resistance” (NDTR) that occurs due to the match/mismatch of vibrational spectra of the terminals’ interface particles, makes the “on” and “off” states both stable, making the thermal logic operations possible.

“Like we explain in our Physical Review Letters article, all these logic gate functions can be achieved only when the system has the so-called negative or super response, by which we mean that the large temperature difference (change) will induce the small heat current,” Li said. “This is the so-called ‘negative differential thermal resistance.’” The NDTR phenomenon was also discovered by Li’s group in 2006.

The researchers demonstrate how combining thermal transistors can be used to build different thermal logic gates, such as a signal repeater. A signal repeater “digitizes” the heat input, so that when the temperature is higher or lower than a critical value, the output is either “on” or “off,” but not in between. By connecting a few thermal transistors in series, the researchers achieved a nearly ideal repeater. Besides signal repeaters, they also demonstrated a NOT gate, which reverses the input signal, and an AND/OR gate, made from the same thermal transistor model.

While the current model simply shows the feasibility of thermal logic gates, Wang and Li predict that an experimental realization of the devices in nanoscale systems may not be too far off. They point out that another thermal device, the solid-state thermal rectifier, was experimentally demonstrated in 2006, just a few years after the proposed theoretical model.

“One advantage of a phononic computer might be that we don't need to consume a lot of electricity,” Li said. “We may use the redundant heat produced by electronic devices or provided by Mother Nature to do useful work. Another advantage is that, one day, human beings can control and use heat wisely so that we may save a lot of energy—which is a big issue nowadays.”

作者： fishwoodok 2007-11-06 17:33:18 引用此发言

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1. 主题：PRL：新加坡科学家提出“声子计算机”

2. 回复：PRL：新加坡科学家提出“声子计算机”

'Phononic Computer' Could Process Information with Heat