Google quantum computer creates a time crystal: the emergence of a "perpetual motion machine" that jumps out of the second law of thermodynamics?

来自全他马嗪

From quantamagazine

作者：Natalie wolchover

Author: Natalie wolchover

机器心脏编译

Machine heart compilation

机器心脏编辑部

Machine heart editorial department

人们一直认为物理学中不可能有"时间晶体"这样奇怪的相位，但现在这一事实已经摆在我们面前。

It has always been thought that there can be no such strange phase as "time crystal" in physics, but now the fact has been put in front of us.

就像人们想象中的永动机一样，时间晶体在状态之间永久循环而不消耗能量。物理学家声称已经在量子计算机中构建了这个新阶段。这可能是近几十年来最重要的物理发现。

Like the perpetual motion machine in people's imagination, the time crystal circulates permanently between states without consuming energy. Physicists claim to have constructed this new phase in quantum computers. This may be the most significant physical discovery in recent decades.

作为物理学家们多年来一直试图实现的一个新的物质阶段，时间晶体是一个相位，其中一些部分定期反复地来回移动，并在不消耗任何能量的情况下保持这种变化。

As a new material stage that physicists have been trying to achieve for many years, time crystal is a phase, some parts of which move back and forth regularly and repeatedly, and maintain this change without consuming any energy.

"这是一个惊人的结果：它打破了热力学第二定律（孤立系统的自发熵增加），"德国德累斯顿马克斯·普朗克复杂系统物理研究所所长、谷歌论文合著者罗德里克·默斯纳（Roderich Moessner）说。

"This is an amazing result: it breaks out of the second law of thermodynamics (spontaneous entropy increase of isolated systems)," said Roderich Moessner, director of Max Planck Institute for complex system physics in Dresden, Germany and co-author of Google paper.

时间晶体也是第一个打破"时间平移对称性"的物体。该规则指的是一个稳定对象在很长时间内保持不变的传统规则。时间晶体是稳定的、不断变化的，在特定时间呈现周期性。

The time crystal is also the first object to break the "time translation symmetry" by itself. This rule refers to the traditional rule that a stable object remains unchanged for a very long time. The time crystal is stable and constantly changing, showing periodicity at special times.

时间晶体是一个新的相位范畴，它扩展了相位的定义。所有其他已知相，如水或冰，都处于热平衡状态：这些物质的原子处于环境温度允许的最低能量状态，其性质不随时间变化。时间晶体是第一个"不平衡"相：即使在激发态和演化态，它仍然有秩序和完美的稳定性。

Time crystal is a new category of phase, which expands the definition of phase. All other known phases, such as water or ice, are in thermal equilibrium: the atoms of these substances are in the lowest energy state allowed by the ambient temperature, and their properties do not change with time. The time crystal is the first "unbalanced" phase: even in the excited and evolved States, it still has order and perfect stability.

"我们正在研究的是一个新的、令人兴奋的领域，"斯坦福大学的凝聚物物理学家维迪卡.克哈尼说。她在研究生学习期间与他人合作发现了这一新阶段，最近与谷歌合作撰写了一篇新论文。

"What we are studying is a new and exciting field," said vedika khemani, a condensed matter physicist at Stanford University. She discovered this new phase in collaboration with others during her graduate study, and recently co authored a new paper with Google.

普林斯顿的Khemani、Moessner、Shivaji Sondhi和英国拉夫堡大学的Achilleas lazarides发现了新阶段的可能性，并在2015描述了他们的主要特征。不久之后，微软站Q的Chetan Nayak和加利福尼亚大学领导的一组物理学家，圣巴巴拉把它定义为时间水晶。

Khemani, Moessner, Shivaji Sondhi of Princeton and Achilleas lazarides of Loughborough University in the UK discovered the possibility of new phases and described their key characteristics in 2015. Soon after, Chetan Nayak of Microsoft station Q and a group of physicists led by the University of California, Santa Barbara defined it as a time crystal.

在过去的五年里，科学家们争相寻找时间晶体，但尽管根据研究人员设定的条件，以前的一些研究已经取得了成功，但它们未能满足确定时间晶体存在的所有标准。"我们完全有理由相信，这些实验并没有完全成功。谷歌等量子计算系统具备完成更令人信服的实验的条件。"牛津大学的凝聚物质物理学家John Chalker说。

In the past five years, scientists have scrambled to find time crystals, but although some previous studies have been successful according to the conditions set by researchers, they have failed to meet all the criteria required to determine the existence of time crystals. " We have every reason to believe that these experiments have not been completely successful. Quantum computing systems such as Google have the conditions to complete more convincing experiments. " Said John Chalker, a condensed matter physicist at Oxford University.

谷歌的量子计算团队在2019年首次实现了量子优势，并因其超越传统计算机的能力出现在《自然》杂志的封面上。然而，当时展示的算法是为速度目标设计的，不具有基础科学探索的意义。对时间晶体的新研究标志着量子计算机首次站在前人无法匹敌的高度。

Google's quantum computing team realized quantum superiority for the first time in 2019 and appeared on the cover of nature because of its ability to surpass conventional computers. However, the algorithm displayed at that time was designed for the speed goal and did not have the significance of basic scientific exploration. The new study of time crystals marks the first time that quantum computers have stood at a height unmatched by predecessors.

"这就是谷歌量子处理器的魅力所在，"纳亚克说。

"That's the beauty of Google's quantum processor," Nayak said.

时间晶体的最初概念有一个致命的缺陷。

The original concept of time crystal has a fatal defect.

这一概念是由诺贝尔物理学奖获得者弗兰克·威尔切克（Frank Wilczek）于2012年在一个普通（空间）晶体班上提出的。弗兰克·威尔切克（Frank Wilczek）告诉《量子杂志》（quantum magazine），他说："如果你想到空间中的晶体，你自然会想到时间中晶体行为的分类。"。

This concept was proposed by Frank Wilczek, a Nobel Laureate in physics, in an ordinary (space) crystal class in 2012. " If you think about crystals in space, you naturally think about the classification of crystal behavior in time, "Frank Wilczek told quantum magazine.

例如，钻石是由碳原子形成的晶相。在空间中，这个原子团在任何地方都由相同的方程控制，但其形式具有周期性的空间变化，并且原子位于晶格点上。物理学家说它"自发地破坏了空间的平移对称性"。只有能量最小的平衡态才能以这种方式自发打破空间对称性。

Diamond, for example, is a crystalline phase formed by carbon atoms. In space, this atomic cluster is governed by the same equation everywhere, but its form has periodic spatial changes, and the atoms are located at the lattice points. Physicists say it "spontaneously breaks the translational symmetry of space". Only the equilibrium state with the smallest energy can spontaneously break the spatial symmetry in this way.

威尔切克设想了一个平衡的多部分物体，很像钻石。但这个物体打破了时间平移的对称性：它经历了周期性运动，并以固定的间隔恢复到原始形状。

Wilczek envisioned a multipart object in equilibrium, much like diamond. But this object breaks the symmetry of time translation: it experiences periodic motion and returns to its original shape at regular intervals.

威尔切克的时间水晶与挂钟大不相同。挂钟也会经历周期性的运动，但它的指针会消耗能量，当能量耗尽时会停止行走。相比之下，wilczekian时间晶体不需要输入，但可以始终保持周期运动，因为系统处于超稳定平衡状态。

Wilczek's time crystal is quite different from a wall clock. The wall clock also experiences periodic movement, but its pointer consumes energy and stops walking when the energy is exhausted. In contrast, wilczekian time crystal does not need input, but can always maintain periodic motion, because the system is in a super stable equilibrium state.

这听起来不可思议，在物理学领域引起了极大的争议。2014，加利福尼亚大学、伯克利和其他机构的研究人员发表了一篇论文，指出Wilczek的想法是行不通的，就像以前所有关于永动机的想法一样。

This sounds incredible and has caused great controversy in the field of physics. In 2014, researchers from the University of California, Berkeley and other institutions published a paper indicating that Wilczek's idea is unworkable, just like all previous ideas about perpetual motion machines.

"35770;"38142;"255091?https://arxiv.org/pdf/1508.03344v1.pdf

"35770;" 38142;"255091; https://arxiv.org/pdf/1508.03344v1.pdf

然而，在预印本的出版和上述论文的官方版本之间有一段插曲：由Wilczek带来的研究生Nayak，他的合著者多米尼克·埃尔斯（Dominic else）和贝拉·鲍尔（Bela Bauer）于2016年3月发表了一篇预印本论文。他们以khemani等人提出的PI自旋玻璃相为例，证明了弗洛凯时间晶体物体的存在。

However, there was an episode between the publication of the preprint and the official version of the above paper: Nayak, a graduate student brought by Wilczek, and his co authors Dominic else and Bela Bauer published a preprint paper in March 2016. They took the PI spin glass phase proposed by khemani et al. As an example to show the existence of Floquet time crystal objects.

"35770;"38142;"255091?https://arxiv.org/pdf/1603.08001.pdf

"35770;" 38142;"255091; https://arxiv.org/pdf/1603.08001.pdf

Floquet时间晶体表现出Wilczek设想的行为，但这只能在外部能源周期性驱动下发生。这一次晶体绕过了威尔切克最初想法的缺陷，因为它从未声称处于热平衡状态。由于它是一个多体局部化系统，其自旋或其他部分无法达到平衡；他们被困在原地。但是，尽管有激光器或其他驱动器，系统仍不会加热。相反，它在局域态之间无限循环。

The Floquet time crystal exhibits the behavior envisaged by Wilczek, but this can only occur when it is periodically driven by an external energy source. This time crystal bypasses the defects of Wilczek's original idea because it never claims to be in thermal equilibrium. Because it is a multi-body localized system, its spin or other parts cannot reach equilibrium; They're stuck where they are. But despite the laser or other drive, the system will not heat up. Instead, it loops back and forth infinitely between localized states.

激光打破了一排自旋之间的对称性，取而代之的是"离散时间平移对称性"。也就是说，相同的条件只存在于激光的每个周期之后。由于激光的多次旋转，它自身的平移对称性被进一步破坏。

The laser has broken the symmetry between a row of spins at all times and replaced it with "discrete-time translational symmetry". That is, the same conditions exist only after each cycle of the laser. But then, by flipping back and forth, this row of spins further breaks the discrete-time translational symmetry imposed by the laser, because its own periodic cycle is a multiple of the laser.

Khemani和她的合著者详细描述了这个阶段，但Nayak的团队用时间、对称性和自发对称破缺来描述它，这是物理学的基本概念。除了这些更吸引人的术语外，它们还提供了一个新的理解角度，并将Floquet时间晶体的概念扩展到PI自旋玻璃相之外（指出它不需要某些对称性）。Nayak等人的研究发表在2016年8月的《物理评论快报》上，比khemani等人关于新阶段第一例的论文晚了两个月。

Khemani and her co-authors described this phase in detail, but Nayak's team described it in terms of time, symmetry and spontaneous symmetry breaking, which are the basic concepts of physics. In addition to these more attractive terms, they also provide a new understanding angle and extend the concept of Floquet time crystal beyond PI spin glass phase (pointing out that some symmetry it has is unnecessary). Nayak et al's research was published in Physical Review Letters in August 2016, two months later than khemani et al's paper on the first example of the new phase.

两个研究小组都声称是这个想法的最初支持者。从那时起，他们和其他研究人员开始在现实世界中竞争制造时间晶体。

Both research teams claim to be the original proponents of the idea. Since then, they and other researchers began to compete to create time crystals in the real world.

完美平台

Perfect platform

Nayak的团队与马里兰大学的Chris Monroe合作，他们利用电磁场来捕捉和控制离子。上个月，研究小组在《科学》杂志上发表了一篇文章，声称他们已经将捕获的离子转化为近似或"预热"的时间晶体。它的周期性变化（在本文中，离子在两种状态之间跳跃）实际上与实时晶体无法区分。但与钻石不同的是，这种预热时间的水晶不是永恒的。如果实验运行足够长的时间，系统将逐渐平衡，周期性行为将崩溃。

Nayak's team works with Chris Monroe of the University of Maryland, who uses electromagnetic fields to capture and control ions. Last month, the research team published an article in science, claiming that they have transformed the captured ions into approximate or "prehrmal" time crystals. Its periodic changes (in this paper, ions jump between two states) are actually indistinguishable from real time crystals. But unlike diamond, this preheating time crystal is not eternal. If the experiment runs long enough, the system will gradually balance and the periodic behavior will collapse.

与此同时，sycamore开发人员也在寻找与他们的机器相关的东西，这台机器太容易出错，无法运行专门为成熟量子计算机设计的加密和搜索算法。当khemani和他的同事联系谷歌的理论研究员Kostya kechedzhi时，他和他的团队很快同意在时间晶体项目上进行合作。Kechedzhi说："我们的工作不仅是离散时间晶体，还包括一些其他项目，包括使用我们的量子计算机研究新的物理或一些化学问题。"

At the same time, sycamore developers are also looking for something related to their machine, which is too error prone to run cryptography and search algorithms specially designed for mature quantum computers. When khemani and his colleagues contacted Kostya kechedzhi, a theoretical researcher at Google, he and his team quickly agreed to cooperate on the time crystal project. Kechedzhi said, "our work is not only discrete-time crystals, but also some other projects, including using our quantum computer to study new physics or some chemical problems."

量子计算机不是下一代超级计算机——它们是完全不同的东西。在我们开始讨论它们的潜在应用之前，我们需要了解驱动量子计算理论的基本物理。

Quantum computers are not the next generation of supercomputers -- they are completely different things. Before we begin to talk about their potential applications, we need to understand the basic physics that drives quantum computing theory.

量子计算机由"量子位"组成。量子位本质上是可控的量子粒子。每个粒子可以同时维持两种可能的状态，标记为0和1。当量子比特相互作用时，它们可以同时处理指数可能性，从而实现计算优势。

Quantum computer consists of "qubits". Qubits are essentially controllable quantum particles. Each particle can maintain two possible states at the same time, marked as 0 and 1. When qubits interact, they can deal with exponential possibilities at the same time, so as to realize the computational advantage.

谷歌的量子位由超导铝条组成。每个都有两种可能的能量状态，可以编程来表示上自旋或下自旋。Kechedzhi和其他研究人员在演示中使用了一个20量子位的芯片作为时间晶体。

Google's qubits consist of superconducting aluminum bars. Each has two possible energy states that can be programmed to represent up or down spin. Kechedzhi and other researchers used a chip with 20 qubits as a time crystal in the demo.

与竞争对手相比，这台机器的主要优势可能在于它可以调整其量子比特之间的相互作用强度。这种可调性是系统成为时间晶体的关键：程序员可以随机化量子比特的相互作用强度。这种随机性会在它们之间产生相消干扰，从而使自旋行实现多体定位。量子位可以锁定一组方向图案，而不是对齐。

Perhaps the main advantage of the machine over its competitors is that it can adjust the interaction strength between its qubits. This tunability is the key to the system becoming a time crystal: programmers can randomize the interaction intensity of qubits. This randomness produces destructive interference between them, which makes the rows of spins realize multi-body localization. Qubits can lock a set of directional patterns instead of alignment.

研究人员为自旋设置了任何初始配置，如向上、向下、向下、向上等。指向上的自旋可以通过微波来降低，反之亦然。通过对每个初始构型进行数万次演示，并在每次运行的不同时间测量量子位的状态，研究人员可以观察到自旋系统在两个多体局域态之间来回翻转。

The researchers set any initial configuration for the spin, such as up, down, down, up, etc. The spin pointing up can be turned down by microwave, and vice versa. By running tens of thousands of demonstrations for each initial configuration and measuring the state of qubits at different times during each run, researchers can observe that the spin system flips back and forth between two multi-body localized states.

这一新阶段的特点是极端稳定。即使温度波动，冰仍然是冰。事实上，研究人员发现，微波脉冲只需将自旋翻转180度左右，这并不一定如此精确，因为两次脉冲后，自旋将恢复到其精确的初始方向，就像船本身变直一样。此外，自旋从不吸收或耗散微波激光的净能量，系统的无序度保持不变。

This new phase is marked by extreme stability. Even if the temperature fluctuates, ice is still ice. In fact, the researchers found that the microwave pulse only needs to flip the spin about 180 degrees, which is not necessarily so accurate, because the spin will return to their exact initial direction after two pulses, just like the boat straightening itself. In addition, the spin never absorbs or dissipates the net energy from the microwave laser, and the disorder of the system remains unchanged.

7月5日，荷兰代尔夫特理工大学的一个研究小组报告说，他们利用金刚石中碳原子的核自旋而不是量子处理器来构造Floquet时间晶体。该系统比Google quantum处理器中实现的时间晶体更小、更有限。

On July 5, a research team from Delft University of technology in the Netherlands reported that they constructed Floquet time crystal by using the nuclear spin of carbon atoms in diamond instead of quantum processor. This system is smaller and more limited than the time crystal implemented in Google quantum processor.

目前尚不清楚Floquet时间晶体是否有实际用途。但对默斯纳来说，其稳定性似乎很有希望。"像这样稳定的东西是不寻常的，特殊的东西往往会变得非常有用，"Moessner说。

It is unclear whether the Floquet time crystal has practical use. But its stability seems promising for Moessner. " Stable things like this are unusual, and special things can often become very useful, "Moessner said.

也许这种状态只在概念上有用。这是第一个也是最简单的非平衡相的例子，但研究人员怀疑，更多的非平衡相在物理上是可能的。

Perhaps this state is only conceptually useful. This is the first and simplest example of a nonequilibrium phase, but the researchers suspect that more such phases are physically possible.

纳亚克认为，时间水晶揭示了时间本质的深刻意义。"通常在物理学中，无论你多么努力地把时间看作另一个维度，它总是一个异常值，"他说

Nayak believes that the time crystal reveals the profound significance of the essence of time. "Usually in physics, no matter how hard you try to think of time as another dimension, it is always an outlier," he said

在统一方面，爱因斯坦做了最好的尝试。他将三维空间和时间编织成一个四维结构：时空。但即使在他的理论中，单向时间也是独一无二的。纳亚克说，在发现了时间晶体之后，"时间突然变成了一个普通的维度。"。

In terms of unification, Einstein made the best attempt. He woven 3D space and time into a four-dimensional structure: space-time. But even in his theory, one-way time is unique. After discovering the time crystal, "time suddenly became an ordinary dimension," Nayak said.

然而，Chacker认为时间仍然是一个异常值。他说，威尔切克的时间水晶将是时间和空间的真正统一体。太空晶体处于平衡状态。因此，它们打破了连续的空间平移对称性。在时间的情况下，只有离散时间的平移对称性可能被时间晶体打破，这为时间和空间的差异提供了一个新的角度。

However, Chalker believes that time is still an outlier. He said that Wilczek's time crystal would have been the real unity of time and space. Space crystals are in equilibrium. Accordingly, they break the continuous spatial translational symmetry. In the case of time, only the discrete time translation symmetry may be broken by the time crystal, which provides a new angle for the difference between time and space.

这些科学讨论将继续探索量子计算机的无限可能性。凝聚态物理学家过去常常关注自然界的各个阶段。现在Chacker说，"是时候把研究重点从大自然赋予我们的东西转移到想象量子力学允许的奇怪物质形式了。"

These scientific discussions will continue with the exploration of the infinite possibilities of quantum computers. Condensed matter physicists used to pay attention to various phases of nature. Now Chalker said, "it's time to shift the research focus from what nature gives us to imagining strange forms of matter allowed by quantum mechanics."

结局

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update time：2021-07-31 17:18:08