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物质的新阶段打开了通往额外时间维度的门户

New Phase of Matter Opens Portal to Extra Time Dimension

When the ancient Incas wanted to archive tax and census records, they used a device made up of a number of strings called a quipu, which encoded the data in knots. Fast-forward several hundred years, and physicists are on their way to developing a far more sophisticated modern equivalent. Their “quipu” is a new phase of matter created within a quantum computer, their strings are atoms, and the knots are generated by patterns of laser pulses that effectively open up a second dimension of time.

当古印加人想要存档税收和人口普查记录时,他们使用了一种由许多字符串组成的设备,称为基普(一种结绳文字),将数据编码成结。快进几百年,物理学家正在开发一种更复杂的现代等效物。他们的“基普”是量子计算机中产生的一种新的物质相,他们的弦是原子,结是由激光脉冲模式产生的,有效地打开了时间的第二维度。

This isn’t quite as incomprehensible as it first appears. The new phase is one of many within a family of so-called topological phases, which were first identified in the 1980s. These materials display order not on the basis of how their constituents are arranged—like the regular spacing of atoms in a crystal—but on their dynamic motions and interactions. Creating a new topological phase—that is, a new “phase of matter”—is as simple as applying novel combinations of electromagnetic fields and laser pulses to bring order or “symmetry” to the motions and states of a substance’s atoms. Such symmetries can exist in time rather than space, for example in induced repetitive motions. Time symmetries can be difficult to see directly but can be revealed mathematically by imagining the real-world material as a lower-dimensional projection from a hypothetical higher-dimensional space, similar to how a two-dimensional hologram is a lower-dimensional projection of a three-dimensional object. In the case of this newly created phase, which manifests in a strand of ions (electrically charged atoms), its symmetries can be discerned by considering it as a material that exists in higher-dimensional reality with two time dimensions.

这并不像最初看起来的那样难以理解。新阶段是在20世纪80年代首次确定的所谓拓扑阶段家族中的许多阶段之一。这些材料显示的顺序不是基于它们的成分如何排列,就像晶体中原子的规则间距,而是基于它们的动态运动和相互作用。创建一个新的拓扑相位,即新的“物质相位”-非常简单,只需应用电磁场和激光脉冲的新组合,使物质原子的运动和状态有序或“对称”。这种对称性可以存在于时间而不是空间中,例如在诱导的重复运动中。时间对称性可能很难直接看到,但可以通过将现实世界的材料想象为来自假想的高维空间的低维投影来从数学上揭示,类似于二维全息图是三维物体的低维投射。在这个新创建的相的情况下,它表现为一股离子(带电原子),其对称性可以通过将其视为存在于具有两个时间维度的高维现实中的材料来辨别。

“It is very exciting to see this unusual phase of matter realized in an actual experiment, especially because the mathematical description is based on a theoretical ‘extra’ time dimension,” says team member Philipp Dumitrescu, who was at the Flatiron Institute in New York City when the experiments were carried out. A paper describing the work was published in Nature on July 20.

“看到在实际实验中实现了这一不寻常的物质阶段非常令人兴奋,特别是因为数学描述是基于理论上的‘额外’时间维度,”团队成员菲利普·杜米特雷斯库说,他在实验进行时在纽约市的扁平铁研究所。描述这项工作的论文于7月20日发表在《自然》杂志上。

Opening a portal to an extra time dimension—even just a theoretical one—sounds thrilling, but it was not the physicists’ original plan. “We were very much motivated to see what new types of phases could be created,” says study co-author Andrew Potter, a quantum physicist at the University of British Columbia. Only after envisioning their proposed new phase did the team members realize it could help protect data being processed in quantum computers from errors.

打开一个通往额外时间维度的入口,即使只是一个理论维度,听起来也令人激动,但这不是物理学家最初的计划。“我们非常积极地想看看能创造出什么样的新相,”研究报告的合著者、不列颠哥伦比亚大学的量子物理学家安德鲁·波特说。只有在设想了他们提出的新阶段后,团队成员才意识到它有助于保护量子计算机中处理的数据免受错误。

Standard classical computers encode information as strings of bits—0’s or 1’s—while the predicted power of quantum computers derives from the ability of quantum bits, or qubits, to store values of either 0 or 1, or both simultaneously (think Schrödinger’s cat, which can be both dead and alive). Most quantum computers encode information in the state of each qubit, for instance in an internal quantum property of a particle called spin, which can point up or down, corresponding to a 0 or 1, or both at the same time. But any noise—a stray magnetic field, say—could wreak havoc on a carefully prepared system by flipping spins willy-nilly and even destroying quantum effects entirely, thereby halting calculations.

标准的经典计算机将信息编码为比特串-0或1,而量子计算机的预测能力来自于量子比特或量子位同时存储0或1的值的能力(想想薛定谔的猫,它可能是死的也可能是活的)。大多数量子计算机以每个量子位的状态对信息进行编码,例如,在一种称为自旋的粒子的内部量子属性中,自旋可以指向上或向下,对应于0或1,或同时指向两者。但是,任何噪音,比如说杂散磁场,都可能通过任意翻转自旋,甚至完全破坏量子效应,从而停止计算,对精心准备的系统造成严重破坏。

Potter likens this vulnerability to conveying a message using pieces of string, with each string arranged in the shape of an individual letter and laid out on the floor. “You could read it fine until a small breeze comes along and blows a letter away,” he says. To create the more error-proof quantum material, Potter’s team looked to topological phases. In a quantum computer that exploits topology, information is not encoded locally in the state of each qubit but is woven across the material globally. “It’s like a knot that’s hard to undo—like quipu,” the Incas’ mechanism for storing census and other data, Potter says.

波特将这种漏洞比喻为使用字符串传递信息,每个字符串都以单个字母的形式排列在地板上。“你可以读得很好,直到一阵微风吹来,把一封信吹走,”他说。为了创造更具防错性的量子材料,波特的团队研究了拓扑相位。在利用拓扑结构的量子计算机中,信息不是在每个量子位的状态中进行局部编码,而是在材料中全局编织。波特说:“这就像是一个难以解开的结,就像基普-印加人存储人口普查和其他数据的机制一样。”

“Topological phases are intriguing because they offer a way to protect against errors that’s built into the material,” adds study co-author Justin Bohnet, a quantum physicist at the company Quantinuum in Broomfield, Colo., where the experiments were carried out. “This is different to traditional error-correcting protocols, where you are constantly doing measurements on a small piece of the system to check if errors are there and then going in and correcting them.”

“拓扑相位很有趣,因为它们提供了一种防止材料中固有错误的方法,”研究合作者贾斯汀·博内特补充道,他是科罗拉多州布鲁姆菲尔德Quantinum公司的量子物理学家,实验是在该公司进行的。“这不同于传统的纠错协议,在传统纠错协议中,您不断地对系统的一小部分进行测量,以检查是否存在错误,然后进入并纠正错误。”

Quantinuum’s H1 quantum processor is made up of a strand of 10 qubits—10 ytterbium ions—in a vacuum chamber, with lasers tightly controlling their positions and states. Such an “ion trap” is a standard technique used by physicists to manipulate ions. In their first attempt to create a topological phase that would be stable against errors, Potter, Dumitrescu and their colleagues sought to imbue the processor with a simple time symmetry by imparting periodic kicks to the ions—all lined up in one dimension—with regularly repeating laser pulses. “Our back-of-the-envelope calculations suggested this would protect [the quantum processor] from errors,” Potter says. This is similar to how a steady drumbeat can keep multiple dancers in rhythm.

Quantinum的H1量子处理器由真空室中的10个量子位-10个镱离子组成,激光器严格控制它们的位置和状态。这种“离子阱”是物理学家用来操纵离子的标准技术。波特、杜米特雷斯库和他们的同事首次尝试创建一个能够稳定地防止错误的拓扑相位,他们试图通过向一维排列的离子施加周期性的脉冲,使处理器具有简单的时间对称性。波特说:“我们的幕后计算表明,这将保护(量子处理器)免受错误的影响。”。这类似于一个稳定的鼓声如何保持多个舞者的节奏。

Read more at Scientificamerican.com

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