時間晶體

時間晶體（英語：time crystal）乃一開放系統，其與周圍環境保持非平衡態，呈現時間平移對稱破缺（英語：time translation symmetry breaking）的特性。2017年3月的科學報導指出，此一理論概念已在實驗上獲得證實；隨著時間演進，時間晶體仍無法與環境達到熱平衡。^[1]^[2]

時間晶體的概念首先由諾貝爾物理學獎得主弗朗克·韋爾切克於2012年提出。相對於尋常晶體在空間上呈週期性重複，時間晶體則在時間上呈週期性重複而呈現永動狀態。時間晶體在時間平移對稱上具有自發對稱破缺現象。時間晶體也與零點能量和動態卡西米爾效應有關。

2016年，姚穎（英語：Norman Y. Yao）與加州大學柏克萊分校物理系的同僚提出在實驗室建構時間晶體的藍圖^[3]；隨後此藍圖經兩組人馬採用，包括馬里蘭大學的Christopher Monroe以及哈佛大學的Mikhail Lukin，兩團隊皆成功創造出時間晶體，實驗成果於2017年3月發表在《自然》期刊。^[4]^[5]

常规晶体是一个三维物体，它们的内部原子按照有规则的顺序重复排列而构成。时间晶体是一种四维以上晶体，在时空中拥有一种周期性结构。一个时间晶体能自发破坏时间平移的对称性，做空间的非平移运动，时间晶体的构成以‘空间’非定域的粒子交叉存在做相互关联运动，是能效粒子的‘额外维’超出‘定域空间’的能动量，时间晶体的存在同样揭示了‘超额外维度’的存在意义。

它可以随着时间改变，但是会持续回到它开始时的相同形态，就如一个钟的移动的指针周期性的回到它的原始位置。与普通的钟或者其他周期性的过程不同的是，时间晶体和空间晶体一样会是最低限度的能量的一种状态。可以将它看作是一只可以永远保持走时精确无误的钟，即便是在宇宙达到热寂之后也是如此。

主要特点

时间晶体的运动应该不消耗任何能量，相反，它应该处于一种稳定的最小能量状态，就像钻石和其他传统的晶体一样。即使这样，它仍然是处于一种永动状态。
时间晶体并不违背能量守恒定律。通常情况下永动机不会长久，因为它们并不是处于一种基态，它们的能量会随着运动而消耗，最终能量会消耗殆尽。在时间晶体中，能量是守恒的，因为没有任何能量被移走。在这些物体中，原子的运动速率并非为零。

设计方法

2012年7月，来自美国加州大学伯克利分校的李统藏博士以及他来自密歇根大学和清华大学的同事们提出了一种新的方案，有可能实现时间晶体的设想。

首先需要一个离子阱，这是一种利用电场来将某一带电粒子固定在某一位置上的装置。这样做将可以让这些离子形成一个环状的晶体，这是因为当离子在极低温度条件下被捕获时，它们会相互排斥。随后科学家施加一个微弱的静磁场，它将驱动电子自旋。

量子力学指出，离子的自旋能量必须大于0，即便是在这个电子环已经被冷冻至最低能级的情况下也是如此。在这种状态下，已经不需要电场和磁场来帮助维持这一晶体的形状以及组成它的各个离子的自旋。这样做的结果就是获得一个时间晶体，或者更准确的说是一个时空晶体，因为这个离子环不但在时间上，在空间上也是不断重复着自身。

研究人员从理论上推理认为，这种时间晶体可以被用作计算机，它可以用不同的自旋状态当做传统计算法中的0和1。利用该系统方案，这一设想将是可能的^[6]

该方案是基于电场离子阱和粒子之间的库伦斥力构建的。离子阱的电场将带电粒子固定住，而库伦斥力让它们自发地形成一个空间环状晶体。在一个微弱的静态磁场作用下，这一环状离子晶体将开始永无止境的转动。由于这一时空晶体已经位于最低量子能态，其时间序列，从理论上说将会永远持续，即便是当宇宙达到熵的极大值，也就是达到“热寂”状态时，情况也是一样。

制造方法：将10个镱原子排成一列，然后用两束激光交替轰击它们，使得这些原子进入一种稳定且重复的自旋翻转模式，符合“时间晶体”的定义。另一个来自哈佛大学的研究团队则通过向钻石中密集充入氮气的方式，也制造出了“时间晶体”。

意义

构建一个时空晶体，存在着实际和重要的科学理由：有了这种4维晶体，科学家们将拥有一种全新的，更加有效的手段对复杂的物理属性和大量粒子的复杂相互作用行为进行研究，或者是研究物理学中所谓的“多体问题”。这种时空晶体同样可以被用来对量子世界进行研究，如量子纠缠现象，在这种状态中，当对其中一个粒子进行操作时，另外一个粒子也会相应地发生变化，即便这两个粒子之间隔开着巨大的距离。

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