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]

常規晶體是一個三維物體，它們的內部原子按照有規則的順序重複排列而構成。時間晶體是一種四維以上晶體，在時空中擁有一種周期性結構。一個時間晶體能自發破壞時間平移的對稱性，做空間的非平移運動，時間晶體的構成以『空間』非定域的粒子交叉存在做相互關聯運動，是能效粒子的『額外維』超出『定域空間』的能動量，時間晶體的存在同樣揭示了『超額外維度』的存在意義。

它可以隨着時間改變，但是會持續回到它開始時的相同形態，就如一個鐘的移動的指針周期性的回到它的原始位置。與普通的鐘或者其他周期性的過程不同的是，時間晶體和空間晶體一樣會是最低限度的能量的一種狀態。可以將它看作是一隻可以永遠保持走時精確無誤的鐘，即便是在宇宙達到熱寂之後也是如此。

主要特點

時間晶體的運動應該不消耗任何能量，相反，它應該處於一種穩定的最小能量狀態，就像鑽石和其他傳統的晶體一樣。即使這樣，它仍然是處於一種永動狀態。
時間晶體並不違背能量守恆定律。通常情況下永動機不會長久，因為它們並不是處於一種基態，它們的能量會隨着運動而消耗，最終能量會消耗殆盡。在時間晶體中，能量是守恆的，因為沒有任何能量被移走。在這些物體中，原子的運動速率並非為零。

設計方法

2012年7月，來自美國加州大學伯克利分校的李統藏博士以及他來自密歇根大學和清華大學的同事們提出了一種新的方案，有可能實現時間晶體的設想。

首先需要一個離子阱，這是一種利用電場來將某一帶電粒子固定在某一位置上的裝置。這樣做將可以讓這些離子形成一個環狀的晶體，這是因為當離子在極低溫度條件下被捕獲時，它們會相互排斥。隨後科學家施加一個微弱的靜磁場，它將驅動電子自旋。

量子力學指出，離子的自旋能量必須大於0，即便是在這個電子環已經被冷凍至最低能級的情況下也是如此。在這種狀態下，已經不需要電場和磁場來幫助維持這一晶體的形狀以及組成它的各個離子的自旋。這樣做的結果就是獲得一個時間晶體，或者更準確的說是一個時空晶體，因為這個離子環不但在時間上，在空間上也是不斷重複着自身。

研究人員從理論上推理認為，這種時間晶體可以被用作計算機，它可以用不同的自旋狀態當做傳統計算法中的0和1。利用該系統方案，這一設想將是可能的^[6]

該方案是基於電場離子阱和粒子之間的庫倫斥力構建的。離子阱的電場將帶電粒子固定住，而庫倫斥力讓它們自發地形成一個空間環狀晶體。在一個微弱的靜態磁場作用下，這一環狀離子晶體將開始永無止境的轉動。由於這一時空晶體已經位於最低量子能態，其時間序列，從理論上說將會永遠持續，即便是當宇宙達到熵的極大值，也就是達到「熱寂」狀態時，情況也是一樣。

製造方法：將10個鐿原子排成一列，然後用兩束激光交替轟擊它們，使得這些原子進入一種穩定且重複的自旋翻轉模式，符合「時間晶體」的定義。另一個來自哈佛大學的研究團隊則通過向鑽石中密集充入氮氣的方式，也製造出了「時間晶體」。

意義

構建一個時空晶體，存在着實際和重要的科學理由：有了這種4維晶體，科學家們將擁有一種全新的，更加有效的手段對複雜的物理屬性和大量粒子的複雜相互作用行為進行研究，或者是研究物理學中所謂的「多體問題」。這種時空晶體同樣可以被用來對量子世界進行研究，如量子糾纏現象，在這種狀態中，當對其中一個粒子進行操作時，另外一個粒子也會相應地發生變化，即便這兩個粒子之間隔開着巨大的距離。

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