科技前沿:關於量子計算機的真相

At the Collider exhibition in London’s Science Museum there is a mock-up of an office corridor at Cern, the huge Geneva laboratory where the Higgs boson was unmasked. A poster on a door, featuring the photograph of a cat, proclaims: “Lost cat”. Then, underneath: “Please return dead and alive to Erwin Schrödinger.”

倫敦科學博物館(Science Museum)的對撞機展上有條走廊，是根據歐洲核子研究中心（Cern，位於日內瓦的一座大型實驗室，曾發現希格斯玻色子）一條辦公室走廊的原樣複製過來的。走廊裏有扇門上貼着一張海報，醒目地印了一隻貓的照片，上書“尋貓啓事”。這幾個字下面寫着：“請將這隻既死又活的貓還給埃爾溫•薛定諤(Erwin Schrödinger)。”

The cat – a feline in a locked box that is both dead and alive until the box is opened – was a thought experiment devised by physicist Schrödinger to expose the counterintuitive weirdness of quantum theory. The theory posits that an entity can exist simultaneously in any number of states until the point at which it is observed, whereupon it will “collapse” into one state – either purring or deceased in the case of the trapped tabby, which is incarcerated with a poison that either has or has not been released through radioactive decay.

“薛定諤貓”（一隻關在箱子裏的既死又活的貓，只有打開箱子才能知道它的死活）是物理學家薛定諤設計的一個思想實驗，用來展示量子力學那有違直覺的怪誕。該理論假設，一個實體可同時處於多種狀態，直到它被觀測到的那一刻爲止，因爲那時它會“坍縮”成明確態——就那隻被囚禁的花貓而言，就是要麼它還在哪兒打呼嚕，要麼已成一具貓的屍體：關貓的箱子裏放有一隻毒氣瓶，裏面的毒氣或者未被或者已被基於放射性衰變機制的觸發器釋放出來。

Geniuses have spotted that tapping into the quantum realm could release fantastic amounts of computing power. Where a classical bit must be either 0 or 1, a quantum bit, called a qubit, can be 0 or 1 – or, crucially, a mixture of both. Freed of this “either-or” constraint, even a modest quantum computer would vastly outpace the fastest supercomputer. Cracking the world’s toughest encryption software, which would take a supercomputer about 1m years, would be an hour’s work.

天才們已經發現，進軍量子領域能釋放出極其龐大的計算能力。一個二進制位(bit)上的數字非“0”即“1”；而一個量子位(qubit)上的數字可是“0”可是“1”——關鍵的來了，還可既是“0”又是“1”。擺脫了這種“非此即彼”的限制後，即便是一臺一般般的量子計算機也能完爆最快的超級計算機。破解全世界最強的加密軟件，超級計算機需要約100萬年，量子計算機只需要一個小時。

Google and Nasa have jointly forked out a reported $10m on a prototype quantum computer from D-Wave Systems, the only commercial company selling them.

D-Wave系統公司(D-Wave Systems)是唯一一家銷售量子計算機的商業公司——據報道，谷歌(Google)和美國國家航空航天局(Nasa)已聯合出資1000萬美元購買該公司生產的一臺量子計算機原型機。

D-Wave’s financial backers include Amazon founder Jeff Bezos, Goldman Sachs and the Canadian government. The company can claim “coolness” in another way: since atoms need to be cooled right down in order for quantum effects to appear, D-Wave’s laboratory near Vancouver houses possibly the coldest place on Earth, just 0.02C above absolute zero (the point at which atoms stop moving).

D-Wave的金主包括亞馬遜(Amazon)創始人傑夫•貝索斯(Jeff Bezos)、高盛(Goldman Sachs)以及加拿大政府。這是一家很“酷”的公司，這裏的“酷”有着另一層含義：爲了顯現出量子效應，原子需要被大幅冷卻，因此人們在D-Wave位於溫哥華附近的實驗室裏可以找到大概是地球上最冷的地方，其溫度僅比絕對零度（原子停止運動的溫度）高0.02攝氏度。

Where tech visionaries tread, national governments follow. The UK will be spending £270m over the next five years to establish centres of excellence. As the world demands ever more powerful computers, and as conventional chips reach their physical limits, early investors hope Schrödinger’s cat can be turned into a cash cow.

科技先鋒走向哪裏，政府就跟向哪裏。未來五年，英國將投資2.7億英鎊建立示範中心(centre of excellence)。既然世界需要更強大的計算機，而常規芯片又達物理極限，早期投資者們就寄望於薛定諤貓能變爲搖錢樹。

There is only one problem: there is a simmering debate over whether D-Wave’s quantum computers are actually quantum at all. Scott Aaronson, a quantum computing expert at Massachusetts Institute of Technology, says that while there is evidence for small-scale quantum effects, there is no definitive evidence that D-Wave has achieved a fully fledged quantum computer. Neither, Mr Aaronson says, is it faster than classical computers.

只有一個問題：圍繞D-Wave的量子計算機是否真的實現了量子計算，即將爆發一場辯論。美國麻省理工學院(MIT)量子計算專家斯科特•阿倫森(Scott Aaronson)說，雖然有證據顯示存在小規模量子效應，但沒有確鑿證據證明D-Wave已造出了完全成熟的量子計算機，而且D-Wave的計算機也不比常規計算機快。

Now IBM researchers have waded in. Two weeks ago scientists from the IBM Thomas J Watson Research Center in New York, abetted by colleagues at the University of California, Berkeley, posted a paper entitled: “How ‘Quantum’ is the D-Wave Machine?” By taking on the same fiendish computing challenge posed to the D-Wave, and showing they could churn out pretty similar results with a classical algorithm, they claimed it was impossible to say definitively whether the machine was truly quantum.

現在，IBM的研究人員也參與進來。近日，紐約IBM托馬斯•J•沃森研究中心(Thomas J Watson Research Center)的科學家在美國加州大學伯克利分校(University of California, Berkeley)同僚的慫恿下，發佈了一篇名爲《D-Wave的機器到底有多‘量子’？》(How 'Quantum' is the D-Wave Machine?)的文章。通過挑戰D-Wave挑戰過的一個極其棘手的計算難題，並用經典算法生成出與D-Wave極爲相似的結果，這些科學家主張，不可能明確認定D-Wave的機器到底屬不屬於量子計算機。

Geordie Rose, D-Wave’s pugilistic founder who is also a former Canadian wrestling champion, defended his machine and accused his detractors of cherry-picking data. On his Hack the Multiverse blog, he wrote: “When I saw how trivially wrong [the paper] was, it was like opening a Christmas present and getting socks.” Ouch.

作爲前加拿大摔跤冠軍，D-Wave創始人喬迪•羅斯(Geordie Rose)的好鬥之風不改。他爲自己的機器進行了辯護，並指責他的批評者挑選支持他們主張的數據。他在自己的“侵入多重宇宙”(Hack the Multiverse)博客上寫道：“當我看到（那篇文章）錯得多麼沒有價值時，感覺就像拆開聖誕禮物後看到裏面是襪子。”哎喲，好辛辣！

For all the delicious backbiting and ego-baiting and megamoney gambles, quantum computing really does look like the natural next step in computational problem-solving, even if it can only crack a limited class of problems. In these early days of the revolution, we may have to take it on faith that the quantum computers around today are the real deal.

雖然這些背後中傷、瞄準別人自負心理展開的求關注行爲以及一擲千金的豪賭讓人看得津津有味，但量子計算看上去確實像是計算求解問題領域的必然發展方向，儘管它只能破解有限類別的問題。處於這場革命早期階段的我們，或許不得不相信目前出現的量子計算機是名副其實的。

Still, there is a pleasing irony to the uncertainty. Central to quantum theory is Heisenberg’s uncertainty principle, which states that we can never measure every property of a particle to the utmost precision. The universe places fundamental limits on our ability to know: just as the fate of Schrödinger’s famous cat remains a mystery to anyone outside the box, so, perhaps, does the truth about today’s quantum computers.

不過，這種不確定性也帶着一絲有意思的反諷意味。量子理論的核心是海森堡(Heisenberg)的不確定性原理(uncertainty principle)，即我們永遠無法極爲精準地測量出一個粒子的每一項屬性。宇宙對我們的求知能力設置了根本性的限制：正如薛定諤那隻著名的貓的命運對箱子外的人來說仍是個謎題一樣，與今日量子計算機有關的真相也有待時間來揭曉。