Page 10 - Science Focus (Issue 017)

another particle, C, to Bob, entangles her particle successfully teleported photons as a proof of
A with C, so B is also remotely influenced by the concept in 1998 [3]. One potential application
combined A-C system even though they have is in secure quantum communication [4]: the
been separated. Then, Alice performs a standard uncertainty principle prevents hackers from
measurement on A-C and sends the result to Bob. eavesdropping quantum communication without
Although the data alone is insufficient to describe alerting the recipient, because any measurement
C, Bob can make use of the data to transform B, on the transmission alters the message. Recent
which is remotely influenced by the measurement, experiments have demonstrated that qutrits, a
so that it becomes identical to the original C. three-state system, can be teleported, which is yet
Meanwhile, the original C and its entangled twin A another step to realize large-scale quantum internet
are both destroyed by the measurement. This is how [5]. On an even grander scale, will we be able to
Alice and Bob can “teleport” a particle without teleport humans? Sci-fi fans will be disappointed
knowing everything about its state. to learn that most mainstream scientists deem
the technological hurdles insurmountable in the
Quantum teleportation has become a staple foreseeable future.
in quantum technology since experimentalists

粒子C傳送給 Bob，所以她把她的粒子 A 和 C 糾纏在一起，
讓在遠處的 B也會受到 A-C 系統影響。然後，Alice 對 A-C
系統進行一次測量，把結果傳送給 Bob。雖然數據本身不
足以描述 C，但 Bob 可以根據這些資料變換（transform）
受到遙距影響的 B，使其變成與原來 C 相同的量子態；而
原來的 C 和與它相互糾纏的「孿生兒」A 則在測量中受到
破壞。這就是 Alice 和 Bob 如何在不知道一顆粒子的量子
態的情況下能夠「遙傳」它的方法。

自從在 1998 年一隊實驗人員成功示範量子遙傳 [3]
之後，它就成為了量子技術的重要一環。它其中一個可能
的應用是在安全量子通信方面 [4]：不確定性原理防止黑
客在接收者不知情的情況下竊聽量子通信，因為傳輸過程
中的任何測量都必定會改變訊息。最近實驗成功遙傳量
子三元（qutrit），一個有三個狀態的系統（three-state
system），而這是實現大規模量子互聯網的另一大步 [5]。
在更大的規模上，我們能夠傳送人類嗎？科幻故事迷可能
會感到失望，因為大多數主流科學家都認為，我們無法在
可預見的將來克服當中的技術困難。
Figure 2. 圖二

References 參考資料：
[1] First teleportation from Earth to orbit. (2017, July 11). BBC News. Retrieved from https://www.bbc.com/news/av/science-
environment-40573621/first-teleportation-from-earth-to-orbit
[2] Bennett, C., Brassard, G., Crépeau, C., Jozsa, R., Peres, A., & Wootters, W. (1993). Teleporting an unknown quantum state via dual
classical and Einstein-Podolsky-Rosen channels. Physical Review Letters, 70(13), 1895-1899. doi: 10.1103/physrevlett.70.1895
[3] Boschi, D., Branca, S., De Martini, F., Hardy, L., & Popescu, S. (1998). Experimental Realization of Teleporting an Unknown Pure Quantum
State via Dual Classical and Einstein-Podolsky-Rosen Channels. Physical Review Letters, 80(6), 1121-1125. doi: 10.1103/physrevlett.80.1121
[4] Giles, M. (2019). Explainer: What is quantum communication? MIT Technology Review. Retrieved from https://www.technologyreview.
com/s/612964/what-is-quantum-communications/
[5] Ananthaswamy, A. (2019). The Quantum Internet Is Emerging, One Experiment at a Time. Scientific American. Retrieved from
https://www.scientificamerican.com/article/the-quantum-internet-is-emerging-one-experiment-at-a-time/