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1.媒體來源: Phys.org

2.完整新聞標題:

Physicists detect exotic looped trajectories of light in three-slit experiment
物理學家從三狹縫實驗中發現 奇異彎曲的光軌跡


3.完整新聞內文:

January 6, 2017 by Lisa Zyga

http://imgur.com/88NumP2.jpg

The red path shows an exotic looped trajectory of light through a three-slit
structure, which was observed for the first time in the new study. Credit:
Magaña-Loaiza et al. Nature Communications

圖中的紅線顯示出，奇異彎曲的光軌跡穿過三狹縫結構，這是第一次從實驗中觀測到這種
現象。來源: Magaña-Loaiza et al. Nature Communications

(Phys.org)—Physicists have performed a variation of the famous 200-year-old
double-slit experiment that, for the first time, involves "exotic looped
trajectories" of photons. These photons travel forward through one slit, then
loop around and travel back through another slit, and then sometimes loop
around again and travel forward through a third slit.



Interestingly, the contribution of these looped trajectories to the overall
interference pattern leads to an apparent deviation from the usual form of
the superposition principle. This apparent deviation can be understood as an
incorrect application of the superposition principle—once the additional
interference between looped and straight trajectories is accounted for, the
superposition can be correctly applied.



The team of physicists, led by Omar S. Magaña-Loaiza and Israel De Leon, has
published a paper on the new experiment in a recent issue of Nature
Communications.

由 Omar S.Magaña-Loaiza 與以色列 De Leon 領導的物理學家團隊，在最近一期的
Nature Communications 上，發表了一篇關於新實驗的論文。


Loops of light
彎曲的光

"Our work is the first experimental observation of looped trajectories," De
Leon told Phys.org. "Looped trajectories are extremely difficult to detect
because of their low probability of occurrence. Previously, researchers had
suggested that these exotic trajectories could exist but failed to observe
them."



To increase the probability of the occurrence of looped trajectories, the
researchers designed a three-slit structure that supports surface plasmons,
which the scientists describe as "strongly confined electromagnetic fields
that can exist at the surface of metals." The presence of these
electromagnetic fields near the three slits increases the contribution of
looped trajectories to the overall interference pattern by almost two orders
of magnitude.



"We provided a physical explanation that links the probability of these
exotic trajectories to the near fields around the slits," De Leon said. "As
such, one can increase the strength of near fields around the slits to
increase the probability of photons following looped trajectories."

De Leon 表示"我們提供了一個物理解釋，將這些奇異軌跡的機率連繫到狹縫周圍的近場
。因此，增加狹縫周圍近場的強度，可以增加光子走彎曲軌跡的機率。"


Superposition principle accounting for looped trajectories
考慮彎曲軌跡的疊加原理

The new three-slit experiment with looped trajectories is just one of many
variations of the original double-slit experiment, first performed by Thomas
Young in 1801. Since then, researchers have been performing versions that use
electrons, atoms, or molecules instead of photons.

有彎曲軌跡的新三狹縫實驗，是原始雙狹縫實驗的許多變種之一。最初的雙狹縫實驗由
 Thomas Young 在1801年進行。從那時起，研究人員一直在使用電子, 原子或分子代替光
子。

One of the reasons why the double-slit experiment has attracted so much
attention is that it represents a physical manifestation of the principle of
quantum superposition. The observation that individual particles can create
an interference pattern implies that the particles must travel through both
slits at the same time. This ability to occupy two places, or states, at
once, is the defining feature of quantum superposition.



http://imgur.com/4wEv3Z6.jpg

Straight trajectories (green) and exotic looped trajectories (red, dashed,
dotted) of light, where the red cloud near the surface depicts the near
fields, which increase the probability of photons to follow looped
trajectories. The graphs at left show simulations (top) and experimental
results (bottom) of the large difference in interference patterns created by
illuminating only one slit being treated independently (gray line) and the
actual coupled system (blue line). The remarkable difference between the gray
and blue lines is caused by the looped trajectories. Credit: Magaña-Loaiza
et al. Nature Communications



So far, all previous versions of the experiment have produced results that
appear to be accurately described by the principle of superposition. This is
because looped trajectories are so rare under normal conditions that their
contribution to the overall interference pattern is typically negligible, and
so applying the superposition principle to those cases results in a very good
approximation.



It is when the contribution of the looped trajectories becomes non-negligible
that it becomes apparent that the total interference is not simply the
superposition of individual wavefunctions of photons with straight
trajectories, and so the interference pattern is not correctly described by
the usual form of the superposition principle.

當彎曲軌跡的貢獻變得不可忽略時，很明顯地，總干涉圖形不是由各別的直線軌跡光子的
波函數疊加，因此干涉圖形不能以疊加原理的通常形式來解釋。

Magaña-Loaiza explained this apparent deviation in more detail:

Magaña-Loaiza 更詳細地解釋了這種明顯的誤差:

"The superposition principle is always valid—what is not valid is the
inaccurate application of the superposition principle to a system with two or
three slits," he said.

他表示: "疊加原理一直是正確的，不正確的是，錯誤的使用疊加原理在兩個或三個狹縫
系統"。

"For the past two centuries, scientists have assumed that one cannot observe
interference if only one slit is illuminated in a two- or three-slit
interferometer, and this is because this scenario represents the usual or
typical case.

在過去的兩個世紀裡，科學家們認為，如果在雙或三狹縫干涉儀中，只有一個狹縫被照射
，那麼人們不能觀察到干涉，這是因為這種情況代表了通常或典型的情況。

"However, in our paper we demonstrate that this is true only if the
probability of photons to follow looped trajectories is negligible.
Surprisingly, interference fringes are formed when photons following looped
trajectories interfere with photons following straight (direct) trajectories,
even when only one of the three slits is illuminated.



"The superposition principle can be applied to this surprising scenario by
using the sum or 'superposition' of two wavefunctions; one describing a
straight trajectory and the other describing looped trajectories. Not taking
into account looped trajectories would represent an incorrect application of
the superposition principle.


"To some extent, this effect is strange because scientists know that Thomas
Young observed interference when he illuminated both slits and not only one.
This is true only if the probability of photons following looped trajectories
is negligible."



In addition to impacting physicists' understanding of the superposition
principle as it is applied to these experiments, the results also reveal new
properties of light that could have applications for quantum simulators and
other technologies that rely on interference effects.

除了影響物理學家用疊加原理解釋這些實驗，其結果還揭示了光的新性質，該性質可能用
於量子模擬器與其它使用干涉效應的技術。

"We believe that exotic looped paths can have important implications in the
study of decoherence mechanisms in interferometry or to increase the
complexity of certain protocols for quantum random walks, quantum simulators,
and other algorithms used in quantum computation," De Leon said.




4.完整新聞連結 (或短網址):
https://goo.gl/lEkPLA


5.備註:

原始論文
Exotic looped trajectories of photons in three-slit interference
http://www.nature.com/articles/ncomms13987

疊加原理 - 維基百科，自由的百科全書
https://zh.wikipedia.org/zh-tw/叠加原理

態疊加原理 - 維基百科，自由的百科全書
https://zh.wikipedia.org/wiki/态叠加原理

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