量子论：如何同时出现在两个地方

www.newscientist.com : How to be in two places at the same time - physics-math - 19 July 2011 - New Scientist

译者： 小无辜 2011年07月20日 17:40 原作者： Michael Brooks

欧洲科学家计划实验将玻璃珠激发至量子叠加态，使其同时出现在两处空间。这是在宏观尺度上对量子论最敏感的验证。

日前，一项雄心勃勃的实验即将展开，诣使玻璃珠出现在空间中的两处。这是对量子论最为敏感的验证。欧洲一位研究员表示，实验将使一个包含数百万原子——比多数病毒都大的玻璃珠在不同空间处于量子叠加态。

自欧文·薛定谔关于猫在叠加态中能处于既死又活状态的假想实验以来，物理学家们一直对宏观物体能否遵循量子论持怀疑态度。

实验构想是将一个直径四十纳米（1纳米=十亿分之一米）的玻璃珠置于小空穴中，再用激光轰击。此举将使玻璃珠从空穴的一侧弹入另一侧。但由于光子在自然界是处于量子态的，所以玻璃珠的位置也将变为量子叠加态。

“本实验将在高度真空跟绝对低温环境中进行，以免玻璃珠受到热噪声或空气分子的干扰。”德国加尔兴普朗克量子光学研究所的主要创始人奥利奥尔·罗梅洛-伊萨特说道。

去年，加州大学圣巴巴拉分校的艾伦·奥康奈尔及同事，在一条长为六十微米（1微米=百万分之一米）的金属条中成功创造了量子叠加态。不过，这段金属条以两种态呈现的物理隔离仅为一个毫微微米（1毫微微米=百万亿分之一米），相当于原子核的直径。

本次全新的实验，与美国同事们的相较，诣在使玻璃珠在瞬间处于两个完全不同的地方，且并不重叠。“我们设想，玻璃珠的质心将在两处空间位置处于量子叠加态，两处的距离大于玻璃珠的直径。”罗梅洛-伊萨特表示。

原子干涉实验曾成功地实现原子级的空间分离，使球壳状碳分子与其他含有数百原子的分子在空间上呈量子叠加态。但本实验将在真正意义的宏观物体上实施这一过程。

科学家表示，此举对验证量子力学具有非凡的价值。观察此类宏观物体的表现是否遵循量子力学，给了我们破解量子论之谜最大的希望。

罗梅洛-伊萨特实验将引领我们“在本质上超越现有技术水平”，伊利诺伊州立大学香槟分校的Anthony Leggett说道。“无论是富勒烯还是奥康奈尔实验，二者都无力在宏观尺度验证量子力学。”

参文出处: 物理评论快报, DOI: 10.1103/PhysRevLett.107.020405

How to be in two places at the same time

• 08:00 19 July 2011 by Michael Brooks
  
• For similar stories, visit the Quantum World Topic Guide
  

www.newscientist.com : How to be in two places at the same time - physics-math - 19 July 2011 - New Scientist

An ambitious experiment to make a glass sphere exist in two places at once could provide the most sensitive test of quantum theory yet. The experiment will place a sphere containing millions of atoms – making it larger than many viruses – into a superposition of states in different places, say researchers in Europe.

Physicists have questioned whether large objects can follow quantum laws ever since Erwin Schrödinger's thought-experiment suggested a cat could exist in a superposition of being both alive and dead.

The idea is to zap a glass sphere 40 nanometres in diameter with a laser while it is inside a small cavity. This should force the sphere to bounce from one side of the cavity to the other. But since the light is quantum in nature, so too will be the position of the sphere. This forces it into a quantum superposition.

The experiment will have to be carried out in high vacuum and at extremely low temperatures so that the sphere is not disturbed by thermal noise or air molecules, says lead author Oriol Romero-Isart from the Max Planck Institute of Quantum Optics in Garching, Germany.

No overlap

Last year Aaron O'Connell and colleagues at the University of California, Santa Barbara, demonstrated that it should be possible to create superpositions in a 60-micrometre-long metal strip. However, the physical separation associated with the two different states of the strip was only 1 femtometre, about the width of the nucleus of an atom.

The new experiment, in contrast, would put the glass sphere in two entirely distinct places at once, with no overlap. "In our proposal the centre of mass is put into a superposition of spatial locations separated by a distance larger than the size of the object," Romero-Isart says.

Atom interferometer experiments have previously achieved good separation, putting fullerene and other molecules containing up to a few hundred atoms into distinct superposition states, but the new scheme will do this with truly macroscopic objects.

This will be particularly valuable in providing tests for quantum mechanics, the researchers say. Observing the behaviour of such very large objects obeying quantum laws offers our best hope of finding ways in which quantum theory breaks down.

The Romero-Isart experiment would take us "substantially beyond the current state of the art", says Anthony Leggett of the University of Illinois at Urbana-Champaign. "Neither the fullerene experiments nor that of O'Connell and his team are able to test well-developed competitors to quantum mechanics."

Journal reference: Physical Review Letters, DOI: 10.1103/PhysRevLett.107.020405