Einstein's brilliant mistake: Entangled states - Chad Orzel

爱因斯坦的伟大错误：量子纠缠态 －查德·欧泽

翻译人员: Jinyuan Liu 校对人员: Qingqing Mao

Albert Einstein played a key role in launching quantum mechanics

凭借着光电效应理论，

阿尔伯特·爱因斯坦在量子力学领域奠定了重要的地位。

through his theory of the photoelectric effect

but remained deeply bothered by its philosophical implications.

但他对这一理论的哲学蕴意始终深感困扰。

And though most of us still remember him for deriving E=MC^2,

虽然爱因斯坦以推导出质能方程E＝mc^2而闻名于世，

his last great contribution to physics was actually a 1935 paper,

但实际上，他对物理学的最后巨献 是一篇发表于1935年的论文。

coauthored with his young colleagues Boris Podolsky and Nathan Rosen.

论文合著者是他年轻的同事们： 鲍里斯·波多尔斯基和纳森·罗森。

Regarded as an odd philosophical footnote well into the 1980s,

即使直到20上世纪80年代， 它都被当作一个奇怪的哲学脚注，

this EPR paper has recently become central to a new understanding of quantum physics,

这篇阐述爱因斯坦－波多尔斯基－罗森悖论（简称EPR） 的论文现在成为了重新理解量子物理学的中心，

with its description of a strange phenomenon

因为文中描述了一个奇怪的现象,

now known as entangled states.

现在人们称这种现象为纠缠态。

The paper begins by considering a source that spits out pairs of particles,

这篇论文先考虑一个可以产生成对的粒子的源，

each with two measurable properties.

每个粒子有两个可测量的属性，

Each of these measurements has two possible results

每个属性的测量都有两种可能的结果，

of equal probability.

两种结果出现的概率是相等的。

Let's say zero or one for the first property,

假设第一个属性的测量结果是：状态0或者状态1，

and A or B for the second.

第二个属性的测量结果是：状态A或者状态B。

Once a measurement is performed,

一旦一个粒子的一个属性被测量了一次，

subsequent measurements of the same property in the same particle

无论再测量多少次这一个粒子中的这一个属性，

will yield the same result.

都会得到同样的结果。

The strange implication of this scenario

这种现象的奇怪之处在于，

is not only that the state of a single particle

它不仅表明了一个单粒子的状态

is indeterminate until it's measured,

在被测量之前是不确定的，

but that the measurement then determines the state.

它也表明了，测量这个行为本身 决定了粒子的状态。

What's more, the measurements affect each other.

而且，测量之间也是互相影响的。

If you measure a particle as being in state 1,

如果你测量一个粒子的第一个属性， 它的测量结果是状态1，

and follow it up with the second type of measurement,

你接着测量这个粒子的第二个属性,

you'll have a 50% chance of getting either A or B,

你有50%的几率得到状态A或者状态B。

but if you then repeat the first measurement,

但是，如果你再回头去测量第一个属性，

you'll have a a 50% chance of getting zero

即使它已经被测量过一次并得到了结果1，

even though the particle had already been measured at one.

你也将有50%的几率得到状态0。

So switching the property being measured scrambles the original result,

所以，轮流测量一个粒子的不同属性会重置原始的结果，

allowing for a new, random value.

让一个全新的、随机的结果变成可能。

Things get even stranger when you look at both particles.

如果你同时观察一对粒子，结果会变得更奇怪。

Each of the particles will produce random results,

两个粒子都会得到随机的测量结果，

but if you compare the two,

但是，如果你把它们放在一起比较，

you will find that they are always perfectly correlated.

你会发现，它们总是完美地彼此相关。

For example, if both particles are measured at zero,

比如，如果两个粒子的测量结果都是状态0，

the relationship will always hold.

它们的关联现象就会一直这样保持着。

The states of the two are entangled.

这两个粒子的状态会互相纠缠。

Measuring one will tell you the other with absolute certainty.

测试其中的一个粒子， 就能准确无误地预测另一个粒子的状态。

But this entanglement seems to defy Einstein's famous theory of relativity

但是量子纠缠似乎违背了爱因斯坦提出的著名的相对论，

because there is nothing to limit the distance between particles.

因为两个粒子之间的距离是没有限制的。

If you measure one in New York at noon,

如果中午时，你在纽约测量一个粒子，

and the other in San Francisco a nanosecond later,

一纳秒后，你在旧金山测试另一个粒子，

they still give exactly the same result.

它们还是会得出同样的测量结果。

But if the measurement does determine the value,

但是，如果测量这一行为决定了所得的结果，

then this would require one particle sending some sort of signal to the other

那么第一个粒子，就需要以光速的一千三百万倍的速度

at 13,000,000 times the speed of light,

向第二个粒子传递某些信息，

which according to relativity, is impossible.

而相对论认为，这是不可能实现的事情。

For this reason, Einstein dismissed entanglement as "spuckafte ferwirklung,"

基于这个理由， 爱因斯坦驳斥这一现象为"spuckafte ferwirklung"，

or spooky action at a distance.

或者说“远距离幽灵行为”。

He decided that quantum mechanics must be incomplete,

他认为，这一定是因为量子力学本身并不完善，

a mere approximation of a deeper reality in which both particles

两个粒子一定有一个我们所不知道的先决状态，

have predetermined states that are hidden from us.

而量子力学太过肤浅，不足以揭露与解释这一事实。

Supporters of orthodox quantum theory lead by Niels Bohr

而在尼尔斯·玻尔的带领下, 正统的量子理论支持者们坚称

maintained that quantum states really are fundamentally indeterminate,

量子状态是真的不可确定，

and entanglement allows the state of one particle

量子纠缠让一个粒子的状态 受另一个粒子的状态的影响，

to depend on that of its distant partner.

即使它们相隔甚远。

For 30 years, physics remained at an impasse,

物理学因此陷入僵局，

until John Bell figured out that the key to testing the EPR argument

直至30年后，约翰·贝尔发现要解决EPR争论，

was to look at cases involving different measurements on the two particles.

我们应当观测对两个粒子的不同属性的测量。

The local hidden variable theories favored by Einstein, Podolsky and Rosen,

爱因斯坦、波尔多斯基、和罗森的“局域隐变量理论”

strictly limited how often you could get results like 1A or B0

严格地限定了得到1A或者B0这样的结果的几率，

because the outcomes would have to be defined in advanced.

因为结果是可以被提前定义的。

Bell showed that the purely quantum approach,

贝尔展示了纯粹的量子方法

where the state is truly indeterminate until measured,

——粒子的状态在测量前是完全不可确定时——

has different limits and predicts mixed measurement results

有着不同的限制，并以此预测了混合的测量结果，

that are impossible in the predetermined scenario.

这些结果在粒子状态可预定的情况下不可能存在。

Once Bell had worked out how to test the EPR argument,

贝尔得出检验EPR的理论的方法后，

physicists went out and did it.

物理学家们照此展开了实验。

Beginning with John Clauster in the 70s and Alain Aspect in the early 80s,

从70年代的约翰·克劳泽 和80年代早期的阿兰·阿斯佩开始，

dozens of experiments have tested the EPR prediction,

大量实验检验了EPR预测，

and all have found the same thing:

并得出了同样的结论：

quantum mechanics is correct.

量子力学是正确的。

The correlations between the indeterminate states of entangled particles are real

两个互相纠缠的粒子之间的 不确定状态的相关性是真实存在的，

and cannot be explained by any deeper variable.

而且无法被任何更深层次的变量所解释。

The EPR paper turned out to be wrong but brilliantly so.

那篇EPR论文被证明是错的，但它是个伟大的错误。

By leading physicists to think deeply about the foundations of quantum physics,

通过引导物理学家们更深入地思考量子物理的基础，

it led to further elaboration of the theory

这篇论文使得量子理论得到了进一步的阐述和完善，

and helped launch research into subjects like quantum information,

也推动了对相关课题的研究，比如说量子信息学。

now a thriving field with the potential to develop computers of unparalleled power.

这是一个新兴的领域，具有创造出超级电脑的潜力。

Unfortunately, the randomness of the measured results

不幸的是，测量结果的随机性

prevents science fiction scenarios,

让科幻小说里的场景无法成为现实，

like using entangled particles to send messages faster than light.

比如利用纠缠粒子超光速地传递信息。

So relativity is safe, for now.

所以就现在而言，相对论是安全的，

But the quantum universe is far stranger than Einstein wanted to believe.

但是量子宇宙的奇特之处远远超出爱因斯坦的想像。