kikyo91的个人博客分享 http://blog.sciencenet.cn/u/kikyo91

博文

[转载](转&翻译)物理学家用量子计算机在量子尺度上实现时光逆行

已有 893 次阅读 2019-7-22 09:35 |个人分类:杂说|系统分类:科普集锦| 量子物理 |文章来源:转载

这是science alert上的一篇科普文章:

https://www.sciencealert.com/physicists-have-reversed-time-on-the-smallest-scale-by-using-a-quantum-computer

它所引述的研究为这篇论文:

https://www.nature.com/articles/s41598-019-40765-6

译者为个人学习转译此文,造诣尚浅,如有不达,敬请指正。


Physicists Have Reversed Time on The Smallest Scale by Using a Quantum Computer

MIKE MCRAE    20 JUL 2019

翻译:静途


It's easy to take time's arrow for granted - but the gears of physics actually work just as smoothly in reverse. Maybe that time machine is possible after all?
时间的线性方向是理所当然的,但是物理的齿轮同样可以平滑的逆向转动。也许时光机器是可能的呢? 

An experiment earlier this year shows just how much wiggle room we can expect when it comes to distinguishing the past from the future, at least on a quantum scale. It might not allow us to relive the 1960s, but it could help us better understand why not.
近来的实验向我们表明我们在区分未来和现在的时间上有多大的空间,至少是在量子级(尺寸上)。 它可能不能够让我们回到1960年代,但是却能够让我们理解为什么不能回去。

Researchers from Russia and the US teamed up to find a way to break, or at least bend, one of physics' most fundamental laws on energy.
俄国和美国的研究者们发现了一种方法来中断,至少是扭曲物理中的一个最基本的能量定理。 

The second law of thermodynamics is less a hard rule and more of a guiding principle for the Universe. It says hot things get colder over time as energy transforms and spreads out from areas where it's most intense.
热力学第二定律是一个不那么塑性的定律,而更像是一个引导宇宙规律的定律。它说热的东西随时间流逝会渐渐冷却,因为能量由高到低的传导和散失 。

It's a principle that explains why your coffee won't stay hot in a cold room, why it's easier to scramble an egg than unscramble it, and why nobody will ever let you patent a perpetual motion machine.
这个定律解释了为什么咖啡在冷的屋子里无法保温,或是鸡蛋搅碎要比复原它容易,或是为什么没有人能制造出来一个永动机。 

It's also the closest we can get to a rule that tells us why we can remember what we had for dinner last night, but have no memory of next Christmas.
这是最像我们能够记得昨晚吃过的晚餐却没有下一个圣诞节的记忆的定律(难以逆转)。 

"That law is closely related to the notion of the arrow of time that posits the one-way direction of time from the past to the future," says quantum physicist Gordey Lesovik from the Moscow Institute of Physics and Technology.
“热力学第二定律与时间由过去向未来单向流动密切相关”,莫斯科物理技术学院(Moscow Institute of Physics and Technology)的量子物理学家Gordey Lesovik说。

Virtually every other rule in physics can be flipped and still make sense. For example, you could zoom in on a game of pool, and a single collision between any two balls won't look weird if you happened to see it in reverse.
基本上所有的其它的物理学定理都能够反过来继续成立。例如,你可以放大一个台球台,所有的碰撞过程如果逆向播放也不会看起来奇怪。 

On the other hand, if you watched balls roll out of pockets and reform the starting pyramid, it would be a sobering experience. That's the second law at work for you.
另一方面,如果你看很多球从台球桌的口袋里掉出来然后形成最初的金字塔形,这会是个奇怪的体验,因为第二定律在作用。 

On the macro scale of omelettes and games of pool, we shouldn't expect a lot of give in the laws of thermodynamics. But as we focus in on the tiny gears of reality - in this case, solitary electrons - loopholes appear.
在宏观的尺度,如蛋卷或者是台球,我们不期望热力学定律能够有多大的让步。但是如果我们把注意力集中到更小的现实的尺度,例如这里,单个电子的尺度,漏洞就会出现。

Electrons aren't like tiny billiard balls, they're more akin to information that occupies a space. Their details are defined by something called the Schrödinger equation, which represents the possibilities of an electron's characteristics as a wave of chance.
电子并不像小的台球,他们更像是占据空间的信息。它们的具体细节由薛定谔方程定义,一个电子的特性表述为由波动方程定义的概率。

If this is a bit confusing, let's go back to imagining a game of pool, but this time the lights are off. You start with the information – a cue ball – in your hand, and then send it rolling across the table.
如果这有些让人困惑,让我们回过头来想象一场台球,但是这次台球桌附近的灯都灭了。你开始的时候有一些信息,例如一个白球在你的手里,然后你把它打出去,它就在台子上滚。 

The Schrödinger equation tells you that ball is somewhere on the pool table moving around at a certain speed. In quantum terms, the ball is everywhere at a bunch of speeds … some just more likely than others.
薛定谔方程告诉你这个白球在台球桌的某个位置,以某个速度行进。用量子的表述来讲,就是这个球在每个地方以各种速度滚着,而某些状态要比其他的状态可能性更大。

You can stick your hand out and grab it to pinpoint its location, but now you're not sure of how fast it was going. You could also gently brush your finger against it and confidently know its velocity, but where it went... who knows?
你可以伸出手去把白球抓住,并且按在那里,但是这下你就不知道它刚才的速度了。你也可以请轻轻的用你的手指扫扫它,然后确定地获知它的速度,但是它去哪里了呢?谁知道呢。 

There's one other trick you could use, though. A split second after you send that ball rolling, you can be fairly sure it's still near your hand moving at a high rate.
还有一种方法,在你击出球的极短的时间里,你可以很确定它仍然在距离你的手非常近的地方,并且在高速的行进。 

In one sense, the Schrödinger equation predicts the same thing for quantum particles. Over time, the possibilities of a particle's positions and velocities expands.
在某种意义上,薛定谔方程对量子预测同样的事情。随着时间的流逝,粒子的位置和速度的可能性会更多。 

"However, Schrödinger's equation is reversible," says materials scientist Valerii Vinokur from the Argonne National Laboratory in the US.
 “然而,薛定谔方程是可逆的”,美国Argonne国家实验室物理学家Valerii Vinokur说。

"Mathematically, it means that under a certain transformation called complex conjugation, the equation will describe a 'smeared' electron localising back into a small region of space over the same time period."
“从数学上来看,它说明在复数共轭变换下,这个方程会描述一个电子在一个小的区域很短时间沿着自己的轨迹复位的样子。” 

It's as if your cue ball was no longer spreading out in a wave of infinite possible positions across the dark table, but rewinding back into your hand.
它就好像你的白球不再在黑暗的桌子上沿着波动方程所定义的概率散开,而是重新回到了你的手上。 

In theory, there's nothing stopping it from occurring spontaneously. You'd need to stare at 10 billion electron-sized pool tables every second and the lifetime of our Universe to see it happen once, though.
理论上,这个过程可以同时发生。不过这个发生的概率很低,你需要在我们的宇宙寿命的时间内,每时每秒盯着一个一百亿倍电子大小的台球桌去观察这个现象的发生。 

Rather than patiently wait around and watch funding trickle away, the team used the undetermined states of particles in a quantum computer as their pool ball, and some clever manipulation of the computer as their 'time machine'.
与其耐心的等待并且看着实验资金一点点的流掉,该团队在一个量子计算器(机)中利用粒子的不确定状态作为他们的台球桌,并且聪明地改造这个计算器成为他们的“时光机器”。 

Each of these states, or qubits, was arranged into a simple state which corresponded to a hand holding the ball. Once the quantum computer was set into action, these states rolled out into a range of possibilities.
每三个状态,或者qubits,被排列成一个简单的状态,并对应一个量子的操纵。一旦量子计算器启动,这些量子的状态会演进成一系列可能的状态。 

By tweaking certain conditions in the computer's setup, those possibilities were confined in a way that effectively rewound the Schrödinger equation deliberately.
通过仔细的调节计算机的初始状态,从而对其中的量子的状态的可能性进行限制 ,从而有效地使薛定谔方程逆向过程发生。

To test this, the team launched the set-up again, as if kicking a pool table and watching the scattered balls rearrange into the initial pyramid shape. In about 85 percent of trials based on just two qubits, this is exactly what happened.
为了验证这个,该团队重新启动了这个初始设定的量子计算器,就像是在踢一脚台球桌然后观看台球们重新排列成开局的三角形。使用2个qubits的信息量,85%的实验都发生了逆向过程。 

On a practical level, the algorithms they used to manipulate the Schrödinger equation into rewinding in this way could help improve the accuracy of quantum computers.
实践上,他们操纵薛定谔方程逆向运算的算法可以提高量子计算机的精度。

It's not the first time this team has given the second law of thermodynamics a good shake. A couple of years ago they entangled some particles and managed to heat and cool them in such a way they effectively behaved like a perpetual motion machine.
这不是该团队第一次动摇热力学第二定律。几年前,他们把一些粒子进行缠绕,并且成功的加热、冷却使粒子的行为像永动机。

Finding ways to push the limits of such physical laws on the quantum scale just might help us better understand why the Universe 'flows' like it does.
寻找方法在量子尺度上接近或打破这种物理学定律可能能够帮助过我们更好的理解为什么宇宙如此流动。

This research was published in Scientific Reports.
这篇研究在科学报告Scientific Reports上发表。

A version of this article was first published in March 2019.
这篇文章在2019年三月第一次发表。 




http://blog.sciencenet.cn/blog-517481-1190557.html

上一篇:[转载]C++程序设计本科教材推荐:适合初学者

0

该博文允许注册用户评论 请点击登录 评论 (0 个评论)

数据加载中...

Archiver|手机版|科学网 ( 京ICP备14006957 )

GMT+8, 2019-11-20 01:31

Powered by ScienceNet.cn

Copyright © 2007- 中国科学报社

返回顶部