S*******l
发帖数: 4637 | 1 Physicists in China challenge Google’s ‘quantum advantage’
Photon-based quantum computer does a calculation that ordinary computers
might never be able to do.
Philip Ball
The interferometer part of our experiment.
This photonic computer performed in 200 seconds a calculation that on an
ordinary supercomputer would take 2.5 billion years to complete.Credit:
Hansen Zhong
A team in China claims to have made the first definitive demonstration of ‘
quantum advantage’ — exploiting the counter-intuitive workings of quantum
mechanics to perform computations that would be prohibitively slow on
classical computers.
They have used beams of laser light to perform a computation which had been
mathematically proven to be practically impossible on normal computers. The
team achieved within a few minutes what would take half the age of Earth on
the best existing supercomputers. Contrary to Google’s first demonstration
of a quantum advantage, performed last year, their version is virtually
unassailable by any classical computer. The results appeared in Science on 3
December1.
“We have shown that we can use photons, the fundamental unit of light, to
demonstrate quantum computational power well beyond the classical
counterpart,” says Jian-Wei Pan at the University of Science and Technology
of China in Hefei. He adds that the calculation that they carried out —
called the boson-sampling problem — is not just a convenient vehicle for
demonstrating quantum advantage, but has potential practical applications in
graph theory, quantum chemistry and machine learning.
“This is certainly a tour de force experiment, and an important milestone,
” says physicist Ian Walmsley at Imperial College London.
Quantum advantage challenged
Teams at both academic and corporate laboratories have been vying to
demonstrate quantum advantage (a term that has now largely replaced the
earlier ‘quantum supremacy’).
Last year, researchers at Google’s quantum-computing laboratory in Santa
Barbara, California, announced the first-ever demonstration of quantum
advantage. They used their state-of-the-art Sycamore device, which has 53
quantum bits (qubits) made from superconducting circuits that are kept at
ultracold temperatures2.
But some quantum researchers contested the claim, on the grounds that a
better classical algorithm that would outperform the quantum one could
exist3. And researchers at IBM claimed that its classical supercomputers
could in principle already run existing algorithms to do the same
calculations in 2.5 days.
To convincingly demonstrate quantum advantage, it should be unlikely that a
significantly faster classical method could ever be found for the task being
tested.
The Hefei team, led by Pan and Chao-Yang Lu, chose a different problem for
its demonstration, called boson sampling. It was devised in 2011 by two
computer scientists, Scott Aaronson and Alex Arkhipov4, then at the
Massachusetts Institute of Technology in Cambridge. It entails calculating
the probability distribution of many bosons — a category of fundamental
particle that includes photons — whose quantum waves interfere with one
another in a way that essentially randomizes the position of the particles.
The probability of detecting a boson at a given position can be calculated
from an equation in many unknowns.
200 seconds
But the calculation in this case is a ‘#P-hard problem’, which is even
harder than notoriously tricky NP-hard problems, for which the number of
solutions increases exponentially with the number of variables. For many
tens of bosons, Aaronson and Arkhipov showed that there’s no classical
shortcut for the impossibly long calculation.
A quantum computer, however, can sidestep the brute-force calculation by
simulating the quantum process directly — allowing bosons to interfere and
sampling the resulting distribution. To do this, Pan and colleagues chose to
use photons as their qubits. They carried out the task on a photonic
quantum computer working at room temperature.
Starting from laser pulses, the researchers encoded the information in the
spatial position and the polarization of particular photon states — the
orientation of the photons’ electromagnetic fields. These states were then
brought together to interfere with one another and generate the photon
distribution that represents the output. The team used photodetectors
capable of registering single photons to measure that distribution, which in
effect encodes the calculations that are so hard to perform classically.
In this way, Pan and colleagues could find solutions to the boson-sampling
problem in 200 seconds. They estimate these would take 2.5 billion years to
calculate on China’s TaihuLight supercomputer — a quantum advantage of
around 1014.
Practical problems
“This is the first time that quantum advantage has been demonstrated using
light or photonics,” says Christian Weedbrook, chief executive of quantum-
computing startup Xanadu in Toronto, Canada, which is seeking to build
practical quantum computers based on photonics.
Walmsley says this claim of quantum advantage is convincing. “Because [the
experiment] hews very closely to the original Aaronson–Arkiphov scheme, it
is unlikely that a better classical algorithm can be found,” he says.
However, Weedbrook points out that as yet, and in contrast to Google’s
Sycamore, the Chinese team’s photonic circuit is not programmable, so at
this point “it cannot be used for solving practical problems”.
But he adds that if the team is able to build an efficient enough
programmable chip, several important computational problems could be solved.
Among those are predicting how proteins dock to one another and how
molecules vibrate, says Lu.
Weedbrook notes that photonic quantum computing started later than the other
approaches, but it could now “potentially leap-frog the rest”. At any
rate, he adds, “It is only a matter of time before quantum computers will
leave classical computers in the dust.”
doi: https://doi.org/10.1038/d41586-020-03434-7
References
1.
Zhong, H.-S. et al. Science https://doi.org/10.1126/science.abe8770 (
2020).
Article
Google Scholar
2.
Arute, F. et al. Nature 574, 505–510 (2019).
PubMed
Article
Google Scholar
3.
Pednault, E., Gunnels, J. A., Nannicini, G., Horesh, L. & Wisnieff, R.
Preprint at https://www.arxiv.org/abs/1910.09534 (2019).
4.
Aaronson, S. & Arkhipov, A. Proc. 43rd Annual Symposium on Theory of
Computing 333–342 (2011). | S*******l
发帖数: 4637 | 2 没人看过？
就是说比谷歌的牛多了。谷歌解决的问题经典计算机好算法几天就解决了。九章解决的
问题是无法用经典计算机解决的，要25亿年。九章200秒。
后面批评说还不能编程。如果能解决一下编程，用什么chip来编程，就能解决实际问题
了。比如蛋白折叠什么的。 | w*******g
发帖数: 9932 | 3 据说要实际应用还要成千上万个qubit才行。不是几十个qubit就完事的。
再说还不知道控制光子的编程有什么不可逾越的困难。如果工程上可行，会有很多私营
资本砸钱进去。
【在 S*******l 的大作中提到】
: 没人看过？
: 就是说比谷歌的牛多了。谷歌解决的问题经典计算机好算法几天就解决了。九章解决的
: 问题是无法用经典计算机解决的，要25亿年。九章200秒。
: 后面批评说还不能编程。如果能解决一下编程，用什么chip来编程，就能解决实际问题
: 了。比如蛋白折叠什么的。
| L**********g
发帖数: 498 | 4 私营资本不会去砸洋人没证实可行过的东西
【在 w*******g 的大作中提到】
: 据说要实际应用还要成千上万个qubit才行。不是几十个qubit就完事的。
: 再说还不知道控制光子的编程有什么不可逾越的困难。如果工程上可行，会有很多私营
: 资本砸钱进去。
| t******x
发帖数: 55 | 5 都是投机取巧
谷歌是量子白噪声发生器，白噪声发生器当然可以做随机码发生器
一个是做模拟实验，计算机其实根本模拟不出来，要多少倍随便说
你可以倒一杯水，这个水流运动计算机也模拟不了，你也可以说我倒水比计算机快100
亿倍 | n********g
发帖数: 6504 | 6 中国（科学界）师从苏联，爱搞模拟计算机。
当年引进使用数字计算机不容易要反复讨论。
100
【在 t******x 的大作中提到】
: 都是投机取巧
: 谷歌是量子白噪声发生器，白噪声发生器当然可以做随机码发生器
: 一个是做模拟实验，计算机其实根本模拟不出来，要多少倍随便说
: 你可以倒一杯水，这个水流运动计算机也模拟不了，你也可以说我倒水比计算机快100
: 亿倍
| t******x
发帖数: 55 | 7 模拟计算机和模拟实验不是一回事
模拟计算机是用运放做加法器乘法器，数字计算机是用逻辑门做加法器乘法器
【在 n********g 的大作中提到】
: 中国（科学界）师从苏联，爱搞模拟计算机。
: 当年引进使用数字计算机不容易要反复讨论。
:
: 100
| n********g
发帖数: 6504 | 8 大庆油田当初就买了两台模拟计算机。一台没开封。一台闲置。因为只能计算很简单情
况下的井压。买两台砸一台。谁说中国没钱。到最后上书石油部长两次，才进了两台数
字计算机。
当年中国的数字计算机应用也很受限。产量每年也就十多台。根子都在（科学院）主席
台。
【在 t******x 的大作中提到】
: 模拟计算机和模拟实验不是一回事
: 模拟计算机是用运放做加法器乘法器，数字计算机是用逻辑门做加法器乘法器
| w******g
发帖数: 189 | 9 说到点子上了。中国人嘴巴吹牛逼，但是要砸钱的时候还是很老实的。
【在 L**********g 的大作中提到】
: 私营资本不会去砸洋人没证实可行过的东西
| L****8
发帖数: 3938 | 10 lol
100
【在 t******x 的大作中提到】
: 都是投机取巧
: 谷歌是量子白噪声发生器，白噪声发生器当然可以做随机码发生器
: 一个是做模拟实验，计算机其实根本模拟不出来，要多少倍随便说
: 你可以倒一杯水，这个水流运动计算机也模拟不了，你也可以说我倒水比计算机快100
: 亿倍
| t*******t
发帖数: 1067 | 11 对了，潘量子有本事就不要国家投钱，看有没有风头砸钱。说来说去就是骗国家的经费
，顺便搞个公司上市圈钱。很同意这句：中国人嘴巴吹牛逼，但是要砸钱的时候还是很
老实的。想起施一公的笑话，西湖大学去美国找人的时候一边说要在5年内达到美国一
流大学水平，一边为了吸引人加盟说我们负责给你孩子以后在美国上大学的费用。施一
公好像有一对双胞胎吧，是不是该上大学了，是上西湖大学吗。
【在 w******g 的大作中提到】
: 说到点子上了。中国人嘴巴吹牛逼，但是要砸钱的时候还是很老实的。
| B*******o
发帖数: 212 | 12 这个倒是个国际接轨了，吹泡泡骗经费本来是米帝专长
：对了，潘量子有本事就不要国家投钱，看有没有风头砸钱。说来说去就是骗国家的经
费，顺便搞个公司上市圈钱。很同意这句：中国人嘴巴吹牛逼，但是要砸钱的时候还是
很老实的。想起施一公的笑话，西湖大学去美国找人的时候一边说要在5年内达到美国一
：流大学水平，一边为了吸引人加盟说我们负责给你孩子以后在美国上大学的费用。施
一公好像有一对双胞胎吧，是不是该上大学了，是上西湖大学吗。 |
|
