Science2014-06-23 3:59 PM

D波量子计算机--比经典硬件更快吗? Defining and detecting quantum speedup

论文摘要 

科学家们对一种D波装置进行了或许是迄今最全面的分析;该装置的创造者声称它是第一台商用量子计算机。科学家们说,量子计算机是一类比如今可能的速度更快的可解决极为复杂问题的机器。他们在十年中一直在尝试创制一种商用量子计算机。该D波装置只是在几年前才出现,它被认为已经实现了这一壮举,但它并不缺少对其持怀疑态度者。他们中的某些人怀疑D波已经取得了一种被称作量子加速的功效水平。他们说,随着更多的像D波装置这样的小规模量子装置的面世,可靠地确定它们是否真的利用了量子力学来取得卓越的功效将是至关重要的。现在,Troels F. Rønnow及其同事设定目标来定义及测量在某D波装置中的量子加速,并同时避免可能掩盖或冒充该现象的各种困难。Rønnow等用来自该503量子比特的D-波Two (DW2)型装置的数据来比较它与经典算法之间的效率。该团队用一种优化算法为该DW2机器及一台常规电脑设置了特定的数学问题。这两款装置都可进行该优化算法。研究人员接着分析了量子加速的证据,寻找DW2确实在性能表现上超越其常规对等物的明确迹象。他们没有在D波装置中发现这样的证据,这提示,还不能肯定地说量子退火--这是在DW2中所用的方法--展现了量子加速,至少量子退火没有对这类问题展现了量子加速。需要做进一步的研究来决定人们是否能发现一类可取得比经典硬件明显加速的问题。注:文章的作者包括那些对D波机器进行过投资的人。

Abstract 

The development of small-scale quantum devices raises the question of how to fairly assess and detect quantum speedup. Here we show how to define and measure quantum speedup, and how to avoid pitfalls that might mask or fake such a speedup. We illustrate our discussion with data from tests run on a D-Wave Two device with up to 503 qubits. Using random spin glass instances as a benchmark, we find no evidence of quantum speedup when the entire data set is considered, and obtain inconclusive results when comparing subsets of instances on an instance-by-instance basis. Our results do not rule out the possibility of speedup for other classes of problems and illustrate the subtle nature of the quantum speedup question.

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