Counterfactual quantum computation through quantum interrogation
Counterfactual quantum computation through quantum interrogation
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DOI：
10.1038/nature04523
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发表时间：
2006-02-23
期刊：
影响因子：
64.8
通讯作者：
Kwiat, PG
中科院分区：
文献类型：
--
作者：
Hosten, O;Rakher, MT;Kwiat, PG
量子信息处理的连贯性背后的逻辑往往偏离直觉推理，导致令人惊讶的效果。反事实计算是一个突出的例子：即使计算机没有运行，量子计算的潜在结果也可以推断出来（1）。依靠与无相互作用测量（2）（或量子询问（3））类似的论点，反事实计算是通过将计算机置于“运行”和“不运行”状态的叠加中，然后干扰两个历史来完成的。在计算的未知结果的条件下，有时可以反事实地推断关于解决方案的信息。在这里，我们展示了反事实计算，用全光学方法实现Grover的搜索算法（4）。人们认为，这种反事实推理的总体概率本质上是有限的（1，5），因此它的平均表现不可能比随机猜测更好。然而，使用量子芝诺效应（6）的一种新的“链式”版本，我们展示了如何将反事实推理概率提高到1，从而超越随机猜测极限。我们的方法是通用的，并适用于任何物理系统，如所示的讨论被困离子系统。最后，我们简要地表明，在某些情况下，反事实计算可以消除由退相干引起的错误。
The logic underlying the coherent nature of quantum information processing often deviates from intuitive reasoning, leading to surprising effects. Counterfactual computation constitutes a striking example: the potential outcome of a quantum computation can be inferred, even if the computer is not run(1). Relying on similar arguments to interaction-free measurements(2) (or quantum interrogation(3)), counterfactual computation is accomplished by putting the computer in a superposition of 'running' and 'not running' states, and then interfering the two histories. Conditional on the as-yet-unknown outcome of the computation, it is sometimes possible to counterfactually infer information about the solution. Here we demonstrate counterfactual computation, implementing Grover's search algorithm with an all-optical approach(4). It was believed that the overall probability of such counterfactual inference is intrinsically limited(1,5), so that it could not perform better on average than random guesses. However, using a novel 'chained' version of the quantum Zeno effect(6), we show how to boost the counterfactual inference probability to unity, thereby beating the random guessing limit. Our methods are general and apply to any physical system, as illustrated by a discussion of trapped-ion systems. Finally, we briefly show that, in certain circumstances, counterfactual computation can eliminate errors induced by decoherence.