一句话:将期望运行时间定义为量子最弱前置条件的推广,给出有限维量子程序期望运行时间计算方法并解决量子随机游走开放问题。
本文研究量子程序的期望运行时间。受概率程序期望运行时间工作的启发,作者首先把期望运行时间定义为量子最弱前置条件的一种推广,并证明量子程序的期望运行时间可表示为某个物理可观测量的期望。随后,针对有限维状态空间,提出计算量子程序期望运行时间的方法,并给出若干应用示例,包括量子伯努利工厂的期望运行时间计算。特别地,该方法解决了 Ambainis 等人 (STOC 2001) 提出的量子随机游走期望运行时间这一开放问题。
We study expected runtimes for quantum programs. Inspired by recent work on probabilistic programs, we first define expected runtime as a generalisation of quantum weakest precondition. Then, we show that the expected runtime of a quantum program can be represented as the expectation of an observable (in physics). A method for computing the expected runtimes of quantum programs in finite-dimensional state spaces is developed. Several examples are provided as applications of this method, including computing the expected runtime of quantum Bernoulli Factory – a quantum algorithm for generating random numbers. In particular, using our new method, an open problem of computing the expected runtime of quantum random walks introduced by Ambainis et al. (STOC 2001) is solved.