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arXiv quant-ph/0702241quant-ph
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一些简单绝热量子算法的局限性

Limitations of some simple adiabatic quantum algorithms

Lawrence M. Ioannou, Michele Mosca

摘要:

令$H(t)=(1-t/T)H_0 + (t/T)H_1$、$t\in [0,T]$是控制绝热量子算法的哈密顿量,其中$H_0$在Hadamard基中是对角的,并且$H_1$在计算基中是对角的。我们证明了,如果算法的运行时间是量子比特数的次指数,则$H_0$和$H_1$必须各自具有至少两个大的相互正交的本征空间。我们还重现Farhi和Gutmann的搜索算法的最优性证明在这种绝热方案的背景下,因为我们只考虑初始哈密顿是对角线的阿达玛基础,我们的结果是略强于原来的。

英文摘要:

Let $H(t)=(1-t/T)H_0 + (t/T)H_1$, $t\in [0,T]$, be the Hamiltonian governing an adiabatic quantum algorithm, where $H_0$ is diagonal in the Hadamard basis and $H_1$ is diagonal in the computational basis. We prove that $H_0$ and $H_1$ must each have at least two large mutually-orthogonal eigenspaces if the algorithm's running time is to be subexponential in the number of qubits. We also reproduce the optimality proof of Farhi and Gutmann's search algorithm in the context of this adiabatic scheme; because we only consider initial Hamiltonians that are diagonal in the Hadamard basis, our result is slightly stronger than the original.

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