Probabilistic storage and retrieval of qubit phase gates

• URL: http://arxiv.org/abs/2008.09555v1
• Date: Fri, 21 Aug 2020 15:49:50 GMT
• Title: Probabilistic storage and retrieval of qubit phase gates
• Authors: Michal Sedl\'ak, and M\'ario Ziman
• Abstract summary: Probabilistic storage and retrieval (PSR) of unitary quantum dynamics is possible with exponentially small failure probability. We study improvements due to a priori knowledge about the unitary transformation to be stored.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Probabilistic storage and retrieval (PSR) of unitary quantum dynamics is possible with exponentially small failure probability with respect to the number of systems used as a quantum memory [PRL 122, 170502 (2019)]. Here we study improvements due to a priori knowledge about the unitary transformation to be stored. In particular, we study $N \rightarrow 1$ PSR of qubit phase gates, i.e. qubit rotations a round $Z$ axis with an unknown angle, and show that if we access the gate only $N$-times, the optimal probability of perfect retrieving of its single use is $N/(N+1)$. We propose a quantum circuit realization for the optimal protocol and show that programmable phase gate [PRL 88, 047905 (2002)] can be turned into $(2^k-1)\rightarrow 1$ optimal PSR of phase gates and requires only $k$ CNOT gates, while having exponentially small failure probability in $k$.

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