Quantum State Preparation via Free Binary Decision Diagram
| Autor: | Tanaka, Yu, Yamasaki, Hayata, Murao, Mio |
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| Rok vydání: | 2024 |
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| Druh dokumentu: | Working Paper |
| Popis: | Quantum state preparation (QSP) is a fundamental task in quantum computation to prepare a quantum state for a given classical description of the quantum state. The classical description of an $n$-qubit quantum state may have $\exp(O(n))$ parameters in general, which are inherently inefficient to deal with in the worst case; however, in many practical cases, we may be able to employ suitable data structures to represent such large-scale data in a compressed way, e.g., by using a free binary decision diagram (FBDD), a rooted directed acyclic graph with two terminal nodes to concisely represent a Boolean function. We here construct a quantum algorithm for QSP when the classical description of a quantum state is given by an FBDD with weighted edges, and analyze the space, and time complexity of QSP in this setting. We provide a nontrivial example of an $n$-qubit state that can be represented by a weighted FBDD with $N=O(\mathrm{poly}(n))$ nodes rather than $\mathrm{exp}(O(n))$. We show that any quantum state represented by the weighted FBDD with $N$ nodes can be prepared by an $O(N)$-sized quantum circuit using $N$ ancillary qubits, exponentially improving the required circuit size for QSP compared to other BDD-based QSPs. We also provide another example of an $n$-qubit state that can be represented by a weighted FBDD with $N=O(n^2)$ nodes, and $O(n^2)$ ancillary qubits, but cannot be prepared efficiently by a QSP based on the amplitude amplification. These results provide techniques to employ FBDDs as a tool for broadening the possibility of efficient QSP. Comment: 19 pages with 1 table and 9 figures |
| Databáze: | arXiv |
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