Equivalence Checking of Quantum Circuits

Publication Type:
Thesis
Issue Date:
2023
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Equivalence checking plays a crucial role in the electronic design automation processes of classical systems, and as quantum devices and circuits continue to grow in scale, the importance of verifying quantum circuits is growing rapidly. It is anticipated that equivalence checking will also become a vital technique in the quantum realm. In this thesis, we explore various types of equivalence checking, encompassing exact equivalence, approximate equivalence, and symbolic equivalence checking. To facilitate these verification tasks, we introduce a novel data structure called the Tensor Decision Diagram (TDD) as a representation for quantum circuits. The TDD provides a compact and canonical framework for manipulating tensor networks, leveraging the benefits of both decision diagrams and tensor networks. By harnessing the uniqueness and compactness of TDDs, we achieve an efficient and canonical representation that captures the essential information of a circuit while minimising computational and memory complexity. Furthermore, we develop specialised algorithms and tools that utilise TDD representation to verify different types of quantum circuits, including combinational quantum circuits, dynamic quantum circuits, noisy quantum circuits, and parameterised quantum circuits. These tools enable us to perform exact equivalence checking, approximate equivalence checking, and symbolic equivalence checking on quantum circuits, empowering researchers and practitioners to ensure the correctness and functionality of their designs. Additionally, we explore the realm of symbolic execution for quantum circuits, offering a novel approach to verify the behaviour and outputs of quantum circuits with symbolic inputs. This work gives us more opportunities to learn the functionality of a quantum circuit clearly. Moreover, we explore the concept of quantum image computation, which enables the calculation of the image of a subspace under a quantum transition system. This technique provides further verification capabilities for quantum circuits.
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