Complex quantum circuits are constituted by combinations of quantum subroutines. The computation is possible as long as the quantum data encoding is consistent throughout the circuit. Despite its fundamental importance, the formalization of quantum data encoding has never been addressed systematically so far. We formalize the concept of quantum data encoding, namely the format providing a representation of a data set through a quantum state, as a distinct abstract layer with respect to the associated data loading circuit. We survey existing encoding methods and their respective strategies for classical-to-quantum exact and approximate data loading, for the quantum-to-classical extraction of information from states, and for quantum-to-quantum encoding conversion. Next, we show how major quantum algorithms find a natural interpretation in terms of data loading. For instance, the Quantum Fourier Transform is described as a quantum encoding converter, while the Quantum Amplitude Estimation as an extraction routine. The new conceptual framework is exemplified by considering its application to quantum-based Monte Carlo simulations, thus showcasing the power of the proposed formalism for the description of complex quantum circuits. Indeed, the approach clarifies the structure of complex quantum circuits and enables their efficient design.
Generalised Bit-Vector Abstractions for Formal Verification of Quantum Error-Detection and Entanglement Circuits over {H,X,C-NOT}: CSS Constructions, Soundness, and Mutation-Based Validation
Synthesis and Optimization of Encoding Circuits for Fault-Tolerant Quantum Computation
Technical University of Munich（慕尼黑工业大学）；Global Technology Applied Research, JPMorgan Chase（摩根大通全球技术应用研究部）；QuTech, Delft University of Technology（代尔夫特理工大学 QuTech）；Quantum and Computer Engineering Department, Delft University of Technology（代尔夫特理工大学量子与计算机工程系）；neQxt
Processing through encoding: Quantum circuit approaches for point-wise multiplication and convolution
Computation-Based Science and Technology Research Center -- The Cyprus Institute（计算科学与技术研究中心——塞浦路斯研究所）；Center for Quantum Technology and Applications -- Deutsches Elektronen-Synchrotron DESY（量子技术与应用中心——德意志电子同步辐射研究中心）
