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One of the major challenges in realizing fault-tolerant quantum computers (FTQCs) is the requirement for a large number of physical qubits. To address this issue, high-rate quantum error correcting codes, which efficiently embed logical…

Quantum Physics · Physics 2026-05-20 Kohei Yamamoto , Keisuke Fujii

Shallow quantum circuits feature not only computational advantages over their classical counterparts but also cutting-edge applications. Storing quantum information generated by shallow circuits is a fundamental question of both theoretical…

Quantum Physics · Physics 2025-01-14 Yuxiang Yang

We consider the preparation of matrix product states (MPS) on quantum devices via quantum circuits of local gates. We first prove that faithfully preparing translation-invariant normal MPS of $N$ sites requires a circuit depth…

Quantum Physics · Physics 2024-01-26 Daniel Malz , Georgios Styliaris , Zhi-Yuan Wei , J. Ignacio Cirac

We propose a new method to extend the size of a quantum computation beyond the number of physical qubits available on a single device. This is accomplished by randomly inserting measure-and-prepare channels to express the output state of a…

We investigate the generation of quantum states for precision metrology in noisy two-level systems. These states are obtained by optimizing a variational quantum circuit to maximize the quantum Fisher information (QFI) of the output state…

Quantum computing is a promising paradigm that may overcome the current computational power bottlenecks. The increasing maturity of quantum processors provides more possibilities for the development and implementation of quantum algorithms.…

Quantum Physics · Physics 2025-10-15 Ge Yan , Wenjie Wu , Yuheng Chen , Kaisen Pan , Xudong Lu , Zixiang Zhou , Yuhan Wang , Ruocheng Wang , Junchi Yan

Quantum state preparation, also known as encoding or embedding, is a crucial initial step in many quantum algorithms and often constrains theoretical quantum speedup in fields such as quantum machine learning and linear equation solvers.…

Quantum Physics · Physics 2025-12-04 Vittorio Pagni , Gary Schmiedinghoff , Kevin Lively , Michael Epping , Michael Felderer

The preparation of quantum states is one of the most fundamental tasks in quantum computing, and a key primitive in many quantum algorithms. Of particular interest to areas such as quantum simulation and linear-system solvers are sparse…

Quantum Physics · Physics 2026-01-15 Felix Rupprecht , Sabine Wölk

Quantum data loading plays a central role in quantum algorithms and quantum information processing. Many quantum algorithms hinge on the ability to prepare arbitrary superposition states as a subroutine, with claims of exponential speedups…

Quantum Physics · Physics 2025-09-25 Chun-Tse Li , Hao-Chung Cheng

We investigate optimized quantum state preparation for quantum metrology applications in noisy environments. Using the QFI-Opt package, we simulate a low-depth variational quantum circuit (VQC) composed of a sequence of global rotations and…

The evaluation of expectation values $Tr\left[\rho O\right]$ for some pure state $\rho$ and Hermitian operator $O$ is of central importance in a variety of quantum algorithms. Near optimal techniques developed in the past require a number…

Quantum Physics · Physics 2020-03-04 Alessandro Roggero , Alessandro Baroni

The initial state creation is a starting point of many quantum algorithms and usually is considered as a separate subroutine not included into the algorithm itself. There are many algorithms aimed on creation of special class of states. Our…

Quantum Physics · Physics 2025-05-01 Alexander I. Zenchuk , Wentao Qi , Junde Wu

We present an extension of the Evolving density matrices on Qubits (E$\rho$OQ) framework that enables efficient fault-tolerant preparation of fermionic quantum states. The original method circumvents state preparation by stochastic…

Quantum Physics · Physics 2026-03-25 Erik J. Gustafson , Henry Lamm

Quantum error correction is vital for implementing universal quantum computing. A key component is the encoding circuit that maps a product state of physical qubits into the encoded multipartite entangled logical state. Known methods are…

Quantum Physics · Physics 2021-04-07 Xiaosi Xu , Simon C. Benjamin , Xiao Yuan

Quantum machine learning (QML) is emerging as an application of quantum computing with the potential to deliver quantum advantage, but its realisation for practical applications remains impeded by challenges. Amongst those, a key barrier is…

Minimizing the use of CNOT gates in quantum state preparation is a crucial step in quantum compilation, as they introduce coupling constraints and more noise than single-qubit gates. Reducing the number of CNOT gates can lead to more…

Information Theory · Computer Science 2024-09-05 Hanyu Wang , Bochen Tan , Jason Cong , Giovanni De Micheli

This work introduces a self-learning protocol that incorporates measurement and feedback into variational quantum circuits for efficient quantum state preparation. By combining projective measurements with conditional feedback, the protocol…

Quantum Physics · Physics 2025-07-16 Daniel Alcalde Puente , Matteo Rizzi

We propose a quantum algorithm for the purification of a generic mixed state $\rho$ of a $n$-qudit system by using an ancillary $n$-qudit system. The algorithm is optimal in that (i) the number of ancillary qudits cannot be reduced, (ii)…

Quantum Physics · Physics 2009-05-04 Giuliano Benenti , Giuliano Strini

We use a random search technique to find quantum gate sequences that implement perfect quantum state preparation or unitary operator synthesis with arbitrary targets. This approach is based on the recent discovery that there is a large…

Quantum Physics · Physics 2024-10-25 Sahel Ashhab , Fumiki Yoshihara , Miwako Tsuji , Mitsuhisa Sato , Kouichi Semba

Inspired by recent advances in the manipulation of superconducting circuits coupled to mechanical modes in the quantum regime, we propose a protocol for generating superpositions of orthogonally squeezed states in a quantum harmonic…

Quantum Physics · Physics 2026-03-05 Marius K. Hope , Jonas Lidal , Francesco Massel