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Optimization of unitary transformations in Variational Quantum Algorithms benefits highly from efficient evaluation of cost function gradients with respect to amplitudes of unitary generators. We propose several extensions of the…

Quantum Physics · Physics 2022-01-12 Artur F. Izmaylov , Robert A. Lang , Tzu-Ching Yen

From a geometric approach, we derive the minimum number of applications needed for an arbitrary Controlled-Unitary gate to construct a universal quantum circuit. A new analytic construction procedure is presented and shown to be either…

Quantum Physics · Physics 2009-11-10 Jun Zhang , Jiri Vala , Shankar Sastry , K. Birgitta Whaley

Quantum circuit model is the most popular paradigm for implementing complex quantum computation. Based on Cartan decomposition, we show that $2(N-1)$ generalized controlled-$X$ (GCX) gates, $6$ single-qubit rotations about the $y$- and…

Quantum Physics · Physics 2022-09-13 Gui-Long Jiang , Hai-Rui Wei , Guo-Zhu Song , Ming Hua

Current proposals for quantum compilers require the synthesis and optimization of linear reversible circuits and among them CNOT circuits. Since these circuits represent a significant part of the cost of running an entire quantum circuit,…

High-throughput QR decomposition is a key operation in many advanced signal processing and communication applications. For some of these applications, using floating-point computation is becoming almost compulsory. However, there are scarce…

Hardware Architecture · Computer Science 2020-10-26 Javier Hormigo , Sergio D. Muñoz

An algorithm for reversible logic synthesis is proposed. The task is, for a given $n$-bit substitution map $P_n: \{0,1\}^n \rightarrow \{0,1\}^n$, to find a sequence of reversible logic gates that implements the map. The gate library…

Logic in Computer Science · Computer Science 2024-07-24 Hochang Lee , Kyung Chul Jeong , Daewan Han , Panjin Kim

In this paper, we propose an iterative algorithm using polar decomposition to approximate a channel characterized by a single unitary matrix based on input-output quantum state pairs. In limited data, we state and prove that the optimal…

Numerical Analysis · Mathematics 2025-06-27 Matthew M. Lin , Hao-Wei Huang , Bing-Ze Lu

Unitary transformations and density matrices are central objects in quantum physics and various tasks require to introduce them in a parameterized form. In the present article we present a parameterization of the unitary group…

Quantum Physics · Physics 2010-08-18 Christoph Spengler , Marcus Huber , Beatrix C. Hiesmayr

Given that quantum error correction processes are unreliable, an efficient error syndrome extraction circuit should use fewer ancillary qubits, quantum gates, and measurements, while maintaining low circuit depth, to minimizing the circuit…

Quantum Physics · Physics 2025-07-14 Pei-Hao Liou , Ching-Yi Lai

We will present a few new generalizations of the multi-controlled X (MCX) gate that uses the quantum Fourier transform (QFT). Firstly, we will optimize QFT-MCX and prove that it is equivalent to a stair MCX gates array. This stair-wise…

Quantum Physics · Physics 2025-02-21 Vladimir V. Arsoski

Low-rank plus diagonal (LRPD) decompositions provide a powerful structural model for large covariance matrices, simultaneously capturing global shared factors and localized corrections that arise in covariance estimation, factor analysis,…

Numerical Analysis · Mathematics 2025-12-22 Kingsley Yeon , Mihai Anitescu

Quantum compilation is the process of decomposing high-level quantum algorithms or arbitrary unitary operations into quantum circuits composed of a specific set of quantum gates. Neutral atom quantum computing platform is a quantum…

Quantum Physics · Physics 2025-01-10 Chongyuan Xu

We present a general method for decomposing non-unitary operators into a linear combination of unitary operators, where the approximation error decays exponentially. The decomposition is based on a smooth periodic extension of the identity…

Quantum Physics · Physics 2026-01-27 Peter Brearley , Thomas Howarth

Quantum graph states are critical resources for various quantum algorithms, and also determine essential interconnections in distributed quantum computing. There are two schemes for generating graph states probabilistic scheme and…

Hardware Architecture · Computer Science 2025-03-26 Xiangyu Ren , Yuexun Huang , Zhiding Liang , Antonio Barbalace

A design framework to implement non-unitary input-output operations to a practical unitary photonic integrated circuit is described. This is achieved by utilising the cosine-sine decomposition to recover the unitarity of the original…

Optics · Physics 2025-01-15 Hussein Talib , Phillip D. Sewell , Ana Vukovic , Sendy Phang

We investigate ancilla-free linear combination of unitaries (LCU) as a framework for approximating complex quantum circuits. This is particularly effective for quantum optimization algorithms, where candidate solutions can be evaluated…

Quantum Physics · Physics 2026-05-20 Almudena Carrera Vazquez , Daniel J. Egger , Stefan Woerner

In variational quantum algorithms, parameterization is typically applied to single-qubit gates.In this study, we instead parameterize a generalized controlled gate and propose an algorithm to locally minimize the cost function by maximally…

We present an exact synthesis algorithm for qutrit unitaries in $\mathcal{U}_{3^n}(\mathbb{Z}[1/3,e^{2\pi i/3}])$ over the Clifford$+T$ gate set with at most one ancilla. This extends the already known result of qutrit metaplectic gates…

Quantum Physics · Physics 2024-05-15 Amolak Ratan Kalra , Manimugdha Saikia , Dinesh Valluri , Sam Winnick , Jon Yard

In this work, we introduce a general n-qubit formulation of control objectives that allows a control target to be specified in a diagonal frame, so that only the diagonal entries must be characterized, thus quadratically reducing the…

Quantum Physics · Physics 2026-02-23 Bora Baran , Tommaso Calarco , Matthias M. Mueller , Felix Motzoi

We develop the first constructive algorithms for compiling single-qubit unitary gates into circuits over the universal $V$ basis. The $V$ basis is an alternative universal basis to the more commonly studied $\{H,T\}$ basis. We propose two…

Quantum Physics · Physics 2013-07-29 Alex Bocharov , Yuri Gurevich , Krysta M. Svore