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Birkhoff's theorem tells that any doubly stochastic matrix can be decomposed as a weighted sum of permutation matrices. A similar theorem reveals that any unitary matrix can be decomposed as a weighted sum of complex permutation matrices.…

Mathematical Physics · Physics 2020-08-03 Alexis De Vos , Stijn De Baerdemacker

We present a novel framework for Linear Combination of Unitaries (LCU)-style decomposition tailored to structured sparse matrices, which frequently arise in the numerical solution of partial differential equations (PDEs). While LCU is a…

Quantum Physics · Physics 2025-07-29 Abeynaya Gnanasekaran , Amit Surana

Herein, we introduce a strategy to decompose an arbitrary square matrix into a linear combination of non-unitaries (LCNU) where each non-unitary term is embedded into a unitary matrix. The result is a linear combination of unitaries (LCU)…

Data centers are increasingly using high-speed circuit switches to cope with the growing demand and reduce operational costs. One of the fundamental tasks of circuit switches is to compute a sparse collection of switching configurations to…

Optimization and Control · Mathematics 2020-11-06 Víctor Valls , George Iosifidis , Leandros Tassiulas

The classic Birkhoff- von Neumann theorem states that the set of doubly stochastic matrices is the convex hull of the permutation matrices. In this paper, we study a generalisation of this theorem in the type $II_1$ setting. Namely, we…

Functional Analysis · Mathematics 2015-06-05 Liviu Paunescu , Florin Radulescu

The iterative method of Sinkhorn allows, starting from an arbitrary real matrix with non-negative entries, to find a so-called 'scaled matrix' which is doubly stochastic, i.e. a matrix with all entries in the interval (0, 1) and with all…

Mathematical Physics · Physics 2015-02-09 Alexis De Vos , Stijn De Baerdemacker

Sinkhorn proved that every entry-wise positive matrix can be made doubly stochastic by multiplying with two diagonal matrices. In this note we prove a recently conjectured analogue for unitary matrices: every unitary can be decomposed into…

Mathematical Physics · Physics 2015-09-07 Martin Idel , Michael M. Wolf

We consider different Linear Combination of Unitaries (LCU) decompositions for molecular electronic structure Hamiltonians. Using these LCU decompositions for Hamiltonian simulation on a quantum computer, the main figure of merit is the…

Quantum Physics · Physics 2023-06-13 Ignacio Loaiza , Alireza Marefat Khah , Nathan Wiebe , Artur F. Izmaylov

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

The Birkhoff polytope (the convex hull of the set of permutation matrices) is frequently invoked in formulating relaxations of optimization problems over permutations. The Birkhoff polytope is represented using $\Theta(n^2)$ variables and…

Optimization and Control · Mathematics 2016-02-16 Cong Han Lim , Stephen J. Wright

The randomized linear combination of unitaries (LCU) method with many applications to early fault-tolerant quantum computing algorithms has been proposed. This quantum algorithm computes the same expectation values as the original, fully…

Quantum Physics · Physics 2026-02-16 Kaito Wada , Hiroyuki Harada , Yasunari Suzuki , Yuuki Tokunaga , Naoki Yamamoto , Suguru Endo

Swap mapping is a quantum compiler optimization that, by introducing SWAP gates, maps a logical quantum circuit to an equivalent physically implementable one. The physical implementability of a circuit is determined by the fulfillment of…

Quantum Physics · Physics 2024-08-06 Nicola Mariella , Sergiy Zhuk

Hyper-Connections (HC) generalizes residual connections by introducing dynamic residual matrices that mix information across multiple residual streams, accelerating convergence in deep neural networks. However, unconstrained residual…

Machine Learning · Computer Science 2026-01-12 Yongyi Yang , Jianyang Gao

The Linear Combination of Unitaries (LCU) method is a powerful scheme for the block encoding of operators but suffers from high overheads. In this work, we discuss the parallelisation of LCU and in particular the SELECT subroutine of LCU…

Quantum Physics · Physics 2024-08-22 Gregory Boyd

A highly anticipated use of quantum computers is the simulation of complex quantum systems including molecules and other many-body systems. One promising method involves directly applying a linear combination of unitaries (LCU) to…

Quantum Physics · Physics 2022-02-02 Richard Meister , Simon C. Benjamin , Earl T. Campbell

Consider the problem of minimizing an expected logarithmic loss over either the probability simplex or the set of quantum density matrices. This problem includes tasks such as solving the Poisson inverse problem, computing the…

Optimization and Control · Mathematics 2024-03-12 Chung-En Tsai , Hao-Chung Cheng , Yen-Huan Li

The success of Hyper-Connections (HC) in neural networks (NN) has also highlighted issues related to its training instability and restricted scalability. The Manifold-Constrained Hyper-Connections (mHC) mitigate these challenges by…

Computation and Language · Computer Science 2026-01-30 Wuyang Zhou , Yuxuan Gu , Giorgos Iacovides , Danilo Mandic

Entropic regularization provides a simple way to approximate linear programs whose constraints split into two or more tractable blocks. The resulting objectives are amenable to cyclic Kullback-Leibler (KL) Bregman projections, with…

Optimization and Control · Mathematics 2026-05-11 Gabriel Peyré

Discrete circular convolution over $\mathbb{Z}/N\mathbb{Z}$ is a linear operator and can be implemented on quantum hardware within the linear-combination-of-unitaries (LCU) framework. In this work, we make this connection explicit through…

Quantum Physics · Physics 2026-03-17 Chen Yang , Kodai Kanemaru , Norio Yoshida , Sergey Gusarov , Hiroshi C. Watanabe

One limitation of the variational quantum eigensolver algorithm is the large number of measurement steps required to estimate different terms in the Hamiltonian of interest. Unitary partitioning reduces this overhead by transforming the…

Quantum Physics · Physics 2021-09-01 Alexis Ralli , Peter Love , Andrew Tranter , Peter Coveney
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