通过稠密对偶基直接测量密度矩阵

Quantum dense coding by spatial state entanglement

We have presented a theoretical extended version of dense coding protocol using entangled position state of two particles shared between two parties. A representation of Bell states and the required unitary operators are shown utilizing symmetric normalized Hadamard matrices. In addition, some explicit and conceivable forms for the unitary operators are presented by using some introduced basic operators. It is shown that, the proposed version is logarithmically efficient than some other multi-qubit dense coding protocols.

All Teleportation and Dense Coding Schemes

We establish a one-to-one correspondence between (1) quantum teleportation schemes, (2) dense coding schemes, (3) orthonormal bases of maximally entangled vectors, (4) orthonormal bases of unitary operators with respect to the Hilbert-Schmidt scalar product, and (5) depolarizing operations, whose Kraus operators can be chosen to be unitary. The teleportation and dense coding schemes are assumed to be ``tight'' in the sense that all Hilbert spaces involved have the same finite dimension d, and the classical channel involved distinguishes d^2 signals. A general construction procedure for orthono…

Effect of matrix sparsity and quantum noise on quantum random walk linear solvers

We study the effects of quantum noise in hybrid quantum-classical solver for sparse systems of linear equations using quantum random walks, applied to stoquastic Hamiltonian matrices. In an ideal noiseless quantum computer, sparse matrices achieve solution vectors with lower relative error than dense matrices. However, we find quantum noise reverses this effect, with overall error increasing as sparsity increases. We identify invalid quantum random walks as the cause of this increased error and propose a revised linear solver algorithm which improves accuracy by mitigating these invalid walks.

非厄米特矩阵的实方差变分量子本征值求解器

Real Variance-Based Variational Quantum Eigensolver for Non-Hermitian Matrices

本文提出基于实方差的变分量子本征值求解器（RVVQE），用于非厄米特算子，通过设计正确的成本函数保证收敛到真实本征态，利用厄米特测量实现算法易实现，并展示了在不同维度的非厄米特矩阵上的性能和可扩展性。

HHL算法的优化

Optimization of the HHL Algorithm

本文研究了HHL算法在近量子模拟器上的实现与优化，通过Suzuki-Trotter分解和块编码方法提升保真度和可扩展性，发现矩阵结构对HHL算法的实际效率至关重要。

Quench Dynamics in Randomly Generated Extended Quantum Models

We analyze the thermalization properties and the validity of the Eigenstate Thermalization Hypothesis in a generic class of quantum Hamiltonians where the quench parameter explicitly breaks a Z_2 symmetry. Natural realizations of such systems are given by random matrices expressed in a block form where the terms responsible for the quench dynamics are the off-diagonal blocks. Our analysis examines both dense and sparse random matrix realizations of the Hamiltonians and the observables. Sparse random matrices may be associated with local quantum Hamiltonians and they show a different spread of …