arXiv:quant-ph/0611146

Voronoi Diagrams and a Numerical Estimation of a Quantum Channel Capacity

Kimikazu Kato, Mayumi Oto, Imai, Hiroshi, Keiko Imai

Published Nov 14, 2006• 5 citations

Abstract

We give a new geometric interpretation of quantum pure states. Using Voronoi diagrams, we reinterpret the structure of the space of pure states as a subspace of the quantum state space. In addition to the known coincidence of some Voronoi diagrams for one-qubit pure states, we will show that even for mixed one-qubit states, as far as sites are given as pure states, the Voronoi diagram with respect to some distances -- the divergence, the Bures distance, and the Euclidean distance -- are all the same. As to higher level pure quantum states, for the divergence, the Fubini-Study distance, and the Bures distance, the coincidence of the diagrams still holds, while the coincidence of the diagrams with respect to the divergence and the Euclidean distance no longer holds. That fact has a significant meaning when we try to apply the method used for a numerical estimation of a one-qubit quantum channel capacity to a higher level system.

DOI: 10.48550/arxiv.quant-ph/0611146

Related papers

On a Geometric Structure of Pure Multi-qubit Quantum States and Its Applicability to a Numerical Computation

Kimikazu Kato

For one-qubit pure quantum states, it is already proved that the Voronoi diagrams with respect to two distances - Euclidean distance and the quantum divergence - coincide. This fact is a support for a known method to calculate the Holevo capacity. To consider an applicability of this method to quantum states of a higher level system, it is essential to check if the coincidence of the Voronoi diagrams also occurs. In this paper, we show a negative result for that expectation. In other words, we mathematically prove that those diagrams no longer coincide in a higher dimension. That indicates that the method used in one-qubit case to calculate the Holevo capacity might not be effective in a higher dimension.

arXiv:quant-ph/0607029International Symposium on Voronoi Diagrams in Science and EngineeringDec 1, 20065 citations

Voronoi Diagrams for Pure 1-qubit Quantum States

Kato, Kimikazu, Oto, Mayumi, Imai, Hiroshi +1 more

1-qubit quantum states form a space called the three-dimensional Bloch ball. To compute Holevo capacity, Voronoi diagrams in the Bloch ball with respect to the quantum divergence have been used as a powerful tool. These diagrams basically treat mixed quantum states corresponding to points in the interior of the Bloch ball. Due to the existence of logarithm in the quantum divergence, the diagrams are not defined on pure quantum states corresponding to points on the two-dimensional sphere. This paper first defines the Voronoi diagrams for pure quantum states on the Bloch sphere by the Fubini-Study distance and the Bures distance. We also introduce other Voronoi diagrams on the sphere obtained by taking a limit of Voronoi diagrams for mixed quantum states by the quantum divergences in the Bloch ball. These diagrams are shown to be equivalent to the ordinary Voronoi diagram on the sphere.

arXiv:quant-ph/0604101Apr 14, 200618 citations

Computational Geometry Analysis of Quantum State Space and Its Applications.

Kimikazu Kato, Mayumi Oto, Hiroshi Imai +1 more

We show some coincidences of Voronoi diagrams in a quantum state space with respect to some distances. This means a computational geometry interpretation of a structure of a quantum state space. More properly, we investigate the Voronoi diagrams with respect to the divergence, Fubini-Study distance, Bures distance, geodesic distance and Euclidean distance.

Jan 1, 20080 citations

Voronoi Diagrams for Quantum States and Its Application to a Numerical Estimation of a Quantum Channel Capacity

Kimikazu Kato

In quantum information theory, a geometric approach, known as "quantum information geometry," has been considered as a powerful method. In this thesis, we give a computational geometric interpretation to the geometric structure of a quantum system. Especially we introduce the concept of the Voronoi diagram and the smallest enclosing ball problem to the space of quantum states. With those tools in computational geometry, we analyze the adjacency structure of a point set in the quantum state space. Additionally, as an application, we show an effective method to compute the capacity of a quantum channel.

arXiv:0803.3109Mar 21, 20083 citations

Quantum Voronoi diagrams and Holevo channel capacity for 1-qubit quantum states

Frank Nielsen, Richard Nock

In this paper, we first introduce a smooth parametric family of Bregman-Csiszar quantum entropies including the von Neumann and Burg quantum entropies. We then describe the dualistic nature of Voronoi diagrams for 1-qubit quantum states inside the 3D Bloch ball representation. We show that these diagrams can be computed as Bregman Voronoi diagrams for the corresponding Bregman generator acting on Hermitian density matrices. This implies that these dual diagrams can be derived from power diagrams of balls in the Laguerre geometry, and allows one to prove by equivalence that the von Neumann quantum Voronoi diagram on the degenerated Bloch sphere of pure quantum states coincides with the ordinary Euclidean Voronoi diagram, bypassing the fact that the quantum divergence is not defined there. We then show how to compute the Holevo channel capacity of 1-qubit quantum states, and provide a practical approximation algorithm based on Bregman core-sets. Finally, we define the quantum sided centroids that yield practical upper bounds on the Holevo capacity in linear time.

IEEE International Symposium on Information Theory (ISIT)Jul 1, 20087 citations

Unveiling the geometric meaning of quantum entanglement: Discrete and continuous variable systems

Arthur Vesperini, Ghofrane Bel-Hadj-Aissa, Lorenzo Capra +1 more

We show that the manifold of quantum states is endowed with a rich and nontrivial geometric structure. We derive the Fubini–Study metric of the projective Hilbert space of a multi-qubit quantum system, endowing it with a Riemannian metric structure, and investigate its deep link with the entanglement of the states of this space. As a measure, we adopt the entanglement distance E preliminary proposed in Phys. Rev. A 101, 042129 (2020). Our analysis shows that entanglement has a geometric interpretation: E(∣ψ〉) is the minimum value of the sum of the squared distances between ∣ψ〉 and its conjugate states, namely the states νμ · σμ∣ψ〉, where νμ are unit vectors and μ runs on the number of parties. Within the proposed geometric approach, we derive a general method to determine when two states are not the same state up to the action of local unitary operators. Furthermore, we prove that the entanglement distance, along with its convex roof expansion to mixed states, fulfils the three conditions required for an entanglement measure, that is: i) E(∣ψ〉) = 0 iff ∣ψ〉 is fully separable; ii) E is invariant under local unitary transformations; iii) E does not increase under local operation and classical communications. Two different proofs are provided for this latter property. We also show that in the case of two qubits pure states, the entanglement distance for a state ∣ψ〉 coincides with two times the square of the concurrence of this state. We propose a generalization of the entanglement distance to continuous variable systems. Finally, we apply the proposed geometric approach to the study of the entanglement magnitude and the equivalence classes properties, of three families of states linked to the Greenberger–Horne–Zeilinger states, the Briegel Raussendorf states and the W states. As an example of application for the case of a system with continuous variables, we have considered a system of two coupled Glauber coherent states.

arXiv:2307.16835Frontiers of PhysicsApr 16, 202414 citations