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Journal of Physics A Mathematical and Theoretical

Characterization of quantum coherence by l p -norm and skew information in MUBs *

Yuan-Hong Tao, Qing Yu, Liu Sun, Wei-Ning Li, Yan-Wei Zhou

Published Feb 4, 2026• 0 citations
Publisher

Abstract

Abstract Quantum coherence stands as a core property of quantum mechanics, its origin rooted in the superposition principle that governs quantum states. Leveraging mutually unbiased bases (MUBs), this paper delves into an in-depth exploration of quantum coherence characteristics through the lens of the l p -norm and s k e w Information. To begin with, we establish rigorous equality relations for the l p -norm coherence of qubit states under Pauli MUBs. Following this, we derive the complementary relations (upper bounds) and uncertainty relations (lower bounds) associated with l p -norm coherence under MUBs within arbitrary d-dimensional systems. Then, by virtue of deducing the connection between the classical purity and quantum purity of the square root of the quantum state, i.e. ρ , we further elaborate on the strict equality relations of skew-information coherence as well as several corresponding entropy-based coherences under MUBs in d-dimensional systems. Additionally, we provide illustrative examples to instantiate each of these relations, enhancing their clarity and practical relevance.

DOI
10.1088/1751-8121/ae41f9

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Abstract Quantum coherence stands as a core property of quantum mechanics, its origin rooted in the superposition principle that governs quantum states. Leveraging mutually unbiased bases (MUBs), this paper delves into an in-depth exploration of quantum coherence characteristics through the lens of the l p -norm and s k e w Information. To begin with, we establish rigorous equality relations for the l p -norm coherence of qubit states under Pauli MUBs. Following this, we derive the complementary relations (upper bounds) and uncertainty relations (lower bounds) associated with l p -norm coherence under MUBs within arbitrary d-dimensional systems. Then, by virtue of deducing the connection between the classical purity and quantum purity of the square root of the quantum state, i.e. ρ , we further elaborate on the strict equality relations of skew-information coherence as well as several corresponding entropy-based coherences under MUBs in d-dimensional systems. Additionally, we provide illustrative examples to instantiate each of these relations, enhancing their clarity and practical relevance.
The concept of quantum coherence, including various ways to quantify the degree of coherence with respect to the prescribed basis, is currently the subject of active research. The complementarity of quantum coherence in different bases was studied by deriving upper bounds on the sum of the corresponding measures. To obtain a two-sided estimate, lower bounds on the coherence quantifiers are also of interest. Such bounds are naturally referred to as uncertainty relations for quantum coherence. We obtain new uncertainty relations for coherence quantifiers averaged with respect to a set of mutually unbiased bases (MUBs). To quantify the degree of coherence, the relative entropy of coherence and the geometric coherence are used. Further, we also derive novel state-independent uncertainty relations for a set of MUBs in terms of the min-entropy.
Abstract The quantum uncertainty relation characterizes the restriction of the quantum coherence on different measurement bases. The skew information of coherence is a coherence measure both operationally and informatically. We study the quantum uncertainty relation for the skew information of coherence under any two orthonormal bases. In qubit and qutrit systems, we derive the quantum uncertainty relations with the lower bounds in the factorized forms by the purity of quantum states and the incompatibility between two orthonormal bases. Especially the lower bound in qubit systems is strictly positive for non-maximally mixed states and incompatible orthonormal bases. These quantum uncertainty relations reveal the intrinsic relation among the coherence, the purity and the incompatibility between two orthonormal bases quantitatively. The advantages of these quantum uncertainty relations are illustrated by some specific examples. This method we developed here is beneficial to some other quantum uncertainty relations.
Abstract We study the skew information-based coherence of quantum states and derive explicit formulas for Werner states and isotropic states in a set of autotensors of mutually unbiased bases (MUBs). We also give surfaces of skew information-based coherence for Bell-diagonal states and a special class of X states in both computational basis and in MUBs. Moreover, we depict the surfaces of the skew information-based coherence for Bell-diagonal states under various types of local nondissipative quantum channels. The results show similar as well as different features compared with relative entropy of coherence and l 1 norm of coherence.
Abstract This study explores the coherence of Bell-diagonal states under two complete sets of mutually unbiased bases (MUBs), focusing on four measures: the l 1 norm, l p norm, Rényi relative α-entropy, and relative entropy. We initially construct a complete set of MUBs in C 4 by incorporating two maximally entangled bases unbiased with respect to the autotensor of mutually unbiased bases (AMUBs), subsequently comparing it with the canonical set documented in existing literature. We establish the expressions for Bell-diagonal states under these two complete sets of MUBs and demonstrate that the aggregate of each coherence measure across both sets is equivalent. Additionally, we present the upper bounds for the sums of the l 1 norm, l p norm, and Rényi relative 2-entropy of coherence. Furthermore, we describe the geometric structure associated with the sum of relative entropy coherence, revealing that an increase in the sum of relative entropy of coherence corresponds to an increase in the parameter of the Bell-diagonal states.
The resource theoretic measure of quantum coherence is basis dependent, and the amount of coherence contained in a state is different in different bases. We obtained analytical solutions for the maximum coherence by optimizing the reference basis and highlighted the essential role of the mutually unbiased bases (MUBs) on attaining the maximum coherence. Apart from the relative entropy of coherence, we showed that the MUBs are optimal for the robustness of coherence, the coherence weight, and the modified skew information measure of coherence for any state. Moreover, the MUBs are optimal for all the faithful coherence measures if the state is pure or is of the single qubit. We also highlighted an upper bound for the l1{l}_{1}l1​ norm of coherence and compared it with the other bounds as well as the maximum one attainable by optimizing the reference basis.
Various measures have been suggested recently for quantifying the coherence of a quantum state with respect to a given basis. We first use two of these, the l1{l}_{1}l1​-norm and relative entropy measures, to investigate tradeoffs between the coherences of mutually unbiased bases. Results include relations between coherence, uncertainty, and purity; tight general bounds restricting the coherences of mutually unbiased bases; and an exact complementarity relation for qubit coherences. We further define the average coherence of a quantum state. For the l1{l}_{1}l1​-norm measure this is related to a natural ``coherence radius'' for the state and leads to a conjecture for an l2{l}_{2}l2​-norm measure of coherence. For relative entropy the average coherence is determined by the difference between the von Neumann entropy and the quantum subentropy of the state and leads to upper bounds for the latter quantity. Finally, we point out that the relative entropy of coherence is a special case of G-asymmetry, which immediately yields several operational interpretations in contexts as diverse as frame alignment, quantum communication, and metrology, and suggests generalizing the property of quantum coherence to arbitrary groups of physical transformations.