arXiv subjects

Cheng-Qian Xu

Publications and source records attributed to Cheng-Qian Xu.

7 recordsLinked to original sources

arXiv2025

Quantum Resource Theories of Anyonic Entanglement

As information carriers for fault-tolerant quantum computing, systems composed of anyons exhibit non-tensor product state spaces due to their distinctive fusion rules, leading to fundamentally different entanglement properties from conventional quantum systems. However, a quantitative characterization of entanglement for general anyonic states remains elusive. In this Letter, within the framework of resource theory, we propose three measures that quantify total entanglement, conventional entanglement, and anyonic charge entanglement (ACE), respectively. We demonstrate that total entanglement can be decomposed into conventional entanglement and ACE, revealing distinct entanglement structures in anyonic systems compared to those in conventional quantum systems. We further illustrate a geometric interpretation of our ACE measure and establish its equivalence to a previously proposed probe of ACE, extending the known equivalence between the geometric interpretation and operational significance of bipartite correlations. Our work broadens the understanding of entanglement.

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arXiv2025

Superactivation of Bell nonlocality in pure anyonic states

Standard quantum information theory is founded on the assumption that multi-party state space possesses a tensor product structure. Anyons, as quasiparticles in two-dimensional systems, exhibit unique entanglement properties that differ from the conventional quantum systems, resulting from the absence of a tensor product structure in their state spaces. This motivates us to investigate the relationship between Bell nonlocality and entanglement in anyonic states. Specifically, we find that certain pure anyonic states with non-zero anyonic entanglement entropy (AEE) are local, yet exhibit nonlocality when subjected to collective measurements on multiple copies-a phenomenon known as superactivation of nonlocality, which is typically observed in conventional mixed states. To analyze this, we decompose the total entanglement of anyonic states into two components: one from the tensor product structure and the other representing residual contributions. By studying their asymptotic behavior, we find that the former gradually increases and approaches the AEE while the latter diminishes with the number of copies. Crucially, the entanglement component associated with the tensor product structure demonstrates a significant correlation with nonlocality, which explains the observed superactivation of nonlocality. Our findings provide new insights into the connection between entanglement and nonlocality in anyonic systems.

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arXiv2024

Learning quantum phases via single-qubit disentanglement

Identifying phases of matter presents considerable challenges, particularly within the domain of quantum theory, where the complexity of ground states appears to increase exponentially with system size. Quantum many-body systems exhibit an array of complex entanglement structures spanning distinct phases. Although extensive research has explored the relationship between quantum phase transitions and quantum entanglement, establishing a direct, pragmatic connection between them remains a critical challenge. In this work, we present a novel and efficient quantum phase transition classifier, utilizing disentanglement with reinforcement learning-optimized variational quantum circuits. We demonstrate the effectiveness of this method on quantum phase transitions in the transverse field Ising model (TFIM) and the XXZ model. Moreover, we observe the algorithm's ability to learn the Kramers-Wannier duality pertaining to entanglement structures in the TFIM. Our approach not only identifies phase transitions based on the performance of the disentangling circuits but also exhibits impressive scalability, facilitating its application in larger and more complex quantum systems. This study sheds light on the characterization of quantum phases through the entanglement structures inherent in quantum many-body systems.

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arXiv2023

Quantum mutual information redistribution by Number Partitioning algorithm

Quantum information distribution in a tripartite state plays a fundamental role in quantum information processes. Here we investigate how a bipartite unitary transformation $U_{AB}$ redistributes the quantum mutual information with the third party $C$ in a tripartite pure state $|ψ\rangle_{ABC}$ in a $d_A\times d_B\times d_C$ dimensional Hilbert space. In particular, we focus on finding out the optimal unitary transformation $U_{AB}^{\ast}$ that maximizes the quantum mutual entropy between party $A$ and party $C$, $I(A:C)=S(ρ_A)-S(ρ_B)+S(ρ_C)$. We show that the mutual entropy $I(A:C)$ is upper bounded by $2S(ρ_C)$ derived from the Araki-Lieb inequality. This upper bound can be realized via an optimal unitary transformation for any pure state with the rank $r_{C}$ of $ρ_C$ satisfying $r_C\le d_A$. For a generic pure state with $r_C> d_A$, the upper bound can not be realized by any bipartite unitary transformation. To maximize the mutual entropy in the latter case, we propose a fast numerical algorithm to produce an approximate optimal unitary transformation, where our optimization is transformed into a modified number partition problem. The validness of our algorithm is confirmed by its comparison with the results from the Adam algorithm for parameterized unitary transformations. Our approximate algorithm thus provides a practical protocol to implement redistribution of quantum mutual information for a tripartite quantum state with high dimensions.

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arXiv2023

Topological correlation: anyonic states cannot be determined by local operations and classical communication

Anyonic system not only has potential applications in the construction of topological quantum computer, but also presents a unique property known as topological entanglement entropy in quantum many-body systems. How to understand topological entanglement entropy is one of the most concerned problems for physicists. For an anyonic bipartite system, we define an operational measure of topological correlation based on the principle of maximal entropy, where the topological correlation is the information that cannot be accessed by local operations constrained by anyonic superselection rules and classical communication. This measure can be extended to measure non-local resources of other compound quantum systems in the presence of superselection rules. For a given anyonic bipartite state with maximal rank, we prove that its topological correlation is equal to its entropy of anyonic charge entanglement that has been shown in the literature to be able to derive topological entanglement entropy. This measure provides a more refined classification of correlations in a multipartite system with superselection rules and an illuminating approach to topological phase classification.

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arXiv2022

Quantum teleportation using Ising anyons

Anyons have been extensively investigated as information carriers in topological quantum computation. However, how to characterize the information flow in quantum networks composed of anyons is less understood, which motivates us to study quantum communication protocols in anyonic systems. Here we propose a general topologically protected protocol for quantum teleportation based on the Ising anyon model and prove that with our protocol an unknown anyonic state of any number of Ising anyons can be teleported from Alice to Bob. Our protocol naturally generalizes quantum state teleportation from systems of locally distinguishable particles to systems of Ising anyons, which may promote our understandings of anyonic quantum entanglement as a quantum resource. In addition, our protocol is expected to be realized with the Majorana zero modes, one of the possible physical realizations for the Ising anyon in experiments.

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arXiv2021

Deterministic quantum one-time pad via Fibonacci anyons

Anyonic states, which are topologically robust originated from their peculiar structure of Hilbert space, have important applications in quantum computing and quantum communication. When an anyonic state is used as an information carrier of the deterministic quantum one-time pad (DQOTP), we find that the Fibonacci particle-antiparticle pair produced from vacuum can be used to asymptotically send $2\log_2 d_τ$ bits of classical information ($d_τ$ is the quantum dimension of a Fibonacci anyon $τ$), which equals to the anyonic mutual information of the pair. Furthermore, by studying the DQOTP via a parameterized state of six Fibonacci anyons with trivial total charge, we give the analytical results of the maximum number of messages that can be sent for different parameters, which is a step function with every step corresponding to a regular simplex from the viewpoint of geometry. The results for the maximum number of messages sent by the DQOTP can be explained by the anyonic accessible information.

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