arXiv subjects

Chunfang Sun

Publications and source records attributed to Chunfang Sun.

At least 19 recordsLinked to original sources

arXiv2026

Nonreciprocal magnon-magnon entanglement in a spinning cavity-magnon system

Cavity-magnon systems, combining magnons and photons, offer a versatile platform for studying quantum entanglement and advancing quantum information science. In this work, we propose a scheme for generating nonreciprocal magnon-magnon entanglement in a hybrid system consisting of two yttrium iron garnet spheres coupled to a spinning whispering-gallery-mode cavity. By leveraging the magnon Kerr nonlinearity and the Sagnac effect arising from the cavity rotation, we show that the entanglement can be substantially enhanced, and the resulting entanglement exhibits pronounced nonreciprocal characteristics. Furthermore, our scheme demonstrates that the entanglement remains robust against thermal noise and persists at bath temperatures up to 100 mK. This work underscores the potential of spinning cavity-magnon systems as a versatile platform for realizing nonreciprocal quantum devices and facilitating the development of quantum technologies.

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arXiv2025

Magnonic entanglement in a chiral cavity-magnon coupling system

The generation of magnon entanglement and squeezing plays a crucial role in quantum information processing. In this study, we propose a scheme based on a chiral cavity-magnon system, which consists of a torus-shaped cavity and two yttrium iron garnet spheres. The magnon mode of each yttrium iron garnet sphere is selectively coupled to one of the two degenerate rotating microwave modes of the toroidal cavity. The system aims to achieve entangled and squeezed magnon states through the mediation of the cavity. We further show that bipartite entanglement can be achieved by tuning external driving parameters. Additionally, our scheme does not rely on the magnon Kerr nonlinearity, which is usually extremely weak in yttrium iron garnet spheres. This work provides insights and methods for the research of quantum states in cavity-magnon systems.

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arXiv2024

Generation of high-fidelity Greenberger-Horne-Zeilinger states in a driven hybrid quantum system

In this study, we propose a theoretical scheme for achieving long-distance Greenberger-Horne-Zeilinger states in a driven hybrid quantum system. By applying a microwave field to the YIG sphere, we utilize the Kerr effect to induce the squeezing of the magnon, thereby achieving an exponential enhancement of the coupling strength between the magnonic mode and spins, and we also discuss in detail the relationship between the squeezing parameter and the external microwave field. By means of the Schrieffer-Wolff transformation, the magnonic mode can be adiabatically eliminated under the large detuning condition, thereby establishing a robust effective interaction between spins essential for realizing the desired entangled state. Numerical simulations indicate that the squeezing parameter can be effectively increased by adjusting the driving field, and our proposal can generate high-fidelity Greenberger-Horne-Zeilinger states even in dissipative systems. Additionally, we extensively discuss the influence of inhomogeneous broadening on the entangled states, and the experimental feasibility shows that our results provide possibilities in the realms of quantum networking and quantum computing.

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arXiv2024

Ground-state chiral current via periodic modulation

In this study, we engineer the Dzyaloshinskii-Moriya interaction mediated by photons to emulate ground-state chiral current based on three-level atoms driven by quantum and classical fields. We employ adiabatic elimination techniques to derive an effective Dzyaloshinskii-Moriya interaction Hamiltonian of two-level systems, which can address the challenges arising from the finite lifetime of excited states. Furthermore, we can ensure to achieve desired dynamics through the implementation of periodic modulation on the atomic ground states. Besides, three-state and multi-state chiral current can be obtained by choosing appropriate driving frequencies and phases. We also design the Dzyaloshinskii-Moriya interaction for the other components based on a toggling frame. The numerical simulation results further indicate that our proposal can generate a perfectly reliable ground-state chiral current and open up possibilities for quantum state transfer and the development of future quantum networks.

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arXiv2023

Entangling two Dicke states in a periodic modulated quantum system

We propose a theoretical approach for entangling two Dicke states in a periodic modulated quantum system. By considering two qubit ensembles that are nonuniformly coupled to a common resonator, we can derive an effective Hamiltonian whose energy levels depend nonlinearly on the excitation number of each qubit ensemble. More simplified effective Hamiltonian can be obtained by selecting appropriate driving parameters and initial state. Based on the dynamic evolution of the effective Hamiltonian, we can selectively achieve Dicke state transitions and generate entangled Dicke states controllably. For a special case, we can obtain ensemble-ensemble entangled states by performing a projective even-odd cat measurement. By implementing Gaussian soft temporal modulation, we can effectively suppress off-resonant contributions in the interaction and enhance the fidelity of target states. Furthermore, by utilizing the Holstein-Primakoff transformation, we study the resonator-ensemble coupling system in the thermodynamic limit and investigate the generation of entangled magnon states. Additionally, we propose a scheme of creating magnon NOON states through frequency modulation and study the influence of decoherence on the fidelity of target states.

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arXiv2022

Decoherences-protected implementation of quantum gates

We present a scheme to implement a universal set of quantum gates based on achievable interactions, and the gates can be protected against decoherences through dynamical-decoupling approach without encoding. By properly designing system evolutions, the desired system interactions commute with the elements forming dynamical decoupling pulses. Thus, the effect of decoherences can be eliminated by repeatedly applying the pulses, without noticeably affecting the system evolutions governed by the desired system interactions given small enough time interval between pulses. Moreover, due to the commutation between the elements forming the pulses and the desired system interactions, our scheme is resistant to different types of decoherences, and so not limited to specific decoherences. Our scheme also works well in the case that the desired system interactions cannot be achieved ideally due to imperfect control of system parameters, through the action of dynamical-decoupling pulses.

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arXiv2022

Switchable selective interactions in a Dicke Model with Driven Biased term

In this work, we propose a method to investigate controllable qubit-resonator interactions in a Dicke model with driven biased term. The nonlinearity of spectrum, which can be induced by qubit-resonator interactions, plays an important role in such controllable interactions. To gain insight into mechanism of the nonlinearity, we perform a unitary transformation to the Hamiltonian. The results show that the nonlinearity of the transformed Hamiltonian depends on the qubit-resonator coupling strength. The general forms of the effective Hamiltonians are discussed in detail based on the frequency modulation approach. The dynamical evolution can be switched on and off by adjusting the modulation parameters. By utilizing such controllable interactions, we discuss the creation of Dicke states and arbitrary superposition of Dicke states. We also consider the nonlinearity of energy level for the limit of large qubit numbers. In the thermodynamics limit, the kerr type nonlinearity is induced from "magnon"-resonator coupling, and the selective preparation of "magnon" Fock states can be studied under "magnon" scenario.

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arXiv2021

Implementation of hybridly protected quantum gates

We explore the implementation of hybridly protected quantum operations combining the merits of holonomy, dynamical decoupling approach and dephasing-free feature based on a simple and experimentally achievable spin model. The implementation of the quantum operations can be achieved in different physical systems with controllable parameters. The protected quantum operations are hence controllable, well-suited for resolving various quantum computation tasks, such as executing quantum error-correction codes or quantum error mitigation. Our scheme is based on experimentally achievable Hamiltonian with reduced requirement of computational resources and thus, it brings us closer towards realizing protected quantum operations for resolving quantum computation tasks in near-term quantum devices.

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arXiv2019

Simulating Anisotropic quantum Rabi model via frequency modulation

Anisotropic quantum Rabi model is a generalization of quantum Rabi model, which allows its rotating and counter-rotating terms to have two different coupling constants. It provides us with a fundamental model to understand various physical features concerning quantum optics, solid-state physics, and mesoscopic physics. In this paper, we propose an experimental feasible scheme to implement anisotropic quantum Rabi model in a circuit quantum electrodynamics system via periodic frequency modulation. An effective Hamiltonian describing the tunable anisotropic quantum Rabi model can be derived from a qubit-resonator coupling system modulated by two periodic driving fields. All effective parameters of the simulated system can be adjusted by tuning the initial phases, the frequencies and the amplitudes of the driving fields. We show that the periodic driving is able to drive a coupled system in dispersive regime to ultrastrong coupling regime, and even deep-strong coupling regime. The derived effective Hamiltonian allows us to obtain pure rotating term and counter-rotating term. Numerical simulation shows that such effective Hamiltonian is valid in ultrastrong coupling regime, and stronger coupling regime. Moreover, our scheme can be generalized to the multi-qubit case. We also give some applications of the simulated system to the Schrödinger cat states and quantum gate generalization. The presented proposal will pave a way to further study the stronger anisotropic Rabi model whose coupling strength is far away from ultrastrong coupling and deep-strong coupling regimes in quantum optics.

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arXiv2019

Multi-qubit Quantum Rabi Model and Multi-partite Entangled States in a Circuit QED System

Multi-qubit quantum Rabi model, which is a fundamental model describing light-matter interaction, plays an important role in various physical systems. In this paper, we propose a theoretical method to simulate multi-qubit quantum Rabi model in a circuit quantum electrodynamics system. By means of external transversal and longitudinal driving fields, an effective Hamiltonian describing the multi-qubit quantum Rabi model is derived. The effective frequency of the resonator and the effective splitting of the qubits depend on the external driving fields. By adjusting the frequencies and the amplitudes of the driving fields, the stronger coupling regimes could be reached. The numerical simulation shows that our proposal works well in a wide range of parameter space. Moreover, our scheme can be utilized to generate two-qubit gate, Schrödinger states, and multi-qubit GHZ states. The maximum displacement of the Schrödinger cat states can be enhanced by increasing the number of the qubits and the relative coupling strength. It should be mention that we can obtain high fidelity Schrödinger cat states and multi-qubit GHZ states even the system suffering dissipation. The presented proposal may open a way to study the stronger coupling regimes whose coupling strength is far away from ultrastrong coupling regimes.

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arXiv2015

Non-adiabatic holonomic quantum computation in linear system-bath coupling

Non-adiabatic holonomic quantum computation in decoherence-free subspaces protects quantum information from control imprecisions and decoherence. For the non-collective decoherence that each qubit has its own bath, we show the implementations of two non-commutable holonomic single-qubit gates and one holonomic nontrivial two-qubit gate that compose a universal set of non-adiabatic holonomic quantum gates in decoherence-free-subspaces of the decoupling group, with an encoding rate of $\frac{N-2}{N}$. The proposed scheme is robust against control imprecisions and the non-collective decoherence, and its non-adiabatic property ensures less operation time. We demonstrate that our proposed scheme can be realized by utilizing only two-qubit interactions rather than many-qubit interactions. Our results reduce the complexity of practical implementation of holonomic quantum computation in experiments. We also discuss the physical implementation of our scheme in coupled microcavities.

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arXiv2014

Multipartite $d-$level GHZ bases associated with generalized braid matrices

We investigate the generalized braid relation ($d-$level $N-$body braid relation) and its application to quantum entanglement. By means of finite-dimensional representations of Heisenberg-Weyl algebra, a set of $d^{N}\times d^{N}$ unitary matrix representations satisfying the generalized braid relation can be constructed. Such generalized braid matrices can entangle $d-$level $N-$partite quantum states. Acting the generalized braid matrices on the standard basis, one can obtain a set of maximally entangled basis. Further study shows that such entangled basis can be viewed as the $d-$level $N-$partite Greenberger-Horne-Zeilinger (GHZ) basis.

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arXiv2014

Topological Basis Associated with B-M-W algebra: Two Spin-1/2 Realization

In this letter, we study the two-spin-1/2 realization for the Birman-Murakami-Wenzl (B-M-W) algebra and the corresponding Yang-Baxter $\breve{R}(θ,ϕ)$ matrix. Based on the two-spin-1/2 realization for the B-M-W algebra, the three-dimensional topological space, which is spanned by topological basis, is investigated. By means of such topological basis realization, the four-dimensional Yang-Baxter $\breve{R}(θ,ϕ)$ can be reduced to Wigner $D^{J}$ function with $J=1$. The entanglement and Berry phase in the spectral parameter space are also explored. The results show that one can obtain a set of entangled basis via Yang-Baxter $\breve{R}(θ,ϕ)$ matrix acting on the standard basis, and the entanglement degree is maximum when the $\breve{R}_{i}(θ,ϕ)$ turns to the braiding operator.

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arXiv2011

Birman-Wenzl-Murakami Algebra, Topological parameter and Berry phase

In this paper, a (3\times3)-matrix representation of the Birman-Wenzl-Murakami(BWM) algebra has been presented. Based on which, unitary matrices (A(θ,ϕ_1,ϕ_2), B(θ,ϕ_1,ϕ_2)) are generated via the Yang-Baxterization approach. A hamiltonian is constructed from the unitary (B(θ,ϕ)) matrix. We then study the Berry phase of the Yang-Baxter system and find the topological parameter d has relationship with berry phase.

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arXiv2011

Birman-Wenzl-Murakami Algebra and the Topological Basis

In this paper, we use entangled states to construct 9x9-matrix representations of Temperley-Lieb algebra (TLA), then a family of 9x9-matrix representations of Birman-Wenzl-Murakami algebra (BWMA) have been presented. Based on which, three topological basis states have been found. And we apply topological basis states to recast nine-dimensional BWMA into its three-dimensional counterpart. Finally, we find the topological basis states are spin singlet states in special case.

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arXiv2010

Quantum tunneling effect and quantum Zeno effect in a Topological system

A spin interaction Hamiltonian for topological basis is constructed in this paper. When we select proper parameters, this Hamiltonian system can be simulated by a quantum double well potential system. If the parameter $Δ=0$, the topological system is equivalent to two independent quantum wells. If the parameter $Δ\neq 0$, the system is equivalent to a double well potential with finite potential barrier. The quantum tunneling effect and quantum Zeno effect for this topological system are investigated in detail.

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arXiv2010

Yang-Baxter $\breve{R}$ matrix, Entanglement and Yangian

We present a method to construct "X" form unitary Yang-Baxter $\breve{R}$ matrices, which act on the tensor product space $V_{i}^{j_{1}}\otimes V_{i+1}^{j_{2}}$. We can obtain a set of entangled states for $(2j_{1}+1)\times (2j_{2}+1)$-dimensional system with these Yang-Baxter $\breve{R}$ matrices. By means of Yang-Baxter approach, a $8\times 8$ Yang-Baxter Hamiltonian is constructed. Yangian symmetry and Yangian generators as shift operators for this Yang-Baxter system are investigated in detail.

math-ph↗

arXiv2010

A study on the relations between the topological parameter and entanglement

In this paper, some relations between the topological parameter $d$ and concurrences of the projective entangled states have been presented. It is shown that for the case with $d=n$, all the projective entangled states of two $n$-dimensional quantum systems are the maximally entangled states (i.e. $C=1$). And for another case with $d\neq n$, $C$ both approach $0$ when $d\rightarrow +\infty$ for $n=2$ and $3$. Then we study the thermal entanglement and the entanglement sudden death (ESD) for a kind of Yang-Baxter Hamiltonian. It is found that the parameter $d$ not only influences the critical temperature $T_{c}$, but also can influence the maximum entanglement value at which the system can arrive at. And we also find that the parameter $d$ has a great influence on the ESD.

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