arXiv subjects

Tiancai Zhang

Publications and source records attributed to Tiancai Zhang.

At least 19 recordsLinked to original sources

arXiv2026

Manipulation of diverse quantum correlations based on a hybrid optomagnomechanical system

Flexible manipulation of quantum correlation resources enables the implementation of diverse quantum tasks based on hybrid quantum networks, where atom-magnon and optomagnonic entanglements and steerings play important roles. In this work, we propose an effective scheme to generate and manipulate quantum entanglements and steerings based on a hybrid optomagnomechanical system, which is composed of a polarizer, an optical cavity with YIG bridge as one end, and an atomic ensemble in it. According to the results of the parameter dependence of various quantum correlations, we can selectively generate bipartite and genuine tripartite entanglements and deterministically manipulate the concrete situation of bipartite, multipartite steerings, and collective pentapartite steering, by adjusting the polarization direction of the driving laser and the Tavis-Cummings coupling strength. Our all-optical controlled scheme is flexible, convenient, compact, and experimentally feasible, because multiple coupling channels can be tuned simultaneously. This work provides a new perspective for implementing specialized quantum tasks, such as hierarchical ultra-secure multi-user quantum communications.

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arXiv2026

A Flexible GKP-State-Embedded Fault-Tolerant Quantum Computation Configuration Based on a Three-Dimensional Cluster State

The integration of diverse quantum resources and the exploitation of more degrees of freedom provide key operational flexibility for universal fault-tolerant quantum computation. In this work, we propose a flexible Gottesman-Kitaev-Preskill-state-embedded fault-tolerant quantum computation architecture based on a three-dimensional cluster state constructed in polarization, frequency, and orbital angular momentum domains. Specifically, we design optical entanglement generators to produce three diverse entangled pairs, and subsequently construct a three-dimensional cluster state via a beam-splitter network with several time delays. Furthermore, we present a partially squeezed surface-GKP code to achieve fault-tolerant quantum computation and ultimately find the optimal choice of implementing the squeezing gate to give the best fault-tolerant performance (the fault-tolerant squeezing threshold is 11.5 dB). Our scheme is flexible, scalable, and experimentally feasible, providing versatile options for future optical fault-tolerant quantum computation architecture.

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arXiv2025

Flexible manipulation of bipartite and multipartite EPR steerings

Bipartite and multipartite quantum steerings are significant resources for various quantum tasks, such as ultrasecure multi-user quantum network, one-site-trusted quantum communication, high-fidelity quantum computation, etc. A flexible steering manipulation scheme of five down-converted Hermitian Gaussian modes generated from an optical parametric oscillator by using a spatial structured pump is presented. In our scheme, not only the direction and types of the bipartite steering, but also different situations of multipartite steering, can be manipulated effectively, by adjusting the pump proportions with a spatial light modulator. In addition, stricter genuine pentapartite steering (only one site is trusted) can also be achieved by making the pump proportions as balanced as possible. Our scheme is versatile and experimentally feasible and offers new insights into the manipulation of steering, especially multipartite steering, which is valuable in many special quantum tasks.

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arXiv2025

Three-dimensional optical characterization of magnetostrictive deformation in magnomechanical systems

Magnomechanical systems with YIG spheres have been proven to be an ideal system for studying magnomechanically induced transparency, dynamical backaction, and rich nonlinear effects, such as the magnon-phonon cross-Kerr effect. Accurate characterization of the magnetostriction induced deformation displacement is important as it can be used for, e.g., estimating the magnon excitation number and the strength of the dynamical backaction. Here we propose an optical approach for detecting the magnetostrictive deformation of a YIG sphere in three dimensions (3Ds) with high precision. It is based on the deformation induced spatial high-order modes of the scattered field, postselection, and balanced homodyne detection. With feasible parameters, we show that the measurement precision of the deformation in $x$, $y$, and $z$ directions can reach the picometer level. We further reveal the advantages of our scheme using a higher-order probe beam and balanced homodyne detection by means of quantum and classical Fisher information. The real-time and high-precision measurement of the YIG sphere's deformation in 3Ds can be used to determinate specific mechanical modes, characterize the magnomechanical dynamical backaction and the 3D cooling of the mechanical vibration, and thus finds a wide range of applications in magnomechanics.

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arXiv2025

Sub-nanometer measuring ellipticity of a suspended optical nanowaveguides based on nondegenerate mechanical modes

Optical waveguides with miniature dimensions to the nanoscale can facilitate the development of highly integrated photonic devices, integrated optical circuits and hybrid quantum system coupling with emitters. Nondegenerate intrinsic flexural mechanical modes of nanowaveguides provide unique insights into the mechanical properties and structural integrity of materials, which is great significance to the applications of the nanowaveguides. Here, we propose and implement a scheme to measure the nondegenerate intrinsic flexural mechanical modes of a suspended optical nanowaveguide, a tapered optical fiber (TOF). A TOF with an elliptical cross section can support two nondegenerate intrinsic flexural mechanical modes (IFMMs) because the two orthogonal modes vibrate along the principal axes (major or minor axis) of the elliptical TOF cross section with splitting vibration frequencies. The frequency ratio for the two IFMMs approaches a constant with increasing mode order, which is equal to the inverse of the TOF ellipticity. Thus, the TOF ellipticity can be determined on the basis of the splitting vibration frequencies of the nondegenerate modes with subnanometer-level accuracy, 0.16 nm for a TOF radius of 260 nm. The elliptical TOF's nondegenerate IFMMs offer a novel pathway for research on nanoscale structures and vector measurement in fields such as quantum optics, atom physics, sensing, optical communications, and micronanomechanics.

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arXiv2025

A complete continuous-variable quantum computation architecture based on the 2D spatiotemporal cluster state

Continuous-variable measurement-based quantum computation, which requires deterministically generated large-scale cluster state, is a promising candidate for practical, scalable, universal, and fault-tolerant quantum computation. In this work, based on our compact and scalable scheme of generating a two-dimensional spatiotemporal cluster state, a complete architecture including cluster state preparation, gate implementations, and error correction, is proposed. First, a scheme for generating two-dimensional large-scale continuous-variable cluster state by multiplexing both the temporal and spatial domains is proposed. Then, the corresponding gate implementations by gate teleportation are discussed and the actual gate noise from the generated cluster state is considered. After that, the quantum error correction can be further achieved by utilizing the square-lattice Gottesman-Kitaev-Preskill (GKP) code. Finally, a fault-tolerant quantum computation can be realized by introducing bias into the square-lattice GKP code (to protect against phase-flip errors) and concatenating a repetition code (to handle the residual bit-flip errors), with a squeezing threshold of 12.3 dB. Our work provides a possible option for a complete fault-tolerant quantum computation architecture in the future.

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arXiv2025

High-precision measurement of microwave electric field by cavity-enhanced critical behavior in a many-body Rydberg atomic system

It has been demonstrated that the Rydberg criticality in a many-body atomic system can enhance the measurement sensitivity of the microwave electric field by increasing the Fisher information. In our previous work, we proposed and experimentally verified that the Fisher information near the critical point can be increased by more than two orders of magnitude with the Rydberg atoms coupled with an optical cavity compared with that in free space. Here we demonstrate the precision measurement of the microwave electric field by cavity-enhanced critical behavior. We show that the equivalent measurement sensitivity of the microwave electric field can be enhanced by an order of magnitude compared with that in free space. The obtained sensitivity can be enhanced to 2.6 nV/cm/Hz$^{1/2}$.

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arXiv2025

Enhancing the coherence time of a neutral atom by an optical quartic trap

The coherence time of an optically trapped neutral atom is a crucial parameter for quantum technologies. We found that optical dipole traps with higher-order spatial forms inherently offer lower decoherence rates compared to those with lower-order spatial forms. We formulated the decoherence rate caused by the variance of the differential energy shift and photon jumping rate. Then, we constructed blue-detuned harmonic and quartic optical dipole traps, and experimentally investigated the coherence time of a trapped single cesium atom. The experimental results qualitatively verified our theory. Our approach provides a novel method to enhance the coherence time of optically trapped neutral atoms.

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arXiv2025

Cavity-Enhanced Rydberg Atomic Superheterodyne Receiver

High-sensitivity measurements of the microwave electric field are important in applications of communication and metrology. \replaced{The sensitivity of traditional Rydberg superheterodyne receivers in free space is effectively determined by the signal-to-noise ratio (SNR), which is often considered equivalent to sensitivity in practical sensing applications.}{The sensitivity of the traditional Rydberg superheterodyne receivers in free space is limited by signal-to-noise contrast.} In this work, we demonstrate a cavity-enhanced receiver, where an optical cavity significantly amplifies the interaction between the probe light and cesium atoms, which substantially improves the signal-to-noise ratio via enhancing the expansion coefficient $ κ$. \added{Here, $κ$ is the edge slope of the single peak obtained by fitting the double-peak EIT-AT spectrum, characterizing the response of the probe light to the frequency detuning of the coupling laser.}The sensitivity is thus boosted by a factor of approximately 19 dB. This study highlights the pivotal role of optical cavities in advancing Rydberg-based detection systems, offering a promising approach for high-sensitivity microwave electric field measurements.

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arXiv2025

A cavity QED system with defect-free single-atom array strongly coupled to an optical cavity

We experimentally realize a new cavity quantum electrodynamics (QED) platform with defect-free single-atom array strongly coupled to an optical cavity. The defect-free single-atom array is obtained by rearranging a probabilistically loaded one-dimensional (1D) optical tweezer array with dimensions of $1 \times 40$. The atom array is enclosed with two cavity mirrors, which compose a miniature optical Fabry-P{é}rot cavity with cavity length of 1.15 mm. By precisely controlling the position of the atom array, we demonstrate uniform and strong coupling of all atoms in the array with the optical cavity. The average coupling strength between the single atom and the cavity is 2.62 MHz. The vacuum Rabi splitting spectra for single-atom arrays with atom number $N$ changing from 3 to 26 are measured. Thus, the collective enhancement of the coupling strength with ${\sqrt N}$-dependence for multiple atoms is validated at the single atom level. Our system holds significant potential for establishing the foundation of distributed quantum computing and advancing fundamental research in many-body physics.

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arXiv2025

Extending the coherence time limit of a single-alkali-atom qubit by suppressing phonon-jumping-induced decoherence

In the fields of quantum metrology and quantum information processing with the system of optically trapped single neutral atoms, the coherence time of qubit encoded in the electronic states is regarded as one of the most important parameters. Longer coherence time is always pursued for higher precision of measurement and quantum manipulation. The coherence time is usually assumed to be merely determined by relative stability of the energy between the electronic states, and the analysis of the decoherence was conducted by treating the atom motion classically. We proposed a complete description of the decoherence of a qubit encoded in two ground electronic states of an optically trapped alkali atom by adopting a full description of the atomic wavefunction. The motional state, i.e., the phonon state, is taken into account. In addition to decoherence due to the variance of differential light shift (DLS), a new decoherence mechanism, phonon-jumping-induced decoherence (PJID), was discovered and verified experimentally. The coherence time of a single-cesium-atom qubit can be extended to $T_2\approx 20$ s by suppressing both the variances of DLS and PJID by trapping the atom in a blue-detuned bottle beam trap (BBT) and preparing the atom in its three-dimensional motional ground states. The coherence time is the longest for a qubit encoded in an optically trapped single alkali atom. Our work provides a deep understanding of the decoherence mechanism for single atom qubits and thus provides a new way to extend the coherence time limit. The method can be applied for other atoms and molecules, opening up new prospects for high-precision control the quantum states of optically trapped atoms or molecules.

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arXiv2025

Flexible generation of optomagnonic quantum entanglement and quantum coherence difference in double-cavity-optomagnomechanical system

Quantum entanglement and quantum coherence generated from the optomagnomechanical system are important resources in quantum information and quantum computation. In this paper, a scheme for flexibly generating optomagnonic quantum entanglement and quantum coherence difference is proposed, based on a double-cavity-optomagnomechanical system. The parameter dependencies of the bipartite optomagnonic entanglement, the genuine tripartite optomagnonic entanglement, the quantum coherence difference, and the stability of the system, are investigated intensively. The results show that this scheme endows the magnon more flexibility to choose different mechanisms, under the condition of maintaining the system stable. This work is valuable for connecting different nodes in quantum networks and manipulating the magnon states with light in the future.

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arXiv2025

Generation of optomicrowave and optomagnonic entanglements in cascaded optomagnomechanical systems

The optomagnomechanical system, which involves flexible nonlinearities, is one of the promising physical platforms for studying the preparation and manipulation of quantum entanglements, as well as the construction of hybrid quantum networks. A scheme for entanglement enhancement and quadripartite entanglement generation is proposed, based on a cascaded optomagnomechanical system. On the one hand, optomicrowave and optomagnonic entanglements within the two subsystems are investigated, and their parameter dependence, such as detuning, decay, coupling strength, and transmission efficiency, is discussed. On the other hand, the parameter conditions for achieving optimal optomicrowave and optomagnonic quadripartite entanglements are also obtained. The results show that significant enhancement of optomicrowave and optomagnonic entanglements in the second cavity can be obtained in a certain range of parameters. Under optimized parameter conditions, optomicrowave and optomagnonic quadripartite entanglements can be generated throughout the entire cascaded system. This research provides a theoretical basis for the manipulation of quantum entanglement, the transmission of the magnon's state, and the construction of hybrid quantum networks involving different physical systems.

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arXiv2024

Generating entanglement of two acoustic modes by driving the qubit in circuit quantum acoustodynamics system

We propose how to generate the entanglement of two long-lived phonon modes in a circuit quantum acoustodynamics system, which consists of a multi-mode high-frequency bulk acoustic wave resonator and a transmon-type superconducting qubit. Two acoustic modes couple to the qubit through piezoelectric interaction, and the qubit is driven by a microwave field. Under the condition of far detuning between the qubit and acoustic modes, the qubit can be eliminated adiabatically, and thus establishing the indirect interaction between the two acoustic modes. We demonstrate that such the indirect interaction can be the parametric-amplification-type interaction by appropriately choosing the drive frequency and strength, so the entanglement between acoustic modes can be created by the direct unitary evolution. We numerically analyze the parameter conditions for generating the entanglement in detail and evaluate the influence of system dissipations and noise. The results show that the scheme can be realized using currently available parameters and has strong robustness against the dissipations and environmental temperature. This work may provide efficient resource for the quantum information processing based on the phononic systems.

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arXiv2024

Proposal of quantum repeater architecture based on Rydberg atom quantum processors

Realizing large-scale quantum networks requires the generation of high-fidelity quantum entanglement states between remote quantum nodes, a key resource for quantum communication, distributed computation and sensing applications. However, entanglement distribution between quantum network nodes is hindered by optical transmission loss and local operation errors. Here, we propose a novel quantum repeater architecture that synergistically integrates Rydberg atom quantum processors with optical cavities to overcome these challenges. Our scheme leverages cavity-mediated interactions for efficient remote entanglement generation, followed by Rydberg interaction-based entanglement purification and swapping. Numerical simulations, incorporating realistic experimental parameters, demonstrate the generation of Bell states with 99\% fidelity at rates of 1.1\,kHz between two nodes in local-area network (distance $0.1\,\mathrm{km}$), and can be extend to metropolitan-area ($25\,\mathrm{km}$) or intercity ($\mathrm{250\,\mathrm{km}}$, with the assitance of frequency converters) network with a rate of 0.1\,kHz. This scalable approach opens up near-term opportunities for exploring quantum network applications and investigating the advantages of distributed quantum information processing.

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arXiv2024

Resolved Raman sideband cooling of a single optically trapped cesium atom

We developed a resolved Raman sideband cooling scheme that can efficiently prepare a single optically trapped cesium (Cs) atom in its motional ground states. A two-photon Raman process between two outermost Zeeman sublevels in a single hyperfine state is applied to reduce the phonon number. Our scheme is less sensitive to the variation in the magnetic field than the commonly used scheme where the two outermost Zeeman sublevels belonging to the two separate ground hyperfine states are taken. Fast optical pumping with less spontaneous emission guarantees the efficiency of the cooling process. After cooling for 50 ms, 82% of the Cs atoms populate their three-dimensional ground states. Our scheme improves the long-term stability of Raman sideband cooling in the presence of magnetic field drift and is thus suitable for cooling other trapped atoms or ions with abundant magnetic sublevels.

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arXiv2023

Quantum squeezing induced quantum entanglement and EPR steering in coupled optomechanical system

We propose a theoretical project in which quantum squeezing induces quantum entanglement and Einstein-Podolsky-Rosen steering in a coupled whispering-gallery-mode optomechanical system. Through pumping the $χ^{(2)}$-nonlinear resonator with the phase matching condition, the generated squeezed resonator mode and the mechanical mode of the optomechanical resonator can generate strong quantum entanglement and EPR steering, where the squeezing of the nonlinear resonator plays the vital role. The transitions from zero entanglement to strong entanglement and one-way steering to two-way steering can be realized by adjusting the system parameters appropriately. The photon-photon entanglement and steering between the two resonators can also be obtained by deducing the amplitude of the driving laser. Our project does not need an extraordinarily squeezed field, and it is convenient to manipulate and provides a novel and flexible avenue for diverse applications in quantum technology dependent on both optomechanical and photon-photon entanglement and steering.

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arXiv2023

Enhancing the quantum entanglement and EPR steering of a coupled optomechanical system with a squeezed vacuum field

Quantum entanglement and Einstein-Podolsky-Rosen (EPR) steering are valuable resources in quantum information processing. How to enhance the quantum entanglement and EPR steering of coupled optomechanical systems with a weak squeezed vacuum field are studied when the displacement of detuning induced by the mechanical mode is considered. Compared with the condition that the system interacts with a vacuum environment, the quantum entanglement and EPR steering are stronger when the squeezed vacuum field is applied. A squeezed vacuum field with a large degree is not beneficial to enhance the quantum entanglement and EPR steering. Rather than the squeezing parameter of the squeezed vacuum field, the reference phase plays a vital role in this model.

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