arXiv subjects

Zheng-Yuan Xue

Publications and source records attributed to Zheng-Yuan Xue.

At least 19 recordsLinked to original sources

arXiv2026

Multi-flux Aharonov-Bohm caging with tunable couplings

Aharonov-Bohm (AB) caging is the complete wavefunction localization effect in translational-invariant lattices induced by destructive phase interference. These phases originate from the gauge fields such as the penetrated magnetic fields, which are directly related to several novel topological quantum states of matter. Recently, this effect has shown significant potential for applications in quantum simulation and topological quantum computation. Here, we propose a scalable protocol to derive universal conditions for AB caging with multi-flux. The numerical simulations validate the theoretical predictions by directly observing AB caging phenomena. We also investigate the breakage of the caging effect with onsite detuning, decoherence and non-Hermitian transitions. Our protocol provides an alternative approach for advancing quantum simulation of exotic states of matter.

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arXiv2026

Extensible Fluxonium Architecture Using Tunable Couplers with Low Shunt Capacitance

Fluxonium qubits have demonstrated high-fidelity operations and long coherence times in small-scale systems, highlighting their promise for quantum computing. However, large-scale integration into a high-performance two-dimensional (2D) qubit array remains the central challenge for practical applications. In this work, we introduce an extensible architecture for scaling up fluxonium qubits in 2D grids. To address the key challenges, namely achieving controllable strong interaction and high connectivity for qubits featuring small shunting capacitors (footprints), we propose using low-shunt-capacitance couplers to enable tunable interactions between fluxonium qubits. When embedded into 2D square lattices, large couplings can be achieved even with relatively small coupling capacitances, thus enabling multiple connections with sufficient capacitance budget. We further propose coupler realizations based on generalized flux qubit circuits, specifically the quarton and the fluxonium, and demonstrate that both enable fast, high-fidelity gates with low spectator errors, while supporting multiple connections on 2D grids.

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arXiv2026

Fast entangling gates on fluxoniums via parametric modulation of plasmon interaction

In superconducting quantum processors, exploring diverse control methods could offer essential versatility and redundancy to mitigate challenges such as frequency crowding, spurious couplings, control crosstalk, and fabrication variability, thus leading to better system-level performance. Here we introduce a control strategy for fast entangling gates in a scalable fluxonium architecture, utilizing parametric modulation of the plasmon interaction. In this architecture, fluxoniums are coupled via a tunable coupler, whose transition frequency is flux-modulated to control the inter-fluxonium plasmon interaction. A bSWAP-type interaction is activated by parametrically driving the coupler at the sum frequency of the plasmon transitions of the two fluxoniums, resulting in the simultaneous excitation or de-excitation of both plasmon modes. This strategy therefore allow the transitions between computational states and non-computational plasmon states, enabling the accumulation of conditional phases on the computational subspace and facilitating the realization of controlled-phase gates. By focusing on a specific case of these bSWAP-type interactions, we show that a simple drive pulse enables sub-100ns CZ gates with an error below $10^{-4}$. Given its operational flexibility and extensibility, this approach could potentially offer a foundational framework for developing scalable fluxonium-based quantum processors.

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arXiv2026

Long-range tunable coupler for modular fluxonium quantum processors

The path toward practical superconducting quantum processors requires the integration of a large number of high-performance qubits. Modular architectures could offer a way to address the scaling limitations of monolithic designs by partitioning a large quantum processor into physically separated modules, or chiplets, linked through long-range interconnects. In this context, although fluxonium qubits have emerged as a compelling platform for quantum computing due to their long coherence times and high-fidelity gates, existing coupling schemes remain restricted to qubits in close proximity on a single chip. This limitation inherently precludes the long-range interconnects essential for modular integration. In this work, we propose a long-range tunable coupler designed to interconnect fluxonium qubits separated by more than one centimeter, thereby supporting the realization of modular fluxonium quantum processors. Under realistic assumptions, the proposed coupler has the potential to achieve inter-module two-qubit gate performance, specifically sub-100-ns gates with intrinsic errors below $10^{-4}$, comparable to that of intra-module (intra-chiplet) gates, while enabling modular integration with low quantum crosstalk, a key requirement for scalable systems. We further discuss the integration of this coupler into modular fluxonium lattices and explore its feasibility for achieving the higher connectivity and longer coupling range required for complex quantum error correction codes. This work could contribute to the development of large-scale fluxonium quantum processors by bridging their demonstrated potential with modular scalability.

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arXiv2026

Crosstalk-robust superconducting two-qubit geometric gates using tunable couplers

The design of coupler-based superconducting two-qubit gates simplifies circuit layout and alleviate frequency crowding, thereby enhancing the scalability and flexibility of quantum chips. However, in such architectures, a trade-off often exists between suppressing crosstalk and reducing gate duration, and how to achieve synergistic optimization of both remains an open challenge. To address this, this paper proposes a coupler-assisted superconducting two-qubit geometric gate scheme oriented towards crosstalk robustness. By introducing additional parametric degrees of freedom, the scheme steers the system evolution along desired trajectories, thereby flexibly avoiding crosstalk-sensitive operational regions. Numerical simulations demonstrate that the proposed scheme can effectively suppress crosstalk errors while enabling fast gate operations, and exhibits strong robustness against typical experimental imperfections such as qubit frequency drift. Moreover, even when accounting for unavoidable high-frequency oscillation terms and qubit decoherence in realistic physical systems, our crosstalk-robust two-qubit geometric gates still achieve high fidelity. This work provides a feasible pathway toward robust and efficient two-qubit gate implementation in superconducting quantum computation.

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arXiv2026

Leakage Suppression in Quantum Control via Static Parameter Offsets

High-fidelity quantum operations require the system dynamics to be strictly confined to the computational subspace. In practice, however, control fields inevitably couple to leakage levels, giving rise to quantum state leakage that significantly reduces the fidelity of the operation. To address this challenge, we propose a general strategy for actively suppressing leakage errors by applying small, static offsets to tunable system parameters. This approach systematically mitigates leakage's detrimental impact on quantum control, without modifying the original control framework or incurring additional time overhead. By avoiding the need for extra suppression pulses or complex optimization procedures altogether, it offers a streamlined solution for leakage compensation while remaining fully compatible with subsequent optimal control techniques. Numerical validation conducted on superconducting quantum circuits demonstrates effective leakage suppression, enabling high-fidelity single-qubit gates, precise control of two-qubit interactions, and perfect state transfer in multi-level systems. Moreover, when integrated with optimal control techniques, our approach also allows for the cooperative suppression of both leakage errors and residual crosstalk. Therefore, this work provides a feasible technical pathway toward the low error thresholds required for fault-tolerant quantum computation.

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arXiv2026

Universal Robust Quantum Gates via Doubly Geometric Control

Geometric quantum computation offers a potential route to fault-tolerant quantum information processing by exploiting the global nature of geometric phases. However, achieving controlled high-order suppression of multiple error sources remains a long-standing limitation, particularly in realistic large-scale circuits with complex noise environments. This limitation is largely due to the absence of a general framework that directly characterizes error accumulation and enables systematic improvement. Here we establish such a framework for universal doubly geometric gates by embedding target operations into a hierarchy of level-n identity constructions. This approach enables direct quantification of error accumulation while removing structural constraints inherent in previous schemes. We analytically show that the defining conditions lead to simultaneous fourth-order suppression of control errors, with a systematic extension to sixth-order suppression via higher-level constructions. Our results establish doubly geometric control as a general and scalable route toward high-order robust quantum gates, with potential implications for fault-tolerant quantum information processing.

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arXiv2026

Non-Abelian Aharonov-Bohm Caging in Synthetic Dimensions with a Trapped Ion

Aharonov-Bohm (AB) caging is a complete localization phenomenon in two-dimensional lattices due to destructive interference induced by the background gauge fields. However, current investigations of AB caging are mostly restricted to the Abelian gauge field case, and the observation of AB caging under non-Abelian gauge fields in a quantum system still remains elusive. Here, we report experimental realization of tunable synthetic non-Abelian SU(2) gauge fields in a rhombic lattice, engineered within the synthetic dimensions of a vibrating trapped ion with multiple levels. We realize AB caging under both Abelian and non-Abelian gauge fields and systematically investigate the distinctive transport properties of the non-Abelian case. In particular, we observe typical emergent quantum dynamics unique to non-Abelian AB caging, including initial-state-dependent dynamics, second-order effects, and asymmetric caging behavior. These observations demonstrate the trapped ion system as a powerful platform for simulating emergent phenomena in high-dimensional quantum systems with exotic synthetic gauge fields.

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arXiv2026

Scalable native multiqubit gates via engineered noncomputational-state interactions in superconducting fluxonium qubits

Native multiqubit gates could be essential for bridging the gap from current noisy devices to future utility-scale quantum computers, as they can substantially reduce circuit depth for near-term applications on noisy devices and may also lower the physical overhead of fault-tolerant quantum computation. Here we introduce a scalable protocol for implementing native multi-controlled gates on fluxonium qubits, supporting an arbitrary number of control qubits ($N > 1$) while remaining compatible with existing single- and two-qubit gate realizations. Our approach leverages engineered interactions in noncomputational state manifolds to enable qubit-state selective transitions, which is activated for the direct implementation of $(C^{\otimes N})Z$ gates. We show that in square lattices with fluxonium qubits, $CCZ$, $CCCZ$, and $CCCCZ$ gates with errors around 0.01 (0.001) are achievable, with gate lengths of $50\,(100)\,\text{ns}$, $100\,(250)\,\text{ns}$, and $150\,(300)\,\text{ns}$, respectively. Looking forward, integrating these native multi-controlled gates with primitive single- and two-qubit gate sets within a single quantum processor could significantly enhance flexibility in circuit synthesis and offer a promising alternative pathway toward utility-scale quantum computing.

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arXiv2025

Recent Advances on Nonadiabatic Geometric Quantum Computation

The geometric phase stands as a foundational concept in quantum physics, revealing deep connections between geometric structures and quantum dynamical evolution. Unlike dynamical phases, geometric phases exhibit intrinsic resilience to certain types of perturbation, making them particularly valuable for quantum information processing, where maintaining coherent quantum operations is essential. This article provides a review of geometric phases in the context of universal quantum gate construction, i.e., the geometric quantum computation (GQC), with special attention to recent progress in nonadiabatic implementations that enhance gate fidelity and/or operational robustness. We first review a unified theoretical framework that can encompass all existing nonadiabatic GQC approaches, then systematically examine the design principles of nonadiabatic geometric gates with a particular focus on how optimal control techniques can be leveraged to improve the accuracy and noise resistance. In addition, we conducted detailed numerical comparisons of various nonadiabatic GQC protocols, offering a quantitative assessment of their respective performance characteristics and practical limitations. Through this focused investigation, our aim is to provide researchers with both fundamental insights and practical guidance for advancing geometric approaches in quantum computing.

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arXiv2025

Robust iSWAP gates for semiconductor spin qubits with local driving

Scalable quantum computation demands high-fidelity two-qubit gates. However, decoherence and control errors are inevitable, which can decrease the quality of implemented quantum operations. We propose a robust iSWAP gate protocol for semiconductor spin qubits, which is a promising platform for scalable quantum computing. Our scheme uses only local microwave drives on conventional exchange-coupled spin qubits. This approach simultaneously addresses two critical challenges on semiconductor quantum computing: it suppresses low-frequency noise via continuous dynamical decoupling, and it circumvents the control difficulties associated with the ac modulation of the exchange interaction. We further develop a composite pulse sequence to remove drive-strength constraints and a dynamically corrected method to provide first-order immunity to microwave amplitude errors.Numerical simulations confirm that our scheme can achieve fidelity above the fault-tolerance threshold under current experimental conditions, offering a building block for practical quantum processors.

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arXiv2025

Composite nonadiabatic geometric quantum gates with optimization on superconducting circuits

Due to its fast and robust characteristics, nonadiabatic geometric quantum computation with various optimized techniques has received much attention. However, these strategies either require precise pulse control or can only mitigate partial systematic errors, hindering their experimental development. Here, we propose a scheme for optimized composite nonadiabatic geometric quantum gates (OCNGQGs), which can further enhance the gate performance of the composite nonadiabatic geometric scheme. Specifically, by optimizing the path parameter, our scheme effectively resists systematic errors in both directions, i.e., Rabi frequency and detuning errors, while preserving the flexibility of pulse shapes. Numerical simulations demonstrate that our scheme offers superior gate robustness against these two types of errors compared to conventional schemes. Additionally, we propose to implement our scheme on superconducting transmon qubits, where the numerical results show the robustness of universal gates remaining evident within current technology. Therefore, our proposal provides a promising approach to achieve robust quantum gates for future scalable quantum computation.

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arXiv2025

Robustness Enhancement of Universal Noncyclic Geometric Gates via Evolution Optimization

Noncyclic geometric gates aim to overcome the stringent constraints of conventional cyclic conditions and enhance the flexibility in evolution choice. Conceptually, they can also avoid the error problems arising from the violation of cyclicity, thus holding significance for improving the fault tolerance of quantum gates. However, current research on noncyclic geometric gates lacks a comprehensive exploration of their flexibility in evolution choice and validation of their effectiveness in resilience against multiple error sources present in practical quantum systems. In this paper, we systematically evaluate all noncyclic evolution conditions, elucidate their corresponding potential geometric trajectories, and identify optimal conditions for enhancing gate robustness by quantifying the resilience of constructed noncyclic geometric gates against universal systematic errors and residual crosstalk error. The optimized gates demonstrate significant robustness advantages over representative dynamical Rabi gates and conventional cyclic geometric gates. Furthermore, we validate the physical feasibility of high-fidelity noncyclic geometric gates in superconducting quantum circuits, with focused investigation into the impacts of intrinsic leakage errors and decoherence effects. Therefore, this work establishes a critical foundation for robust gate implementation toward practical fault-tolerant quantum processors.

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arXiv2025

Variational Quantum Algorithm for Solving the Liouvillian Gap

In open quantum systems, the Liouvillian gap characterizes the relaxation time toward the steady state. However, accurately computing this quantity is notoriously difficult due to the exponential growth of the Hilbert space and the non-Hermitian nature of the Liouvillian superoperator. In this work, we propose a variational quantum algorithm for efficiently estimating the Liouvillian gap. By utilizing the Choi-Jamiokowski isomorphism, we reformulate the problem as finding the first excitation energy of an effective non-Hermitian Hamiltonian. Our method employs variance minimization with an orthogonality constraint to locate the first excited state and adopts a two-stage optimization scheme to enhance convergence. Moreover, to address scenarios with degenerate steady states, we introduce an iterative energy-offset scanning technique. Numerical simulations on the dissipative XXZ model confirm the accuracy and robustness of our algorithm across a range of system sizes and dissipation strengths. These results demonstrate the promise of variational quantum algorithms for simulating open quantum many-body systems on near-term quantum hardware.

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arXiv2025

Experimental Proposal on Non-Abelian Aharonov-Bohm Caging Effect with a Single Trapped Ion

In the lattice system, when the synthetic flux reaches a $π$ phase along a closed loop under the synthetic gauge field, destructive interference occurs and gives rise to the localization phenomenon. This is known as the Aharonov-Bohm (AB) caging effect. It provides a powerful tool for the study of quantum transportation and dynamical effects. In the system where lattice sites possess internal structure and the underlying gauge field is non-Abelian, localization can also occur, forming the non-Abelian AB caging. Here, we propose an experimental scheme to synthesize non-Abelian gauge fields with a single trapped ion by coupling multiple internal levels and Fock states in its motion via laser fields. In contrast to the Abelian AB caging, we numerically observe that the non-Abelian AB caging occurs either when the interference matrix is nilpotent, or when the initial state is specifically set. Our experimental scheme broadens the study of localization phenomena and provides a novel tool for the study of non-Abelian physics.

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arXiv2025

Error-mitigated Geometric Quantum Control over an Oscillator

Quantum information is very fragile to environmentally and operationally induced imperfections. Therefore, the construction of practical quantum computers requires quantum error-correction techniques to protect quantum information. In particular, encoding a logical qubit into the large Hilbert space of an oscillator is a hardware-efficient way of correcting quantum errors. In this strategy, selective number-dependent arbitrary phase (SNAP) gates are vital for universal quantum control. However, the quality of SNAP gates is considerably limited by the small coupling-induced nonlinearity of the oscillator. Here, to resolve this limitation, we propose a robust scheme based on quantum optimal control via functional theory, by designing an appropriate trajectory for a target operation. Besides, we combine the geometric phase approach with our trajectory design scheme to minimize the decoherence effect, by shortening the gate time. Numerical simulation shows that both errors can be significantly mitigated and that the robustness of the geometric gate against both $X$ and $Z$ errors can be maintained. Therefore, our scheme provides a promising alternative for fault-tolerant quantum computation.

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arXiv2025

High-fidelity initialization a logical qubit with multiple injections

Quantum error correction represents a significant advancement in large-scale quantum computing. However, achieving fault-tolerant implementations of non-Clifford logical gates with reduced overhead remains a challenge in the popular surface code strategy. Recent advances have underscored the need for a substantial code distance to attain complete fault tolerance. Here, we introduce a continuous fault-tolerant scheme for non-Clifford logical gates via multiple injections. Unlike existing protocols that focus on a single logical chain, our approach utilizes multiple logical chains, each can employ the same or different logical rotation angles, to initialize a non-Clifford state. Compared to previous efforts, our protocol significantly alleviates the challenges associated with the requirement for a large code distance and reduces the corresponding resource overhead, making it more feasible to be implemented in current mid-scale chips via the surface code strategy.

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arXiv2024

Error-mitigated initialization of surface codes with non-Pauli stabilizers

Quantum error correction represents a significant milestone in large-scale quantum computing, with the surface code being a prominent strategy due to its high error threshold and experimental feasibility. However, it is challenging to implement non-Clifford logical gates in a fault-tolerant way with low overhead, through the conventional magic state distillation technique. Here, we enhance the performance of the conventional surface code by incorporating non-Pauli stabilizers and introduce two innovative initialization protocols. Our approach enhances the fidelity of the initialization of non-Clifford logical state by avoiding unprotected operations before the encoding process. This improved fidelity of the initialization of non-Clifford logical states reduces the necessary number of logical qubits for precise state distillation, ultimately decreasing the overall resource overhead. Furthermore, we demonstrate the ability to entangle logical qubits in non-Pauli and Pauli bases via the lattice surgery technique. This integration enables the use of Pauli-based surface codes for computation while non-Pauli codes are employed for auxiliary qubit initialization, thus compatible with the conventional wisdom of logical Clifford operation based on the Pauli-based surface code.

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