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Split-Qubit Noise-Resistant Strategy for Bell State Preparation in Qiskit

Ou Yang, W. Y. Sun

Published Oct 4, 2025• 0 citations
Publisher

Abstract

This paper addresses high-fidelity Bell state preparation under depolarizing noise. A split-qubit approach is proposed: dynamic decoupling for the control qubit and error correction for the target qubit. Qiskit simulations show fidelity maintained at 1.0000, with error rates reduced from ~24% to 0.4%, requiring only four X gates. The method achieves low-complexity, high-fidelity entanglement preparation.

DOI
10.20944/preprints202510.0281.v1

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This paper addresses high-fidelity Bell state preparation under depolarizing noise. A split-qubit approach is proposed: dynamic decoupling for the control qubit and error correction for the target qubit. Qiskit simulations show fidelity maintained at 1.0000, with error rates reduced from ~24% to 0.4%, requiring only four X gates. The method achieves low-complexity, high-fidelity entanglement preparation.
This study focuses on achieving high-fidelity preparation of Bell states in depolarization noise environments. Based on Qiskit simulations, we propose a quantum-bit-by-quantum-bit noise-resistant strategy: applying dynamic decoupling to control qubits and implementing quantum error correction for target qubits. Experimental results demonstrate that this strategy maintains fidelity at 1. 0000 while significantly reducing the error rate from approximately 24% to 0. 4%, requiring only four additional quantum gate operations. The method achieves high-fidelity quantum entanglement with low complexity, showcasing significant practical value. As the standard form. of two-qubit maximum entanglement state, the Bell states are widely applied in critical tasks such as quantum teleportation, superdense coding, and quantum key distribution. However, real quantum systems inevitably interact with their environment, leading to quantum state decoherence and a significant decrease in the fidelity of the Bell state. Existing anti-jamming schemes mainly fall into two categories: dynamic decoupling through periodic pulse application to cancel noise, and quantum error correction through redundant encoding to fix errors. However, dynamic decoupling requires extremely high synchronization for multi-qubit systems, while quantum error correction necessitates additional auxiliary qubits, resulting in an exponential growth in circuit complexity.
Realistic quantum computing is subject to noise. Therefore, an important frontier in quantum computing is to implement noise-resilient quantum control over qubits. At the same time, dynamical decoupling can protect the coherence of qubits. Here we demonstrate non-trivial quantum evolution steered by dynamical decoupling control, which simultaneously suppresses noise effects. We design and implement a self-protected controlled-NOT gate on the electron spin of a nitrogen-vacancy centre and a nearby carbon-13 nuclear spin in diamond at room temperature, by employing an engineered dynamical decoupling control on the electron spin. Final state fidelity of 0.91(1) is observed in preparation of a Bell state using the gate. At the same time, the qubit coherence time is elongated at least 30 fold. The design scheme does not require the dynamical decoupling control to commute with the qubit interaction and therefore works for general qubit systems. This work marks a step towards implementing realistic quantum computing systems. Realistic quantum computers require a high degree of qubit control and must also be resilient to noise. Using dynamical decoupling control techniques, Liuet al.implement a self-protected controlled-NOT gate for electron and nuclear spins that retains a high final state fidelity.
Dynamic decoupling (DD) can suppress decoherence caused by environmental noise, while in hybrid system it also hinders coherent manipulation between qubits. We realized the universal high-fidelity quantum gate set and the preparation of Bell states using dynamical decoupling gates (DD gates) in a silicon-based phosphorus-doped (Si:P) system, effectively resolving the contradiction between decoherence protection and manipulation of qubits. The simulation results show that the fidelity of the universal quantum gate set are all above 99%, and the fidelity of Bell state preparation is over 96%. This work realized the compatibility between coherent protection and high-fidelity manipulation of quantum states, provided a reliable theoretical support for high-fidelity quantum computing.
Decoherence is a primary barrier to practical quantum computation, causing quantum states to degrade through phase randomization and irreversible energy relaxation. This study presents a simulation-based evaluation of echo-based dynamical decoupling (DD) pulse sequences as a software-level mitigation strategy in single-qubit systems. Using the Qiskit Aer density matrix simulator, four strategies—baseline, Hahn Echo, Carr-Purcell-Meiboom-Gill (CPMG), and Mixed Synchronization—were evaluated across low-frequency phase noise, high-frequency phase noise, and combined T₁ + T₂ noise regimes. Hahn Echo restored mean fidelity to 100.00% under low-frequency noise (baseline: 57.90%), while CPMG achieved 97.62% under high-frequency noise (baseline: 2.45%). Under combined noise, all strategies showed limited improvement, with Mixed-Sync reaching 65.34% versus 60.95%. Coefficient of variation (CV) analysis across 500 Monte Carlo trials showed that CPMG reduced purity-decay variance threefold under high-frequency noise, with bootstrap confidence intervals confirming statistical significance. Time-resolved analysis showed that CPMG suppressed variance growth throughout evolution, reducing variance growth from +267% (baseline) to +89%, while baseline and Hahn Echo exhibited progressive amplification of variance. These results show that dynamical decoupling influences the temporal structure of noise, not just mean fidelity. In T₂-dominated regimes, pulse sequences constrain variability; in mixed regimes, they partially shape it; and in T₁-dominated regimes, both mean performance and variability converge to hardware-limited behavior. DD effectively corrects reversible phase errors but cannot overcome irreversible T₁ loss, with implications for NISQ circuit design.
Individual neutral atoms excited to Rydberg states are a promising platform for quantum simulation and quantum information processing. However, experimental progress to date has been limited by short coherence times and relatively low gate fidelities associated with such Rydberg excitations. We report progress towards high-fidelity quantum control of Rydberg-atom qubits. Enabled by a reduction in laser phase noise, our approach yields a significant improvement in coherence properties of individual qubits. We further show that this high-fidelity control extends to the multi-particle case by preparing a two-atom entangled state with a fidelity exceeding 0.97(3), and extending its lifetime with a two-atom dynamical decoupling protocol. These advances open up new prospects for scalable quantum simulation and quantum computation with neutral atoms.