arXiv subjects

Si-Qi Chen

Publications and source records attributed to Si-Qi Chen.

4 recordsLinked to original sources

arXiv2026

Experimental High-Accuracy and Broadband Quantum Frequency Sensing via Geodesic Control

Accurate frequency estimation of oscillating signals over a broad bandwidth is a central task in quantum sensing, yet it is often compromised by spurious responses to higher-order harmonics in realistic multi-frequency environments. Here we experimentally demonstrate a high-accuracy and broadband quantum frequency sensing protocol based on geodesic control, implemented using the electron spin of a single nitrogen-vacancy center in diamond. By engineering an intrinsically single-frequency response, geodesic control enables bias-free frequency estimation with strong suppression of harmonic-induced systematic errors across a wide spectral range spanning from the megahertz to the gigahertz regime. Furthermore, by incorporating synchronized readout, we achieve millihertz-level frequency resolution under noisy signal conditions. Our results provide systematic experimental benchmarking of geodesic control for quantum frequency sensing and establish it as a practical approach for high-accuracy metrology in realistic environments.

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arXiv2025

Floquet Diamond Sensor with Optimal Precision

The diamond sensor has emerged as a promising platform for quantum sensing, enabling the estimation of physical quantities -- such as microwave~(MW) field -- with precision unattainable by classical counterpart. However, traditional diamond sensors suffer severe precision degradation when the signal MW is not resonant with the sensor transition frequency. Here, we propose and demonstrate a Floquet diamond sensor~(FDS) for high-precision off-resonant MW amplitude sensing without attenuating the strength of the signal MW. The periodic driven field effectively induces an quasi-energy shift that matches the off-resonant MW frequency. The measurement precision of FDS is characterized by quantum Fisher information, which approaches the ultimate precision -- Heisenberg limit -- within the coherent time. Furthermore, the FDS exhibits robust tolerance to practical control errors and is compatible with dynamical coupling protocol, enabling a robust and high-sensitivity magnetic sensing. Our results confirm the quantum advantage of quantum sensing and provide a practical technology for high-precision off-resonant MW sensing.

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arXiv2025

Multiple-Noise-Resilient Nonadiabatic Geometric Quantum Control of Solid-State Spins in Diamond

Reliable and robust control lies at the core of implementing quantum information processing with diamond nitrogen-vacancy (NV) centers. However, control pulses inevitably introduce multiple errors, leading to decoherence and hindering scalable applications. Here, we experimentally report an experiment-friendly multiple-noise-resilient nonadiabatic geometric quantum gate~(MNR-NGQG) that can significantly improve conventional dynamical gate in both robustness and coherence. Notably, even when the detuning fluctuation range is comparable to the maximum Rabi frequency, the single-qubit gate performance of the MNR-NGQG remains almost unchanged. Besides, the coherence time of the electron spin is significantly extended to 690 $\pm$ 30 $ \mu$s, 3.5 times that of the naive dynamical counterpart. As a result, the fidelity of single-qubit gates reaches 0.9992(1), as characterized by quantum process tomography. With its experimentally feasible design and relaxed hardware requirements, our work offers a solid paradigm for achieving high-fidelity quantum control in NV center system, paving the way for practical applications in quantum information science.

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arXiv2024

Experimental Acceleration of Spin Transition in Nitrogen-Vacancy Center

Shortcuts to adiabaticity~(STA) enables fast and robust coherent control of quantum system, which has been well placed in quantum technologies. In particular, inverse engineering STA provides much more freedom for the optimization of shortcut, which alleviates the complexity for experimental realization. Here, we implement a STA technique, known as invariant-based inverse engineering, to speed up the adiabatic control of the electron triplet ground state of a single nitrogen-vacancy~(NV) center. The microwave pulses to drive inversely engineered STA are obtained with space curve quantum control, where the evolution of spin transition is mapped to a three-dimensional closed space curve and the design of shortcut is obtained by optimization over the space curve. We demonstrate the fast and high-fidelity drive of dipole-forbidden transition between two spin sublevels of the ground state. Moreover, we demonstrate the robustness of the spin transition by introducing the detuning of driving microwave field. The acceleration and robustness is further confirmed by the comparison with two traditional Raman control schemes. Our results suggest invariant-based inverse engineering is powerful for fast and robust manipulation of NV system, and thus benefits quantum sensing and quantum computation based on the NV platform.

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