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1. Modeling correlated-noise in silicon spin qubit device

   https://doi.org/10.1063/5.0216833  

   Cheng, Guoting; Guo, Jing (January 2025, APL Quantum)

   Silicon-based spin qubit platform is a promising candidate for the hardware realization of quantum computing. Charge noise, however, plays a critical role in limiting the fidelity and scalability of silicon-based quantum computing technologies. This work presents Green’s transfer function approach to simulate the correlated noise power spectral density (PSD) in silicon spin qubit devices. The simulation approach relates the dynamics of the charge noise source of two-level fluctuators (TLFs) to the correlated noise of spin qubit device characteristics through a transfer function. It allows the noise auto-correlation and cross correlation between any pairs of physical quantities of interest to be systematically computed and analyzed. Because each spin qubit device involves only a small number of TLFs due to its nanoscale device size, the distribution of TLFs impacts the noise correlation significantly. In both a two-qubit quantum gate and a spin qubit array device, the charge noise shows strong cross correlation between neighboring qubits. The simulation results also reveal a phase-flipping feature of the noise cross-PSD between neighboring spin qubits, consistent with a recent experiment. 

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2. An Interactive Tool of Spin Qubit for Quantum Science and Engineering Education

   Yang, Qimao; Williams, Raiden; Song, Yukyeong; Xing, Wanli; Guo, Jing (September 2024, Quantum Science and Engineering Education Conference (QSEEC24))

   Silicon-based spin qubits represent a promising technology for scalable quantum computing. However, the complex nature of this field, which requires a deep understanding of quantum mechanics, materials science, and nanoelectronics, poses a significant challenge in making it accessible to future engineers and scientists. Spin Quantum Gate Lab, a spin qubit simulation tool, is proposed in this paper to address this obstacle. This tool is designed to introduce key concepts of spin qubit to undergraduate students, enabling the simulation of single-qubit rotational gates and two-qubit controlled-phase gates. By providing hands-on experience with quantum gate operations, it effectively links theoretical quantum concepts to practical experience, fostering a deeper understanding of silicon-based quantum computing. 

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3. Charge-noise spectroscopy of Si/SiGe quantum dots via dynamically-decoupled exchange oscillations

   https://doi.org/10.1038/s41467-022-28519-x  

   Connors, Elliot J.; Nelson, J.; Edge, Lisa F.; Nichol, John M. (December 2022, Nature Communications)

   Abstract Electron spins in silicon quantum dots are promising qubits due to their long coherence times, scalable fabrication, and potential for all-electrical control. However, charge noise in the host semiconductor presents a major obstacle to achieving high-fidelity single- and two-qubit gates in these devices. In this work, we measure the charge-noise spectrum of a Si/SiGe singlet-triplet qubit over nearly 12 decades in frequency using a combination of methods, including dynamically-decoupled exchange oscillations with up to 512 π pulses during the qubit evolution. The charge noise is colored across the entire frequency range of our measurements, although the spectral exponent changes with frequency. Moreover, the charge-noise spectrum inferred from conductance measurements of a proximal sensor quantum dot agrees with that inferred from coherent oscillations of the singlet-triplet qubit, suggesting that simple transport measurements can accurately characterize the charge noise over a wide frequency range in Si/SiGe quantum dots. 

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4. Variability and Fidelity Limits of Silicon Quantum Gates Due to Random Interface Charge Traps

   https://doi.org/10.1109/LED.2020.2997009  

   Wu, Tong; Guo, Jing (January 2020, IEEE Electron Device Letters)

   null (Ed.)

   Silicon offers an attractive material platform for hardware realization of quantum computing. In this study, a microscopic stochastic simulation method is developed to model the effect of random interface charge traps in silicon metal-oxide-semiconductor (MOS) quantum gates. The statistical results show that by using a fast two-qubit gate in isotopically purified silicon, the two-qubit silicon-based quantum gates have the fidelity >98% with a probability of 75% for the state-of-the-art MOS interface quality. By using a composite gate pulse, the fidelity can be further improved to >99.5% with the 75% probability. The variations between the quantum gate devices, however, are largely due to the small number of traps per device. The results highlight the importance of variability consideration due to random charge traps and potential to improve fidelity in silicon-based quantum computing. 

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5. Adiabatic quantum state transfer in a semiconductor quantum-dot spin chain

   https://doi.org/10.1038/s41467-021-22416-5  

   Kandel, Yadav P.; Qiao, Haifeng; Fallahi, Saeed; Gardner, Geoffrey C.; Manfra, Michael J.; Nichol, John M. (December 2021, Nature Communications)

   null (Ed.)

   Abstract Semiconductor quantum-dot spin qubits are a promising platform for quantum computation, because they are scalable and possess long coherence times. In order to realize this full potential, however, high-fidelity information transfer mechanisms are required for quantum error correction and efficient algorithms. Here, we present evidence of adiabatic quantum-state transfer in a chain of semiconductor quantum-dot electron spins. By adiabatically modifying exchange couplings, we transfer single- and two-spin states between distant electrons in less than 127 ns. We also show that this method can be cascaded for spin-state transfer in long spin chains. Based on simulations, we estimate that the probability to correctly transfer single-spin eigenstates and two-spin singlet states can exceed 0.95 for the experimental parameters studied here. In the future, state and process tomography will be required to verify the transfer of arbitrary single qubit states with a fidelity exceeding the classical bound. Adiabatic quantum-state transfer is robust to noise and pulse-timing errors. This method will be useful for initialization, state distribution, and readout in large spin-qubit arrays for gate-based quantum computing. It also opens up the possibility of universal adiabatic quantum computing in semiconductor quantum-dot spin qubits. 

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