Atomic fluctuations lifting the energy degeneracy in Si/SiGe quantum dots

Wuetz, Brian Paquelet; Losert, Merritt P.; Koelling, Sebastian; A., Stehouwer, Lucas E.; Zwerver, Anne-Marije J.; Philips, Stephan G. J.; Mądzik, Mateusz T.; Xue, Xiangxin; Zheng, Guoji; Lodari, Mario; Amitonov, Sergey V.; Samkharadze, Nodar; Sammak, Amir; Vandersypen, L. M. K.; Rahman, Rajib; Coppersmith, S. N.; Moutanabbir, Oussama; Friesen, Mark; Scappucci, Giordano

doi:10.1038/s41467-022-35458-0

Cited by 43 publications

(82 citation statements)

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“…We study devices in 28 Si/SiGe heterostructures and investigate how the pinch-off voltage of a single gate evolves depending on the previously applied gate voltages. To that end, we conduct systematic transport measurements at 4.2 K similar to sequences in refs − following the procedure depicted in Figure a.…”

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confidence: 99%

Electrical Control of Uniformity in Quantum Dot Devices

et al. 2023

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Highly uniform quantum systems are essential for the practical implementation of scalable quantum processors. While quantum dot spin qubits based on semiconductor technology are a promising platform for large-scale quantum computing, their small size makes them particularly sensitive to their local environment. Here, we present a method to electrically obtain a high degree of uniformity in the intrinsic potential landscape using hysteretic shifts of the gate voltage characteristics. We demonstrate the tuning of pinch-off voltages in quantum dot devices over hundreds of millivolts that then remain stable at least for hours. Applying our method, we homogenize the pinch-off voltages of the plunger gates in a linear array for four quantum dots, reducing the spread in pinch-off voltages by one order of magnitude. This work provides a new tool for the tuning of quantum dot devices and offers new perspectives for the implementation of scalable spin qubit arrays.

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confidence: 99%

Electrical Control of Uniformity in Quantum Dot Devices

et al. 2023

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“…S13 of ref. 40 and the Ge concentration in the SiGe layers is confirmed by quantitative electron energy loss spectroscopy (EELS). 2 of a charge qubit (circle) and of a spin-qubit (star) using S ϵ,min from heterostructure A (red), B (blue), C (green).…”

Section: Methodsmentioning

confidence: 92%

“…2a. Using the same device design, two-qubit gates with fidelity above 99% were demonstrated 6 , silicon quantum circuits were controlled by CMOS-based cryogenic electronics 31 , and energy splittings in 28 Si/SiGe heterostructures were studied with statistical significance 40 .…”

Section: Charge Noise Measurements In Quantum Dotsmentioning

confidence: 99%

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Reducing charge noise in quantum dots by using thin silicon quantum wells

Wuetz

Esposti²,

Zwerver³

et al. 2023

Nat Commun

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Charge noise in the host semiconductor degrades the performance of spin-qubits and poses an obstacle to control large quantum processors. However, it is challenging to engineer the heterogeneous material stack of gate-defined quantum dots to improve charge noise systematically. Here, we address the semiconductor-dielectric interface and the buried quantum well of a 28Si/SiGe heterostructure and show the connection between charge noise, measured locally in quantum dots, and global disorder in the host semiconductor, measured with macroscopic Hall bars. In 5 nm thick 28Si quantum wells, we find that improvements in the scattering properties and uniformity of the two-dimensional electron gas over a 100 mm wafer correspond to a significant reduction in charge noise, with a minimum value of 0.29 ± 0.02 μeV/Hz½ at 1 Hz averaged over several quantum dots. We extrapolate the measured charge noise to simulated dephasing times to CZ-gate fidelities that improve nearly one order of magnitude. These results point to a clean and quiet crystalline environment for integrating long-lived and high-fidelity spin qubits into a larger system.

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“…The strong effect of random alloy disorder on the valley splitting can also be understood from Wiggle Well theory. Due to the finite size of a quantum dot, the electron naturally experiences small layer-bylayer fluctuations of the Ge concentration, as recently explored experimentally 32 . Fourier transforming this distribution assigns random weights across the whole q spectrum in Fig.…”

Section: Resultsmentioning

confidence: 99%

SiGe quantum wells with oscillating Ge concentrations for quantum dot qubits

et al. 2022

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Large-scale arrays of quantum-dot spin qubits in Si/SiGe quantum wells require large or tunable energy splittings of the valley states associated with degenerate conduction band minima. Existing proposals to deterministically enhance the valley splitting rely on sharp interfaces or modifications in the quantum well barriers that can be difficult to grow. Here, we propose and demonstrate a new heterostructure, the “Wiggle Well”, whose key feature is Ge concentration oscillations inside the quantum well. Experimentally, we show that placing Ge in the quantum well does not significantly impact our ability to form and manipulate single-electron quantum dots. We further observe large and widely tunable valley splittings, from 54 to 239 μeV. Tight-binding calculations, and the tunability of the valley splitting, indicate that these results can mainly be attributed to random concentration fluctuations that are amplified by the presence of Ge alloy in the heterostructure, as opposed to a deterministic enhancement due to the concentration oscillations. Quantitative predictions for several other heterostructures point to the Wiggle Well as a robust method for reliably enhancing the valley splitting in future qubit devices.

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Atomic fluctuations lifting the energy degeneracy in Si/SiGe quantum dots

Cited by 43 publications

References 50 publications

Electrical Control of Uniformity in Quantum Dot Devices

Electrical Control of Uniformity in Quantum Dot Devices

Reducing charge noise in quantum dots by using thin silicon quantum wells

SiGe quantum wells with oscillating Ge concentrations for quantum dot qubits

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