How Valley-Orbit States in Silicon Quantum Dots Probe Quantum Well Interfaces

Dodson, J. P.; Ercan, Hamdi; Corrigan, J.; Losert, Merritt P.; Holman, Nathan; McJunkin, Thomas; Edge, L. F.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.

doi:10.1103/physrevlett.128.146802

Cited by 23 publications

(22 citation statements)

References 51 publications

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“…17 When combined with the conventional microwave toolbox, the tip of the SGM can be used for local spectroscopy 18 in the few tens of GHz range. This frequency range overlaps nicely with the reported 25−300 μeV 19−23 parameters affecting valley splitting 24 and its spatial variation 25 is of particular interest to the semiconductor spin qubit community since this unwanted degree of freedom 23,26 can cause fast qubit relaxation. 27 SGM provides spatial resolution, but it has not been applied to realistic quantum devices.…”

Section: ■ Introductionsupporting

confidence: 81%

Microwave-Frequency Scanning Gate Microscopy of a Si/SiGe Double Quantum Dot

Gordian

et al. 2022

Nano Lett.

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Conventional transport methods provide quantitative information on spin, orbital, and valley states in quantum dots but lack spatial resolution. Scanning tunneling microscopy, on the other hand, provides exquisite spatial resolution at the expense of speed. Working to combine the spatial resolution and energy sensitivity of scanning probe microscopy with the speed of microwave measurements, we couple a metallic tip to a Si/SiGe double quantum dot (DQD) that is integrated with a charge detector. We first demonstrate that the dc-biased tip can be used to change the occupancy of the DQD. We then apply microwaves through the tip to drive photon-assisted tunneling (PAT). We infer the DQD level diagram from the frequency and detuning dependence of the tunneling resonances. These measurements allow the resolution of ∼65 μeV excited states, an energy consistent with valley splittings in Si/SiGe. This work demonstrates the feasibility of scanning gate experiments with Si/SiGe devices.

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Section: ■ Introductionsupporting

confidence: 81%

Microwave-Frequency Scanning Gate Microscopy of a Si/SiGe Double Quantum Dot

Gordian

et al. 2022

Nano Lett.

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“…1(b). This quenching of the gaps, which recently was observed experimentally in Si [28,51] (but also in GaAs [7]) DQD qubits, is the result of strong-electron correlations and of the formation of Wigner molecules. Namely, the ensuing spatial localization of the electrons within the left or right QD reduces the Coulomb repulsion between them, a process that leads to the convergence of the energies between the states with symmetric and antisymmetric space parts.…”

Section: Resultssupporting

confidence: 55%

“…The evolution of the VFCI low-energy spectra in this case is investigated in Fig. 3 As mentioned earlier, experimental reports [28,51] from the Wisconsin-Madison group indicated that the rst excited state in the (2,0) conguration in a Si/SiGe DQD is the spin-triplet state with both electrons in the same lower-energy valley, whereas experimental measurements [13,15] from other groups on Si-DQD devices (with apparently dierent parameters) indicated that the rst excited energy level in this conguration is associated with a state having each electron in a dierent valley [see states nos. 2 or 3 in Fig.…”

Section: B First-excited State With Electrons In Dierent Valleysmentioning

confidence: 85%

“…As elaborated in the main text, the VFCI results presented here are in agreement with the many trends revealed in experimental measurements on actual DQD artificial devices that aim at establishing the proof-ofprinciple feasibility of solid-state qubits and logical gates; specifically, among others, the VFCI results were shown to emulate trends reported in Refs. [13,15,28,51,52].…”

Section: The Spin-isospin Coupling and The Valley Splittingmentioning

confidence: 99%

“…Related experimental situations have been reported in Refs. [28,51]. The VFCI results concerning this case are presented in Sec.…”

Section: Introductionmentioning

confidence: 99%

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Valleytronic full configuration-interaction approach: An application to the excitation spectra of Si double-dot qubits

Yannouleas

Landman

2022

Preprint

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A study of the influence of strong electron-electron interactions and Wigner-molecule (WM) formation on the spectra of 2e singlet-triplet double-dot Si qubits is presented based on a full configuration interaction (FCI) approach that incorporates the valley degree of freedom (VDOF) in the context of the continuous (effective mass) description of semiconductor materials. Our FCI solutions correspond to treating the VDOF as an isospin in addition to the regular spin. A major advantage of our treatment is its capability to assign to each energy curve in the qubit's spectrum a complete set of good quantum numbers for both the spin and the valley isospin. This allows for the interpretation of the Si double-dot spectra according to an underlying SU(4) ⊃ SU(2) × SU(2) group-chain organization. Considering parameters in the range of actual experimental situations, we demonstrate for the first time in a double-dot qubit that, in the (2,0) charge configuration and compared to the expected large, and dot-size determined, single-particle (orbital) energy gap, the strong e − e interactions drastically quench the spin-singlet−spin-triplet energy gap, E^⊕_ST, within the same valley, making it competitive to the small energy gap, E_V , between the two valleys. We present results for both the E^⊕_ST < E_V and E^⊕_ST > E_V cases, which have been reported to occur in different experimental qubit devices. In particular, we investigate the spectra as a function of detuning and demonstrate the strengthening of the all-important avoided crossings due to a lowering of the interdot barrier and/or the influence of valley-orbit coupling. We further demonstrate, as a function of an applied magnetic field, the emergence of avoided crossings in the (1,1) charge configuration due to the more general spin-valley coupling, in agreement with experiments. The valleytronic FCI method formulated and implemented in this paper, and demonstrated for the case of two electrons confined in a tunable double quantum dot, offers also a most effective tool for analyzing the spectra of Si qubits with more than two wells and/or more than two electrons, in field-free conditions, as well as under the influence of an applied magnetic field. Furthermore, it can also be straightforwardly extended to the case of bilayer graphene quantum dots.

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Progress of Gate‐Defined Semiconductor Spin Qubit: Host Materials and Device Geometries

Liu,

Guan,

Luo

et al. 2024

Adv Funct Materials

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Quantum computing offers the potential to revolutionize information processing by exploiting the principles of quantum mechanics. Among the diverse quantum bit (qubit) technologies, silicon‐based semiconductor spin qubits have emerged as a promising contender due to their potential scalability and compatibility with existing semiconductor technologies. In this paper, the latest developments of spin qubits in gate‐defined semiconducting nanostructures made of silicon and germanium, starting from the basic properties of electron and hole states in group‐IV semiconductors, are reviewed. Specifically, various nanostructures that exploit their unique microscopic properties for qubit implementations, elaborating on the advances and challenges in experiments, are discussed. Strategies for enhancing qubit performance, such as designing new nanostructures and identifying suitable operating points, particularly those involving the valleys of electron qubits and the heavy‐hole–light‐hole mixing of hole qubits, are also highlighted. This comprehensive review thus provides valuable insights into the current state‐of‐the‐art in semiconductor quantum computing and suggests avenues for future research.

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How Valley-Orbit States in Silicon Quantum Dots Probe Quantum Well Interfaces

Cited by 23 publications

References 51 publications

Microwave-Frequency Scanning Gate Microscopy of a Si/SiGe Double Quantum Dot

Microwave-Frequency Scanning Gate Microscopy of a Si/SiGe Double Quantum Dot

Valleytronic full configuration-interaction approach: An application to the excitation spectra of Si double-dot qubits

Progress of Gate‐Defined Semiconductor Spin Qubit: Host Materials and Device Geometries

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