Direct Measurement of Electron Intervalley Relaxation in a 
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 Quantum Dot

Penthorn, Nicholas; Schoenfield, Joshua S.; Edge, L. F.; Jiang, Hong-Wen

doi:10.1103/physrevapplied.14.054015

Cited by 11 publications

(6 citation statements)

References 40 publications

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“…The relaxation of the valley state in a gate defined quantum dot may be treated analogously to the spin relaxation in gate confined quantum dot systems [46,49,101], in that hybridization of valley and orbital leads to the dominant relaxation mechanism [102,103]. However, the valley relaxation rate is higher than the spin one due to the stronger valley-orbit coupling, and the lack of Van Vleck cancellation [104][105][106][107] for this process compared to (intrinsic) spin-orbit mediated spin relaxation.…”

Section: Valley Relaxation Due To Electron-phonon Couplingmentioning

confidence: 99%

Blueprint of a scalable spin qubit shuttle device for coherent mid-range qubit transfer in disordered Si/SiGe/SiO$_2$

Langrock¹,

Krzywda²,

Focke³

et al. 2022

Preprint

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Silicon spin qubits stand out due to their very long coherence times, compatibility with industrial fabrication, and prospect to integrate classical control electronics. To achieve a truly scalable architecture, a coherent mid-range link between qubit registers has been suggested to solve the signal fan-out problem. Here we present a blueprint of such a ∼ 10 µm long link, called a spin qubit shuttle, which is based on connecting an array of gates into a small number of sets. The number of these gate sets and thus the number of required control signal is independent of the link distance to coherently shuttle the electron qubit. We discuss two different operation modes for the spin qubit shuttle: A qubit conveyor, i.e. a potential minimum that smoothly moves laterally, and a bucket brigade, in which the electron is transported through a series of tunnel-coupled quantum dots by adiabatic passage. We find the former approach more promising considering a realistic Si/SiGe device including potential disorder from the charged defects at the Si/SiO2 layer, as well as typical charge noise. Focusing on the qubit transfer fidelity of the conveyor shuttling mode, motional narrowing, the interplay between orbital and valley excitation and relaxation in presence of g-factors that depend on orbital and valley state of the electron, and effects from spin-hotspots are discussed in detail. We find that a transfer fidelity of 99.9 % is feasible in Si/SiGe at a speed of ∼10 m/s, if the average valley splitting and its inhomogeneity stay within realistic bounds. Operation at low global magnetic field ≈ 20 mT and material engineering towards high valley splitting is favourable to reach high transfer fidelities.

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Section: Valley Relaxation Due To Electron-phonon Couplingmentioning

confidence: 99%

Blueprint of a scalable spin qubit shuttle device for coherent mid-range qubit transfer in disordered Si/SiGe/SiO$_2$

Langrock¹,

Krzywda²,

Focke³

et al. 2022

Preprint

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“…Qubit-level modification due to SVM Here we assume that the Zeeman energy is much smaller than the orbital splitting so that it is sufficient for us to only consider the two low-lying valley-orbital states given by Eqs. (19) and (20). We then consider only the following unperturbed states,…”

Section: Spin-qubit Levelsmentioning

confidence: 99%

“…In Si heterostructures and quantum dots, a combination of biaxial strain together with the sharp interface potential lifts the valley degeneracy and gives rise to two low-lying states [1]. These two valley states can in principle be used to encode the quantum information [16][17][18][19][20]. However, for spin qubits, the presence of the valley states significantly limits the qubit lifetime when the valley energy splitting becomes comparable to the qubit Zeeman splitting.…”

Section: Introductionmentioning

confidence: 99%

Relaxation of single-electron spin qubits in silicon in the presence of interface steps

Hosseinkhani

Burkard

2021

Phys. Rev. B

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We develop a valley-dependent envelope function theory that can describe the effects of arbitrary configurations of interface steps and miscuts on the qubit relaxation time. For a given interface roughness, we show how our theory can be used to find the valley-dependent dipole matrix elements, the valley splitting, and the spin-valley coupling as a function of the electromagnetic fields in a Si/SiGe quantum dot spin qubit. We demonstrate that our theory can quantitatively reproduce and explain the result of experimental measurements for the spin relaxation time with only a minimal set of free parameters. Investigating the sample dependence of spin relaxation, we find that at certain conditions for a disordered quantum dot, the spin-valley coupling vanishes. This, in turn, completely blocks the valley-induced qubit decay. We show that the presence of interface steps can in general give rise to a strongly anisotropic behavior of the spin relaxation time. Remarkably, by properly tuning the gate-induced out-of-plane electric field, it is possible to turn the spin-valley hotspot into a "coldspot" at which the relaxation time is significantly prolonged and where the spin relaxation time is additionally first-order insensitive to the fluctuations of the magnetic field. This electrical tunability enables on-demand fast qubit reset and initialization that is critical for many quantum algorithms and error correction schemes. We therefore argue that the valley degree of freedom can be used as an advantage for Si spin qubits.

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“…The valley Hamiltonian strongly depends on the microscopic environment [62][63][64]. The hybridization of valley, orbital and spin states [52] may give rise to unwanted effects such as enhanced relaxation near the spin-valley hotspot [65][66][67][68], lifted Pauli blockade [53,69] or an altered probability distribution of spin measurements [70].…”

Section: Introductionmentioning

confidence: 99%

Proposal for a cavity-induced measurement of the exchange coupling in quantum dots

Ginzel¹,

Burkard²

2022

Preprint

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In spin qubit arrays the exchange coupling can be harnessed to implement two-qubit gates and to realize intermediate-range qubit connectivity along a spin bus. In this work, we propose a scheme to characterize the exchange coupling between electrons in adjacent quantum dots. We investigate theoretically the transmission of a microwave resonator coupled to a triple quantum dot (TQD) occupied by two electrons. We assume that the right quantum dot (QD) is always occupied by one electron while the second electron can tunnel between the left and center QD. If the two electrons are in adjacent dots they interact via the exchange coupling. By means of analytical calculations we show that the transmission profile of the resonator directly reveals the value of the exchange coupling strength between two electrons. From perturbation theory up to second order we conclude that the exchange can still be identified in the presence of magnetic gradients. A valley splitting comparable to the inter-dot tunnel coupling will lead to further modifications of the cavity transmission dips that also depend on the valley phases.

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Direct Measurement of Electron Intervalley Relaxation in a Si/Si - Ge Quantum Dot

Cited by 11 publications

References 40 publications

Blueprint of a scalable spin qubit shuttle device for coherent mid-range qubit transfer in disordered Si/SiGe/SiO$_2$

Blueprint of a scalable spin qubit shuttle device for coherent mid-range qubit transfer in disordered Si/SiGe/SiO$_2$

Relaxation of single-electron spin qubits in silicon in the presence of interface steps

Proposal for a cavity-induced measurement of the exchange coupling in quantum dots

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