Large, Tunable Valley Splitting and Single-Spin Relaxation Mechanisms in a Si / Six Ge1

Abstract

Valley splitting is a key feature of silicon-based spin qubits. Quantum dots in Si/Si x Ge 1−x heterostructures reportedly suffer from a relatively low valley splitting, limiting the operation temperature and the scalability of such qubit devices. Here, we demonstrate a robust and large valley splitting exceeding 200 μeV in a gate-defined single quantum dot, hosted in molecular-beam-epitaxy-grown 28 Si/Si x Ge 1−x. The valley splitting is monotonically and reproducibly tunable up to 15% by gate voltages, originating from a 6-nm lateral displacement of the quantum dot. We observe static spin relaxation times T 1 > 1 s at low magnetic fields in our device containing an integrated nanomagnet. At higher magnetic fields, T 1 is limited by the valley hotspot and by phonon noise coupling to intrinsic and artificial spin-orbit coupling, including phonon bottlenecking.

Low-frequency spin qubit energy splitting noise in highly purified 28Si/SiGe

“…For details of the device see the "Methods" section and ref. 23 . We apply an external magnetic field of 668 mT along the x-direction.…”

“…The device studied in this work is fabricated with an undoped 28 Si/SiGe heterostructure 23 . The layer structure is grown on a Si-wafer by means of a solid source molecular beam epitaxy.…”

“…In ref. 23 , we measured the orbital splitting of this QD to be 2.5 meV. Assuming a harmonic potential, we calculate the size of the QD, taken to be the full-width-at-half-maximum of the ground state wavefunction.…”

Effect of Quantum Hall Edge Strips on Valley Splitting in Silicon Quantum Wells

“…However, spin qubits in silicon suffer from a twofold degeneracy of the conduction-band valleys [10][11][12], complicating quantum operation. While the valley splitting energy can be large in silicon metal-oxide-semiconductor devices [13], even allowing for qubit operation above one Kelvin [14,15], atomic-scale disorder in Si/SiGe heterostructures at the Si quantum well top interface yields a valley splitting energy that is typically modest and poorly controlled, with values ranging from 10 to 200 μeV in quantum dots [5,[16][17][18][19][20][21][22][23][24]. While Si/SiGe heterostructures may provide a superior host for scalable qubit arrays due to the low disorder, a key challenge is thus to increase the valley splitting energy for scalable quantum information.…”

Поведение доноров фосфора в объемных монокристаллических моноизотопных сплавах -=SUP=-28-=/SUP=-Si-=SUB=-1-x-=/SUB=--=SUP=-72-=/SUP=-Ge-=SUB=-x-=/SUB=-

“…Слои Si 1−x Ge x применяются для создания кремниевой квантовой ямы и индуцированных затвором квантовых точек и формирования в них спиновых кубитов [4]. В настоящее время уже научились создавать одиночные и двойные квантовые точки в таких структурах и производить одно-и двухкубитовые операции, лежащие в основе работы квантового компьютера.…”