Full-scale quantum computers require the integration of millions of qubits, and the potential of using industrial semiconductor manufacturing to meet this need has driven the development of quantum computing in silicon quantum dots. However, fabrication has so far relied on electron-beam lithography and, with a few exceptions, conventional lift-off processes that suffer from low yield and poor uniformity. Here we report quantum dots that are hosted at a 28Si/28SiO2 interface and fabricated in a 300 mm semiconductor manufacturing facility using all-optical lithography and fully industrial processing. With this approach, we achieve nanoscale gate patterns with excellent yield. In the multi-electron regime, the quantum dots allow good tunnel barrier control—a crucial feature for fault-tolerant two-qubit gates. Single-spin qubit operation using magnetic resonance in the few-electron regime reveals relaxation times of over 1 s at 1 T and coherence times of over 3 ms.

We report on the fabrication and electrical characterization of both single layer graphene micronsized devices and nanoribbons on a hexagonal boron nitride substrate. We show that the micronsized devices have significantly higher mobility and lower disorder density compared to devices fabricated on silicon dioxide substrate in agreement with previous findings. The transport characteristics of the reactive-ion-etched graphene nanoribbons on hexagonal boron nitride, however, appear to be very similar to those of ribbons on a silicon dioxide substrate. We perform a detailed study in order to highlight both similarities as well as differences. Our findings suggest that the edges have an important influence on transport in reactive ion-etched graphene nanodevices.

An open resonator fabricated in a two-dimensional electron gas is used to explore the transition from strongly invasive scanning gate microscopy to the perturbative regime of weak tip-induced potentials. With the help of numerical simulations that faithfully reproduce the main experimental findings, we quantify the extent of the perturbative regime in which the tip-induced conductance change is unambiguously determined by properties of the unperturbed system. The correspondence between the experimental and numerical results is established by analyzing the characteristic length scale and the amplitude modulation of the conductance change. In the perturbative regime, the former is shown to assume a disorder-dependent maximum value, while the latter linearly increases with the strength of a weak tip potential. arXiv:1709.08559v1 [cond-mat.mes-hall]

The spin-flip tunneling rates are measured in GaAs-based double quantum dots by time-resolved charge detection. Such processes occur in the Pauli spin blockade regime with two electrons occupying the double quantum dot. Ways are presented for tuning the spin-flip tunneling rate, which on the one hand gives access to measuring the Rashba and Dresselhaus spin-orbit coefficents. On the other hand they make it possible to turn on and off the effect of spin-orbit interaction with a high on/off-ratio. The tuning is accomplished by choosing the alignment of the tunneling direction with respect to the crystallographic axes, as well as by choosing the orientation of the external magnetic field with respect to the spin-orbit magnetic field. Spin-lifetimes of 10 s are achieved at a tunnel rate close to 1 kHz.Spin-orbit interaction (SOI) couples the orbital motion of electrons to the spin via electric fields. Electrons moving in a crystal experience spin-orbit coupling originating from electric fields with bulk (Dresselhaus) and structure (Rashba) inversion asymmetries. Theoretical work predicts the SOI to bring about interesting physical phenomena, such as the quantum spin Hall effect [1][2][3] and, in conjuction with superconductivity, Majorana states in nanowires [4]. Large SOI can be used for driving spin qubits [5], and vanishing spin-orbit magnetic fields are required for observing a persistent spin-helix [6][7][8].Considering the varying influence of SOI in different systems, measuring its anisotropy and finding ways to tune its strength are essential for taking advantage of it.Despite the relevance of SOI for various experimental systems, only few experiments exist testing the effect of its anisotropy on spin relaxation in quantum dots which are candidates for qubits. [9,10]. It has been studied in single quantum dots [11][12][13][14][15][16][17][18][19] with undefined direction of electron momentum and large energy gap between the different spin states [12]. In coupled quantum dots, theoretical studies predict anisotropic singlet-triplet splitting [15,[19][20][21][22][23][24], and experimental evidence has been obtained recently in highly coupled dots but with ambiguity about the crystallographic direction of the main DQD axis defining the electron momentum [25]. In this paper, we probe the SOI in GaAs by measuring spin-flip tunneling of individual electrons between energetically resonant (1,1) and (0,2) charge states of double quantum dots [see Fig. 1(a)] and with well-defined direction of electron tunneling. A magnetic field is applied in the plane of the underlying two-dimensional electron gas. In particular, we experimentally explore the two-fold anisotropy of the spin-orbit magnetic fieldwith respect to the crystallographic direction p of electron motion, as well as with respect to the spin quantization axis given by the external magnetic field. In 500 nm arXiv:1612.06199v2 [cond-mat.mes-hall]