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Coherent charge-photon and spin-photon coupling has recently been achieved in silicon double quantum dots (DQDs). Here, we demonstrate a versatile split-gate cavity-coupler that allows more than one DQD to be coupled to the same microwave cavity. Measurements of the cavity transmission as a function of level detuning yield a charge cavity coupling rate of g c / 2 π = 58 MHz, a charge decoherence rate of γ c / 2 π = 36 MHz, and a cavity decay rate of κ / 2 π = 1.2 MHz. The charge cavity coupling rate is in good agreement with device simulations. Our coupling technique can be extended to enable simultaneous coupling of multiple DQDs to the same cavity mode, opening the door to long-range coupling of semiconductor qubits using microwave frequency photons. [ABSTRACT FROM AUTHOR]

We report on an experimental demonstration of graphene-metal ohmic contacts with contact resistance below 100 Ω µm. These have been fabricated on graphene wafers, both with and without hydrogen intercalation, and measured using the transmission line method. Specific contact resistivities of 3 × 10-7 to 1.2 × 10-8 Ω cm2 have been obtained. The ultra-low contact resistance yielded short-channel (source-drain distance of 0.45 µm) HfO2/graphene field effect transistors (FETs) with a low on-resistance (Ron) of 550 Ω µm and a high current density of 1.7 A/mm at a source-drain voltage of 1 V. These values represent state-of-the-art (SOA) performance in graphene-metal contacts and graphene FETs. This ohmic contact resistance is comparable to that of SOA high-speed III-V high electron mobility transistors. [ABSTRACT FROM AUTHOR]

We demonstrate double quantum dots fabricated in undoped Si/SiGe heterostructures relying on a double top-gated design. Charge sensing shows that we can reliably deplete these devices to zero charge occupancy. Measurements and simulations confirm that the energetics are determined by the gate-induced electrostatic potentials. Pauli spin blockade has been observed via transport through the double dot in the two electron configuration, a critical step in performing coherent spin manipulations in Si. [ABSTRACT FROM AUTHOR]

We have demonstrated few-electron quantum dots in Si/SiGe and InGaAs, with occupation number controllable from N=0. These display a high degree of spatial symmetry and identifiable shell structure. Magnetospectroscopy measurements show that two Si-based devices possess a singlet N=2 ground state at low magnetic field, and therefore, the twofold valley degeneracy is lifted. The valley splittings in these two devices were 270 and 120 μeV, suggesting the presence of atomically sharp interfaces in our heterostructures. [ABSTRACT FROM AUTHOR]

We report on the fabrication and characterization of a few-electron quantum dot controlled by a single gate electrode. Our device has a double-quantum-well design, in which the doping controls the occupancy of the lower well while the upper well remains empty under the free surface. Electrons tunneling between this accumulation-mode dot and the lower well are detected using a quantum point contact, located slightly offset from the dot gate. Addition spectra starting with N=0 were observed as a function of gate voltage. DC sensitivity to single electrons was determined to be as high as 8.6%. [ABSTRACT FROM AUTHOR]

Threshold photoemission yields for As and In terminated reconstructions of InAs (001) are measured in situ and the variation of the photoyield is correlated with the surface stoichiometry. A significant excess in the measured photoelectron yield is found for the In terminated surfaces. These results are compared to a semiempirical model based on density-functional theory calculations of the surface local densities of states for the As terminated β2-(2×4) and newly predicted ζ-(4×2) reconstructions. The calculations are in good agreement with the measured trends, and provide a basis for the interpretation of threshold photoemission sensor signatures. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]