Emerging many-body effects in semiconductor artificial graphene with low disorder.

The interplay between electron-electron interactions and the honeycomb topology is expected to produce exotic quantum phenomena and find applications in advanced devices. Semiconductor-based artificial graphene (AG) is an ideal system for these studies that combines high-mobility electron gases with AG topology. However, to date, low-disorder conditions that reveal the interplay of electron-electron interaction with AG symmetry have not been achieved.

Demonstration of universal parametric entangling gates on a multi-qubit lattice.

We show that parametric coupling techniques can be used to generate selective entangling interactions for multi-qubit processors. By inducing coherent population exchange between adjacent qubits under frequency modulation, we implement a universal gate set for a linear array of four superconducting qubits. An average process fidelity of ℱ = 93% is estimated for three two-qubit gates via quantum process tomography.

Observation of Dirac bands in artificial graphene in small-period nanopatterned GaAs quantum wells.

Charge carriers in graphene behave like massless Dirac fermions (MDFs) with linear energy-momentum dispersion , providing a condensed-matter platform for studying quasiparticles with relativistic-like features. Artificial graphene (AG)-a structure with an artificial honeycomb lattice-exhibits novel phenomena due to the tunable interplay between topology and quasiparticle interactions . So far, the emergence of a Dirac band structure supporting MDFs has been observed in AG using molecular , atomic and photonic systems , including those with semiconductor microcavities .

Too Hot for Photon-Assisted Transport: Hot-Electrons Dominate Conductance Enhancement in Illuminated Single-Molecule Junctions.

We investigate light-induced conductance enhancement in single-molecule junctions via photon-assisted transport and hot-electron transport. Using 4,4'-bipyridine bound to Au electrodes as a prototypical single-molecule junction, we report a 20-40% enhancement in conductance under illumination with 980 nm wavelength radiation. We probe the effects of subtle changes in the transmission function on light-enhanced current and show that discrete variations in the binding geometry result in a 10% change in enhancement.

Nanoscale Engineering of Closely-Spaced Electronic Spins in Diamond.

Numerous theoretical protocols have been developed for quantum information processing with dipole-coupled solid-state spins. Nitrogen vacancy (NV) centers in diamond have many of the desired properties, but a central challenge has been the positioning of NV centers at the nanometer scale that would allow for efficient and consistent dipolar couplings. Here we demonstrate a method for chip-scale fabrication of arrays of single NV centers with record spatial localization of about 10 nm in all three dimensions and controllable inter-NV spacing as small as 40 nm, which approaches the length scale of strong dipolar coupling.