Topological Bloch Bands in Graphene Superlattices

We outline an approach to endow a plain vanilla material with topological properties by creating topological bands in stacks of manifestly nontopological atomically thin materials. The approach is illustrated with a model system comprised of graphene stacked atop hexagonal-boron-nitride. In this case, the Berry curvature of the electron Bloch bands is highly sensitive to the stacking configuration. As a result, electron topology can be controlled by crystal axes alignment, granting a practical route to designer topological materials. Berry curvature manifests itself in transport via the valley Hall effect and long-range chargeless valley currents. The non-local electrical response mediated by such currents provides diagnostics for band topology

Topological Valley Currents in Gapped Dirac Materials

Gapped 2D Dirac materials, in which inversion symmetry is broken by a gap-opening perturbation, feature a unique valley transport regime. The system ground state hosts dissipationless persistent valley currents existing even when topologically protected edge modes are absent or when they are localized due to edge roughness. Topological valley currents in such materials are dominated by bulk currents produced by electronic states just beneath the gap rather than by edge modes. Dissipationless currents induced by an external bias are characterized by a quantized half-integer valley Hall conductivity. The under-gap currents dominate magnetization and the charge Hall effect in a light-induced valley-polarized state.Comment: 5pgs 3fg

Passive intrinsic-linewidth narrowing of ultraviolet extended-cavity diode laser by weak optical feedback

We present a simple method for narrowing the intrinsic Lorentzian linewidth of a commercial ultraviolet grating extended-cavity diode laser (TOPTICA DL Pro) using weak optical feedback from a long external cavity. We achieve a suppression in frequency noise spectral density of 20 dB measured at frequencies around 1 MHz, corresponding to the narrowing of the intrinsic Lorentzian linewidth from 200 kHz to 2 kHz. The system is suitable for experiments requiring a tunable ultraviolet laser with narrow linewidth and low high-frequency noise, such as precision spectroscopy, optical clocks, and quantum information science experiments.Comment: 8 pages, 3 figure

Indistinguishable photons from an artificial atom in silicon photonics

Silicon is the ideal material for building electronic and photonic circuits at scale. Integrated photonic quantum technologies in silicon offer a promising path to scaling by leveraging advanced semiconductor manufacturing and integration capabilities. However, the lack of deterministic quantum light sources and strong photon-photon interactions in silicon poses a challenge to scalability. In this work, we demonstrate an indistinguishable photon source in silicon photonics based on an artificial atom. We show that a G center in a silicon waveguide can generate high-purity telecom-band single photons. We perform high-resolution spectroscopy and time-delayed two-photon interference to demonstrate the indistinguishability of single photons emitted from a G center in a silicon waveguide. Our results show that artificial atoms in silicon photonics can source single photons suitable for photonic quantum networks and processors

Anomalous Hall effect and persistent valley currents in graphene p-n junctions/

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2014.Cataloged from PDF version of thesis.Includes bibliographical references (pages 39-40).Dirac particles can exhibit Hall-like transport induced by Berry's gauge field in the absence of magnetic field. We develop a detailed picture of this unusual effect for charge carriers in graphene nanostructures. The Hall effect is nonzero in each valley but is of opposite signs in different valleys, giving rise to charge-neutral valley currents. Our analysis reveals that p-n junctions in graphene support persistent valley currents that remain nonzero in the system ground state (in thermodynamic equilibrium). The valley currents can be controlled via the bias and gate voltages, enabling a variety of potentially useful valley transport phenomena.by Polnop Samutpraphoot.S.B

Entanglement transport and a nanophotonic interface for atoms in optical tweezers

Quantum trapping and shuffling Programmable arrays of atoms or ions trapped in optical potentials have recently emerged as a leading platform for quantum simulation. Being able to interface into these arrays to access the quantum information being processed and pass it along to another module remains a challenge. Ðorđević et al . developed a hybrid quantum system that combines atoms held in optical tweezers and a nanophotonic cavity to demonstrate full quantum control, efficient quantum nondestructive readout, and entanglement of atom pairs (see the Perspective by Kaufman). By combining atomic manipulation both inside and away from the cavity field and shuffling the atom qubits into and out of the cavity mode, the authors demonstrate a viable optical interface that could be scaled to larger systems. —ISO </jats:p

Strong coupling of two individually controlled atoms via a nanophotonic cavity

We demonstrate photon-mediated interactions between two individually trapped atoms coupled to a nanophotonic cavity. Specifically, we observe collective enhancement when the atoms are resonant with the cavity and level repulsion when the cavity is coupled to the atoms in the dispersive regime. Our approach makes use of individual control over the internal states of the atoms and their position with respect to the cavity mode, as well as the light shifts to tune atomic transitions individually, allowing us to directly observe the anticrossing of the bright and dark two-atom states. These observations open the door for realizing quantum networks and studying quantum many-body physics based on atom arrays coupled to nanophotonic devices. ©2020 Keywords: cavity quantum electrodynamics; collective effects in quantum optics; hybrid quantum systems; quantum control; quantum optics; superradiance & subradianceCenter for Ultracold Atoms (grant no. PHY-1125846)National Science Foundation (grant no. PHY-1506284)AFOSR (grant no. FA9550-16-1-0323)Vannevar Bush Faculty Fellowship (grant no. N00014-15-1-2846)ARL CDQI (grant no. W911NF1520067

Supplementary document for Three-dimensional programming of nanolaser arrays through a single optical microfiber - 6105989.pdf

1. Propagation modes in optical microfiber, 2. Estimation of minimum beat length, 3. Theoretical analysis of modal interference, 4. Efficiency of laser pumping, 5. Fabrication of tapered microfiber, 6. Laser characteristics, 7. Spectral filtering o