Monday, June 29, 2009

Control of a magnetic Feshbach resonance with laser light

By Dominik M. Bauer, Matthias Lettner, Christoph Vo, Gerhard Rempe & Stephan Dürr

The capability to tune the strength of the elastic interparticle interaction is crucial for many experiments with ultracold gases. Magnetic Feshbach resonances [1, 2] are widely harnessed for this purpose, but future experiments [3, 4, 5, 6, 7, 8] would benefit from extra flexibility, in particular from the capability to spatially modulate the interaction strength on short length scales. Optical Feshbach resonances [9, 10, 11, 12, 13, 14, 15] do offer this possibility in principle, but in alkali atoms they induce rapid loss of particles due to light-induced inelastic collisions. Here, we report experiments that demonstrate that light near-resonant with a molecular bound-to-bound transition in 87Rb can be used to shift the magnetic field at which a magnetic Feshbach resonance occurs. This enables us to tune the interaction strength with laser light, but with considerably less loss than using an optical Feshbach resonance.

**Groupmeeting by Adam Weir**

Bio-Imaging and Super-resolution

Imaging Intracellular Fluorescent Proteins at Nanometer Resolution

Eric Betzig,1,2*{dagger} George H. Patterson,3 Rachid Sougrat,3 O. Wolf Lindwasser,3 Scott Olenych,4Juan S. Bonifacino,3 Michael W. Davidson,4 Jennifer Lippincott-Schwartz,3 Harald F. Hess5*
We introduce a method for optically imaging intracellular proteins at nanometer spatial resolution. Numerous sparse subsets of photoactivatable fluorescent protein molecules were activated, localized (to ~2 to 25 nanometers), and then bleached. The aggregate position information from all subsets was then assembled into a superresolution image. We used this method—termed photoactivatedlocalization microscopy—to image specific target proteins in thin sections of lysosomes and mitochondria; in fixed whole cells, we imaged vinculin at focal adhesions, actin within a lamellipodium, and the distribution of the retroviral protein Gag at the plasma membrane.

Three-Dimensional Super-Resolution Imaging by Stochastic Optical Reconstruction Microscopy

Bo Huang,1,2 Wenqin Wang,3 Mark Bates,4 Xiaowei Zhuang1,2,3*
Recent advances in far-field fluorescence microscopy have led to substantial improvements in image resolution, achieving a near-molecular resolution of 20 to 30 nanometers in the two lateral dimensions. Three-dimensional (3D) nanoscale-resolution imaging, however, remains a challenge. We demonstrated 3D stochastic optical reconstruction microscopy (STORM) by using optical astigmatism to determine both axial and lateral positions of individual fluorophores with nanometer accuracy. Iterative, stochasticactivation of photoswitchable probes enables high-precision 3D localization of each probe, and thus the construction of a 3D image, without scanning the sample. Using this approach, we achieved an image resolution of 20 to 30 nanometers in the lateral dimensions and 50 to 60 nanometers in the axial dimension. This development allowed us to resolve the 3D morphology of nanoscopic cellular structures.

Interferometric fluorescent super-resolution microscopy resolves 3D cellular ultrastructure
  • Gleb Shtengela
  • James A. Galbraithb
  • Catherine G. Galbraithc
  • Jennifer Lippincott-Schwartzd,1,
  • Jennifer M. Gilletted
  • Suliana Manleyd
  • Rachid Sougratd
  • Clare M. Watermane,
  • Pakorn Kanchanawonge
  • Michael W. Davidsonf
  • Richard D. Fettera and 
  • Harald F. Hessa,1
    1. Understanding molecular-scale architecture of cells requires determination of 3D locations of specific proteins with accuracy matching their nanometer-length scale. Existing electron and light microscopy techniques are limited either in molecular specificity or resolution. Here, we introduce interferometric photoactivated localization microscopy (iPALM), the combination of photoactivated localization microscopy with single-photon, simultaneous multiphase interferometry that provides sub-20-nm 3D protein localization with optimal molecular specificity. We demonstrate measurement of the 25-nm microtubule diameter, resolve the dorsal and ventral plasma membranes, and visualize the arrangement of integrin receptors within endoplasmic reticulum and adhesion complexes, 3D protein organization previously resolved only by electron microscopy. iPALM thus closes the gap between electron tomography and ight microscopy, enabling both molecular specification and resolution of cellular nanoarchitecture.

    Thursday, June 11, 2009

    Q-bits from Nitrogen Vacancy Centers in Diamond

    The first half of the talk is a background on nitrogen-vacancy defects. Some references on this are:
    • Optical Properties of Solids by Mark Fox,
    • Spin-flip and spin-conserving optical transitions of the nitrogen-vacancy centre in diamond, NJP 10, 045004 (2008)
    • Ab initio supercell calculations on nitrogen-vacancy center in diamond: Electronic structure and hyperfine tensors, PRB 79, 075203 (2009)
    • Quantum Mechanics by Landau and Lifshitz (good reference for symmetry groups)

    The second half of the talk was based on the paper Coherent Dynamics of Coupled Electron and Nuclear Spins in Diamond. L. Childress et al., Science 314, 281 (2006)

    Abstract: Understanding and controlling the complex environment of solid-state quantum bits is a central challenge in spintronics and quantum information science. Coherent manipulation of an individual electron spin associated with a nitrogen-vacancy center in diamond was used to gain insight into its local environment. We show that this environment is effectively separated into a set of individual proximal 13C nuclear spins, which are coupled coherently to the electron spin, and the remainder of the 13C nuclear spins, which cause the loss of coherence. The proximal nuclear spins can be addressed and coupled individually because of quantum back-action from the electron, which modifies their energy levels and magnetic moments, effectively distinguishing them from the rest of the nuclei. These results open the door to coherent manipulation of individual isolated nuclear spins in a solid-state environment even at room temperature.

    Monday, June 8, 2009

    Theoretical On-Demand Adiabatic Transfer of Light Between Adjacent Optical Cavities

    By Nick Chisholm, Ian Linington, Duncan O'Dell

    Cavity quantum electrodynamics is one of the most promising systems for realizing quantum computing and communication. One of the most important problems facing researchers today is finding a way to coherently transfer light between two optical cavities connected by an optical fibre. In this work, we provide a method for coherently transferring light between two adjacent optical cavities that share a slightly transmissive common mirror. By using the mode structure of our model, we expect a Landau-Zener adiabatic approach to the time dependence of the shared mirror’s position will allow for this coherent transfer. We believe this work is the first step towards resolving the problem involving two optical cavities connected by an optical fibre.