Collective Oscillations of an Imbalanced Fermi Gas: Axial Compression Modes and Polaron Effective Mass

By S. Nascimbene, ..., & C. Salomon

We investigate the low-lying compression modes of a unitary Fermi gas with imbalanced spin populations. For low polarization, the strong coupling between the two spin components leads to a hydrodynamic behavior of the cloud. For large population imbalance we observe a decoupling of the oscillations of the two spin components, giving access to the effective mass of the Fermi polaron, a quasi-particle composed of an impurity dressed by particle-hole pair excitations in a surrounding Fermi sea. We find $m^*/m=1.17(10)$, in agreement with the most recent theoretical predictions.

**Groupmeeting by Jason McKeever**

Entangled Mechanical Oscillators

By J.D. Jost, ..., & D. Wineland

Superposition and entanglement are hallmarks of quantum mechanics. One system ubiquitous to nature where entanglement has not previously been shown is distinct mechanical oscillators, such as springs or pendula. Here, deterministic entanglement of separated mechanical oscillators—consisting of the vibrational states of two pairs of atomic ions held in different locations—is demonstrated.

**Groupmeeting by Chris Paul**

Quantum Walk in Position Space with Single Optically Trapped Atoms

By Michal Karski, ..., & Dieter Meschede

The quantum walk is the quantum analog of the well-known random walk, which forms the basis for models and applications in many realms of science. Its properties are markedly different from the classical counterpart and might lead to extensive applications in quantum information science. In our experiment, we implemented a quantum walk on the line with single neutral atoms by deterministically delocalizing them over the sites of a one-dimensional spin-dependent optical lattice. With the use of site-resolved fluorescence imaging, the final wave function is characterized by local quantum state tomography, and its spatial coherence is demonstrated. Our system allows the observation of the quantum-to-classical transition and paves the way for applications, such as quantum cellular automata.

**Groupmeeting by Alma Bardon**

Attosecond Ionization and Tunneling Delay Time Measurements in Helium

By P. Eckle, ... , & U. Keller

It is well established that electrons can escape from atoms through tunneling under the influence of strong laser fields, but the timing of the process has been controversial and far too rapid to probe in detail. We used attosecond angular streaking to place an upper limit of 34 attoseconds and an intensity-averaged upper limit of 12 attoseconds on the tunneling delay time in strong field ionization of a helium atom. The ionization field derives from 5.5-femtosecond-long near-infrared laser pulses with peak intensities ranging from 2.3 x 10¹⁴ to 3.5 x 10¹⁴ watts per square centimeter (corresponding to a Keldysh parameter variation from 1.45 to 1.17, associated with the onset of efficient tunneling). The technique relies on establishing an absolute reference point in the laboratory frame by elliptical polarization of the laser pulse, from which field-induced momentum shifts of the emergent electron can be assigned to a temporal delay on the basis of the known oscillation of the field vector..

**Groupmeeting by Rockson Chang**

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* 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. Hess^5*

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 Zhuang^1,2,3*

^{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 Shtengel^a, 

James A. Galbraith^b, 

Catherine G. Galbraith^c, 

Jennifer Lippincott-Schwartz^d,¹,

Jennifer M. Gillette^d, 

Suliana Manley^d, 

Rachid Sougrat^d, 

Clare M. Waterman^e,

Pakorn Kanchanawong^e, 

Michael W. Davidson^f, 

Richard D. Fetter^a and 

Harald F. Hess^a,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.

**Groupmeeting by Krister Shalm**

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.

**Groupmeeting by David McKay**