Coherent transport of neutral atoms in spin-dependent optical lattice potentials

We demonstrate the controlled coherent transport and splitting of atomic wave packets in spin-dependent optical lattice potentials. Such experiments open intriguing possibilities for quantum state engineering of many body states. After first preparing localized atomic wave functions in an optical lattice through a Mott insulating phase, we place each atom in a superposition of two internal spin states. Then state selective optical potentials are used to split the wave function of a single atom and transport the corresponding wave packets in two opposite directions. Coherence between the wave packets of an atom delocalized over up to 7 lattice sites is demonstrated.Comment: 4 pages, 6 figure

Molecular snapshots of the Pex1/6 AAA + complex in action

The peroxisomal proteins Pex1 and Pex6 form a heterohexameric type II AAA+ ATPase complex, which fuels essential protein transport across peroxisomal membranes. Mutations in either ATPase in humans can lead to severe peroxisomal disorders and early death. We present an extensive structural and biochemical analysis of the yeast Pex1/6 complex. The heterohexamer forms a trimer of Pex1/6 dimers with a triangular geometry that is atypical for AAA+ complexes. While the C-terminal nucleotide-binding domains (D2) of Pex6 constitute the main ATPase activity of the complex, both D2 harbour essential sub-strate-binding motifs. ATP hydrolysis results in a pumping motion of the complex, suggesting that Pex1/6 function involves substrate translocation through its central channel. Mutation of the Walker B motif in one D2 domain leads to ATP hydrolysis in the neighbouring domain, giving structural insights into inter-domain communication of these unique heterohexameric AAA + assemblies

Exploring phase coherence in a 2D lattice of Bose-Einstein condensates

Bose-Einstein condensates of rubidium atoms are stored in a two-dimensional periodic dipole force potential, formed by a pair of standing wave laser fields. The resulting potential consists of a lattice of tightly confining tubes, each filled with a 1D quantum gas. Tunnel-coupling between neighboring tubes is controlled by the intensity of the laser fields. By observing the interference pattern of atoms released from more than 3000 individual lattice tubes the phase coherence of the coupled quantum gases is studied. The lifetime of the condensate in the lattice and the dependence of the interference pattern on the lattice configuration are investigated.Comment: 4 pages, 6 figure

Controlled Collisions for Multiparticle Entanglement of Optically Trapped Atoms

Entanglement lies at the heart of quantum mechanics and in recent years has been identified as an essential resource for quantum information processing and computation. Creating highly entangled multi-particle states is therefore one of the most challenging goals of modern experimental quantum mechanics, touching fundamental questions as well as practical applications. Here we report on the experimental realization of controlled collisions between individual neighbouring neutral atoms trapped in the periodic potential of an optical lattice. These controlled interactions act as an array of quantum gates between neighbouring atoms in the lattice and their massively parallel operation allows the creation of highly entangled states in a single operational step, independent of the size of the system. In the experiment, we observe a coherent entangling-disentangling evolution in the many-body system depending on the phase shift acquired during the collision between neighbouring atoms. This dynamics is indicative of highly entangled many-body states that present novel opportunities for theory and experiment.Comment: 17 pages, including 5 figures, accepted for publication in Natur

Many-Body Physics with Ultracold Gases

This article reviews recent experimental and theoretical progress on many-body phenomena in dilute, ultracold gases. Its focus are effects beyond standard weak-coupling descriptions, like the Mott-Hubbard-transition in optical lattices, strongly interacting gases in one and two dimensions or lowest Landau level physics in quasi two-dimensional gases in fast rotation. Strong correlations in fermionic gases are discussed in optical lattices or near Feshbach resonances in the BCS-BEC crossover.Comment: revised version, accepted for publication in Rev. Mod. Phy

Einblick in den Mechanismus des Pex1p/Pex6p‐AAA+^{+}‐Komplexes der peroxisomalen Matrixprotein‐Importmaschinerie mittels Struktur‐Funktionsanalysen

Diese Arbeit beschäftigt sich mit den Typ II AAA$^{+}$-ATPasen Pex1p und Pex6p der Hefe $\textit {S. cerevisiae}$, die als Motor der Matrixprotein-Importmaschinerie die Rückführung des PTS1-Rezeptors Pex5p von der Peroxisomen-Membran zurück in das Zytosol katalysieren. Elektronenmikroskopische Strukturanalysen zeigen eine Nukleotid-abhängige Formierung hetero-hexamerer AAA$^{+}$-Komplexe mit alternierend organisierten Pex1p und Pex6p Untereinheiten. Durch ATP-Hydrolyse-Ereignisse induzierte Konformationsänderungen konservierter "Pore Loops" deuten auf einen Mechanismus hin, bei dem Pex5p durch die zentrale Pore des AAA$^{+}$-Komplexes geführt wird. Dabei vermitteln die konservierten D2 Domänen von Pex6p die hauptsächliche ATPase-Aktivität. Ein Ausschalten dieser ATPase-Aktivität in Folge einer Pex6p Walker B Punktmutation resultiert in einer stabilisierten Anbindung des AAA$^{+}$-Komplexes an den Membrananker Pex15p und deutet auf einen mit dem Pex5p-Export verknüpften Pex1/6p-Pex15p Dissoziationsmechanismus hin

Nucleotide-dependent assembly of the peroxisomal receptor export complex

Pex1p and Pex6p are two AAA-ATPases required for biogenesis of peroxisomes. Both proteins form a hetero-hexameric complex in an ATP-dependent manner, which has a dual localization in the cytosol and at the peroxisomal membrane. At the peroxisomal membrane, the complex is responsible for the release of the import receptor Pex5p at the end of the matrix protein import cycle. In this study, we analyzed the recruitment of the AAA-complex to its anchor protein Pex15p at the peroxisomal membrane. We show that the AAA-complex is properly assembled even under ADP-conditions and is able to bind efficiently to Pex15p $\textit {in vivo}$. We reconstituted binding of the Pex1/6p-complex to Pex15p $\textit {in vitro}$ and show that Pex6p mediates binding to the cytosolic part of Pex15p via a direct interaction. Analysis of the isolated complex revealed a stoichiometry of Pex1p/Pex6p/Pex15p of 3:3:3, indicating that each Pex6p molecule of the AAA-complex binds Pex15p. Binding of the AAA-complex to Pex15p in particular and to the import machinery in general is stabilized when ATP is bound to the second AAAdomain of Pex6p and its hydrolysis is prevented. The data indicate that receptor release in peroxisomal protein import is associated with a nucleotide-depending Pex1/6p-cycle of Pex15p-binding and release