LMU
MPQ
Quantum Optics Group (LMU) - Quantum Many Body Systems Division (MPQ)

The Pauli exclusion principle is one of the most fundamental manifestations of quantum statistics. Here, we report on its local observation in a spin-polarized degenerate gas of fermions in an optical lattice. We probe the gas with single-site resolution using a new generation quantum gas microscope avoiding the common problem of light induced losses. In the band insulating regime, we measure a strong local suppression of particle number fluctuations and a low local entropy per atom. Our work opens a new avenue for studying quantum correlations in fermionic quantum matter both in and out of equilibrium.

Phys. Rev. Lett. 115, 263001 (2015)

Press release: English (.pdf), Deutsch (.pdf)

Topological charge pumping, a dynamic version of the quantum Hall effect, enables a robust and quantized  transport of charge through an adiabatic cyclic evolution of the underlying Hamiltonian. We have realized such a pump with ultracold bosonic atoms forming a Mott insulator in a dynamically controlled optical superlattice. We observed a quantized deflection per pump cycle for groundstate particles as well as a counterintuitive reversed deflection for atoms in the first excited band, illustrating the pump’s genuine quantum nature.

Nature Physics (advance online publication), DOI 10.1038/nphys3584

Press release: English (.pdf), Deutsch (.pdf)

Long-range coherence is typically restricted to equilibrium situations at low temperatures. Here we have, in stark contrast, for the first time managed to observe the dynamic emergence of coherence in a system far from equilibrium following a strong quantum quench. Furthermore, the emerging order is different from the ground-state one and cannot be found in the equilibrium phase diagram.

Phys. Rev. Lett. 115, 175301 (2015)

Physics Viewpoint by Stephen R. Clark

Using the strong and long range interacting Rydberg states, we were able to realize a superatom, a collective system of more than 100 “normal” atoms. Due to the many constituents, these systems are very robust and could be used as quantum memories. We demonstrate microscopic control and coherent manipulation of the superatoms, laying the fundament to future applications.

Phys. Rev. X 5, 031015 (2015)

 

 

We have recently observed a novel state of matter that, despite being interacting, never thermalizes. This Many-Body Localized States represent a new class of systems that fail to be described by standard thermodynamics and statistical physics and require new theoretical and experimental approaches to characterize them.

Science Express

Science 349, 842 (2015)

Monika Aidelsburger receives PhD prize

Monika Aidelsburger receives the PhD prize of the "Münchener Universitätsgesellschaft" for her thesis  "Artificial gauge fields with ultracold atoms in optical lattices".

In a recent experiment, we locally observed an entanglement wave in quantum magnets made out of ultracold rubidium atoms. In contrast to ion systems, local atom number fluctuations influence the propagation of the magnetic excitation and we developed a novel in-situ Stern-Gerlach imaging technique to measure their impact on the detected entanglement.

Phys. Rev. Lett. 115, 035302 (2015)

Viewpoint on our work.

We succeeded to prepare magnetic quantum crystals based on laser-controlled long-range interactions between Rydberg atoms. These experiments critically relied on our local manipulation techniques that allow to control the atomic density of many-body systems at the single atom level. The crystals have been identified by a characteristic staircase in the magnetization that emerges due to the incompressibility of the system.

Science 347, 1455 (2015)

Press release: german, english

Quantum phase transitions are characterized by a dramatic change of the ground-state behavior; famous examples include the appearance of magnetic order or superconductivity as a function of doping in cuprates.

In this work, we explore how a system dynamically crosses such a transition and investigate in detail how coherence emerges when an initially incoherent Mott insulating system enters the superfluid regime.

PNAS 112, 3641 (2015)

Press release: german, english

One of the leading experts in theoretical condensed matter physics, Professor Eugene Demler from Harvard University (Cambridge, USA), has joined the LMU and MPQ as a winner of a Humboldt Research Award. This Award is granted by the Alexander von Humboldt Foundation to out-standing foreign academics in order to promote cooperation with excellent German researchers. Prof. Demler was nominated by Prof. Immanuel Bloch  and Prof. Wilhelm Zwerger (TU München) who will host him during his stay in Germany. Having started his visit on January 20th Demler will work in Munich until March 20th, and then again from May to July next year.

Chern numbers are topological invariants characterizing Bloch bands. A striking manifestation of non-zero Chern numbers is the quantization of the Hall conductivity revealed by the quantum Hall effect. Here, we report on the first non-electronic Chern-number measurement with ultracold bosonic atoms that were loaded into an optical lattice potential subjected to artificial gauge fields. By applying a linear force to the atoms they experience a transverse motion proportional to the Chern number of the occupied band. By analyzing the in-situ evolution of the cloud we determined an experimental value of the Chern number νexp=0.99(5) in agreement with theory.

Nature Physics 11, 162-166 (2015), AOP 3171 (2014)

See also: Commentary by Wolfgang Ketterle

Press release: English, Deutsch

The geometric structure of a single-particle energy band in a solid is fundamental for a wide range of many-body phenomena and is uniquely characterized by the distribution of Berry curvature over the Brillouin zone. We have demonstrated a matter-wave interferometer that precisely measures Berry curvature in an graphene-like optical honeycomb lattice and could demonstrate the highly singular nature of the Dirac point.

Science 347, 288 (2015), Science Express (2014)

See also: Science perspective by A. Lamacroft

Press release:English (.pdf), Deutsch (.pdf)

Media gallery