Immanuel Bloch

Quantum Many Body Systems

Ludwig-Maximilians-Universität München, Max Planck Institute of Quantum Optics

LMU | Fakultät für Physik

Schellingstr. 4

80799 München

Tel. +49 89 2180 6130

immanuel.bloch[at]physik.uni-muenchen.de

Group Webpage

Description

Research focus: quantum optics, quantum many-body physics, ultracold atoms

Understanding interacting quantum many body system and engineering and exploiting such quantum systems for quantum simulation or quantum information purposes pose some of the most outstanding challenges in quantum physics.

Quantum Control

Our research focuses on realizing and controlling such systems using ultracold atomic or molecular quantum gases. Starting with ultracold gases of degenerate quantum matter of bosons or fermions held in optical and magnetic traps, we e.g. impose crystals of light on top of the atoms in order to trap them in controlled periodic potentials. Recent advances by our Munich research team have enabled us to probe and control such quantum many-body systems at the single-atom level and with single-site resolution, thereby extending the control over quantum many-body systems to a qualitatively new level.

llustration of the cyclotron orbits of atoms exposed to extremely strong effective magnetic fields in specially engineered light crystals. llustration of the cyclotron orbits of atoms exposed to extremely strong effective magnetic fields in specially engineered light crystals. © Quantum Many-Body Systems Division
With the addressing scheme arbitrary patterns of atoms in the lattice can be prepared. With the addressing scheme arbitrary patterns of atoms in the lattice can be prepared. The atomic patterns each consist of 10 - 30 single atoms that are kept in an artificial crystal of light.© Quantum Many-Body Systems Division

Quantum Phases

Furthermore, our group investigates novel means to realize and probe topological features that can exist within quantum matter. For example, using laser induced hopping one may create lattices including effective artificial magnetic fields a thousand times stronger than the magnetic fields of the most powerful magnets on earth. Using completely novel interferometric probes, our experiments have in addition been able to gain unprecedented access to the topological structure of the underlying system. All this enables one to probe topological quantum matter in novel, previously unexplored parameter regimes.

Ultracold quantum gases in optical lattices overall offer remarkable opportunities to address fundamental questions in diverse fields of physics ranging from condensed matter physics to statistical and high-energy physics with table-top experiment.


Roles within MCQST

Publications

Time-resolved observation of spin-charge deconfinement in fermionic Hubbard chains

J. Vijayan, P. Sompet, G. Salomon, J. Koepsell, S. Hirthe, A. Bohrdt, F. Grusdt, I. Bloch, and C. Gross

Science 10, 186-189 (2020).

Show Abstract

Elementary particles carry several quantum numbers, such as charge and spin. However, in an ensemble of strongly interacting particles, the emerging degrees of freedom can fundamentally differ from those of the individual constituents. For example, one-dimensional systems are described by independent quasiparticles carrying either spin (spinon) or charge (holon). Here, we report on the dynamical deconfinement of spin and charge excitations in real space after the removal of a particle in Fermi-Hubbard chains of ultracold atoms. Using space- and time-resolved quantum gas microscopy, we tracked the evolution of the excitations through their signatures in spin and charge correlations. By evaluating multipoint correlators, we quantified the spatial separation of the excitations in the context of fractionalization into single spinons and holons at finite temperatures.

10.1126/science.aay2354

Floquet approach to Z2 lattice gauge theories with ultracold atoms in optical lattices

C. Schweizer, F. Grusdt, M. Berngruber, L. Barbiero, E. Demler, N. Goldman, I. Bloch, M. Aidelsburger.

Nature Physics (2019).

Show Abstract

Quantum simulation has the potential to investigate gauge theories in strongly-interacting regimes, which are up to now inaccessible through conventional numerical techniques. Here, we take a first step in this direction by implementing a Floquet-based method for studying Z2 lattice gauge theories using two-component ultracold atoms in a double-well potential. For resonant periodic driving at the on-site interaction strength and an appropriate choice of the modulation parameters, the effective Floquet Hamiltonian exhibits Z2 symmetry. We study the dynamics of the system for different initial states and critically contrast the observed evolution with a theoretical analysis of the full time-dependent Hamiltonian of the periodically-driven lattice model. We reveal challenges that arise due to symmetry-breaking terms and outline potential pathways to overcome these limitations. Our results provide important insights for future studies of lattice gauge theories based on Floquet techniques.

DOI: 10.1038/s41567-019-0649-7

Classifying snapshots of the doped Hubbard model with machine learning

A. Bohrdt, C. S. Chiu, G. Ji, M. Xu, D. Greif, M. Greiner, E. Demler, F. Grusdt und M. Knap.

Nature Physics (2019).

Show Abstract

Quantum gas microscopes for ultracold atoms can provide high-resolution real-space snapshots of complex many-body systems. We implement machine learning to analyse and classify such snapshots of ultracold atoms. Specifically, we compare the data from an experimental realization of the two-dimensional Fermi–Hubbard model to two theoretical approaches: a doped quantum spin liquid state of resonating valence bond type (1,2), and the geometric string theory (3,4), describing a state with hidden spin order. This technique considers all available information without a potential bias towards one particular theory by the choice of an observable and can therefore select the theory that is more predictive in general. Up to intermediate doping values, our algorithm tends to classify experimental snapshots as geometric-string-like, as compared to the doped spin liquid. Our results demonstrate the potential for machine learning in processing the wealth of data obtained through quantum gas microscopy for new physical insights.

DOI: 10.1038/s41567-019-0565-x

Observation of many-body localization in an one-dimensional system with a single-particle mobility edge

T. Kohlert, S. Scherg, X. Li, H.P. Lüschen, S. Das Sarma, I. Bloch, M. Aidelsburger.

Physical Review Letters 122, 170403 (2019).

Show Abstract

We experimentally study many-body localization (MBL) with ultracold atoms in a weak one-dimensional quasiperiodic potential, which in the noninteracting limit exhibits an intermediate phase that is characterized by a mobility edge. We measure the time evolution of an initial charge density wave after a quench and analyze the corresponding relaxation exponents. We find clear signatures of MBL when the corresponding noninteracting model is deep in the localized phase. We also critically compare and contrast our results with those from a tight-binding Aubry-André model, which does not exhibit a single-particle intermediate phase, in order to identify signatures of a potential many-body intermediate phase.

DOI:10.1103/PhysRevLett.122.170403

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