Welcome to the
Institute for Theoretical Physics III
The Institute for Theoretical Physics III (ITP3) combines two chairs in theoretical physics with focus on quantum many-body phenomena and strongly correlated systems. The institute provides expertise in the fields of quantum optics, condensed matter physics, quantum information theory, as well as atomic and molecular physics. We combine analytical as well as numerical methods and explore machine learning approaches for the study of strongly interacting quantum systems. We are driven by fundamental scientific questions and strive to find applications in quantum information processing and to harvest quantum systems as a resource for novel technologies.
Recent publications
Machine learning the microscopic form of nematic order in twisted double-bilayer graphene
In this work, we show how convolutional neural networks can be used to learn effective theoretical models from scanning tunneling microscopy data on correlated moiré superlattices. Using electronic nematic order in twisted double-bilayer graphene as an example, we show that incorporating correlations between the local density of states at different energies allows convolutional neural networks not only to learn the microscopic nematic order parameter, but also to distinguish it from heterostrain.
Quantum fluctuations in one-dimensional supersolids
Chris Bühler, Tobias Ilg, Hans Peter Büchler
In one dimension, quantum fluctuations prevent the appearance of long-range order in a supersolid, and only quasi long-range order can survive. We derive this behaviour in the analysis of an effective low-energy description accounting for the two coupled Goldstone modes and find that the quantum phase transition from the superfluid to the supersolid is shifted by quantum fluctuations compared to the local formation of a solid structure. For current experimental parameters with dipolar atomic gases, this shift can not yet be resolved.
Absorbing State Phase Transition with Clifford Circuits
Nastasia Makki, Nicolai Lang, Hans Peter Büchler
The role of quantum fluctuations in modifying the critical behavior of non-equilibrium phase transitions is a fundamental but unsolved question. In this study, we examine the absorbing state phase transition of a 1D chain of qubits undergoing a contact process that involves both coherent and classical dynamics. The extracted critical exponents indicate that the absorbing state phase transition of this Clifford circuit model belongs to the directed percolation universality class.
Decoding the Projective Transverse Field Ising Model
Felix Roser, Hans Peter Büchler, Nicolai Lang
The competition between non-commuting projective measurements in discrete quantum circuits can give rise to entanglement transitions. It separates a regime where stored quantum information survives the time evolution from a regime where the measurements destroy it. Here we study the projective transverse field Ising model with focus on its capabilities as a quantum error correction code. We demonstrate that there is a finite threshold below which quantum information encoded in an initially entangled state can be retrieved reliably.
Motional ground-state cooling of single atoms in state-dependent optical tweezers
Christian Hölzl, Aaron Götzelmann, Moritz Wirth, Marianna S. Safronova, Sebastian Weber, Florian Meinert
Laser cooling of single atoms in optical tweezers is a prerequisite for neutral atom quantum computing and simulation. Resolved sideband cooling comprises a well-established method for efficient motional ground-state preparation, but typically requires careful cancellation of light shifts in so-called magic traps. Here, we study a novel laser cooling scheme which overcomes such constraints, and applies when the ground-state of a narrow cooling transition is trapped stronger than the excited state.
Creation of non-classical states of light in a chiral waveguide
K. Kleinbeck, H. Busche, N. Stiesdal, S. Hofferberth, K. Mølmer, H. P. Büchler
Creating non-classical states of light from simple quantum systems together with classical resources is a challenging problem. We show how chiral emitters under a coherent drive can generate non-classical photon states. For our analysis, we select a specific temporal mode in the transmitted light field, resulting in a coupled master equation for the relevant mode and the chiral emitters. We argue that these non-classical states are experimentally accessible and show their application for quantum metrology.
Ground-state stability and excitation spectrum of a one-dimensional dipolar supersolid
Tobias Ilg, Hans Peter Büchler
We study the behavior of the excitation spectrum across the quantum phase transition from a superfluid to a supersolid phase of a dipolar Bose gas confined to a one-dimensional geometry. Our results suggest that there exists an experimentally achievable parameter regime for dysprosium atoms, where the supersolid phase exhibits a stable excitation spectrum in the thermodynamic limit and the transition into the supersolid phase is of second order driven by the roton instability.
Functional completeness of planar Rydberg blockade structures
Simon Stastny, Hans Peter Büchler, Nicolai Lang
We show that planar structures of trapped atoms in the Rydberg blockade regime are functionally complete: Their ground state manifold can realize any Hilbert space that can be characterized by local constraints in the product basis. As examples, we present lattice realizations of the string-net Hilbert spaces that underlie the surface code and the Fibonacci anyon model. We discuss possible optimizations of planar Rydberg structures to increase their geometrical robustness.
