Dynamical Gauge Fields
Within the Standard Model of Particle Physics, the interaction between fundamental particles is described by gauge theories. These theories have an enormous predictive power, but to compute the dynamics they generate is an extremely hard task. As a consequence, high-energy physics contains many unsolved problems such as quark confinement or the dynamics of quarks and gluons during heavy-ion collisions. Instead of computing them in classical devices or investigating them in enormous accelerator facilities, we aim at implementing lattice gauge theories on the optical table by having atomic gases in optical lattices mimic the interplay between particles, anti-particles, and gauge bosons. In this way, experiments at temperatures just above absolute zero could give insights into unsolved phenomena that in Nature appear at very high energies.
Aiming at a better understanding of anomalous and topological effects in gauge theories out-of-equilibrium, we study the real-time dynamics of a prototype model for CP-violation, the massive Schwinger model with a θ-term. We identify dynamical quantum phase transitions between different topological sectors that appear after sufficiently strong quenches of the θ-parameter. Moreover, we establish a general dynamical topological order parameter, which can be accessed through fermion two-point correlators and, importantly, which can be applied for interacting theories. Enabled by this result, we show that the topological transitions persist beyond the weak-coupling regime. Finally, these effects can be observed with table-top experiments based on existing cold-atom, superconducting-qubit, and trapped-ion technology. Our work, thus, presents a significant step towards quantum simulating topological and anomalous real-time phenomena relevant to nuclear and high-energy physics.
A fundamental challenge in digital quantum simulation (DQS) is the control of inherent errors. These appear when discretizing the time evolution generated by the Hamiltonian of a quantum many-body system as a sequence of quantum gates, called Trotterization. Here, we show that quantum localization-by constraining the time evolution through quantum interference-strongly bounds these errors for local observables. Consequently, for generic quantum many-body Hamiltonians, Trotter errors can become independent of system size and total simulation time. For local observables, DQS is thus intrinsically much more robust than what one might expect from known error bounds on the global many-body wave function. This robustness is characterized by a sharp threshold as a function of the Trotter step size. The threshold separates a regular region with controllable Trotter errors, where the system exhibits localization in the space of eigenstates of the time-evolution operator, from a quantum chaotic regime where the trajectory is quickly scrambled throughout the entire Hilbert space. Our findings show that DQS with comparatively large Trotter steps can retain controlled Trotter errors for local observables. It is thus possible to reduce the number of quantum gate operations required to represent the desired time evolution faithfully, thereby mitigating the effects of imperfect individual gate operations.
Quantum simulators have the exciting prospect of giving access to real-time dynamics of lattice gauge theories, in particular in regimes that are difficult to compute on classical computers. Future progress towards scalable quantum simulation of lattice gauge theories, however, hinges crucially on the efficient use of experimental resources. As we argue in this work, due to the fundamental non-uniqueness of discretizing the relativistic Dirac Hamiltonian, the lattice representation of gauge theories allows for an optimization that up to now has been left unexplored. We exemplify our discussion with lattice quantum electrodynamics in two-dimensional space-time, where we show that the formulation through Wilson fermions provides several advantages over the previously considered staggered fermions. Notably, it enables a strongly simplified optical lattice setup and it reduces the number of degrees of freedom required to simulate dynamical gauge fields. Exploiting the optimal representation, we propose an experiment based on a mixture of ultracold atoms trapped in a tilted optical lattice. Using numerical benchmark simulations, we demonstrate that a state-of-the-art quantum simulator may access the Schwinger mechanism and map out its non-perturbative onset.
We discuss the experimental engineering of model systems for the description of QED in one spatial dimension via a mixture of bosonic 23Na and fermionic 6Li atoms. The local gauge symmetry is realized in an optical superlattice, using heteronuclear boson-fermion spin-changing interactions which preserve the total spin in every local collision. We consider a large number of bosons residing in the coherent state of a Bose-Einstein condensate on each link between the fermion lattice sites, such that the behavior of lattice QED in the continuum limit can be recovered. The discussion about the range of possible experimental parameters builds, in particular, upon experiences with related setups of fermions interacting with coherent samples of bosonic atoms. We determine the atomic system's parameters required for the description of fundamental QED processes, such as Schwinger pair production and string breaking. This is achieved by benchmark calculations of the atomic system and of QED itself using functional integral techniques. Our results demonstrate that the dynamics of one-dimensional QED may be realized with ultracold atoms using state-of-the-art experimental resources. The experimental setup proposed may provide a unique access to longstanding open questions for which classical computational methods are no longer applicable.
In contrast to classical empty space, the quantum vacuum fundamentally alters the properties of embedded particles. This paradigm shift allows one to explain the discovery of the celebrated Lamb shift in the spectrum of the hydrogen atom. Here, we engineer a synthetic vacuum, building on the unique properties of ultracold atomic gas mixtures, offering the ability to switch between empty space and quantum vacuum. Using high-precision spectroscopy, we observe the phononic Lamb shift, an intriguing many-body effect originally conjectured in the context of solid-state physics. We find good agreement with theoretical predictions based on the Fröhlich model. Our observations establish this experimental platform as a new tool for precision benchmarking of open theoretical challenges, especially in the regime of strong coupling between the particles and the quantum vacuum.
- Nitrogen Vacancy Center Magnetometry as a New Approach for an Active Magnetic Field Control
Kerim Köster, Bachelorarbeit, 2018 PDF-File
- Simulation and Measurements of Single and Coupled Coaxial Qubits
Tanja Behrle, Masterarbeit, 2018 PDF-File
- Design and Implementation of a Versatile Imaging Objective for Imaging of Ultracold Mixtures of Sodium and Lithium
Alexander Mil, Masterarbeit, 2016 PDF-File
- Spin Dynamics and Feshbach Resonances in Ultracold Sodium-Lithium Mixtures
Arno Trautmann, Dissertation, 2016 PDF-File
- Observation of the Phononic Lamb Shift in a Synthetic Vacuum
Tobias Rentrop, Dissertation, 2016 PDF-File
- Active Magnetic Field Stabilisation for Ultracold
Sodium Lithium Mixtures
Marcell Gall, Masterarbeit, 2015 PDF-File
- Dynamics and Motional Coherence of Fermions Immersed in a Bose Gas
Raphael Scelle, Dissertation, 2013 PDF-File
- Feshbach Resonances and Periodic Potentials in Ultracold Bose-Fermi Mixtures
Tobias Schuster, Dissertation, 2012 PDF-File
- Immersed Quantum Systems: A Sodium Bose-Einstein Condensate for Polaron Studies
Jens Appmeier, Dissertation, 2010 PDF-File
- Zeeman-Slower und Experimentsteuerung für das NaLi-Experiment
Jan Krieger, Diplomarbeit, 2008 PDF-File
- Setup of a Laser System for Ultracold Sodium - Towards a Degenerate Gas of Ultracold Fermions
Stefan Weis, Diplomarbeit, 2007
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