Publications Robert OTT

2025

Articles

R. Ott, T. Zache, N. Maskara, M. Lukin, P. Zoller, H. Pichler Probing topological entanglement on large scales, Phys. Rev. Lett. 135 90401 (2025-08-25), http://dx.doi.org/10.1103/mdsf-wrbj doi:10.1103/mdsf-wrbj (ID: 721272) Toggle Abstract
Topologically ordered quantum matter exhibits intriguing long-range patterns of entanglement, which reveal themselves in subsystem entropies. However, measuring such entropies, which can be used to certify topological order, on large partitions is challenging and becomes practically unfeasible for large systems. We propose a protocol based on local adiabatic deformations of the Hamiltonian which extracts the universal features of long-range topological entanglement from measurements on small subsystems of finite size, trading an exponential number of measurements against a polynomial-time evolution. Our protocol is general and readily applicable to various quantum simulation architectures. We apply our method to various string-net models representing both abelian and non-abelian topologically ordered phases, and illustrate its application to neutral atom tweezer arrays with numerical simulations.
R. Ott, D. González-Cuadra, T. Zache, P. Zoller, A. Kaufman, H. Pichler Error-corrected fermionic quantum processors with neutral atoms, Phys. Rev. Lett. 135 90601 (2025-08-25), http://dx.doi.org/10.1103/zkpl-hh28 doi:10.1103/zkpl-hh28 (ID: 721389) Toggle Abstract
Many-body fermionic systems can be simulated in a hardware-efficient manner using a fermionic quantum processor. Neutral atoms trapped in optical potentials can realize such processors, where non-local fermionic statistics are guaranteed at the hardware level. Implementing quantum error correction in this setup is however challenging, due to the atom-number superselection present in atomic systems, that is, the impossibility of creating coherent superpositions of different particle numbers. In this work, we overcome this constraint and present a blueprint for an error-corrected fermionic quantum computer that can be implemented using current experimental capabilities. To achieve this, we first consider an ancillary set of fermionic modes and design a fermionic reference, which we then use to construct superpositions of different numbers of referenced fermions. This allows us to build logical fermionic modes that can be error corrected using standard atomic operations. Here, we focus on phase errors, which we expect to be a dominant source of errors in neutral-atom quantum processors. We then construct logical fermionic gates, and show their implementation for the logical particle-number conserving processes relevant for quantum simulation. Finally, our protocol is illustrated using a minimal fermionic circuit, where it leads to a quadratic suppression of the logical error rate.
H. Froland, T. Zache, R. Ott, N. Müller Entanglement Structure of Non-Gaussian States and How to Measure It, Phys. Rev. Lett. 135 40201 (2025-07-23), http://dx.doi.org/10.1103/pnp2-g1g5 doi:10.1103/pnp2-g1g5 (ID: 721640) Toggle Abstract
Rapidly growing capabilities of quantum simulators to probe quantum many-body phenomena require new methods to characterize increasingly complex states. We present a protocol that constrains quantum states using experimentally measured correlation functions. This method enables measurement of a quantum state’s entanglement structure, opening a new route to study entanglement-related phenomena. Our approach extends Gaussian state parameterizations by systematically incorporating higher-order correlations. We show the protocol’s usefulness in conjunction with current and forthcoming experimental capabilities, focusing on weakly interacting fermions as a proof of concept. Here, the lowest nontrivial expansion quantitatively predicts early time thermalization dynamics, including signaling the onset of quantum chaos indicated by the entanglement Hamiltonian.

Preprint

G. Calliari, R. Ott, H. Pichler, T. Zache Field digitization scaling in a Z symmetric model, (2025-07-30), arXiv:2507.22984 arXiv:2507.22984 (ID: 721491) Toggle Abstract
The simulation of quantum field theories, both classical and quantum, requires regularization of infinitely many degrees of freedom. However, in the context of field digitization (FD) -- a truncation of the local fields to discrete values -- a comprehensive framework to obtain continuum results is currently missing. Here, we propose to analyze FD by interpreting the parameter as a coupling in the renormalization group (RG) sense. As a first example, we investigate the two-dimensional classical -state clock model as a Z FD of the -symmetric -model. Using effective field theory, we employ the RG to derive generalized scaling hypotheses involving the FD parameter , which allows us to relate data obtained for different -regularized models in a procedure that we term (FDS). Using numerical tensor-network calculations at finite bond dimension , we further uncover an unconventional universal crossover around a low-temperature phase transition induced by finite , demonstrating that FDS can be extended to describe the interplay of and . Finally, we analytically prove that our calculations for the 2D classical-statistical Z clock model are directly related to the quantum physics in the ground state of a (2+1)D Z lattice gauge theory which serves as a FD of compact quantum electrodynamics. Our study thus paves the way for applications of FDS to quantum simulations of more complex models in higher spatial dimensions, where it could serve as a tool to analyze the continuum limit of digitized quantum field theories.

2024

Article

R. Ott, T. Zache, M. Prüfer, S. Erne, M. Tajik, H. Pichler, J. Schmiedmayer, P. Zoller Hamiltonian Learning in Quantum Field Theories, Phys. Rev. Research 6 43284 (2024-12-16), http://dx.doi.org/10.1103/PhysRevResearch.6.043284 doi:10.1103/PhysRevResearch.6.043284 (ID: 721175) Toggle Abstract
We discuss Hamiltonian learning in quantum field theories as a protocol for systematically extracting the operator content and coupling constants of effective field theory Hamiltonians from experimental data. Learning the Hamiltonian for varying spatial measurement resolutions gives access to field theories at different energy scales, and allows to learn a flow of Hamiltonians reminiscent of the renormalization group. Our method, which we demonstrate in both theoretical studies and available data from a quantum gas experiment, promises new ways of addressing the emergence of quantum field theories in quantum simulation experiments.

2021

Article

R. Ott, T. Zache, F. Jendrzejewski , J. Berges Scalable Cold-Atom Quantum Simulator for Two-Dimensional QED, Phys. Rev. Lett. 127 (2021-09-24), http://dx.doi.org/10.1103/PhysRevLett.127.130504 doi:10.1103/PhysRevLett.127.130504 (ID: 720773) Toggle Abstract
We propose a scalable analog quantum simulator for quantum electrodynamics in two spatial dimensions. The setup for the U(1) lattice gauge field theory employs interspecies spin-changing collisions in an ultracold atomic mixture trapped in an optical lattice. We engineer spatial plaquette terms for magnetic fields, thus solving a major obstacle toward experimental realizations of realistic gauge theories in higher dimensions. We apply our approach to the pure gauge theory of compact QED and discuss how the phenomenon of confinement of electric charges can be described by the quantum simulator.

Preprints

N. Mueller, T. Zache, R. Ott Quantum thermalization of gauge theories: chaos, turbulence and universality, (2021-11-01), arXiv:2111.01155 arXiv:2111.01155 (ID: 720769) Toggle Abstract
In this talk, we discuss real-time thermalization dynamics of Z2 Lattice Gauge Theory in 2+1 spacetime dimensions. While classical thermalization is commonly associated with chaotic behavior, turbulence and universality, the manifestation of these phenomena in quantum mechanical systems is not clear. However, when viewed through the lens of Entanglement Structure, we find that quantum thermalization proceeds in characteristic stages and reveals phenomena remarkably similar to their classical counterparts: chaos, turbulence and universality.
N. Mueller, T. Zache, R. Ott Thermalization of Gauge Theories from their Entanglement Spectrum, (2021-07-23), arXiv:2107.11416 arXiv:2107.11416 (ID: 720771) Toggle Abstract
Using dual theories embedded into a larger unphysical Hilbert space along entanglement cuts, we study the Entanglement Structure of Z2 lattice gauge theory in (2+1) spacetime dimensions. We find that Li and Haldane's conjecture holds for gauge theories, and show consistency of the Entanglement Hamiltonian with the Bisognano-Wichmann theorem. Studying non-equilibrium dynamics after a quench, we provide a complete description of thermalization in Z2 gauge theory which proceeds in a characteristic sequence: Maximization of the Schmidt rank and spreading of level repulsion at early times, self-similar evolution with scaling coefficients α=0.8±0.1 and β=0.05±0.03 at intermediate times, and finally thermal saturation of the von Neumann entropy.