09:45  10:00

Roderich Moessner (director of the MPIPKS) & scientific coordinators
Opening


Chair: Adam Smith

10:00  10:45

Ulrich Schneider
(University of Cambridge)
Quantum simulation with ultracold atoms in optical lattices (virtual)
During the last twenty years, ultracold atoms in optical lattices have emerged as very versatile and powerful Quantum Simulators to study the manybody physics of interacting particles in periodic potentials. Not only can they faithfully reproduce many prototypical effects from condensed matter physics, they also enable radically new systems with fascinating physics and hold promise for wider quantum information applications.
After a brief review of fundamental properties and key experiments that already reach far beyond what can be computed classically, this talk will present an outlook into current and coming developments and discuss future prospects of this platform in and beyond the NISQ era.

10:45  11:30

Norbert Linke
(Joint Quantum Institute/University of Maryland)
Quantum simulations on an analogdigital trappedion quantum system
Our quantum experiment consists of a chain of 171Yb+ ions with individual Raman beam addressing and individual readout [1]. This fully connected system can be configured to run any sequence of single and twoqubit gates, making it in effect an arbitrarily programmable digital quantum computer. The high degree of control can be used for digital, but also for analog and hybrid quantum simulations. We also add a classical optimization layer to our quantum stack to realize variational optimization methods.
Using such an approach we produce socalled thermofield doubles [2], which allow the efficient creation of finite temperature quantum states. We recently employed these states to perform the first measurement at finite temperature of outoftimeordered correlators, which are are powerful tools to probe quantum information scrambling in quantum manybody systems [3].
We also present results from the digital simulation of the realtime dynamics of a lattice gauge theory in 1+1 dimensions, i.e., the lattice Schwinger model, and demonstrate effects such as pair creation for times much longer than previously accessible [4].
Finally, we show the first realization of paraparticle dynamics using an analog simulation involving both spin and motional degrees of freedom of a trapped ion. These exotic particles are unlikely to be found in nature, but their dynamics have been used to study dark matter and excitations in solids, and our technique is a promising tool for other quantum manybody models. Finally, work towards scaling up the architecture will be discussed.
[1] S. Debnath et al., Nature 563:63 (2016)
[2] D. Zhu et al., Proc. Natl. Acad. Sci. 117:41 (2020)
[3] A. M. Green et al., arXiv:2112.02068 (2021)
[4] N. H. Nguyen et al., arXiv:2112.14262 (2021)
[5] C. Huerta Alderete et al., arXiv:2108.05471 (2021)

11:30  12:15

Takahiro Tsunoda
(Yale University)
Quantum computation using alwayson coupling in superconducting circuits
We present recent theoretical and experimental developments on a hardwareefficient quantum computing architecture requiring only fixed couplings and singlequbit gates [1, 2, 3]. The control strategy saves the cost of calibrating pulsed twoqubit gates by replacing the entangling operation with the free evolution of the native Hamiltonian, inspired by dynamical decoupling techniques developed in the Nuclear Magnetic Resonance (NMR).
We introduce algorithms for designing pulse sequences that can leverage static Ising Hamiltonians to perform quantum simulation, with favourable total time duration and pulse count scaling [2, 3]. We then show how the pulse sequence generated by this method can be applied to hardwareefficient Noisy IntermediateScale Quantum (NISQ) algorithms and quantum error mitigation.
We then discuss the practicality of such quantum computing strategy on superconducting circuits by showing a proofofprinciple experiment on a two transmon qubit system, using the alwayson residual ZZ coupling to perform a Variational Quantum Eigensolver algorithm. We will address practical challenges in controlling and measuring a device with alwayson couplings and outline future circuit design improvements to circumvent these issues.
[1] A. ParraRodriguez, P. Lougovski, L. Lamata, E. Solano, and M. Sanz, Phys, Rev. A 101, 022305 (2020)
[2] G. Bhole, T. Tsunoda, P. J. Leek, and J. A. Jones, Phys. Rev. Applied 13, 034002 (2020).
[3] T. Tsunoda, G. Bhole, S. A. Jones, J. A. Jones, and P. J. Leek, Phys, Rev. A 102, 032405 (2020).

12:15  14:00

lunch break & discussion


Lightning talks  Chair: Daniel Malz

14:00  14:15

Rick van Bijnen
(Institute for Quantum Optics and Quantum Information)
Entanglement Hamiltonian tomography
Entanglement is the crucial ingredient of quantum manybody physics, and
characterizing and quantifying entanglement in closed system dynamics of quantum
simulators is an outstanding challenge in today's era of intermediate scale quantum devices. Here we discuss an efficient tomographic protocol for reconstructing reduced density matrices and entanglement spectra for spin systems. The key step is a parametrization of the reduced density matrix in terms of an entanglement Hamiltonian involving only quasi local fewbody terms. We show the validity and efficiency of the protocol and demonstrate experimentally the measurement of the evolution of the entanglement spectrum in quench dynamics in trapped ion quantum simulators.
[1] C. Kokail, R. van Bijnen, A. Elben, B. Vermersch and P. Zoller,
Nature Physics 17, 936 (2021)

14:15  14:30

Christian Kokail
(Institute for Quantum Optics and Quantum Information)
Quantum variational learning of entanglement Hamiltonians
In this talk, I will discuss a hybrid quantumclassical approach to learn the entanglement Hamiltonian for subsystems of quantum states prepared in quantum simulation experiments. The approach is based on timeevolving subsystems of the quantum state under a deformed Hamiltonian which is physically realized on the programmable quantum device. Subsequent manybody spectroscopy allows for a direct measurement of the entanglement spectrum, which I will discuss for a Hubbard model in a topological phase.

14:30  14:45

Sean Greenaway
(Imperial College London)
Efficient assessment of process fidelity
The accurate implementation of quantum gates is essential for the realisation of quantum algorithms and digital quantum simulations. We demonstrate a method by which this accuracy may be increased on noisy hardware through variational optimisation techniques, using a hierarchy of fidelity approximations to overcome the difficulty of estimating the process fidelity of a quantum gate. We demonstrate the utility of this protocol through the successful optimisation of a quantum gate on a commercial quantum processor.

14:45  15:00

Hongzheng Zhao
(MPIPKS Dresden)
Suppression of interband heating for random driving
Heating to highlying states strongly limits the experimental observation of driving induced nonequilibrium phenomena, particularly when the drive has a broad spectrum. Here we show that, for entire families of structured random drives known as random multipolar drives, particle excitation to higher bands can be well controlled even away from a highfrequency driving regime. This opens a window for observing driveinduced phenomena in a longlived prethermal regime in the lowest band.

15:00  15:15

Roderich Moessner
(MPIPKS Dresden)
Manybody echo to distinguish internal from external decoherence

15:15  15:30

Germán Sierra
(CSIC Madrid)
Algebraic Bethe circuits
The Algebraic Bethe Ansatz (ABA) is a highly successful analytical method used to exactly solve several physical models in both statistical mechanics and condensedmatter physics. It will be shown how to transform the ABA into a quantum circuit that can be implemented on a quantum computer. We illustrate our method in the spin 1/2 XX and XXZ models running numerical simulations, for systems of up to 24 qubits and 12 magnons. Furthermore, we run smallscale errormitigated implementations on the IBM quantum computers, including the preparation of the ground state for the XX and XXZ models in 4 sites.

15:30  16:00

coffee break & discussion


Chair: Yujie Liu

16:00  16:45

Zohreh Davoudi
(University of Maryland)
Trapped ions, gauge theories, and NISQera simulation strategies

16:45  17:30

Andreas Elben
(CALTECH)
Probing manybody quantum chaos in quantum simulators via randomized measurements
Randomized measurements provide a novel toolbox to probe today’s noisy intermediate scale quantum devices. In this talk, I will mostly focus on the study of manybody quantum chaos in quantum simulation experiments. For quantum spin models, I will present a protocol to access the spectral form factor revealing properties of the energy eigenvalue statistics. Furthermore, I will define partial spectral form factors which refer to subsystems of the manybody system. I will show that partial spectral form factors give unique insights into energy eigenstate statistics determining thermalization in closed quantum systems. The presented measurement protocol allows to access both, SFF and pSFFs, from a single experimental dataset. It provides a unified testbed to probe manybody quantum chaotic behavior and thermalization, determined by properties of energy eigenvalues and eigenstates, in quantum simulators.

18:30  21:00

workshop dinner at the restaurant "Sprout" (https://www.sproutfood.de/)
