J. Mögerle, K. Brechtelsbauer, A. T. Gea-Caballero, J. Prior, G. Emperauger, G. Bornet, C. Chen, T. Lahaye, A. Browaeys, H. P. Büchler

We present a protocol to implement a spin-1 chain in Rydberg systems using three Rydberg states close to a Förster resonance. The resulting phase diagram is studied using the infinite density-matrix renormalization group and reveals a highly robust Haldane phase. We find experimentally accessible parameters to probe the Haldane phase in current Rydberg systems, and demonstrate an efficient adiabatic preparation scheme.

Joseph Eix, Rukmani Bai, Thierry Lahaye, Antoine Browaeys, Hans Peter Büchler, Sebastian Weber

We present a method for generating homogeneous and tunable magnetic flux for bosonic particles in a lattice using Rydberg atoms. Our setup relies on Rydberg excitations hopping through the lattice by dipolar exchange interactions. The magnetic flux arises from complex hopping via ancilla atoms. With the ancillas optimized for homogeneous flux, we get a topological flat band in the single-particle regime and in the many-body regime we obtain indications of a bosonic fractional Chern insulator state at ν = 1/2 filling.

Sayan Banerjee & Mathias S. Scheurer 

Nonreciprocal superconductivity, also known as the superconducting diode effect, has been extensively studied
in the presence of a magnetic field or some form of ferromagnetic order breaking time-reversal symmetry.
We here show that another class of magnetic order known as altermagnetism, which also breaks time-reversal
symmetry but does not exhibit a finite net magnetic moment, can also give rise to a superconducting diode effect, if certain symmetry requirements are met.

Prathyush P. Poduval & Mathias S. Scheurer 

Motivated by the phenomenology of graphene moiré superlattices, we study a 2D model with strong tendencies towards both magnetism and triplet superconductivity. Our main focus is on a phase characterized by finite d ⋅ N, which shares similarities with the BCS state but has rather different spectral properties: most notably, the suppression of the electronic density of states at the Fermi level can resemble that of either a fully gapped or nodal superconductor, possibly explaining recent tunneling experiments.

Sayan Banerjee and Mathias S. Scheurer 

The superconducting diode effect refers to an asymmetry in the critical supercurrent along opposite directions. Current models do not capture large diode effecs well. We propose and develop a theory for an enhancement mechanism of the diode effect arising from spontaneous symmetry breaking. We show—both within a phenomenological and a microscopic theory—that there is a coupling of the supercurrent and the underlying symmetry-breaking order parameter. This coupling can enhance the current asymmetry significantly.

Maine Christos, Subir Sachdev & Mathias S. Scheurer 

Superconductivity is not yet well understood in twisted graphene systems. Recent tunneling experiments indicate a transition between nodal and gapped pairing with electron filling, which is not naturally understood within current theory. We demonstrate that the coexistence of superconductivity and flavor polarization leads to pairing channels that are guaranteed by symmetry to be entirely band-off-diagonal and show that band-off-diagonal pairing can be the leading state when considering only phonons, reconciling the experimental observation.

João Augusto Sobral, Stefan Obernauer, Simon Turkel, Abhay N. Pasupathy, Mathias S. Scheurer 

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.

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.

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.

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.

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.