Understanding the confinement mechanism in gauge theories and the universality of effective string-like descriptions of gauge flux tubes remains a fundamental challenge in modern physics. We probe string modes of motion with dynamical matter in a digital quantum simulation of a (2+1) dimensional gauge theory using a superconducting quantum processor with up to 144 qubits, stretching the hardware capabilities with quantum-circuit depths comprising up to 192 two-qubit layers. We realize the $Z_2$-Higgs model ($Z_2$HM) through an optimized embedding into a heavy-hex superconducting qubit architecture, directly mapping matter and gauge fields to vertex and link superconducting qubits, respectively [1]. Using the structure of local gauge symmetries, we implement a comprehensive suite of error suppression, mitigation, and correction strategies to enable real-time observation and manipulation of electric strings connecting dynamical charges. Our results resolve a dynamical hierarchy of longitudinal oscillations and transverse bending at the endpoints of the string, which are precursors to hadronization and rotational spectra of mesons. We further explore multi-string processes, observing the fragmentation and recombination of strings. The experimental results are compared against extensive tensor network simulations. The ground state phase diagram of the $Z_2$ Higgs model has been analyzed by the density matrix renormalization group (DMRG), while the recently introduced "basis update and Galerkin" method has been used to predict large-scale real-time dynamics and validate our error-aware protocols [2]. This work establishes a milestone for probing non-perturbative gauge dynamics via superconducting quantum simulation and elucidates the real-time behavior of confining strings [1].

 

[1] J. Cobos, J. Fraxanet, C. Benito, F. di Marcantonio, P. Rivero, K. Kapás, M. A. Werner, Ö. Legeza, A. Bermudez, and E. Rico, arXiv:2507.08088 (2025).

[2] Gianluca Ceruti, Christian Lubich, and Dominik Sulz, SIAM Journal on Numerical Analysis 61, 194-222 (2023).

I will present recent experiments, and exciting new directions, for the use of high-spin nuclei in silicon for quantum information, quantum foundations, and spin-mechanics entanglement. Nuclear spins in silicon are among the most coherent quantum objects to be found in the solid state. They have infinite relaxation time, and second-scale coherence time [1]. By using the I=7/2, 8-dimensional nucleus of antimony [2], we have prepared a nuclear Schroedinger cat within a functional nanoelectronic device [3]. This can be used to encode a cat-qubit similar to the bosonic encodings used in microwave cavities, but with atomic size, and even more extreme noise bias. 

 

Recent work on the simpler phosphorus atoms has shown the ability to entangle nuclear spins that are not bound to the same electron [4]. As the next step for scaling up donor quantum processors, we are working to integrate the donors with lithographic quantum dots, and I will present preliminary results in that direction.

 

We then used the Schroedinger cat and other nonclassical states to perform a curious experiment, where the quantumness of the state is certified by monitoring its uniform precession, in seeming contradiction with Ehrenfest's theorem [4]. 

 

High-spin nuclei possess a quadrupole moment that couples them to lattice strain [5]. I will discuss plans to entangle a single nuclear spin with a MHz-range mechanical oscillator, and perspectives to scale up the mass of the oscillator to test gravitational collapse models.

 

[1] J. Muhonen et al., Nature Nanotechnology 9, 986 (2014)

[2] S. Asaad, V. Mourik et al., Nature 579, 205 (2020)

[3] X. Yu et al., Nature Physics 21, 362 (2025)

[4] H. Stemp et al, Science 389, 1234 (2025)

[5] A. Vaartjes et al., Newton 1, 100017 (2025)

[6] L. O'Neill et al., Applied Physics Letters 119, 174001 (2021)

We connect the zero energy states of bipartite tight-binding models with bond disorder and vacancy disorder, as well as collective zero-energy Majorana excitations of networks (not necessarily bipartite) of coupled localized Majorana modes to the random geometry of regions of the underlying disordered lattice which host the monomers of any maximum-density dimer packing of the lattice. This allows us to place upper bounds on the localization length of the zero-energy Green function in both cases, and use these upper bounds to draw conclusions about heat transport in the Majorana networks or electrical transport in binary alloys described by such bipartite random hopping models. For the Majorana contribution to the heat conductance in the mixed triangular vortex lattice state of topological p+ip superconductors, we argue that our results imply a strong violation of self-averaging if the positional disorder of the vortex lattice is strong, and the vacancy-disorder is weak.

[collaborators: Sounak Biswas, Mursalin Islam, and Ritesh Bhola]

Parameter-dependent quantum systems often exhibit energy degeneracy points, whose comprehensive description naturally leads to the application of methods from singularity theory. A prime example is an electronic band structure where two energy levels coincide in a point of momentum space.  It may happen, and this case is our focus, that three or more levels coincide at a parameter point, called multifold degeneracy. For example, the Hamiltonian of a spinful particle in an external magnetic field has a (2s+1) -fold degeneracy for zero magnetic field, where s is the total spin. Upon a generic perturbation, such a multifold degeneracy point is dissolved into a set of Weyl points, that is, generic two-fold degeneracy points. We provide an upper bound to the number of Weyl points born from a multifold degeneracy point. Our work attempts to bridge two disciplines, quantum mechanics and singularity theory (algebraic geometry).

 

Joint work with György Frank, Dániel Varjas, András Pályi with a significant contribution of Alex Hof. 

https://arxiv.org/abs/2507.17485