Short answer: Arrays of Rydberg atoms with blockade interactions have been used as quantum simulators of a quantum spin liquid on a kagome lattice, and theorists are now working out why that state appears. A variational wave function paper (arXiv 2112.13688, with a later journal version in New Journal of Physics) compares its predictions with measured string order, and a 2022 preprint (arXiv 2205.13000) links the model to a solvable lattice gauge theory. Both are theory papers that interpret experiments, and the second is a preprint.
The experiment they build on
Both abstracts refer to earlier atomic physics experiments in which the Rydberg blockade effect was used to realize a quantum spin liquid on the kagome lattice. In the variational paper's abstract, evidence of the spin liquid came from directly measuring non-local string order. This post does not describe those experiments beyond that, because only the theory abstracts were read.
A variational wave function
The authors of the variational paper (Cheng, Li and Zhai, per the arXiv listing) report a Bardeen-Cooper-Schrieffer type variational wave function study of the spin liquid state in this model. The wave function is motivated by mapping the Rydberg blockade model to a lattice gauge theory, in which local gauge conservation replaces the role of the blockade constraints. They fix the variational parameter from the experimentally measured Rydberg atom population, then compare predictions with the measured non-local string order. By combining open and closed string measurements, they extract the fluctuations associated only with the closed loop as an indicator of topological order. They report that the prediction agrees reasonably well with the experimental data, with one fitting parameter, and that the wave function gives a simple picture that can be generalized to similar spin liquid phases in other lattice geometries. The arXiv abstract was last revised in March 2023 (version 3), and the journal abstract uses slightly different wording.
A gauge-theory origin
The 2022 preprint, arXiv 2205.13000, says the mechanism that stabilizes the topological phase in blockaded models was still unclear. The authors introduce an exact relation between an Ising-Higgs lattice gauge theory on the kagome lattice and blockaded models on ruby lattices. They say this links the observed spin liquids to a deconfined phase of a solvable gauge theory. Using exact diagonalization and quantum Monte Carlo simulations, they report that the deconfined phases extend over a broad region of parameter space, with large ground state overlap with resonating valence bond wave functions. They add that such models can be realized with Rydberg-dressed atoms.
Why it matters for simulation
A quantum simulator earns its keep when it prepares a state that is hard to compute classically and when theory can interpret what it shows. These two papers sit on the interpretation side. They do not report new hardware results, and they do not claim that a classical computer could not reproduce the spin liquid.
Limits
Both are theoretical. The first compares its model with data from an earlier experiment and agrees only reasonably. The second is a preprint whose claims about experiments are suggestions. Neither abstract says anything about fault-tolerant computing.
FAQ
What is a quantum spin liquid?
A topologically ordered phase of spins that the papers study on the kagome lattice, and in related models on ruby lattices.
How do Rydberg atoms create it?
Through the blockade effect, which forbids certain neighboring atoms from both being excited, per the abstracts.
What did the variational paper test?
Whether a simple wave function with one fitting parameter reproduces measured string order. The authors report reasonable agreement.
Is the gauge-theory paper peer reviewed?
The version read is the arXiv preprint, so treat it as a preprint.
Does this build a quantum computer?
No. These are simulation and theory results.
All field notes