  Quantum spin liquids, exotic phases of matter with topological order, have
been a major focus of explorations in physical science for the past several
decades. Such phases feature long-range quantum entanglement that can
potentially be exploited to realize robust quantum computation. We use a
219-atom programmable quantum simulator to probe quantum spin liquid states. In
our approach, arrays of atoms are placed on the links of a kagome lattice and
evolution under Rydberg blockade creates frustrated quantum states with no
local order. The onset of a quantum spin liquid phase of the paradigmatic toric
code type is detected by evaluating topological string operators that provide
direct signatures of topological order and quantum correlations. Its properties
are further revealed by using an atom array with nontrivial topology,
representing a first step towards topological encoding. Our observations enable
the controlled experimental exploration of topological quantum matter and
protected quantum information processing.
