Non-Abelian braiding of graph vertices in a superconducting processor

Indistinguishability of particles is a fundamental principle of quantum mechanics(1). For all elementary and quasiparticles observed to date-including fermions, bosons and Abelian anyons-this principle guarantees that the braiding of identical particles leaves the system unchanged(2,3). However, in two spatial dimensions, an intriguing possibility exists: braiding of non-Abelian anyons causes rotations in a space of topologically degenerate wavefunctions(4-8). Hence, it can change the observables of the system without violating the principle of indistinguishability. Despite the well-developed mathematical description of non-Abelian anyons and numerous theoretical proposals(9-22), the experimental observation of their exchange statistics has remained elusive for decades. Controllable many-body quantum states generated on quantum processors offer another path for exploring these fundamental phenomena. Whereas efforts on conventional solid-state platforms typically involve Hamiltonian dynamics of quasiparticles, superconducting quantum processors allow for directly manipulating the many-body wavefunction by means of unitary gates. Building on predictions that stabilizer codes can host projective non-Abelian Ising anyons(9,10), we implement a generalized stabilizer code and unitary protocol(23) to create and braid them. This allows us to experimentally verify the fusion rules of the anyons and braid them to realize their statistics. We then study the prospect of using the anyons for quantum computation and use braiding to create an entangled state of anyons encoding three logical qubits. Our work provides new insights about non-Abelian braiding and, through the future inclusion of error correction to achieve topological protection, could open a path towards fault-tolerant quantum computing.

Automated summary

Indistinguishability of particles is a fundamental principle in quantum mechanics. While braiding of Abelian anyons leaves the system unchanged, braiding of non-Abelian anyons can change the observables of the system without violating the principle of indistinguishability. Experimental observation of non-Abelian anyons' exchange statistics has remained elusive, but using quantum processors, it is now possible to manipulate and braid them, allowing for the verification of their fusion rules and statistics. This work provides insights into non-Abelian braiding and its potential application in fault-tolerant quantum computing with the inclusion of error correction.