Logical quantum processor based on reconfigurable atom arrays

Abstract

Suppressing errors is the central challenge for useful quantum computing<jats:sup>1</jats:sup>, requiring quantum error correction (QEC)<jats:sup>2–6</jats:sup> for large-scale processing. However, the overhead in the realization of error-corrected ‘logical’ qubits, in which information is encoded across many physical qubits for redundancy<jats:sup>2–4</jats:sup>, poses substantial challenges to large-scale logical quantum computing. Here we report the realization of a programmable quantum processor based on encoded logical qubits operating with up to 280 physical qubits. Using logical-level control and a zoned architecture in reconfigurable neutral-atom arrays<jats:sup>7</jats:sup>, our system combines high two-qubit gate fidelities<jats:sup>8</jats:sup>, arbitrary connectivity<jats:sup>7,9</jats:sup>, as well as fully programmable single-qubit rotations and mid-circuit readout<jats:sup>10–15</jats:sup>. Operating this logical processor with various types of encoding, we demonstrate improvement of a two-qubit logic gate by scaling surface-code<jats:sup>6</jats:sup> distance from <jats:italic>d</jats:italic> = 3 to <jats:italic>d</jats:italic> = 7, preparation of colour-code qubits with break-even fidelities<jats:sup>5</jats:sup>, fault-tolerant creation of logical Greenberger–Horne–Zeilinger (GHZ) states and feedforward entanglement teleportation, as well as operation of 40 colour-code qubits. Finally, using 3D [[8,3,2]] code blocks<jats:sup>16,17</jats:sup>, we realize computationally complex sampling circuits<jats:sup>18</jats:sup> with up to 48 logical qubits entangled with hypercube connectivity<jats:sup>19</jats:sup> with 228 logical two-qubit gates and 48 logical CCZ gates<jats:sup>20</jats:sup>. We find that this logical encoding substantially improves algorithmic performance with error detection, outperforming physical-qubit fidelities at both cross-entropy benchmarking and quantum simulations of fast scrambling<jats:sup>21,22</jats:sup>. These results herald the advent of early error-corrected quantum computation and chart a path towards large-scale logical processors.</jats:p>