University of Sydney Demonstrates Multi-Qubit Logical Entanglement and 170-Round Stability on IBM Square-Lattice Nighthawk r2 Processor

Researchers from the University of Sydney have shown multi-qubit fault-tolerant logic and sustained error suppression on IBM Quantum’s cloud-deployed ibm_phoenix processor, a 120-qubit superconducting system built on the square-lattice Nighthawk r2 architecture. The work, detailed in arXiv:2610.32347 and highlighted by IBM Research, validates distance-3 and distance-5 rotated surface code memories, logical Bell-state preparation via lattice surgery, and state and gate teleportation across three logical qubits. To address leakage into non-computational states, the team used a dynamic “walking” syndrome circuit that swaps data and ancilla roles each round, ensuring every qubit is measured and reset every two rounds. The experiments achieved memory error per round below 1%, logical Bell-state fidelity above 93%, three-qubit teleportation process fidelity between 78% and 93%, and sustained error suppression for about 170 rounds with an error probability near 2 × 10⁻⁷. ¹