On December 6, 2023, Professor Mikhail Lukin's group at Harvard University published a landmark paper in Nature demonstrating a reconfigurable neutral-atom logical qubit processor. The collaborative work involved researchers from Harvard, MIT, Caltech, and NIST/University of Maryland, with QuEra Computing holding a financial interest.
Using an AOD-based reconfigurable neutral-atom array with a zoned architecture (three zones: storage, entangling, and readout), the team simultaneously activated 48 logical qubits via 16 [[8,3,2]] code blocks (128 physical qubits). They executed a 4D hypercube connectivity sampling circuit containing 228 logical two-qubit gates and 48 logical CCZ gates. Separately, 40 logical qubits were also implemented using 2D color codes ([[7,1,3]]) with 280 physical qubits.
Three key achievements were demonstrated:
- Below-threshold scaling: For surface codes at distances d=3 through d=7, logical Bell error rates via transversal CNOT gates were observed to decrease with increasing code distance, confirming below-threshold operation.
- Fault-tolerant state preparation: Logical qubit |0L⟩ initialization fidelity of 99.91% was achieved — exceeding the physical qubit gate fidelity (99.5%). A 4-logical-qubit GHZ state fidelity of 99.85% was recorded.
- Universal non-Clifford gates: CCZ gates were transversally implemented using physical T·S rotations within the [[8,3,2]] code, realizing non-Clifford universal gates. With error detection applied, the XEB score improved by approximately 10× compared to comparable-scale physical qubit implementations.
These results represent the first demonstration of Early Error-Corrected Quantum Computation (Early ECQC): by co-designing error-correcting codes and quantum algorithms, logical encoding is shown to substantially improve algorithm performance — a key milestone on the path to scalable fault-tolerant quantum computing.