Surface code memories below the threshold with superconducting qubits

Quantum error correction (QEC) promises to exponentially suppress error rates by combining many noisy physical qubits into logical qubits. However, this exponential error reduction is only possible if physical error rates are below a certain threshold and are well behaved. In this talk, I will discuss the building blocks for a superconducting logical memory: high fidelity gates, fast readout and reset, and leakage removal. By putting together these operations in a 105-qubit processor, we demonstrate that logical error rate decreases by 2 when increasing the code distance from 3 to 5 to 7 [1], definitively demonstrating below-threshold memory operation.

[1] Quantum error correction below the surface code threshold, Google Quantum AI, arXiv:2408.13687 (2024)