High-fidelity measurements and laser cooling in Cs qubits at finite magnetic fields

Fast quantum error correction in neutral atom arrays requires syndrome measurements that are compatible with the finite magnetic fields used for qubit stabilization and quantum gate operations. Combining high-fidelity qubit measurements with laser cooling in this regime remains an outstanding challenge for neutral atom platforms. We address this by leveraging the 6s_1/2 - 5d_5/2 electric-quadrupole transition in Cs. This transition offers a narrow linewidth for achieving low Doppler temperatures, and a relatively large hyperfine splitting that suppresses hyperfine-changing Raman errors. We analyze an approach to measurement and cooling at finite magnetic field motivated by our recent demonstration of high fidelity qubit measurement on this transition [1]. By adding an auxiliary field to quench the excited state, we present solutions that achieve measurement fidelities exceeding 0.999 in under 100 μs while maintaining qubit temperatures near 10 μK, demonstrating the method’s suitability for repeated low-loss measurements.

[1] J. Scott, H. M. Lim, U. Singla, Q. Meece, J. T. Choy, S. Kolkowitz, T. M. Graham, and M. Saffman, PRL 135, 223403 (2025).