May 2, 2025
In this preprint (https://arxiv.org/abs/2504.12538), we present a novel mid-circuit measurement and readout (MCMR) scheme for atomic quantum computers.
Atoms use cycling fluorescence for qubit readout, which can easily cause errors in neighboring atoms if the operation is done in the middle of a quantum circuit. The scatter could happen by absorbing even a single photon, either from the excitation laser or the radiated light itself. This type of error is typically obviated by either moving neighboring atoms farther away or using a different atomic species that has a widely separated absorption spectrum. Both approaches carry significant overhead that may prevent scaling. We present a scheme that uses existing tightly focused gate beams to shift otherwise global operations into an “ancilla frame,” leaving data qubits unperturbed.
In collaboration with Chris Monroe and Alex Kozhanov at DQC, we demonstrate the necessary ingredients for this MCMR scheme on a single trapped barium ion. Based on the experimental results shown here, we supply realistic conditions to reach data qubit error rates below 10e-3, proving the feasibility of this MCMR implementation.
This result sets the stage for next generation atomic quantum computing systems to easily add MCMR operations and access a host of new applications requiring this capability.