Reduced mid-circuit measurement error with trapped ions using micromotion

The ability to perform measurements on subsets of qubits without inducing decoherence on the rest of the system is a key capability for many quantum information protocols including error correction, quantum teleportation and measurement-based quantum computing.  In many systems, achieving sufficient isolation of neighboring qubits while performing strong measurements on selected qubits is a significant technical challenge.  For trapped-ion systems, where laser-induced fluorescence is the standard measurement technique, both stray light from the detection beam as well as the fluorescence from the measured ions can be significant sources of unwanted decoherence of the unmeasured qubits.  Here we present a technique using the micromotion of the ions to reduce these sources of decoherence by over an order of magnitude. We implement the technique in Honeywell trapped ions systems where it plays a key role in achieving the low measurement crosstalk error needed for many recent demonstrations.