Why is coherence dropping in topological qubit braiding?

SuperCondQ

Topological qubit braiding sequences produce unexpected phase errors under standard readout conditions.
I adjusted the inter-qubit coupling strength to 10 MHz and measured the fidelity after each exchange operation across 50 trials, yet the average coherence dropped to 85% by the third cycle instead of holding above 95%. The readout pulse duration was fixed at 200 ns with a detuning of 50 MHz, but the parity outcomes flipped inconsistently in 12% of cases.

squidsavant

The 12% parity flips line up with what happens when the exchange gate leaves a small dynamical phase that the fixed readout pulse doesn’t cancel. (200 ns at 50 MHz detuning is usually marginal once the coupling sits at 10 MHz.)

qubitrider

The readout pulse needs an extra phase offset to cancel that leftover dynamical phase from the exchange, otherwise the parity readouts will stay inconsistent.