probabilistic error cancellation
An exact but costly error mitigation method that cancels each of the machine's errors.
Probabilistic error cancellation first measures precisely each kind of error the machine makes. It then runs many altered versions of the program and combines them so the errors cancel out. Its answer is right on average for any program. But the shots it needs multiply as programs get bigger, so it becomes too expensive for large problems.
Think of it as
Like reconciling every single transaction in a company's books: always right, but the work explodes as the business grows.
Example
A small 10-qubit test is corrected exactly this way at a modest cost. The same method on a much larger chemistry circuit would need so many shots that the job is not worth running.
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