  Mitigating errors is a significant challenge for near term quantum computers.
One of the most important sources of errors is related to the readout of the
quantum state into a classical bit stream. A variety of techniques have been
proposed to mitigate these errors with post-hoc corrections. We propose a
complementary scheme to actively reduce readout errors on a shot-by-shot basis
by encoding single qubits, immediately prior to readout, into multi-qubit
states. The computational resources of our technique are independent of the
circuit depth and fully compatible with current hardware error rates and
connectivity. We analyze the potential of our approach using two types of
error-correcting codes and, as a proof of principle, demonstrate an 80%
improvement in readout error on the IBMQ Mumbai quantum computer.
