  A significant problem for current quantum computers is noise. While there are
many distinct noise channels, the depolarizing noise model often appropriately
describes average noise for large circuits involving many qubits and gates. We
present a method to mitigate the depolarizing noise by first estimating its
rate with a noise-estimation circuit and then correcting the output of the
target circuit using the estimated rate. The method is experimentally validated
on the simulation of the Heisenberg model. We find that our approach in
combination with readout-error correction, randomized compiling, and zero-noise
extrapolation produces results close to exact results even for circuits
containing hundreds of CNOT gates.
