  Quantum computing has the potential to revolutionize computing for certain
classes of problems with exponential scaling, and yet this potential is
accompanied by significant sensitivity to noise, requiring sophisticated error
correction and mitigation strategies. Here we simulate the relaxations of
stationary states at different frequencies on several quantum computers to
obtain unique spectroscopic fingerprints of their noise. Response functions
generated from the data reveal a clear signature of non-Markovian dynamics,
demonstrating that each of the quantum computers acts as a non-Markovian bath
with a unique colored noise profile. The study suggest that noisy
intermediate-scale quantum computers (NISQ) provide a built-in noisy bath that
can be analyzed from their simulation of closed quantum systems with the
results potentially being harnessed for error mitigation or open-system
simulation.
