Polarizability of a superconducting qubit environment probed by quantum jump correlations

Achieving fault tolerance with superconducting quantum processors requires qubits to operate

within the assumptions of threshold theorems, particularly the Born approximation, which reduces

the effect of dissipation into the environment to a constant qubit energy decay rate. However, this

approximation breaks down when the qubit couples to two-level systems (TLSs) that outlive it and

can become polarized during operation, retaining a memory of past qubit states. Here, we show that

non-Poissonian quantum jump traces enable us to distinguish polarizable TLSs from the standard

Born-Markov bath. By fitting the Solomon equations to post-selected traces with different initial

polarizations, arising naturally due to thermal fluctuations, we can disentangle the spectra of the

two environments. Sweeping the qubit frequency reveals resolved peaks, offering valuable insights

into the microscopic origins of dissipation in superconducting devices.