Two-level system hyperpolarization using a quantum Szilard engine

The innate complexity of solid-state physics exposes superconducting quantum circuits to interactions with uncontrolled degrees of freedom degrading their coherence. By implementing a quantum Szilard engine with an active feedback control loop, we show that a superconducting fluxonium qubit is coupled to a two-level system (TLS) environment of unknown origin, with a relatively long intrinsic energy relaxation time exceeding 50 ms. The TLSs can be cooled down, resulting in a four times lower qubit population, or they can be heated to manifest themselves as a negative-temperature environment corresponding to a qubit population of similar to 80%. We show that the TLSs and qubit are the dominant loss mechanism for each other and that qubit relaxation is independent of the TLS populations. Understanding and mitigating TLS environments is, therefore, not only crucial to improve the qubit lifetimes but also to avoid non-Markovian qubit dynamics.