Strongly-driven transmon as an incoherent noise source

Transmons are ubiquitous today in quantum computing applications. Under strong drives, which are becoming necessary for fast high fidelity operations, transmons can become structurally unstable. Due to chaotic effects, the computational manifold is no longer well separated from the remainder of the spectrum, which correlates with enhanced offset charge sensitivity and non-QND effects in readout [1,2]. In this work, we show that a coherently driven transmon can act as a source of incoherent noise driving another circuit element coupled to it. By using a full quantum model and a semiclassical analysis, we perform the noise spectroscopy of the driven transmon.