Temporal Diffraction Grating for Engineered Superconducting Qubit Dissipation

How does the temporal structure of a parametrically induced dissipation channel affect the decay dynamics of a superconducting transmon qubit? While continuous parametric modulation is a standard technique for engineering dissipation, this study investigates whether rapid, periodic switching of this interaction can be used to shape the qubit's dissipation spectrum in the frequency domain.

The researchers utilized a flux-tunable transmon qubit coupled to a lossy readout resonator. By applying a microwave drive to the qubit's flux line, they activated a Purcell decay channel via sideband modulation. They then introduced a high-speed microwave switch to gate this modulation, creating a sequence of 'on' windows (where the qubit is coupled to the lossy resonator) and 'off' windows (where the qubit is protected). They modeled the resulting qubit survival probability using a Chebyshev-propagator approach, which treats the repeated on/off cycles as a temporal equivalent to an N-slit diffraction grating.

The experiment demonstrates that pulsing the Purcell decay channel does not simply result in a time-averaged decay rate. Instead, it reorganizes the dissipation spectrum into a complex interference pattern. The central features of this spectrum are determined by the cycle time of the pulse sequence, while the overall envelope is defined by the single-window response. The researchers successfully mapped this behavior to Fraunhofer diffraction, where each 'on' pulse acts as a temporal aperture. They further identified that sharp switching edges in the control pulses introduce additional spectral features, which they modeled by accounting for the transient dynamics at the pulse boundaries.