Interferometric Purcell Suppression of Spontaneous Emission in a Superconducting Qubit

Experimental device and measured qubit lifetiem T1

  In conclusion, we have demonstrated a technique to suppress the Purcell decay of a qubit using destructive interference. The interferometric Purcell filter does not require dedicated filter components or impedance mismatch in the feedline, making it an attractive option for applications such as all-pass readout. We have presented an intuitive picture of the operation and design of this filter with circuit simulation. We have designed and fabricated a device with this filter and observed strong agreement between simulation and experiment. The use of interference to suppress Purcell decay is a versatile principle that can be extended to other lengths of transmission line resonators and for other combinations of couplings. For example, the same effect can be achieved by coupling a λr/2 resonator capacitively at both ends to the waveguide at a separation of λq/2. To minimize the footprint, we have elected to use a λr/4 resonator with λq/4 separation in the feedline. This makes the overall footprint of our device comparable to that of a conventional quarter-wavelength low-Q bandpass filter. In our presented layout, the capacitive coupling length takes up significant space; this could be compacted straightforwardly using meandering or interdigitated capacitors