Rapid transfer of a qubit state into a microwave pulse using a notch Purcell filter*

Modules in a distributed quantum computer need to communicate rapidly and coherently with each other. A recent implementation [1] involves transferring the quantum state between a superconducting qubit and an itinerant microwave pulse. To realize high-speed communication with this scheme, the qubit has to be coupled to a waveguide via a low-Q resonator. However, this increases the energy decay rate of the qubit through the Purcell effect. To break this trade-off, a Purcell filter with a high extinction ratio is required. Here, we use a notch filter to demonstrate the rapid transfer of a qubit state into a microwave pulse. The Purcell decay is suppressed by the destructive interference between multiple decay paths through a multi-mode resonator. This is realized in a simple device with one port and one coaxial transmission line resonator [2]. We report our progress on analyzing the filter performance and the fidelity of the state transfer.
[1] P. Kurpiers et al., Nature 558, 264 (2018).
[2] C. Axline et al., Appl. Phys. Lett. 109, 042601 (2016).