Superconducting Qubit Control with Single Flux Quantum Pulses in A Multichip Module: Part II Qubit and Quasiparticle Measurement

We demonstrate coupling of a Single Flux Quantum (SFQ) driver on a classical control chip to a superconducting qubit on a quantum chip in a multi-chip module package. A DC-SFQ driver on the classical chip emits quantized pulses that are capacitively coupled to the qubit island of a transmon on the quantum chip, allowing subharmonic driving of qubit rotations. We examine the effects of on- and off-resonant SFQ pulses on the state of the qubit and the response of the read-out cavity. Quasiparticle (QP) excitations created from the operation of the SFQ circuitry can be a source of decoherence and temporal instability in the qubit. QP contribution to the qubit admittance are examined by monitoring how relaxation and dephasing times correlate with QP creation. Mitigation strategies for QP poisoning will be discussed.