R.-P. Riwar

Optimal configurations for normal-metal traps in transmon qubits

  1. A. Hosseinkhani,
  2. R.-P. Riwar,
  3. R. J. Schoelkopf,
  4. L. I. Glazman,
  5. and G. Catelani
Controlling quasiparticle dynamics can improve the performance of superconducting devices. For example, it has been demonstrated effective in increasing lifetime and stability of superconducting
qubits. Here we study how to optimize the placement of normal-metal traps in transmon-type qubits. When the trap size increases beyond a certain characteristic length, the details of the geometry and trap position, and even the number of traps, become important. We discuss for some experimentally relevant examples how to shorten the decay time of the excess quasiparticle density. Moreover, we show that a trap in the vicinity of a Josephson junction can reduce the steady-state quasiparticle density near that junction, thus suppressing the quasiparticle-induced relaxation rate of the qubit. Such a trap also reduces the impact of fluctuations in the generation rate of quasiparticles, rendering the qubit more stable.
arxiv pdf

Normal-metal quasiparticle traps for superconducting qubits

  1. R.-P. Riwar,
  2. A. Hosseinkhani,
  3. L. D. Burkhart,
  4. Y. Y. Gao,
  5. R. J. Schoelkopf,
  6. L. I. Glazman,
  7. and G. Catelani
The presence of quasiparticles in superconducting qubits emerges as an intrinsic constraint on their coherence. While it is difficult to prevent the generation of quasiparticles, keeping
them away from active elements of the qubit provides a viable way of improving the device performance. Here we develop theoretically and validate experimentally a model for the effect of a single small trap on the dynamics of the excess quasiparticles injected in a transmon-type qubit. The model allows one to evaluate the time it takes to evacuate the injected quasiparticles from the transmon as a function of trap parameters. With the increase of the trap size, this time decreases monotonically, saturating at the level determined by the quasiparticles diffusion constant and the qubit geometry. We determine the characteristic trap size needed for the relaxation time to approach that saturation value.
arxiv pdf