Vantablack Shielding of Superconducting Qubit Systems

  1. J.M. Kitzman,
  2. J.R. Lane,
  3. T. Stefanski,
  4. N.R. Beysengulov,
  5. D. Tan,
  6. K. W. Murch,
  7. and J. Pollanen
Circuit quantum electrodynamics (cQED) experiments on superconducting qubit systems typically employ radiation shields coated in photon absorbing materials to achieve high qubit coherence
and low microwave resonator losses. In this work, we present preliminary results on the performance of Vantablack as a novel infrared (IR) shielding material for cQED systems. We compare the coherence properties and residual excited state population (or effective qubit temperature) of a single-junction transmon qubit housed in a shield coated with a standard epoxy-based IR absorbing material, i.e. Berkeley Black, to the coherence and effective temperature of the same qubit in a shield coated in Vantablack. Based on a statistical analysis of multiple qubit coherence measurements we find that the performance of the radiation shield coated with Vantablack is comparable in performance to the standard coating. However, we find that in the Vantablack coated shield the qubit has a higher effective temperature. These results indicate that improvements are likely required to optimize the performance of Vantablack as an IR shielding material for superconducting qubit experiments and we discuss possible routes for such improvements. Finally we describe possible future experiments to more precisely quantify the performance of Vantablack to improve the coherences of more complex cQED systems.

A superfluid-tunable 3D transmon qubit

  1. J.R. Lane,
  2. D. Tan,
  3. N.R. Beysengulov,
  4. K. Nasyedkin,
  5. E. Brook,
  6. L. Zhang,
  7. T. Stefanski,
  8. H. Byeon,
  9. K. W. Murch,
  10. and J. Pollanen
Superfluid helium at milli-Kelvin temperatures is a dielectric liquid with an extremely low loss tangent at microwave frequencies. As such, it is a promising candidate for incorporation
into hybrid quantum systems containing superconducting qubits. We demonstrate the viability of this hybrid systems approach by controllably immersing a three-dimensional superconducting transmon qubit in superfluid 4He. By measuring spectroscopic and coherence properties we find that the cavity, the qubit, and their coupling are all modified by the presence of the dielectric superfluid, which we analyze within the framework of circuit quantum electrodynamics (cQED). At temperatures relevant to quantum computing experiments, the energy relaxation time of the qubit is not significantly changed by the presence of the superfluid, while the pure dephasing time modestly increases, which we attribute to improved thermalization via the superfluid.