  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.
