Matthias Steffen

Superconducting qubit in a waveguide cavity with a coherence time approaching 0.1 ms

We report a superconducting artificial atom with a coherence time of

Low loss superconducting titanium nitride coplanar waveguide resonators

{T}_{2}^{*}=92

Building logical qubits in a superconducting quantum computing system

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Experimental Demonstration of a Resonator-Induced Phase Gate in a Multiqubit Circuit-QED System

s and energy relaxation time

Fault-tolerant computing with biased-noise superconducting qubits: a case study

{T}_{1}=70

Quantum computing: an IBM perspective

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Reducing Spontaneous Emission in Circuit Quantum Electrodynamics by a Combined Readout/Filter Technique

s. The system consists of a single Josephson junction transmon qubit on a sapphire substrate embedded in an otherwise empty copper waveguide cavity whose lowest eigenmode is dispersively coupled to the qubit transition. We attribute the factor of four increase in the coherence quality factor relative to previous reports to device modifications aimed at reducing qubit dephasing from residual cavity photons. This simple device holds promise as a robust and easily produced artificial quantum system whose intrinsic coherence properties are sufficient to allow tests of quantum error correction.

Efficient one- and two-qubit pulsed gates for an oscillator-stabilized Josephson qubit

Thin films of TiN were sputter-deposited onto Si and sapphire wafers with and without SiN buffer layers. The films were fabricated into rf coplanar waveguide resonators, and internal quality factor measurements were taken at millikelvin temperatures in both the many photon and single photon limits, i.e., high and low electric field regimes, respectively. At high field, we found the highest internal quality factors (∼107) were measured for TiN with predominantly a (200)-TiN orientation. The (200)-TiN is favored for growth at high temperature on either bare Si or SiN buffer layers. However, growth on bare sapphire or Si(100) at low temperature resulted in primarily a (111)-TiN orientation. Ellipsometry and Auger measurements indicate that the (200)-TiN growth on the bare Si substrates is correlated with the formation of a thin, ≈2 nm, layer of SiN during the predeposition procedure. On these surfaces we found a significant increase of Qi for both high and low electric field regimes.