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Coherence in a transmon qubit with epitaxial tunnel junctions
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Image of FIG. 1.
FIG. 1.

(a) Circuit diagram of transmon (split JJ shunted with IDCs) coupled to λ/2 resonator. (b) Optical micrograph shows cavity resonator (top), transmon qubit (middle), and part of flux bias (bottom). All features are surrounded by flux holes in S1. (c) Cross-section (not to scale) of JJ and IDC. (d) Scanning electron microscopy micrograph of 1.1 μm2 JJ with minimal SiN x insulation.

Image of FIG. 2.
FIG. 2.

(Color online) The qubit spectroscopy shows some avoided level crossings (arrows). They are stable over the timescale of days but change position after thermal cycling to room temperature. Maximum observed splitting size is 7 MHz. Upper inset: Level splitting at 7.273 GHz. Lower inset: Vacuum Rabi oscillations at sweet spot. The solid line represents a fit to the data.

Image of FIG. 3.
FIG. 3.

(Color online) Qubit population in time domain: T 1 = 0.73 μs and echo T 2 = 1.36 μs at the sweet spot, and T 1 = 0.86 μs (detuned). Successive time traces have been offset vertically for clarity. The lines represent fits to the data.


Generic image for table
Table I.

Overview on single-photon loss tangent, capacitance, and participation for the individual elements. The losses for Al2O3 tunnel barrier, SiN x overlaps, and Re/Ti IDCs are inferred from lumped LC and coplanar waveguide resonators. Elements with a small contribution are neglected, e.g., the split JJ loop. The calculated effective weighted transmon loss tangent is 5.7 × 10−5.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Coherence in a transmon qubit with epitaxial tunnel junctions