Direct microwave spectroscopy of Andreev bound states in planar Ge Josephson junctions
arxiv(2024)
摘要
We demonstrate microwave measurements of the Andreev bound state (ABS)
spectrum in planar Josephson junctions (JJs) defined in Ge high mobility
two-dimensional hole gases contacted by superconducting PtSiGe. The JJs and
readout circuitry are located on separate chips and inductively coupled via
flip-chip bonding. For a device with 350 nm junction length,
spectroscopic signatures were consistent with the short-junction limit, with an
induced superconducting gap Δ^*≈48 μ eV and
transmission τ≈ 0.94. The interaction between the
highest-transmission ABS and the resonator was well described by a
Jaynes-Cummings model with a vacuum Rabi splitting of approximately
6 MHz. A device with junction length of 1 μ m showed an ABS
spectrum consistent with a long junction model. Time-resolved monitoring of the
readout resonator in the dispersive regime revealed gate-voltage tunable
junction parity fluctuations on the timescale of seconds. Our work indicates a
viable path towards hybrid quantum devices based on planar Ge.
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