Granular aluminium nanojunction fluxonium qubit

Area of Science:

• Quantum Computing
• Condensed Matter Physics
• Materials Science

Background:

• Mesoscopic Josephson junctions are crucial for nonlinearity in superconducting quantum circuits.
• Standard fluxonium qubits utilize overlapping superconducting electrodes with a thin oxide layer.

Purpose of the Study:

• To investigate the use of a self-structured granular aluminum nanojunction as a Josephson junction in a fluxonium qubit.
• To characterize the performance and properties of this novel granular aluminum qubit, termed 'gralmonium'.

Main Methods:

• Fabrication of a superconductor-insulator-superconductor Josephson junction using single-layer, zero-angle evaporation of granular aluminum.
• Integration of the granular aluminum nanojunction into a fluxonium qubit architecture.
• Spectroscopic measurements to compare the gralmonium qubit's spectrum with a standard fluxonium qubit.
• Measurement of coherence times and observation of Josephson energy fluctuations.

Main Results:

• The gralmonium qubit's measured spectrum is indistinguishable from that of a standard fluxonium qubit.
• The granular aluminum nanojunction exhibits a large charging energy, comparable to its Josephson energy, due to the absence of a mesoscopic parallel plate capacitor.
• Microsecond coherence times were measured.
• Spontaneous jumps in Josephson energy were observed over various timescales, indicating potential for defect diagnostics.

Conclusions:

• Granular aluminum nanojunctions are a viable alternative to traditional Josephson junctions for fluxonium qubits.
• The gralmonium qubit offers unique properties, including a significant charging energy, and serves as a sensitive tool for diagnosing microscopic defects in superconducting materials.