arXiv subjects

Niels Tas

Publications and source records attributed to Niels Tas.

3 recordsLinked to original sources

arXiv2026

Nanoscale wireframe SQUID on a cantilever by corner lithography

We present the fabrication of nanoscale superconducting quantum interference devices (SQUIDs) at the apex of wireframe tips on self-aligned superconducting cantilever probes. The probes are made on silicon wafers using molding techniques in combination with corner lithography, which results in a nanowire frame tip with a tuneable apex structure. A shadow effect deposition using magnetron sputtering of Nb creates self-aligned superconducting wireframes on cantilevers with accompanying device circuitry. Superconducting weak links are realized at the apex of the wireframes with the use of focused ion beam nanopatterning. The realized SQUIDs have effective diameters ranging from several micrometers down to 100 nm and can be operated in magnetic fields up to 1 T. Furthermore, the nanowires in the wireframe can be used to flux modulate the SQUID locally. This fabrication process enables the production of wafer-scale templates for probes based on on-tip superconducting devices.

cond-mat.mes-hall↗

arXiv2025

On-chip stencil lithography for superconducting qubits

Improvements in circuit design and more recently in materials and surface cleaning have contributed to a rapid development of coherent superconducting qubits. However, organic resists commonly used for shadow evaporation of Josephson junctions (JJs) pose limitations due to residual contamination, poor thermal stability and compatibility under typical surface-cleaning conditions. To provide an alternative, we developed an inorganic SiO$_2$/Si$_3$N$_4$ on-chip stencil lithography mask for JJ fabrication. The stencil mask is resilient to aggressive cleaning agents and it withstands high temperatures up to 1200{\deg}C, thereby opening new avenues for JJ material exploration and interface optimization. To validate the concept, we performed shadow evaporation of Al-based transmon qubits followed by stencil mask lift-off using vapor hydrofluoric acid, which selectively etches SiO$_2$. We demonstrate average $T_1 \approx 75 \pm 11 \mu$s over a 200 MHz frequency range in multiple cool-downs for one device, and $T_1 \approx 44\pm 8 \mu$s for a second device. These results confirm the compatibility of stencil lithography with state-of-the-art superconducting quantum devices and motivate further investigations into materials engineering, film deposition and surface cleaning techniques.

quant-ph↗

arXiv2021

Integration of topological insulator Josephson junctions in superconducting qubit circuits

The integration of semiconductor Josephson junctions (JJs) in superconducting quantum circuits provides a versatile platform for hybrid qubits and offers a powerful way to probe exotic quasiparticle excitations. Recent proposals for using circuit quantum electrodynamics (cQED) to detect topological superconductivity motivate the integration of novel topological materials in such circuits. Here, we report on the realization of superconducting transmon qubits implemented with $(Bi_{0.06}Sb_{0.94})_{2}Te_{3}$ topological insulator (TI) JJs using ultra-high vacuum fabrication techniques. Microwave losses on our substrates with monolithically integrated hardmask, used for selective area growth of TI nanostructures, imply microsecond limits to relaxation times and thus their compatibility with strong-coupling cQED. We use the cavity-qubit interaction to show that the Josephson energy of TI-based transmons scales with their JJ dimensions and demonstrate qubit control as well as temporal quantum coherence. Our results pave the way for advanced investigations of topological materials in both novel Josephson and topological qubits.

cond-mat.mes-hall↗