📄 Showing the "Simple" version — "Advanced" is not ready yet. Add it to favorites to help prioritize it. Ask for the full read

A bridge of aluminum just a few atoms thick is the heart of many quantum devices. Current flows through such a bridge without resistance, and it can be controlled with a magnetic field. These bridges are called Josephson junctions, after the British physicist who described their behavior. They are usually made with an electron beam, but that is expensive and slow.

The new method does away with the electron beam. First, a mask is patterned on the substrate using light (photolithography), then excess metal is removed with a stream of argon ions, like sandblasting, but on a microscopic scale. The resulting junctions have areas from 1 to 6 square micrometers — roughly the size of a few bacteria laid end to end. By varying the oxidation conditions, the junction's resistance can be tuned by a factor of 100.

Junctions made this way were assembled into a superconducting quantum interference device (SQUID)—an instrument that senses magnetic fields with incredible precision. SQUIDs made with the new method showed less chip-to-chip variation than those made with electron-beam lithography. And when a SQUID was embedded in a cavity and used as a parametric amplifier, it boosted weak signals by 40 decibels, like turning a whisper into the roar of a rock concert.

This simple fabrication method for Josephson junctions could become the basis for mass-producing superconducting quantum circuits. Less complexity means lower cost, bringing quantum computers and sensitive detectors closer to everyday life.

Original abstract

as written by the authors arXiv:2604.25195

A minimal method to fabricate Al/AlO$$_x$$/Al Josephson junctions (JJs) using photolithography and argon etching, before metallization and oxidation, is demonstrated. JJs with areas ranging from 1 to 6 $$\mu$$m$$^2$$ can be fabricated and, with the appropriate oxidation conditions, the junction resistance can be varied by $$\sim$$2 orders of magnitude. Transmission electron microscopy reveals the successful fabrication of JJs with few grain boundaries suggesting reduced energy loss from two-level-systems. Superconducting QUantum Interference Devices (SQUIDs) fabricated from this methodology exhibit reduced resistance variation over multiple chips, compared with electron beam lithography, and the devices can sustain repeated thermal cycles to 10 mK with the excellent flux response remaining unchanged. The quantum applications of this technology are demonstrated by embedding a SQUID resonator into a 3D cavity and parametrically amplifying low photon numbers with gains of $$\sim$$40 dB. This work establishes the simplest approach to fabricating JJs to date, and it could prove pivotal to the widespread utilization of superconducting circuit-based quantum technologies.