- Person
- Brian Josephson
- Lived
- b. 1940
- Field
- Physics
- From
- British (Welsh)
The story
Brian Josephson was born in Cardiff in 1940 to Jewish parents, Abraham and Mimi Josephson. As a PhD student at Cambridge, he studied what happens when two superconductors are separated by a very thin insulating layer. In a paper received by Physics Letters on June 8, 1962, he predicted that pairs of electrons could tunnel through the barrier, so that a current would flow with no voltage at all, and that a steady voltage across the junction would instead produce a current oscillating at a frequency fixed only by the voltage and by fundamental constants. John Bardeen doubted it, but in January 1963 Philip Anderson and John Rowell at Bell Labs reported the effect, and devices built on it are now called Josephson junctions.
The precise link between voltage and frequency transformed electrical measurement. Frequency can be measured extremely accurately, so a junction driven by microwaves produces a voltage that depends on nothing but the frequency and constants of nature. From 1972 the American national standards laboratory began using the Josephson effect to maintain the volt, replacing banks of chemical cells. Modern chips link tens of thousands of junctions to produce precise voltages up to ten volts that agree to better than one part in ten billion, and since the 2019 redefinition of the international units, Josephson standards have been the authoritative way to realise the volt.
Two junctions in a superconducting ring form a SQUID, the most sensitive magnetic sensor known. Arrays of SQUIDs are the most common sensors in magnetoencephalography, or MEG, which records the faint magnetic fields of the working brain. Doctors use MEG to find the source of seizures in people with epilepsy and to map areas controlling movement and speech before surgery.
Josephson junctions are also the key component of superconducting qubits, one of the leading designs for quantum computers. In 1984 and 1985 John Clarke, Michel Devoret and John Martinis showed that a Josephson junction circuit could behave as a single quantum object, work recognised by the 2025 Nobel Prize in Physics. Josephson himself shared the 1973 Nobel Prize in Physics for his prediction.
Why it matters
Josephson junctions define the volt worldwide, let doctors map brain activity with SQUID sensors, and are the building blocks of superconducting quantum computers.
About Brian Josephson
Welsh physicist who, as a 22-year-old student, predicted the Josephson effect, now used to define the volt, to map brain activity with SQUID sensors and to build superconducting quantum computers.
Sources
- Josephson effect Wikipedia
- Programmable Josephson Voltage Standards and Arbitrary Waveform NIST
- Magnetoencephalography Wikipedia
- Press release: The Nobel Prize in Physics 2025 NobelPrize.org
- Brian Josephson Wikipedia
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