John Bardeen and the Quantum Roots of the Transistor
May 23, 2025
Celebrating a giant of modern technology on his 117th birthday
This Friday, 23 May, marks the 117th anniversary of the birth of John Bardeen. The vast majority of people, despite being surrounded by billions of transistors every day, have no idea what a transistor is, who invented it, or how its discovery radically changed the course of history.
The anonymity of John Bardeen in the public eye borders on surreal. After all, he is the only person in history to have received the Nobel Prize in Physics twice. His first Nobel, awarded in 1956, was shared with his colleague Walter Brattain and their supervisor William Shockley, for the invention of the transistor. His second came in 1972, alongside his former student Robert Schrieffer and postdoctoral researcher Leon Cooper, for developing the BCS theory of superconductivity — one of the most influential achievements in quantum physics in the second half of the 20th century.
Transistors are the building blocks of electronic devices. Therefore, they are present, in astonishingly large numbers, in every electronic gadget: computers, mobile phones, TV screens, cars, domestic appliances. A transistor is essentially an electric tap. Just as a tap controls the flow of water through a pipe, a transistor regulates the flow of electrical current between two terminals using a voltage applied to a third. This simple principle allows one electrical signal to modulate another — an idea at the heart of amplification. When Bardeen and Brattain invented the first working transistor in 1947 at AT&T’s Bell Labs, they weren’t just solving a technical problem — replacing bulky, fragile vacuum tubes — they were laying the foundation for modern electronics.
‘John Bardeen’, illustration by Gary Brown / Science Photo Gallery
Their breakthrough was only possible thanks to the understanding of the effect of impurities (dopants) on semiconductors like silicon and germanium, and their electronic states, especially at surfaces and interfaces. This was only possible thanks to the development of quantum theory. Today it may seem obvious, but in 1947, quantum theory was only just coming of age — and the physics of solids was still full of rough edges. One of the great physicists of the time, Wolfgang Pauli (Nobel 1945), famously dismissed the whole endeavour: “One shouldn’t work on semiconductors, that is a filthy mess; who knows if they really exist!” As for surfaces: “God created the solids, the devil their surfaces.”
And yet, from this “filthy mess” emerged one of the most transformative inventions in human history. The transistor was born at the legendary Bell Labs, a unique institution that would go on to produce technologies like the laser, the communications satellite, and the Unix operating system. The role of physicists and engineers in the Manhattan Project and wartime radar development had convinced both governments and corporations of the strategic value of investing in fundamental and applied research. Bell Labs embodied that vision, supporting pioneering work across the spectrum. It was a place where basic science and technological innovation went hand in hand — an inspired vision for INL.
The team at Bell, under the leadership of William Shockley, quickly realised the potential of semiconducting devices to amplify signals and replace vacuum tubes. The rise of integrated circuits in the 1960s then unleashed the power of mass transistor production, thanks to miniaturisation, measured by the famous Moore’s law — fueling the consumer electronics revolution, the personal computer era, and the nanoelectronics-based digital world we live in today. To give a sense of scale: by 2024, humanity was producing over 225 billion transistors per person per year, and their physical dimensions are just a few nanometres each. Of course, all scientific instrumentation at INL is unthinkable without transistors, and the field of nanoscience is a consequence of the miniaturisation race predicated by Moore’s law.
As if being one of the inventors of the building block of the prevailing technology were not enough, Bardeen was also the leader of the team that figured out the mechanism of superconductivity in metals, postulating one of the most elegant quantum states — the so-called BCS wave function. In this theory, the electrons in superconductors overcome their tendency to repel each other and form pairs that create a Bose condensate, acting cooperatively and making dissipationless electrical flow possible. The BCS theory also paved the way for groundbreaking technologies. Notably, it led to the prediction and subsequent discovery of the Josephson effect, which underpins devices like SQUIDs (Superconducting Quantum Interference Devices) used in ultra-sensitive magnetometry — one of our favourite toys at INL. The Josephson effect is also a key ingredient in superconducting qubits, a leading platform in the race toward practical quantum computing.
Hence, Bardeen’s transistor has radically transformed civilisation, and Bardeen’s theory of superconductivity may be on the way to bringing a second quantum revolution. In this International Year of Quantum, it is worth remembering that the world we’ve built on transistors started with a deep dive into the quantum behaviour of matter. And that one of the greatest minds behind it all, John Bardeen, remains largely unknown to the very people whose lives his work has reshaped.
Text by Joaquín Fernández-Rossier, research group leader at INL
