Quantum Gets Big: Physics Nobel Awarded for Macroscopic Effects That Birthed the Qubit

Quantum Leaps: 2025 Nobel Physics Laureates Reveal Macroscopic Quantum Effects, Opening the Path to Advanced Quantum Technologies

STOCKHOLM, Sweden, October 9, 2025 - The 2025 Nobel Prize in Physics has been bestowed upon U.S.-based scientists John Clarke, Michel H. Devoret, and John M. Martinis for their groundbreaking discovery of "macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit." Their pioneering work in 1984 and 1985 fundamentally demonstrated quantum phenomena at an unprecedented scale, shifting these effects from the microscopic domain of individual particles to observable macroscopic systems. This research has laid essential groundwork for the development of superconducting qubits and the rapidly growing field of quantum computing.

The Royal Swedish Academy of Sciences honored their achievement, which centred on meticulously crafted experiments using superconducting Josephson-junction circuits. These circuits, where two superconductors are separated by a thin insulating barrier, enabled the researchers to witness quantum mechanical behaviours that had previously been limited to theoretical forecasts or experiments involving far fewer particles.

The Macroscopic Manifestation of Quantum Mechanics

The heart of the laureates' discovery lies in showing that collective assemblies of particles can still display distinct quantum properties. In their experiments, charged particles within the superconductor, particularly Cooper pairs, acted as a single quantum mechanical entity spanning the whole circuit.

Key observations included:

• Macroscopic Quantum Tunnelling: The system, initially in a zero-voltage state, effectively trapped behind an energy barrier, was observed to escape this state through quantum tunnelling. This phenomenon, where a particle can pass through a barrier without possessing enough energy to overcome it classically, manifested on a scale encompassing billions of Cooper pairs. The escape was detectable as the emergence of voltage across the circuit.
• Energy Quantisation: The laureates also demonstrated that this macroscopic system absorbed or emitted energy only in specific, discrete amounts, exactly as predicted by quantum mechanics. This quantised behaviour, a hallmark of the quantum world, was observed not in individual electrons but in the collective state of the superconducting circuit.

"It is wonderful to be able to celebrate the way that century-old quantum mechanics continually offers new surprises," said Olle Eriksson, Chair of the Nobel Committee for Physics. "It is also enormously useful, as quantum mechanics is the foundation of all digital technology."

Foundations for Quantum Computing and Beyond

The ramifications of these discoveries reach far into the ongoing race to develop next-generation quantum technologies. The ability to observe and manipulate quantum states in macroscopic systems provides an experimental bedrock for advanced applications such as:

• Superconducting Qubits: Martinis, building on this foundational work, directly employed the observed energy quantisation to create a quantum bit (qubit) based on superconducting circuits. The lowest two energy states of the quantised circuit served as the '0' and '1' of quantum information, a crucial step toward scalable quantum processors.
• Quantum Cryptography: Controlling quantum effects at a larger scale opens avenues for crafting inherently secure communication protocols.
• Quantum Sensors: Enhanced precision in measurement, leveraging quantum phenomena, could lead to sensors with unprecedented sensitivity for a variety of scientific and industrial uses.

The work by Clarke, Devoret, and Martinis effectively forged an "artificial atom" on a macroscopic scale-an atom that can be wired and incorporated into complex experimental setups, providing a controllable environment to explore quantum phenomena directly. This represents a significant leap from microscopic quantum effects, where an ordinary ball shows no quantum behavior and simply rebounds from a wall. Their circuits, roughly a centimetre in size, displayed a quantum mechanical system comprising billions of Cooper pairs, yet behaving as a unified quantum object.

The Laureates: A Profile

The 11 million Swedish kronor prize will be divided equally among the three laureates:

• John Clarke, born 1942 in Cambridge, UK, received his PhD from the University of Cambridge in 1968. He is a Professor at the University of California, Berkeley, USA, where he founded a research group dedicated to investigating superconducting phenomena.
• Michel H. Devoret, born 1953 in Paris, France, earned his PhD from Paris-Sud University in 1982. He is a Professor at Yale University, New Haven, CT, and the University of California, Santa Barbara, USA. He joined Clarke's research group as a postdoc in the mid-1980s.
• John M. Martinis, born 1958, completed his PhD at the University of California, Berkeley, in 1987. He holds a professorship at the University of California, Santa Barbara, USA, and serves as Chief Technology Officer at Qolab, Los Angeles, CA, USA, a leading entity in quantum technology development.

Their collaborative work at the University of California, Berkeley, during the mid-1980s, particularly the refinement of measurement techniques for Josephson junctions, was instrumental in achieving these breakthroughs. By introducing microwaves of varying wavelengths into their zero-voltage state circuits, they could observe the system transition to higher energy levels, confirming quantum mechanical predictions regarding the duration of the zero-voltage state.

This Nobel Prize underscores the continuing relevance of quantum mechanics in generating new understanding and practical technologies, demonstrating that the "bizarre properties of the quantum world can be made concrete in a system big enough to be held in the hand," according to a Nobel information release. The award highlights a crucial bridge between fundamental physics and the engineering of future quantum-enabled devices.