The 2025 Nobel Prize in Physics was awarded to John Clarke, Michel H. Devoret, and John M. Martinis for showing that quantum effects, usually restricted to the microscopic world of atoms, can actually be observed in devices large enough to hold in your hand. Their experiments proved that truly quantum behavior exists even in familiar, “macroscopic” electrical circuits.
What Is “Macroscopic Quantum Tunneling”?
Quantum mechanics describes how things behave at very small scales, such as atoms and photons. It predicts strange behaviors like tunneling (where a particle passes through a barrier it classically shouldn’t cross) and quantization (energy only comes in fixed packets, not a continuous range). Normally, these effects are visible only in small systems.
This year’s Nobel Prize winners demonstrated quantum tunneling and quantized energy in a device “big enough to be seen and touched”, an electrical circuit made using superconductors, bridging the divide between the quantum and everyday worlds.
The Science Behind the Breakthrough – Quantum Tunneling
Imagine throwing a ball at a wall: classically, the ball bounces back unless you throw it hard enough to break through. In the quantum world, a particle could “magically” appear on the other side, even without the energy to cross the barrier—this is tunneling.
The Experiment: Josephson Junction
- The scientists built a circuit from two superconductors (materials that carry current without resistance) separated by a thin non-conducting layer, forming what’s known as a Josephson junction.
- At very low temperatures, in this set-up, electric current flows with zero voltage, an unusual quantum state.
- Sometimes, though, the system would spontaneously jump to a state where a voltage appeared, even though, classically, there wasn’t enough energy present to do this. The only explanation: all the electrons (paired up as “Cooper pairs”) together tunneled through the barrier, behaving like a single quantum particle.
Energy Quantization
- When energy was added, the system only absorbed or emitted set amounts (“quanta”), just like electrons in atoms can only jump between specific energy levels.
- The energy levels of the entire system were “quantized,” and the experimenters could “see” these jumps by measuring how the circuit responded to microwaves.
Why Does It Matter? Real-World Impact
- Quantum Computing: Superconducting quantum bits (qubits), which underpin many quantum computers, are based on precisely these kinds of circuits. The Nobel-winning work provided the essential experimental foundation for building working quantum computers, which today promise faster computation for some types of problems.
- Bridging Worlds: These experiments show quantum rules still govern even large systems under the right conditions, challenging the intuition that quantum effects are “washed out” in big objects.
Meet the Laureates
- John Clarke: Professor, University of California Berkeley
- Michel H. Devoret: Professor, Yale University and University of California, Santa Barbara
- John M. Martinis: Professor, University of California, Santa Barbara
Good Books:
PHYSICS IN MINUTES (IN MINUTES SERIES) by Giles Sparrow
Quantum Mechanics: The Theoretical Minimum (Paperback) – Leonard Susskind
Quantum Mechanics – Concepts and Applications by Nouredine Zettili
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