What Is Quantum Tunneling? How a 2025 Nobel-Winning Experiment Brought It Into the Real World

Updated: October 19, 2026

Insider Brief

• Quantum tunneling is a phenomenon in which a particle passes through an energy barrier it classically lacks the energy to overcome.
• The effect arises from the wave-like nature of matter described by quantum mechanics, allowing a particle’s probability wave to extend into and beyond forbidden regions.
• First observed in radioactive decay and later in superconducting systems, quantum tunneling underpins technologies from semiconductors to quantum computers.

Quantum tunneling (or quantum tunnelling) is when a particle passes through an energy barrier it does not have enough energy to cross. It happens because particles behave like waves, and it drives everything from fusion in the Sun to flash memory and quantum computers.

Whether it’s playing a lonely game of tennis against a garage door or shooting a game of pool at the local bar, we’re used to balls bouncing off solid objects — not passing through them. (Depending on how hard you serve, I suppose.)

It’s hard to play snooker or solo tennis in the quantum world, though.

In quantum mechanics, a particle can slip through a barrier. Although that may sound like a cross between magic and science fiction, quantum tunneling is a real and measurable effect at the heart of modern physics. This year’s Nobel Prize in Physics recognized the scientists who proved that, while we can still bounce a tennis ball off a wall, tunneling isn’t limited to atoms or subatomic particles.

According to the Royal Swedish Academy of Sciences, John Clarke, Michel Devoret, and John Martinis demonstrated that entire electrical circuits — large enough to hold in one’s hand — can behave like single quantum particles.

What Is Quantum Tunneling?

Quantum tunneling emerges from the wave-like nature of matter described by Erwin Schrödinger in 1926, according to information provided by the Royal Swedish Academy of Sciences. In classical physics, a particle can’t cross a barrier higher than its energy. Quantum physics, however, treats particles as waves that extend into classically forbidden regions. Even if a barrier is too high for a particle to cross conventionally, there is a finite probability that its wavefunction will “leak” through to the other side.

This process is called tunneling, and, before you write it off as a scientific anomaly, it underlies several natural phenomena.

Real-World Examples of Quantum Tunneling

For instance, tunneling explains radioactive decay, where alpha particles trapped inside an atomic nucleus escape through potential barriers. It also makes nuclear fusion possible in the Sun, where protons would otherwise lack the energy to overcome their mutual repulsion. The phenomenon has been verified countless times at microscopic scales and has powered technologies from flash memory to quantum sensors. Yet until the 1980s, physicists assumed tunneling couldn’t be seen in anything larger than an atom.

From Microscopic to Macroscopic: How Did Scientists Prove Large Objects Can Tunnel?

The laureates changed that. Working at the University of California, Berkeley, Clarke, Devoret and Martinis built an electrical circuit made of superconductors — materials that carry current with zero resistance — separated by an insulating layer called a Josephson junction. When cooled to near absolute zero, this system allowed billions of paired electrons, called Cooper pairs, to move collectively as if they were a single quantum object.

By carefully measuring the circuit’s behavior, the researchers found that its electrical state could “tunnel” through an energy barrier. Instead of transitioning smoothly from one state to another, it switched abruptly, a sign that the circuit obeyed quantum, not classical, rules. They also observed that the system’s energy levels were quantized, changing only in discrete steps rather than continuously. This confirmed that a macroscopic object could indeed act as a quantum particle.

The Royal Swedish Academy described the discovery as the first clear demonstration of “macroscopic quantum tunneling” — quantum mechanics operating in a system visible to the naked eye.

The Physics Behind the Phenomenon: What Happens During Tunneling?

The experiment focuses on the so-called tilted washboard potential, a metaphor for the forces acting on the superconducting circuit.

The system’s electrical phase behaves like a particle trapped in a series of wells separated by energy barriers. In the classical picture, the particle would stay trapped unless pushed hard enough to escape. Quantum mechanics allows it to tunnel through the barrier instead. This event shows up as a sudden appearance of voltage across the junction, marking the moment the “particle” escapes.

By cooling the system and filtering out noise, the Berkeley team observed tunneling at temperatures where thermal energy couldn’t explain the behavior. Their measurements agreed precisely with quantum theory’s predictions, confirming that the effect was genuinely quantum in nature.

Why It Matters: How Quantum Tunneling Powers Modern Technology

Quantum tunneling isn’t just a curiosity to attract a Swedish scientific committee with a large amount of prize money to give out annually. (Although, over the past half-century, quantum tunneling has been a recurring theme in Nobel Prizes in Physics — from the 1972 award to John Bardeen, Leon Cooper, and Robert Schrieffer for the BCS theory explaining superconductivity, to the 1973 prizes recognizing Leo Esaki and Ivar Giaever for electron tunneling in semiconductors and superconductors, and Brian Josephson for predicting tunneling currents between superconductors.) It’s also the mechanism behind superconducting qubits — and those are the building blocks of quantum computers used by companies such as Google, IBM and other hardware developers. The same Josephson junctions that revealed macroscopic tunneling now serve as controllable quantum systems capable of encoding information in quantized energy states.

The Academy noted that the laureates’ experiments bridged the boundary between the microscopic and macroscopic worlds, laying the foundation for technologies that rely on manipulating quantum states at human scales. These include quantum sensors capable of detecting minute magnetic fields and new approaches to secure communication.

In essence, Clarke, Devoret, and Martinis turned quantum tunneling from a theoretical oddity into an engineered reality, proving that the invisible laws of the quantum world can be brought into the laboratory, one superconducting circuit at a time.

Frequently Asked Questions

What is quantum tunneling?

Quantum tunneling is a phenomenon where a particle passes through an energy barrier it classically lacks the energy to overcome. It arises from the wave-like nature of matter, allowing a particle’s wavefunction to “leak” through to the other side of a barrier.

Is it quantum tunneling or quantum tunneling?

Both are correct. “Tunnelling” is the British spelling and “tunneling” is the American spelling; they describe the same phenomenon.

Who won the 2025 Nobel Prize in Physics related to quantum tunneling?

John Clarke, Michel Devoret, and John Martinis won the award for demonstrating that entire electrical circuits — large enough to hold in one’s hand — can behave like single quantum particles. Their work at UC Berkeley provided the first clear demonstration of macroscopic quantum tunneling.

Can quantum tunneling happen to everyday objects like tennis balls?

No. While quantum tunneling has been demonstrated in macroscopic electrical circuits, the probability of tunneling decreases exponentially with the object’s mass. A tennis ball contains roughly 10²⁵ atoms, making the tunneling probability so infinitesimally small that it would never occur even over the lifetime of the universe. Quantum tunneling remains a phenomenon observable only in carefully controlled microscopic and mesoscopic systems.

How does quantum tunneling enable quantum computers?

Quantum tunneling is the core mechanism behind superconducting qubits, the building blocks of quantum computers. Josephson junctions—the same devices used in the Nobel-winning experiments—allow quantum information to be encoded in energy states that can tunnel between configurations. This enables quantum computers to explore multiple computational paths simultaneously, giving them advantages over classical computers for specific problems.

Is quantum tunneling faster than the speed of light?

No. While tunneling appears instantaneous at quantum scales, it doesn’t involve information or matter traveling faster than light. The particle’s wavefunction already extends through the barrier before tunneling occurs, and the process respects relativity’s speed limit. Quantum tunneling is better understood as a probability phenomenon rather than conventional movement through space.

What temperature is needed to observe macroscopic quantum tunneling?

The 2025 Nobel laureates observed macroscopic quantum tunneling at temperatures near absolute zero (approximately -273°C or a few millikelvin). At these ultra-low temperatures, thermal noise is suppressed enough that quantum effects dominate over classical behavior. Superconducting circuits must be cooled to these extreme temperatures to maintain their quantum properties and enable tunneling observations.

Beyond quantum computers, where else is quantum tunneling used?

Quantum tunneling is already embedded in everyday technology:

• Flash memory and SSDs: Store data by tunneling electrons through insulating barriers
• Scanning tunneling microscopes (STM): Image individual atoms by measuring tunneling currents
• Tunnel diodes: Enable high-speed electronic switches in telecommunications
• Quantum sensors: Detect minute magnetic and electric field changes for medical imaging and materials analysis
• Nuclear fusion research: Understanding proton tunneling helps improve fusion reactor designs