Dr. Beauty Pandey Associate Dean, School of Sciences, Woxsen University
Understanding the Idea Behind the 2025 Nobel Prize in Physics
One of the first rules we learn in physics is simple and intuitive: a system cannot cross an energy barrier unless it has enough energy. A ball cannot roll over a hill that is higher than its energy, and an object trapped in a valley will remain there unless energy is supplied. This rule works extremely well in everyday life and forms the basis of classical physics. However, nature does not always follow rules that feel obvious. One of the clearest examples of this is quantum tunneling. Quantum tunneling refers to the ability of a system to pass through an energy barrier even when it does not have enough energy to climb over it. In quantum physics, a system is not confined to a single position. Instead, it is described as spread out over space, with a probability of being found in different regions. When such a system encounters a barrier, its probability distribution does not stop abruptly at the barrier. It decreases inside the barrier and, in some cases, extends beyond it. As a result, the system may appear on the other side. This phenomenon, impossible in classical physics, is called quantum tunneling. A useful analogy is fog spreading in a valley. A solid object would need enough energy to climb the surrounding hills, but fog behaves differently. It slowly spreads in all directions, and some of it naturally appears beyond the hills without ever climbing them. Similarly, a quantum system does not “jump” over the barrier. Its spread‑out nature allows it to appear beyond the barrier.
For many years, tunneling was accepted only for microscopic systems such as electrons or atomic nuclei. These systems are small, isolated, and clearly quantum in nature. Physicists believed that for large systems made of many particles, interactions with the environment would suppress quantum effects. According to this view, quantum tunneling should disappear as systems become larger and more complex. The discovery recognized by the 2025 Nobel Prize in Physics overturned this belief. John Clarke, Michel Devoret, and John Martinis demonstrated that quantum tunneling can occur in an entire electric circuit, a system large enough to be seen and handled. This result was path‑breaking because it showed that quantum mechanics is not limited by size alone. Their experiments used a device called a Josephson junction, which consists of two superconductors separated by a very thin insulating layer. At extremely low temperatures, electrons in a superconductor form Cooper pairs and move together coherently. Although the insulating layer should block current according to classical physics, quantum mechanics allows these Cooper pairs to tunnel through it.
What made the result extraordinary was that tunneling did not involve a single electron. Billions of electrons acted together as one quantum object, escaping an energy barrier as a whole. This collective tunneling produced a sudden measurable voltage, providing direct experimental evidence of macroscopic quantum behavior. The Nobel Prize is path‑breaking because it marked a turning point in our understanding of the boundary between the quantum and classical worlds. It showed that classical behavior is not guaranteed simply because a system is large. If noise, temperature, and environmental disturbances are carefully controlled, quantum effects can dominate even in engineered systems. This discovery laid the foundation for modern quantum technologies such as superconducting qubits and quantum computers. More importantly, it delivered a deep conceptual message: quantum mechanics is not a theory of the small—it is a theory of nature itself. Under the right conditions, even everyday circuits can do what classical intuition says is impossible.