The Royal Swedish Academy of Sciences has awarded the Nobel Prize in Physics to John Clarke, Michel H. Devoret, and John M. Martinis “for the discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit.”Their work sounds esoteric at first glance, but its significance runs deep. They showed that quantum “weirdness” — normally confined to atoms and subatomic particles — can reveal itself in electrical circuits big enough to hold in one’s hand. It’s a discovery that bridges the invisible world of the very small with the tangible one we inhabit.Quantum Tunnelling and Energy QuantaTo understand what they achieved, imagine throwing a ball at a wall. Classically, it either bounces back or stops. But in the quantum world, a particle can sometimes “tunnel” straight through. That’s tunnelling — one of quantum mechanics’ strangest predictions.Story continues below this adAnother hallmark of the quantum realm is quantisation: energy isn’t continuous but comes in fixed amounts. Atoms, for instance, can only absorb or emit certain “chunks” of energy.Also Read | Quantum Computing: Journey from bits to qubits still has far to goIn the mid-1980s, Clarke, Devoret, and Martinis used superconducting circuits cooled to near absolute zero, where electric current flows with zero resistance. At the heart of their setup was a Josephson junction — two superconductors separated by a thin insulating layer. Under these conditions, pairs of electrons (called Cooper pairs) can tunnel across the barrier, behaving as a single quantum system.When they passed a current through such a circuit, the entire system acted like a macroscopic particle. It could “escape” from one quantum state to another — tunnelling through an energy barrier and producing a tiny measurable voltage. They also found that the system absorbed and released energy only in discrete steps, confirming energy quantisation in a man-made circuit.Bridging the Quantum and the EverydayFor decades, physicists wondered how big a system could be and still show quantum effects. Normally, when many particles are involved, quantum behaviour fades. The laureates demonstrated that, with the right materials and extreme precision, even a chip visible to the naked eye can display unmistakable quantum signatures.Story continues below this adTheir experiments took years of refinement. Clarke, known for his precision in low-temperature physics, once recalled spending months chasing a noise source that turned out to be a loose screw vibrating in the cryostat. Martinis later brought this same obsessive attention to building superconducting qubits — the building blocks of quantum computers — at Google. And Devoret became one of the field’s great mentors, helping train the next generation of quantum engineers.When the Nobel announcement came, Clarke admitted to being “completely stunned.” Devoret, reached at Yale, reflected on the long road from skepticism to proof: “We were trying to see if nature would let us stretch quantum mechanics to human scales — and she did.”From the lab to the quantum futureMacroscopic quantum circuits are more than scientific curiosities. They form the backbone of technologies like quantum computing, quantum cryptography, and ultra-precise sensors. Their experiments helped scientists learn how to preserve quantum coherence — the fragile property that allows quantum systems to remain in superpositions without collapsing into classical states.Also Read | The universe, the atom, and a cat both dead and alive: Understanding Quantum MechanicsThat same technology is now being developed into practical applications. In Martinis’s lab at UC Santa Barbara, for instance, similar circuits evolved into the Sycamore processor, which Google used to demonstrate “quantum advantage” in 2019.Story continues below this adSuperconducting qubits: Their circuits became the blueprint for qubits in today’s quantum computers. By showing that macroscopic systems can maintain quantum states, their work directly enabled platforms developed by Google, IBM, and others.Quantum sensors: The same principles underlie ultra-sensitive magnetic field detectors and gravimeters, capable of probing brain activity or underground structures with unprecedented precision.Metrology and fundamental tests: Their experiments helped refine the definition of electrical standards such as the volt and the ampere, using Josephson junctions as quantum-accurate voltage references.A century-old theory, still full of surprisesQuantum mechanics, born in the early 20th century, continues to astonish. “It’s wonderful,” said Olle Eriksson, chair of the Nobel Committee, “that century-old quantum mechanics still offers new surprises — and remains the foundation of all digital technology.”Story continues below this adIndeed, the transistors in every computer chip rely on quantum tunnelling at the nanoscale. The 2025 Nobel Prize reminds us that even familiar circuits can still teach us new lessons about the universe’s most fundamental rules.A century after Planck, Schrödinger, and Einstein argued about the limits of the quantum world, three experimentalists showed that the same mysteries can play out not just in atoms, but in devices built by human hands. The line between quantum and classical, it seems, is not a wall at all — but a door we’ve only just begun to open.Shravan Hanasoge is an astrophysicist at the Tata Institute of Fundamental Research.