The Royal Swedish Academy of Sciences has awarded the 2025 Nobel Prize in Physics to 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. This recognition comes for experiments conducted in the 1980s that showed quantum effects—usually seen only in tiny particles—can occur in larger, hand-held systems, opening doors to advanced technologies like quantum computers and sensors.
What are quantum effects and their importance?
Definition: Quantum mechanical effects refer to strange behaviors shown by very small particles, like atoms or electrons, that do not follow the normal rules of everyday physics: for example, a particle can be in two places at once (superposition), pass through solid barriers as if they are not there (tunnelling), or stay connected over long distances even after separating (entanglement).
Importance: These effects are important because they form the basis of modern technologies like computer chips and lasers, and they open up new ways to solve hard problems: in simple terms, quantum rules allow particles to do things that seem impossible, helping scientists create faster computers and better sensors.
Background: In the background, quantum mechanics started in the early 1900s with scientists like Max Planck and Albert Einstein, who showed that energy comes in small packets called quanta, not in a smooth flow, leading to big changes in how we understand the world at tiny scales.
What is macroscopic quantum tunnelling and quantisation?
Macroscopic Quantum Tunnelling: Macroscopic quantum mechanical tunnelling means a large group of particles, like in a hand-held circuit, can pass through a barrier together without breaking it, just like a single tiny particle would: imagine a whole cricket ball going through a wall instead of bouncing off, but only under special conditions.
Energy Quantisation: Energy quantisation is when energy in a system can only change in fixed steps or amounts, like jumping up stairs instead of walking up a ramp: the system cannot have any energy level in between, which is a key sign of quantum behavior.
Key Insight: These concepts were thought to only work for very small things, but the winners showed they can happen in bigger systems if you protect them from outside disturbances, like noise or heat, which usually destroy the delicate quantum states.
What is the historical background and key experiment?
Foundational Work: The work builds on the 1973 Nobel Prize to Brian Josephson for discovering that current can tunnel through an insulator between two superconductors, creating the Josephson junction, a basic setup for studying quantum effects in electricity.
Experimental Setup: In the 1980s at UC Berkeley, John Clarke (supervisor), Michel Devoret (postdoc), and John Martinis (PhD student) refined this setup: they built a circuit with superconductors separated by a thin non-conducting layer, carefully shielding it from any interference to keep the quantum effects intact.
Key Results: In their 1984-1985 experiments, they showed the entire circuit acting like one big quantum particle, with current flowing without voltage (tunnelling) and energy absorbed or released in discrete quanta, proving quantum rules apply to macroscopic scales for the first time.
Who are the winners and their contributions?
John Clarke: John Clarke (born 1942, UK) led the research group at UC Berkeley, focusing on superconductors and Josephson junctions, providing the expertise to explore quantum phenomena in circuits.
Michel H. Devoret: Michel H. Devoret (born 1953, France) joined as a postdoc and helped design experiments to measure and control the circuit's properties, demonstrating tunnelling in large systems.
John M. Martinis: John M. Martinis (born 1958, USA) worked as a PhD student, contributing to building and testing the setup that showed energy quantisation and macroscopic quantum behavior.
Collaborative Impact: Together, they turned theoretical predictions by Tony Leggett into real experiments, showing quantum effects in a system of billions of particles, which was not widely recognized at first but later became key for technology.
What are the key applications of this discovery?
Quantum Computing: The main application is in quantum computing, where these circuits help create qubits (quantum bits) that process information much faster than regular computers: this can solve complex problems like designing new medicines by modeling molecules or improving materials for better batteries.
Quantum Sensors and Cryptography: It also advances quantum sensors for precise measurements, like detecting tiny magnetic fields, useful in medical imaging or navigation, and quantum cryptography for unbreakable secure communication.
Broader Impacts: Globally, it reduces reliance on classical computers for tough tasks, such as breaking or creating strong encryption, and supports fields like renewable energy by optimizing chemical reactions.
Challenges and Progress: Challenges include keeping systems isolated from interference, but solutions are leading to practical devices, with companies like Google (where Martinis later worked) building on this for real quantum machines.
Why is this Nobel significant for India and globally?
Relevance to India: For India, it boosts the National Quantum Mission (launched 2023 with ₹6,000 crore), aiming for quantum computers by 2031: Indian scientists like Arindam Ghosh from IISc note this 1980s work is the foundation for today's quantum tech, inspiring local research in qubits.
Indian Connections: Rajamani Vijayraghavan from TIFR, who trained under Devoret, highlights how it answers questions on quantum scale limits and enables qubits using superconducting circuits, a popular method in India.
Global Impact: Globally, it shows quantum mechanics—over 100 years old—still drives innovation, building on transistors for digital tech, and addresses UN goals like sustainable energy through efficient computing.
Future Prospects: Future prospects include faster drug discovery and secure data, but issues like high costs and error correction remain, with the market for quantum tech projected to reach billions by 2030.
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