QUANTUM TUNNELLING
1. Context
The Nobel Prize for Physics this year will be awarded to three scientists — John Clarke, Michel Devoret and John Martinis, the Royal Swedish Academy of Sciences said on Tuesday. The three worked together and devised experiments to tease greater insight into the workings of the quantum world: the realm of the ultra-small when objects, broken down to single, constituent particles, cease to behave in the way we ordinarily expect them to.One of the mind-boggling behaviours that particles are capable of here is “tunnelling”, literally, the ability of particles to pass through physical walls.
2. What is Quantum Tunnelling?
- Quantum tunnelling is one of those fascinating phenomena in physics that almost feels like it breaks the rules of common sense. To understand it, imagine a tiny particle—like an electron—approaching a barrier, something it doesn’t seem to have enough energy to climb over.
- In our everyday world, if you don’t have enough energy to jump over a wall, you simply bounce back. But in the quantum world, particles don’t behave like little billiard balls; they are also described by waves of probability.
- These probability waves spread out, and some part of the wave can extend into and even beyond the barrier. This means that while most of the time the particle reflects back, there is still a small chance that it will appear on the other side of the barrier without ever having gone “over” it in the classical sense. It’s as if the particle has slipped, or “tunnelled,” through the wall.
- This strange effect arises because quantum mechanics deals with probabilities and wave functions, not definite paths. The barrier doesn’t completely forbid the particle—it just makes the likelihood of passing through very small, depending on the thickness and height of the barrier.
- In the real world, quantum tunnelling is not just theory—it plays a role in many important processes. For example, it allows nuclear fusion to occur in the sun, because protons don’t have enough classical energy to overcome their mutual repulsion, but tunnelling lets them get close enough to fuse. It’s also the principle behind technologies like tunnel diodes and scanning tunnelling microscopes
3. Applications of Quantum tunnelling
- Quantum tunnelling may sound like a purely theoretical quirk of quantum mechanics, but in fact it has very practical and far-reaching applications in science, technology, and even the functioning of the universe itself.
- For instance, the very reason stars like our Sun shine is because of tunnelling. Inside the Sun, hydrogen nuclei (protons) need to get extremely close together to fuse into helium, but their natural electric repulsion makes this almost impossible at the temperatures present.
- Classically, fusion shouldn’t occur. Yet, because of quantum tunnelling, protons can “slip through” their mutual energy barrier, allowing fusion to happen, which in turn produces the sunlight and energy that sustain life on Earth.
- In electronics, tunnelling is deliberately harnessed in devices. Tunnel diodes, for example, use the tunnelling effect to achieve very fast switching speeds and are important in high-frequency applications. Similarly, the flash memory used in USB drives and SSDs relies on electrons tunnelling through insulating barriers to store and erase data.
- Another remarkable use is the Scanning Tunnelling Microscope (STM), which revolutionized nanotechnology. This instrument brings a sharp tip extremely close to a surface, and electrons tunnel between the tip and the surface. By measuring this tunnelling current, scientists can map surfaces at the atomic scale, even “seeing” individual atoms.
- Tunnelling also plays a role in quantum computing and superconductivity. In Josephson junctions, where two superconductors are separated by a thin insulating barrier, pairs of electrons can tunnel across, giving rise to highly sensitive devices like SQUIDs (Superconducting Quantum Interference Devices), which can detect extremely faint magnetic fields.
- Even in biology, tunnelling is believed to contribute to enzyme reactions, where tiny particles like protons or electrons tunnel during biochemical processes, making reactions faster than classical chemistry would predict
4. Quantum Tunnelling and the Light Speed Threshold
- Quantum tunnelling and the light speed threshold (the universal speed limit of relativity) seem to be pulling in opposite directions at first glance. Relativity says: no particle carrying information or mass can travel faster than the speed of light in vacuum.
- Quantum tunnelling, on the other hand, sometimes appears to let a particle “get through” a barrier faster than if it had gone over or around it—almost as if it were cheating the speed limit
- When a particle tunnels through a barrier, its wave function (the mathematical object that describes its probability of being somewhere) extends into the barrier. If the barrier is thin enough, there’s a finite chance that the particle will show up on the other side.
- Now, the time it takes for this tunnelling to occur is strange. In some experiments, it looks like particles “emerge” on the other side almost instantly, faster than light could have crossed the same distance.
- But this doesn’t mean the particle literally travels through the barrier at superluminal speed. Instead, tunnelling is a non-classical process where the concept of a well-defined trajectory inside the barrier simply doesn’t apply.
- In fact, most physicists say: the particle doesn’t really “cross” the barrier in the ordinary sense—it’s more accurate to say that the probability of finding it on the other side suddenly becomes nonzero.
- Crucially, no usable information or signal can be transmitted faster than light via tunnelling. This is why relativity is not violated. The appearance of faster-than-light behaviour comes from how we interpret timing in quantum processes, not from actual superluminal motion
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5.National Quantum Mission
- The National Quantum Mission (NQM) is an initiative launched by the Government of India in 2023 to advance research and development in quantum science and technology. With a focus on four core areas—Quantum Computing, Quantum Communication, Quantum Sensing & Metrology, and Quantum Materials & Devices—the mission seeks to position India as a global leader in quantum innovation.
- The mission is funded with an allocation of ₹6,003.65 crore over a span of eight years (2023-2031) and aims to drive both scientific breakthroughs and industrial applications. A key feature of the mission is the establishment of four Thematic Hubs (T-Hubs), each dedicated to one of the key areas, to address specific research objectives and challenges in quantum technologies.
- The NQM is expected to support a range of applications, from secure communication systems to advanced computing, with the potential to transform fields like healthcare, defense, and cryptography
6. Way Forward
Quantum tunnelling, while counterintuitive, does not violate the universal light-speed limit set by relativity. The apparent superluminal effect during tunnelling arises because the process is governed by probability waves rather than classical trajectories. A particle does not physically “travel through” the barrier faster than light; instead, quantum mechanics allows for the possibility of it being found on the other side without following a conventional path. Thus, tunnelling highlights the non-classical, probabilistic nature of quantum reality but preserves the deeper principles of causality and relativity. It stands as a reminder that the quantum world operates under rules that often defy intuition, yet remain consistent with the fundamental laws of physics
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For Prelims: Quantum computing, supercomputers, Qiskit Runtime, IBM, National Mission on Quantum Technologies and Applications, superconductors,
For Mains:
1. What is Quantum computing? Discuss the need for Quantum Computers in emerging countries like India. (250 Words)
2. What are quantum computers and how are they different from conventional computers? Where does India stand in the race to build quantum computers that can realise their full potential? (250 Words)
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Previous Year Questions
1. India's first Supercomputer is (TSPSC AEE 2015)
A. Aditya
B. Param Yuva
C. Param
D. Vikram-100
Answer: C
2. What is the full form of IBM? (SSC Steno 2017)
A. International Business Machine
B. Indian Beta Machine
C. Integral Business Machine
D. Internal Beta Machine
Answer: A
3. Which one of the following is the context in which the term "qubit" is mentioned? (UPSC 2022)
A. Cloud Services
B. Quantum Computing
C. Visible Light Communication Technologies
D. Wireless Communication Technologies
Answer: B
4. Quantum computing uses (ACC 124 CGAT 2021)
A. Qubit
B. Bits
C. Bytes
D. Qubytes
Answer: A
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Source: The Hindu
