Physics, Materials & Energy Technologies: Chips, Light, Quantum, Storage and Clean Power

A light-emitting diode is a p-n junction run in forward bias. Electrons crossing the junction fall into holes and give up their energy as photons — electroluminescence — and because each photon carries roughly the band-gap energy, the material decides the colour. Red and green LEDs came early; an efficient blue LED, made from gallium nitride, took until the early 1990s and won Isamu Akasaki, Hiroshi Amano and Shuji Nakamura the 2014 Nobel Prize in Physics, because blue completed the set needed for white light. Most white LEDs are blue LEDs coated with a yellow phosphor. LEDs waste far less energy as heat than filament bulbs and, unlike compact fluorescent lamps, contain no mercury. India’s UJALA programme (January 2015) distributed LED bulbs at scale.

LASER stands for Light Amplification by Stimulated Emission of Radiation. Einstein predicted stimulated emission in 1917: a photon passing an excited atom can trigger it to emit a second photon identical in wavelength, phase and direction. If more atoms are kept excited than relaxed — a population inversion, maintained by "pumping" with light or current — and the medium sits between two mirrors, the light builds into a beam that is monochromatic (one wavelength), coherent (waves in step), highly directional and intense. Theodore Maiman built the first laser, using a ruby crystal, in 1960.

Lasers also measure: LiDAR times laser pulses to map terrain, forests and roads, and the most sensitive ruler ever built is a laser interferometer — the LIGO detectors that first caught gravitational waves in 2015. LIGO-India, approved in 2023 for Hingoli district, Maharashtra, is to be the third detector of that network, built with the US LIGO laboratory.

An optical fibre guides light by total internal reflection. It has a glass core surrounded by cladding of lower refractive index; light travelling in the core strikes the boundary at more than the critical angle and is reflected back every time, so it follows the fibre round bends. Total internal reflection needs two conditions together: light must go from the optically denser to the rarer medium, and the angle of incidence must exceed the critical angle. Single-mode fibres have a very narrow core, carry one path of laser light and suit long-distance links; multimode fibres have a wider core and serve short runs inside buildings. Fibre carries far more data than copper, loses little over distance and is immune to electromagnetic interference. Charles Kao won the 2009 Nobel Prize in Physics for showing that sufficiently pure glass could carry light over long distances; Narinder Singh Kapany is called the father of fibre optics. The same principle lights the inside of the body in an endoscope.

In 1911 Heike Kamerlingh Onnes found that mercury cooled to about 4.2 K (−269°C) lost all electrical resistance. A superconductor has zero resistance below its critical temperature, so a current set flowing in a loop circulates indefinitely, and it expels magnetic field from its interior — the Meissner effect (1933), which makes a magnet float above it. Conventional superconductors are explained by electrons pairing up (Cooper pairs, BCS theory, 1957). In 1986 Bednorz and Müller discovered ceramic copper-oxide (cuprate) superconductors, and within a year YBCO was superconducting at about 92 K — above the 77 K of liquid nitrogen, which is cheap, unlike the liquid helium older materials need. Even so, no material yet superconducts at room temperature and ordinary pressure; the LK-99 claim of 2023 collapsed when other laboratories could not reproduce it.

• MRI scanners use superconducting magnets (niobium-titanium wire in liquid helium) to make strong, steady fields.
• Particle accelerators such as CERN’s Large Hadron Collider bend beams with superconducting magnets.
• Fusion devices: tokamaks confine plasma with superconducting coils — ITER in France, of which India is a member, and the SST-1 steady-state superconducting tokamak at the Institute for Plasma Research, Gandhinagar.
• Maglev: Japan’s SCMaglev line uses superconducting magnets; the Shanghai maglev uses conventional electromagnets, so magnetic levitation does not by itself mean superconductivity.
• Superconducting qubits, the basis of several quantum computers (next section).

At the nanoscale, two things change. A larger share of atoms sits at the surface, so a gram of nanoparticles has an enormous surface area and reacts or catalyses far faster than a lump; and quantum effects start to set optical and electronic properties. Gold nanoparticles look red, not gold, which is why medieval stained glass glowed ruby. Quantum dots are semiconductor nanocrystals whose emitted colour depends on their size — smaller dots emit bluer light, larger dots redder — used in QLED displays and medical imaging; their discovery and synthesis won Moungi Bawendi, Louis Brus and Alexei Ekimov the 2023 Nobel Prize in Chemistry. In farming, IFFCO’s liquid nano urea (2021) and nano DAP (2023) apply nutrients as nanoparticles sprayed on leaves. The worry that keeps pace with the benefits is nanotoxicity: particles small enough to enter cells may harm them in ways bulk material does not.

A qubit exploits superposition and entanglement, but it has to be built out of something, and every option is a compromise. Superconducting circuits are fast and use chip-making methods but must be cooled to a few hundredths of a degree above absolute zero; trapped ions held by electric fields are very accurate but slow; photons work at room temperature and travel well, which suits communication; neutral atoms held by laser "tweezers" and spins in silicon are other routes. All share one enemy, decoherence — the loss of the fragile quantum state through any contact with the surroundings — so a useful machine needs error correction, spreading one reliable logical qubit over many physical qubits. That is why a raw qubit count says little on its own.

Quantum computers matter to security because of Shor’s algorithm (1994): a large enough, error-corrected machine could factor the big numbers on which RSA and similar public-key systems rest. The answer on the software side is post-quantum cryptography — new mathematical schemes believed hard even for quantum machines, the first of which the US standards body NIST published in 2024. The answer from physics is quantum key distribution (QKD). Two parties share a secret key encoded in the quantum states of single photons (the first protocol, BB84, dates from 1984). Because measuring a quantum state disturbs it, and an unknown quantum state cannot be copied (the no-cloning theorem), an eavesdropper leaves errors that the parties can detect, and they discard the key. QKD protects the key; the message itself is then encrypted with that key and sent over an ordinary channel. Photons are lost in fibre over a few hundred kilometres, so long links use trusted relay nodes or satellites — China’s Micius satellite demonstrated this from 2016.

Two recent Nobel Prizes in Physics mark the field’s foundations: 2022 to Alain Aspect, John Clauser and Anton Zeilinger for experiments with entangled photons that founded quantum information science, and 2025 to John Clarke, Michel Devoret and John Martinis for showing quantum tunnelling and quantised energy levels in a superconducting electric circuit — the effect on which superconducting qubits are built. Quantum sensing — atomic clocks, magnetometers and gravimeters of extreme sensitivity — is likely to reach everyday use, in navigation and mineral exploration, before quantum computing does.

Every battery cell has a negative electrode (anode), a positive electrode (cathode), an electrolyte that lets ions through but not electrons, and a separator. On discharge, electrons travel from anode to cathode through the outside circuit — doing work on the way — while ions cross inside through the electrolyte; charging pushes both back. In a lithium-ion cell the anode is usually graphite, lithium ions shuttle between the electrodes, and the electrolyte is a lithium salt in a flammable organic solvent. John Goodenough, Stanley Whittingham and Akira Yoshino shared the 2019 Nobel Prize in Chemistry for developing it. If a damaged or overheated cell starts a self-feeding reaction — thermal runaway — it can catch fire.

Batteries make critical minerals a strategic question. The Geological Survey of India reported inferred lithium resources of 5.9 million tonnes in Reasi district, Jammu and Kashmir, in 2023 — inferred resources are an early-stage estimate, not proven reserves. KABIL (Khanij Bidesh India Ltd, 2019) seeks lithium and cobalt assets abroad, and a National Critical Mineral Mission was approved in 2025. On manufacturing, a PLI scheme for Advanced Chemistry Cell batteries (2021) supports 50 GWh of cell capacity, and the Battery Waste Management Rules, 2022 put extended producer responsibility for collection and recycling on producers.

A fuel cell is a battery that is never charged, only fed. In the common proton-exchange membrane (PEM) cell, hydrogen at the anode splits into protons and electrons; the protons pass through the membrane, the electrons go round the external circuit as current, and at the cathode they recombine with oxygen to form water — the only exhaust, with some heat. Because it converts chemical energy straight into electricity without burning, a fuel cell is not bound by the heat-engine (Carnot) limit, and it keeps running as long as fuel and oxygen are supplied. A battery, by contrast, stores a fixed amount of energy and must be recharged.

In regenerative braking the motor runs as a generator while the vehicle slows, turning kinetic energy back into charge instead of heat in the brake pads. India’s demand incentives began with FAME India in 2015 and its second phase in 2019, and continue under the PM E-DRIVE scheme of 2024. An EV has no tailpipe, but its life-cycle emissions depend on how the electricity is generated — on a coal-heavy grid the gain is smaller than on a clean one.

Hydrogen burns or reacts to give only water, but almost none of it occurs free on Earth, so how it is made decides whether it is clean. The industry names production routes by colour:

An electrolyser splits water into hydrogen at the cathode and oxygen at the anode; the main designs are alkaline, PEM and high-temperature solid oxide. Every kilogram of hydrogen needs about 9 kg of water in principle, and hydrogen is hard to store: it is the lightest gas, packs little energy per litre unless compressed to hundreds of atmospheres or liquefied at −253°C, and makes some steels brittle. Converting it to green ammonia is one way to ship it. Its first users are those that already consume grey hydrogen — refineries and fertiliser plants — followed by steel made by direct reduction, shipping and heavy transport. India’s National Green Hydrogen Mission (January 2023; its target and incentives are in the economy chapter on industry and infrastructure) is backed by a Green Hydrogen Standard (2023): hydrogen counts as green only if its emissions from well to production gate do not exceed 2 kg of CO₂-equivalent per kg of hydrogen, averaged over twelve months.

The National Policy on Biofuels, 2018 (amended 2022) widened the feedstocks allowed for ethanol and set a target of 20% ethanol in petrol (E20), whose target year was advanced in 2022 to 2025-26. Ethanol has a higher octane rating than petrol but less energy per litre, so mileage falls slightly and vehicles need materials compatible with higher blends. Compressed biogas is methane-rich gas from the anaerobic digestion of farm waste, cattle dung and municipal waste, purified to vehicle-fuel quality; the SATAT initiative (2018) promotes CBG plants and GOBARdhan (2018) turns dung and village waste into biogas. Used cooking oil can be converted into biodiesel. India launched the Global Biofuels Alliance at the G20 summit in New Delhi in September 2023.

Carbon capture, utilisation and storage (CCUS) traps CO₂ before it reaches the air. Post-combustion capture scrubs CO₂ from flue gas, usually with amine solvents; pre-combustion capture gasifies the fuel and removes CO₂ before the hydrogen-rich gas is burnt; oxy-fuel combustion burns fuel in pure oxygen so the exhaust is almost all CO₂ and water. Direct air capture pulls CO₂ from ambient air, at much higher cost because it is so dilute. Captured CO₂ is stored in deep saline aquifers or depleted oil and gas fields (injecting it to push out more oil is enhanced oil recovery), mineralised in basalt, where it turns to carbonate rock, or used to make urea, methanol and building materials. Pairing bioenergy with storage (BECCS) can give negative emissions, because the plants drew the carbon from the air in the first place. NITI Aayog published a CCUS policy framework for India in 2022.

A solar photovoltaic (PV) cell is a large p-n junction: a photon with more energy than the band gap frees an electron-hole pair, the junction’s built-in field separates them, and a direct current flows — the photovoltaic effect, first seen by Edmond Becquerel in 1839. Cells are wired into modules and arrays, and an inverter converts their DC into the AC of the grid. A single-junction silicon cell cannot convert more than about a third of sunlight into electricity (the Shockley–Queisser limit), so higher efficiency comes from stacking materials in tandem cells.

The power in the wind is ½ρAv³ — proportional to the air density, the area swept by the blades and the cube of the wind speed. Doubling the wind speed therefore gives eight times the power, and doubling the blade length gives four times (area goes with the square of the radius). That cube is why turbines are put on tall towers, ridges and offshore, where winds are stronger and steadier, though offshore foundations and cables cost far more. No turbine can extract more than 16/27, about 59%, of the wind’s energy — the Betz limit — because the air must keep moving to leave the rotor. India adopted a National Offshore Wind Energy Policy in 2015, with the coasts of Gujarat and Tamil Nadu identified for the first projects, and a wind-solar hybrid policy in 2018; the International Solar Alliance, launched by India and France at the Paris climate conference in 2015, promotes solar power among its member countries.

• Tidal energy uses the rise and fall of the sea, either by a barrage across an estuary (La Rance in France, operating since 1966) or by underwater turbines in tidal streams. It is perfectly predictable but needs a large tidal range; in India the Gulfs of Khambhat and Kachchh and the Sundarbans have been studied.
• Wave energy captures the motion of surface waves — abundant but battered by storms.
• Ocean thermal energy conversion (OTEC) runs a heat engine on the difference between warm surface water and cold deep water, and needs a gap of about 20°C, so it suits only tropical seas. The same temperature difference drives the low-temperature thermal desalination plants that India’s National Institute of Ocean Technology built in Lakshadweep, the first at Kavaratti (2005).
• Geothermal energy taps the Earth’s internal heat — dry-steam, flash-steam and binary-cycle plants — and, unlike sun and wind, runs round the clock. It is strongest along plate boundaries and hot spots (Iceland draws heavily on it); in India the Puga valley in Ladakh is the site of the first geothermal project, led by ONGC.

Every navigation satellite broadcasts its position and the exact time from an on-board atomic clock. A receiver measures how long each signal took to arrive, turns the delay into a distance and finds the one point consistent with all of them — trilateration. Three distances would fix a point in space if the receiver’s clock were perfect, but a phone’s quartz clock is not, so a fourth satellite is needed to solve for the clock error along with latitude, longitude and height. Four systems are global — the US GPS, Russia’s GLONASS, Europe’s Galileo and China’s BeiDou — and two are regional: India’s NavIC and Japan’s QZSS.

• NavIC (formerly IRNSS) was designed as seven satellites — three in geostationary orbit and four in inclined geosynchronous orbits — so that all are always visible over India. Its primary service area covers India and about 1,500 km beyond its borders. It offers a Standard Positioning Service for civilians and an encrypted Restricted Service for authorised users. It broadcast first in the L5 and S bands; the second-generation NVS-01 (2023) added the L1 band used by most phones and carried an indigenous rubidium atomic clock, after imported clocks on earlier satellites had failed.
• GAGAN (GPS-Aided GEO Augmented Navigation), built by ISRO and the Airports Authority of India, is a satellite-based augmentation system: ground stations measure GPS errors and geostationary satellites broadcast corrections, giving the accuracy and integrity that civil aviation needs for approaches and landings. It improves GPS; it is not a separate constellation.

Remote sensing is observing the Earth without touching it, by the electromagnetic radiation it reflects or emits. Passive sensors record reflected sunlight or emitted heat, so optical imaging stops at night and under cloud; active sensors send their own signal and time the echo — radar, and especially synthetic aperture radar (SAR), uses microwaves that pass through cloud and work day and night, which is why it is used to map floods during the monsoon; LiDAR does the same with laser light. Healthy vegetation absorbs red light and reflects near-infrared strongly, so the NDVI index built from those two bands measures crop vigour and drought stress.

India’s operational Earth-observation programme began with IRS-1A in 1988. The family now includes Cartosat (high-resolution imagery for mapping), Resourcesat (agriculture and land use), Oceansat (ocean colour and winds) and the radar satellites RISAT and EOS-04, whose SAR sees through monsoon cloud. NISAR, the NASA-ISRO SAR mission carrying an L-band radar from NASA and an S-band radar from ISRO, was launched in 2025. Data are received and processed by the National Remote Sensing Centre, Hyderabad, and served through the Bhuvan geoportal; uses range from crop forecasting and forest-cover assessment to flood mapping and groundwater prospecting.