Quantum computing uses the principles of quantum mechanics — superposition, entanglement and interference — to perform certain classes of computation exponentially faster than classical machines. Google, IBM, IonQ and China's USTC have demonstrated "quantum advantage" on niche benchmarks. For India, the National Quantum Mission (NQM, 2023-31) with an outlay of Rs 6,003 crore has made quantum tech a strategic priority. UPSC treats quantum computing under GS Paper III — Science & Technology, Cyber Security, Emerging Economy.
The science — classical vs quantum
A classical bit is either 0 or 1. A quantum bit (qubit) can be 0, 1, or any quantum superposition of both, described by a probability amplitude.
| Principle | Meaning |
|---|---|
| Superposition | A qubit exists in many states at once until measured |
| Entanglement | Two qubits share correlated states; measuring one instantly fixes the other |
| Interference | Probability amplitudes add or cancel — used to amplify correct answers |
| No-cloning theorem | An unknown quantum state cannot be perfectly copied |
| Decoherence | Qubits lose quantumness rapidly when disturbed |
An n-qubit system can represent 2ⁿ states simultaneously. 300 qubits in principle exceed the number of atoms in the observable universe — this is the mathematical source of quantum speed-up.
Quantum hardware technologies
| Approach | Key player | Note |
|---|---|---|
| Superconducting qubits | IBM, Google, Rigetti | Fast; needs near absolute-zero cryostats |
| Trapped ions | IonQ, Quantinuum | Long coherence; slower gates |
| Photonics | Xanadu, PsiQuantum | Room temperature; modular |
| Topological qubits | Microsoft | Theoretically robust; experimental |
| Neutral atoms | QuEra, Atom Computing | Scalable atom arrays |
| NV-centres (diamond) | QuNu Labs (India), Element Six | Good for QKD networks |
Classes of quantum computing
- Gate-based quantum computers — general-purpose; run Shor, Grover algorithms.
- Quantum annealers — D-Wave; solve optimisation problems.
- Analog quantum simulators — model chemistry and materials.
- NISQ (Noisy Intermediate-Scale Quantum) — today's 50-1000 qubit machines without full error correction.
Why it matters — applications
| Domain | Use case |
|---|---|
| Cryptography | Shor's algorithm threatens RSA/ECC; drives post-quantum cryptography |
| Drug discovery | Molecular simulation at quantum accuracy |
| Materials science | New battery chemistries, superconductors, catalysts |
| Optimisation | Supply chain, traffic, portfolio, energy routing |
| Machine learning | Quantum kernel methods, quantum neural nets |
| Climate modelling | High-dimensional weather and ocean systems |
| Defence & intel | Radar, codebreaking, navigation beyond GPS |
| Finance | Risk analysis, derivative pricing |
India's National Quantum Mission (NQM)
Approved in April 2023, the NQM is an eight-year mission with four Thematic Hubs (T-Hubs) at the IITs/IISc:
| Hub | Theme | Lead institution |
|---|---|---|
| T-Hub 1 | Quantum Computing | IISc Bengaluru |
| T-Hub 2 | Quantum Communication | IIT Madras |
| T-Hub 3 | Quantum Sensing & Metrology | IIT Bombay |
| T-Hub 4 | Quantum Materials & Devices | IIT Delhi |
Mission targets (by 2031):
- 20-50 physical qubit machine (2027), 50-100 qubits (2029), 1000 qubits by 2031.
- Long-distance Quantum Key Distribution (QKD) network up to 2000 km.
- Satellite-based secure quantum communication.
- Magnetometers, atomic clocks, and gravimeters of Indian manufacture.
India's quantum ecosystem
Public bodies: DST, MeitY, DRDO (DYSL-QT), ISRO (satellite QKD experiments). Labs & institutes: IISc, IIT Bombay, IIT Delhi, IIT Madras, TIFR, RRI, QuIC C-DAC. Startups: QNu Labs (QKD hardware), Taqbit Labs, BosonQ Psi, Quantumpedia, Krutrim Quantum, Qulabs. Corporates: TCS Quantum Lab, Infosys, Wipro quantum practices.
Landmark demonstrations
- ISRO + RRI (2022): Free-space QKD over 300 m.
- DRDO + IIT Delhi (2022): Intercity QKD over ~100 km fibre (Prayagraj-Vindhyachal).
- C-DAC India's first 8-qubit processor (2024) announced.
- BSNL + QNu Labs (2024): First commercial QKD service offered in India.
Quantum cryptography — why it matters urgently
Current public-key cryptography (RSA, ECC) rests on the difficulty of factoring large numbers. A sufficiently large quantum computer running Shor's algorithm can break it. This has two responses:
- Post-Quantum Cryptography (PQC) — classical algorithms resistant to quantum attack. NIST finalised the first PQC standards (CRYSTALS-Kyber, Dilithium, SPHINCS+, FALCON) in August 2024. Migration of banking, PKI, blockchains and government IT must begin now.
- Quantum Key Distribution (QKD) — uses the no-cloning theorem so eavesdropping disturbs the channel. Ideal for critical point-to-point links.
"Harvest now, decrypt later" — adversaries are already storing encrypted traffic, anticipating future decryption. India's sensitive data (defence, diplomatic, health) needs PQC migration plans.
Challenges
| Challenge | Detail |
|---|---|
| Decoherence & error rates | Requires ~1000 physical qubits per one logical qubit |
| Cryogenic infrastructure | Dilution refrigerators at 10 mK cost millions |
| Talent pool | Quantum PhDs are globally scarce; India needs to scale training |
| Supply chain | Specialised parts (lasers, cryostats) mostly imported |
| Export controls | US and allies tightening quantum export regulations |
| Funding | US ~$3.8 bn, China ~$15 bn committed; India's Rs 6,003 crore (~$750 mn) modest |
Global race
- USA — National Quantum Initiative Act (2018), CHIPS & Science Act top-up; IBM 1,121-qubit Condor (2023), Heron (2024).
- China — Jiuzhang photonic supremacy; Micius QKD satellite; leads QKD networks.
- EU — Quantum Flagship (€1 bn+).
- UK — National Quantum Strategy, £2.5 bn over ten years (2023).
- Japan, Canada, Australia, Israel — sector strategies and public funds.
- India — NQM places India in the top 8 quantum investors globally.
Latest developments (2024-26)
- Atom Computing (Oct 2023) crossed 1,000 neutral-atom qubits; IBM Condor announced same month; Google Willow (Dec 2024) showed below-threshold error correction.
- NIST PQC standards finalised (Aug 2024) — migration planning for Indian banks and CIIs begins.
- NQM T-Hubs operational — research grants disbursed from 2024; first outputs expected 2025-26.
- BSNL + QNu Labs commercial QKD service (2024).
- DRDO + IIT Delhi secure video call demo (2024).
- ISRO satellite QKD trial in SSLV payload (2025).
- DeepTech Policy 2024 names quantum a priority deep-tech vertical.
- AI Action Summit, Paris (Feb 2025) — India tabled quantum-AI cross-strategy.
- India Semiconductor Mission — control electronics for qubits targeted.
- Gaganyaan progress & Chandrayaan-4 plan — quantum sensors explored for inertial navigation.
UPSC Relevance
GS Paper III — Science & Technology
- Qubits, superposition, entanglement, quantum supremacy vs advantage, NQM architecture.
GS Paper III — Cyber Security
- Post-quantum cryptography, QKD, "harvest now, decrypt later".
GS Paper III — Economy
- Quantum as strategic tech, export controls, semi-con linkage.
GS Paper II — International Relations
- Quantum export controls, India-US iCET, Quad critical tech track.
Prelims pointers — NQM (Rs 6,003 crore, 2023-31, 4 T-Hubs), QKD, Shor/Grover, NIST PQC algorithms, Micius, QNu Labs.
Interview probes — how should India prioritise quantum investments; PQC migration for banks; quantum and national security; role of start-ups.
Quantum computing will not replace classical computing — it will complement it for specific, high-value problems. Nations that set the standards and build the tools in this decade will define a new layer of global technological power. India is, for the first time, in the room.
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