BharatNotes What is Quantum Computing?
Quantum computing harnesses the laws of quantum mechanics to process information in fundamentally new ways. Where a classical computer uses bits (each strictly 0 or 1), a quantum computer uses qubits, which exploit three quantum properties:
- Superposition — a qubit can represent 0 and 1 at the same time, so n qubits can encode 2ⁿ states simultaneously.
- Entanglement — qubits become correlated so that the state of one instantly constrains another, multiplying computational reach.
- Interference — probability amplitudes are combined to amplify correct answers and cancel wrong ones.
On measurement, a qubit's superposition "collapses" to a definite 0 or 1, so quantum algorithms are designed to steer interference toward the right result.
Why It Matters
Quantum machines do not replace classical computers; they excel at specific intractable problems—factoring large numbers, simulating molecules, and optimisation.
- Cryptography: Shor's algorithm can, in principle, break RSA and elliptic-curve encryption, prompting NIST to publish the first post-quantum cryptography standards (FIPS 203/204/205) in August 2024. Grover's algorithm halves the effective strength of symmetric ciphers such as AES.
- Drug discovery & materials: quantum simulation can model molecules beyond classical reach.
- National security: the "harvest-now, decrypt-later" risk means encrypted data stolen today could be decrypted by future quantum machines.
Current Status (as of 2026)
The field remains in the NISQ (Noisy Intermediate-Scale Quantum) era, where error correction is the central challenge. In December 2024, Google unveiled its 105-qubit "Willow" chip, demonstrating that adding qubits can reduce errors—a key step toward fault-tolerant computing.
India's National Quantum Mission (NQM)
| Feature | Detail (verified) |
|---|---|
| Approved | 19 April 2023 by Union Cabinet |
| Nodal body | Department of Science & Technology (DST) |
| Outlay | Rs 6,003.65 crore (2023-24 to 2030-31) |
| Qubit target | 50–1000 physical qubits over 8 years |
| Quantum communication | Satellite-based QKD up to ~2000 km |
The NQM operates through four Thematic Hubs (T-Hubs) announced in 2024:
| Hub | Lead institution |
|---|---|
| Quantum Computing | IISc Bengaluru |
| Quantum Communication | IIT Madras (with C-DOT) |
| Quantum Sensing & Metrology | IIT Bombay |
| Quantum Materials & Devices | IIT Delhi |
Indigenous progress includes QpiAI-Indus, a 25-qubit superconducting quantum computer launched in April 2025, and the Amaravati Quantum Valley in Andhra Pradesh, where an MoU (May 2025) with IBM, TCS and L&T plans to host an IBM 156-qubit Heron processor.
UPSC Angle
For GS3, link quantum computing to (a) India's technology self-reliance through the NQM, (b) cyber-security and the post-quantum encryption transition, and (c) global tech competition. Remember the distinction: a qubit is not simply "faster bits"—its power comes from superposition and entanglement scaling exponentially. Do not confuse the NQM (quantum) with the India Semiconductor Mission or the IndiaAI Mission.
Foundation concept — no single direct PYQ; underpins Prelims/Mains questions on emerging technologies, cryptography and India's strategic science missions.
