Maarg Manthan · Topic 14.15

Quantum Computing

Science & Technology › IT, Telecommunications and Computers · Topic 14.15

A quantum computer uses the rules of quantum mechanics to process information. An ordinary computer stores data as bits that are either 0 or 1, while a quantum computer uses quantum bits, or qubits, which can be in a superposition of 0 and 1 at the same time and can be linked by entanglement, so that the state of one qubit is tied to another. Quantum algorithms can solve some problems much faster than ordinary computers: Peter Shor's algorithm of 1994 can factor large numbers, which threatens present public key encryption, and Lov Grover's algorithm speeds up searching. In 2019 Google claimed quantum supremacy with its 53-qubit Sycamore processor. India's National Quantum Mission was approved in April 2023 with an outlay of Rs 6,003 crore for 2023 to 2031.

5 min read · UPSC Prelims · Science & Technology · IT, Telecommunications and Computers

At a Glance

Unit Qubit
Key ideas Superposition, entanglement
Threat Breaks RSA encryption
India’s mission National Quantum Mission, 2023
Outlay Rs 6,003 crore
Exam link UPSC Prelims, Science & Technology: IT, Telecommunications and Computers

Where Does It Fit?

This topic follows the account of blockchain. It looks ahead to a technology that may change computing and encryption, and which links with the topics on encryption and cyber security later in the macro. Previous topic: Blockchain Technology and Cryptocurrencies (Bitcoin). Next topic: Biometrics and Virtual Reality.

How Does Quantum Computing Differ from Classical Computing?

Concept	Explanation
Classical bit	Holds 0 or 1
Qubit	Can be 0, 1 or a combination of both at once, called superposition, until measured
Entanglement	Qubits can be linked so that the state of one depends on another even at a distance, which gives extra computing power
Interference	Quantum algorithms use wave-like interference to strengthen right answers and cancel wrong ones
Hardware types	Superconducting circuits (Google, IBM), trapped ions, photons and neutral atoms. Most need extremely low temperatures near absolute zero
Decoherence	Qubits lose their quantum state easily from heat and noise, which causes errors and is the main hurdle
Error correction	Requires many physical qubits to make one reliable logical qubit

What Are the Applications, Risks and the Indian Mission?

Factoring and cryptography: Shor’s algorithm could break RSA and elliptic curve encryption on a large enough quantum computer
Search: Grover’s algorithm gives a speed-up for unstructured search
Drug and materials design: simulating molecules, as nature is quantum
Optimisation: logistics, finance and traffic problems
Post-quantum cryptography: new encryption methods that resist quantum attacks; the United States standards body NIST published its first standards in 2024
Quantum key distribution: communication whose security is based on physics, detecting any eavesdropping
National Quantum Mission: approved on 19 April 2023, with Rs 6,003.65 crore for 2023-24 to 2030-31, to build quantum computers of 50 to 1,000 physical qubits, secure communication links of 2,000 km and quantum sensors
Hubs: four thematic hubs at institutions for computing, communication, sensing and materials

What Else Should You Remember?

Quantum supremacy: Google claimed in October 2019 that its Sycamore processor with 53 qubits performed a task in about 200 seconds that would take a classical supercomputer thousands of years, a claim disputed by IBM
Quantum advantage: the more modest idea of solving a useful problem better than classical computers
Companies: IBM, Google, Microsoft, Intel, and start-ups such as IonQ and Rigetti. In India, QpiAI and others are building quantum hardware
Indian efforts: institutions such as TIFR, IISc, IISER, the Raman Research Institute and the Defence Research and Development Organisation are working on qubits and quantum communication
Satellite quantum communication: China’s Micius satellite did quantum key distribution in 2016, and ISRO and DRDO have done tests in India
International Year of Quantum: the United Nations marked 2025 as the International Year of Quantum Science and Technology
Limits: quantum computers will not replace ordinary computers, and are suited only to certain problems
Quantum sensing: ultra-precise clocks, magnetometers and gravimeters, as in Deep Space Atomic Clock
Harvest now, decrypt later: the risk that encrypted data stolen today can be read in future when quantum computers arrive
Link with encryption: see Encryption and Cybersecurity (Cyber Swachhta Kendra)
Link with supercomputers: see Supercomputers and Their Applications
Caution: qubit counts and company claims change quickly, so check recent sources
Quantum gates: operations on qubits are done with quantum gates, which are the equivalent of logic gates in ordinary computers
Cooling needs: superconducting quantum computers work in dilution refrigerators at around a hundredth of a degree above absolute zero
Skills gap: quantum technology needs physicists, engineers and software developers, so training programmes are part of the national mission

Why Does It Matter for the Exam?

Terms: qubit, superposition, entanglement
Algorithms: Shor and Grover
Indian mission: year, outlay and targets
Current affairs link: post-quantum standards and new qubit records
Common errors: saying that a qubit is always both 0 and 1, or that quantum computers will replace all computers

As an analytical point, quantum computers are still immature, but their effect on cryptography means that governments must prepare early. India’s mission builds capability in computing, communication and sensing together.

Why Is This Topic Important?

Concepts Qubit and entanglement
Threat Encryption
Mission NQM

What Came Next?

The next topic covers biometrics and virtual reality. Next topic: Biometrics and Virtual Reality.

Key People and Terms

Qubit Quantum bit
Superposition Both states at once
Entanglement Linked quantum states
Decoherence Loss of quantum state
QKD Quantum key distribution
PQC Post-quantum cryptography

Exam Corner

Points to Remember

National Quantum Mission: April 2023, Rs 6,003 crore.
Shor’s algorithm: 1994.
Sycamore: 53 qubits (2019).
Qubits need very low temperature.
NIST post-quantum standards: 2024.

Do Not Confuse With

Qubit and bit Superposition versus 0 or 1
Quantum supremacy and advantage Beating classical on any task versus on a useful task
QKD and post-quantum cryptography Physics-based keys versus new maths-based codes

Memory Hook

Qubit is both until seen, entangled pairs are linked; Shor breaks the codes, NQM builds the future.

Mains Angle

Questions ask for concepts and the Indian mission. These points help.

Potential Speed-ups
Risk Encryption
Policy NQM

A Question You May Face

An original practice question, not a past paper question.

“Explain the principles of quantum computing and discuss the objectives of the National Quantum Mission and the security implications.”

How to Answer

Principles Superposition, entanglement.
Uses Chemistry, optimisation.
Risks Encryption.
Mission NQM targets.

GS Relevance

Prelims: qubit, superposition, entanglement, National Quantum Mission details, applications. GS Paper 3: science and technology, quantum technologies, cyber security.

Frequently Asked Questions

What is a qubit?

A qubit, or quantum bit, is the basic unit of quantum information. Unlike an ordinary bit, which is either 0 or 1, a qubit can exist in a superposition of both states at the same time until it is measured. Qubits can also be entangled, which allows quantum computers to handle certain calculations very efficiently.

What is quantum entanglement?

Quantum entanglement is a phenomenon in which two or more particles become linked so that the state of one is connected to the state of the other, however far apart they are. Entanglement is a key resource for quantum computing and for secure quantum communication.

Why are quantum computers a threat to encryption?

Shor's algorithm shows that a large, error-corrected quantum computer could factor big numbers quickly, which would break widely used public key systems such as RSA and elliptic curve cryptography. Governments and companies are therefore moving to post-quantum cryptography, which is designed to resist quantum attacks.

What is the National Quantum Mission?

The National Quantum Mission was approved by the Union Cabinet on 19 April 2023 with an outlay of Rs 6,003.65 crore for 2023-24 to 2030-31. It aims to develop quantum computers with 50 to 1,000 physical qubits, secure quantum communication over distances up to 2,000 kilometres, and quantum sensors and materials, through four thematic hubs.

What was Google's quantum supremacy claim?

In October 2019 Google announced that its 53-qubit Sycamore processor had performed a specific calculation in about 200 seconds that, it estimated, would take the best classical supercomputer thousands of years. IBM disputed the estimate, but the result was seen as a milestone in showing that quantum machines can beat classical ones at some tasks.

PYQ Practice — Statement Analysis

1 A qubit can exist in a superposition of 0 and 1.

True

Until measured.

2 Shor's algorithm is mainly used to speed up database searching.

False

That is Grover's; Shor factors numbers.

3 The National Quantum Mission was approved in 2023.