IIT-Gandhinagar scientists demo quantum link through 5.5 km of air

Science & Technology · 5 October 2026 · Based on The Hindu (original report)

2-minute summary

Scientists at IIT-Gandhinagar, in collaboration with the Bhaskaracharya National Institute for Space Applications and Geo-informatics (BISAG-N) and private firm QNu Labs, have successfully demonstrated India's first free-space quantum-key distribution (QKD) link over a distance of 5.56 km. Conducted in October 2026, this demonstration achieved a Quantum Bit Error Rate (QBER) of under 5% and generated secure keys at 230-260 bits per second. Unlike fiber-optic QKD, free-space QKD transmits photons directly through the atmosphere, requiring precise alignment to counter atmospheric turbulence and light pollution. The team also integrated Post-Quantum Cryptography (PQC) to establish a hybrid, dual-layer security framework. This milestone is a critical stepping stone toward satellite-based quantum communications, aligning with India's National Quantum Mission targets of establishing a 2,000-km inter-city fiber network and satellite-to-ground quantum links.

Why it's in the news

Scientists at IIT-Gandhinagar have successfully demonstrated India's first free-space quantum-key distribution (QKD) link over a distance of 5.56 km. This achievement marks a significant scale-up from previous terrestrial open-air tests and brings India closer to satellite-based secure quantum communications.

Facts to remember

IIT-Gandhinagar and BISAG-N demonstrated India's first free-space quantum-key distribution (QKD) link over a distance of 5.56 km in October 2026.
The demonstration achieved a quantum bit error rate (QBER) of under 5% and generated secure keys at a rate of 230-260 bits per second.
The National Quantum Mission (NQM) targets a 2,000-km inter-city QKD network over fibre-optic cables and satellite-based secure quantum communications.
China launched the world's first QKD-active satellite, 'Micius', in 2016, which orbits the Earth at approximately 500 km.
The Bengaluru-based deep-tech startup QNu Labs supplied the quantum equipment used in the IIT-Gandhinagar demonstration.

Background and context

Classical cryptographic systems (like RSA and ECC) rely on the mathematical complexity of factoring large numbers, which can be easily cracked by future quantum computers using algorithms like Shor's Algorithm. To counter this threat, two primary security paradigms have emerged: Quantum Key Distribution (QKD) and Post-Quantum Cryptography (PQC). QKD uses the fundamental laws of quantum mechanics (such as the no-cloning theorem and superposition) to transmit secure keys via photons; any interception by an eavesdropper alters the quantum states, immediately alerting the communicating parties. PQC, on the other hand, relies on mathematical algorithms that are secure against both classical and quantum hacking. India's progress in terrestrial QKD has evolved rapidly: ISRO demonstrated a 300-meter link in 2021, IIT-Delhi and DRDO achieved a 1-km link in 2025, and the IIT-Gandhinagar feat has now extended this to 5.56 km. These terrestrial open-air tests are vital precursors for establishing secure satellite-to-ground quantum communication channels.

Committees and reports

Prime Minister’s Science, Technology, and Innovation Advisory Council (PM-STIAC) — Recommended the launch of the National Quantum Mission to build indigenous capabilities in quantum technologies.

Government schemes

National Quantum Mission (NQM) — Aims to seed, nurture, and scale up scientific and industrial R&D in quantum technology, including quantum communication, computing, and sensing.

Previous UPSC questions on this theme

Prelims GS-1 2026 — Which of the following statements with regard to the National Quantum Mission (NQM) is/are correct ? 1. It aims at developing intermediate-scale quantum computers with 50 – 1000 physical qubits. 2. Its implementation includes setting up of four Thematic Hubs (T-Hubs) in academic and national R&D institutes across India. Select the answer using the code given below : (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2

Mains practice: What is Quantum Key Distribution (QKD), and how does it differ from Post-Quantum Cryptography (PQC)? Discuss the strategic significance of the National Quantum Mission in securing India's critical digital infrastructure.

Quantum computing poses an existential threat to classical encryption systems like RSA, which secure global financial, military, and administrative data. To counter this, technologies like Quantum Key Distribution (QKD) and Post-Quantum Cryptography (PQC) are being developed. The successful demonstration of a 5.56 km free-space QKD link by IIT-Gandhinagar in October 2026 marks a major milestone in India's quantum readiness.

• **QKD vs. PQC: Technical Distinctions**

- **Mechanism**: QKD relies on the laws of physics (quantum mechanics, such as the no-cloning theorem) to transmit cryptographic keys via single photons. Any interception alters the quantum state, alerting the users. PQC, conversely, relies on complex mathematical equations (like lattice-based cryptography) that are secure against both classical and quantum computers.

- **Infrastructure**: QKD requires specialized hardware (lasers, single-photon detectors, and fiber/satellite links), whereas PQC is software-based and can be deployed on existing classical networks.

• **Strategic Significance of the National Quantum Mission (NQM)**

- **Securing Critical Infrastructure**: NQM, under the Ministry of Science and Technology, aims to safeguard defense communications, banking networks, and power grids from 'harvest now, decrypt later' cyber threats.

- **Technological Sovereignty**: By partnering with domestic startups like QNu Labs, India reduces its dependence on foreign quantum hardware, ensuring strategic autonomy.

- **Global Leadership**: NQM targets a 2,000-km inter-city fiber network and satellite-based links, positioning India alongside global leaders like China, which demonstrated this via its 'Micius' satellite in 2016.

• **Way Forward**

- **Hybrid Security Architectures**: Deploying a dual-layer defense by combining the physical security of QKD with the algorithmic strength of PQC.

- **Satellite Integration**: Accelerating ISRO's quantum satellite program to bypass terrestrial atmospheric limitations.

- **Standardization**: Formulating national cryptographic standards for quantum-resistant algorithms.

In conclusion, achieving quantum security is vital for safeguarding India's digital sovereignty, directly supporting the vision of a resilient, technologically self-reliant nation under the National Quantum Mission.

Prelims practice questions

Q1. Consider the following statements regarding quantum communication technologies: 1. Quantum Key Distribution (QKD) secures communication by relying on the mathematical complexity of cryptographic algorithms. 2. In free-space QKD, the transmitter and receiver require a direct line of sight and must adjust for atmospheric turbulence. 3. Post-Quantum Cryptography (PQC) can secure data against hacking attempts from both conventional and quantum computers. How many of the above statements are correct?

Only one
Only two
All three
None

Answer: B. Statement 1 is incorrect because QKD secures communication by relying on the laws of quantum physics (such as the no-cloning theorem and superposition), not mathematical complexity. PQC is the technology that relies on mathematical complexity. Statement 2 is correct because free-space QKD transmits photons through the atmosphere, requiring precise line-of-sight alignment and adjustments for atmospheric turbulence and light pollution. Statement 3 is correct because PQC is designed to be secure against cryptographic attacks from both classical and quantum computers.

Q2. Consider the following statements: Statement-I: Terrestrial free-space Quantum Key Distribution (QKD) is highly challenging to implement over very long distances on Earth. Statement-II: Photons traveling through the atmosphere suffer from attenuation, light pollution, and require a direct line of sight between the transmitter and receiver. Which one of the following is correct in respect of the above statements?

Both Statement-I and Statement-II are correct and Statement-II explains Statement-I
Both Statement-I and Statement-II are correct but Statement-II does not explain Statement-I
Statement-I is correct but Statement-II is incorrect
Statement-I is incorrect but Statement-II is correct

Answer: A. Both statements are correct. Terrestrial free-space QKD is limited to shorter distances (like the 5.56 km achieved by IIT-Gandhinagar) because the photons must travel through the atmosphere, where they are subject to scattering, absorption (attenuation), and light pollution. They also require a strict, unobstructed line of sight, which is difficult to maintain over long distances due to the Earth's curvature and obstacles. Therefore, Statement-II directly explains the challenges mentioned in Statement-I.

Q3. With reference to quantum communications, what does the term 'Quantum Bit Error Rate' (QBER) primarily measure?

The rate at which quantum superposition decoheres due to environmental temperature fluctuations in a fiber-optic cable.
The ratio of classical bits required to correct one single-photon quantum state error in a post-quantum cryptographic system.
The fraction of quantum bits received incorrectly during the transmission of a shared key between two parties.
The percentage of qubits that undergo quantum entanglement collapse during transmission through a vacuum.

Answer: C. As mentioned in the context of the IIT-Gandhinagar demonstration, the Quantum Bit Error Rate (QBER) is the fraction of quantum bits received incorrectly. In QKD, monitoring QBER is crucial because an eavesdropper attempting to intercept the photons will inevitably introduce errors, raising the QBER and alerting the communicating parties.

Revision flashcards

What is the fundamental physical principle that makes Quantum Key Distribution (QKD) secure against eavesdropping? The laws of quantum mechanics (specifically superposition and the no-cloning theorem). Any attempt to measure or intercept the quantum states of the transmitted photons alters their state, introducing detectable errors.
Which Union Ministry is the nodal agency for implementing the National Quantum Mission (NQM) in India? The Ministry of Science and Technology (specifically through the Department of Science and Technology).
In October 2026, which two institutions in Gujarat were successfully connected using India's first 5.56 km free-space QKD link? IIT-Gandhinagar and the Bhaskaracharya National Institute for Space Applications and Geo-informatics (BISAG-N).
What target did the National Quantum Mission set for inter-city fiber-optic QKD networks and satellite-based quantum communications? A 2,000-km inter-city QKD network over fibre-optic cables and satellite-based secure quantum communications between ground stations up to 2,000 km apart.
Why is a hybrid security approach combining QKD and Post-Quantum Cryptography (PQC) considered superior to using either alone? It provides dual-layer defense: QKD secures the transmission channel using physical laws, while PQC secures the data mathematically, protecting against both physical interception and algorithmic hacking.