India demonstrates a 5.56 km free-space quantum key distribution link in Gandhinagar
A secret key sent through open air across 5.56 km: how does physics catch an eavesdropper?
Published 4 October 2026. Written by Pratidin from the reports linked at the end; every fact checked by a separate review before publishing. How we work
The Ministry of Electronics and Information Technology (MeitY) said on 3 October 2026 that India has demonstrated a free-space Quantum Key Distribution (QKD) link over 5.56 km. The field trial, on the night of 27 to 28 September, set up a quantum-secure channel through the open air between the Bhaskaracharya National Institute for Space Applications and Geo-informatics (BISAG-N) and IIT Gandhinagar. It was carried out by the quantum security firm QNu Labs with BISAG-N and IIT Gandhinagar.
The link achieved a quantum bit error rate (QBER) below 5% and generated secure keys at 230 to 260 bits per second, and messages were encrypted and decrypted end to end. The system combined two layers: QNu Labs' hardware QKD device 'Armos', adapted for free-space optical channels, and BISAG-N's software platform 'Vedic Kavach' for post-quantum cryptography. BISAG-N is an autonomous scientific institution under MeitY. QNu Labs said the result paves the way for long-distance quantum-secure networks and satellite-based quantum communication.
QKD uses single particles of light to share an encryption key; any attempt to intercept them disturbs their quantum state and raises the error rate, so the parties can detect it. Free-space links matter because satellite QKD must work through air, not fibre. The demonstration builds on earlier Indian work, including a DRDO and IIT Delhi entanglement-based free-space link of about 1 km in 2025. The National Quantum Mission, approved on 19 April 2023 with ₹6,003.65 crore for 2023-24 to 2030-31, targets satellite-based secure quantum communication over 2,000 km between ground stations. Free-space links still face limits from distance, sunlight and weather, which is why such trials are often run at night.
Prelims facts
- MeitY announced on 3 October 2026 a 5.56 km free-space QKD link between BISAG-N and IIT Gandhinagar, tested on the night of 27 to 28 September.
- The link achieved a quantum bit error rate below 5% and secure key rates of 230 to 260 bits per second.
- It combined QNu Labs' QKD device 'Armos' with BISAG-N's post-quantum cryptography platform 'Vedic Kavach'.
- In QKD, eavesdropping disturbs the quantum states and shows up as a higher error rate.
- The National Quantum Mission (2023-24 to 2030-31, ₹6,003.65 crore) targets satellite-based secure quantum communication over 2,000 km.
Quick recall
- Over what distance was the free-space QKD link in Gandhinagar demonstrated?
- 5.56 km.
- Which two institutions did the 2026 free-space QKD link connect?
- BISAG-N and IIT Gandhinagar.
- What quantum bit error rate did the Gandhinagar link achieve?
- Below 5%.
- What secure key rate did the Gandhinagar link achieve?
- 230 to 260 bits per second.
- What is 'Vedic Kavach'?
- BISAG-N's software platform for post-quantum cryptography.
- What is 'Armos'?
- QNu Labs' hardware QKD device, here used over a free-space optical channel.
- What is the National Quantum Mission's outlay and period?
- ₹6,003.65 crore, 2023-24 to 2030-31.
- Under which ministry does BISAG-N function?
- The Ministry of Electronics and Information Technology (MeitY).
Prelims practice question
With reference to the free-space quantum key distribution (QKD) link demonstrated in Gujarat in September 2026, consider the following statements:
1. The link connected BISAG-N and IIT Gandhinagar over 5.56 km.
2. It used optical fibre laid between the two campuses.
3. It combined a hardware QKD device with a post-quantum cryptography software platform.
Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Show answer
Answer: (c) 1 and 3 only. 1 is correct. 2 is wrong: it was a free-space link, through the open air, not fibre. 3 is correct: QNu Labs' 'Armos' QKD device worked with BISAG-N's 'Vedic Kavach' post-quantum cryptography platform.
Asked before in UPSC
Recurring theme: Quantum technologies and their use in securing India's communications.
Quantum-secure key exchange and post-quantum cryptography are emerging measures to protect encrypted communications against future threats.
Qubits and quantum states are the basis of both quantum computers and QKD; the Gandhinagar link encodes key bits on quantum states of photons.
Mains practice question
What is quantum key distribution? Discuss its significance for India's communication security and the challenges in scaling it up, with reference to recent demonstrations. (150 words)
Model answer
Quantum key distribution (QKD) shares encryption keys using single photons; any interception disturbs their quantum states and is detected as a higher error rate. In September 2026 India tested a 5.56 km free-space QKD link between BISAG-N and IIT Gandhinagar.
Significance
- Future quantum computers could break today's public-key encryption; QKD gives keys whose security rests on physics.
- Free-space links are the stepping stone to satellite QKD, a National Quantum Mission target of 2,000 km.
- Pairing QKD with post-quantum cryptography (Armos with Vedic Kavach) gives layered security for defence, banking and government networks.
- Indigenous capability through QNu Labs, BISAG-N, IIT Gandhinagar, DRDO and IIT Delhi.
Challenges
- Low key rates (230 to 260 bits per second) and short ranges.
- Weather, daylight and alignment limit free-space links.
- Costly hardware and trusted-node requirements.
Way forward
- Satellite trials, standards and certification, and industry partnerships under the Mission.
QKD can make India's critical communications future-proof if scale and cost are tackled.
The basics
Why this matters
Almost all online security today rests on mathematical problems that ordinary computers find too hard to solve. A large quantum computer could solve some of them. Countries are therefore building two defences: new mathematics that resists quantum attack, and keys protected by physics itself. The Gandhinagar test combined both.
How QKD works
In Quantum key distribution, the sender encodes bits of a secret key on single photons. The receiver measures them, and the two compare a part of the results over an ordinary channel. Quantum rules mean that measuring a photon can change it. An eavesdropper who tries to read the photons leaves a trace: more errors.
- 1SendThe sender transmits single photons, each carrying one bit in its quantum state
- 2MeasureThe receiver measures each photon
- 3CompareBoth compare a sample over a normal channel to estimate the quantum bit error rate
- 4DecideA low error rate means no significant eavesdropping; the remaining bits become the key
- 5EncryptThe key encrypts messages sent over ordinary networks
What was achieved
The link ran 5.56 km through open air between BISAG-N and IIT Gandhinagar on the night of 27 to 28 September 2026. The error rate stayed below 5% and keys were produced at 230 to 260 bits per second. Night testing reduces sunlight noise, one reason Free-space optical communication is harder than fibre.
Two layers of protection
QKD protects how a key is shared. Post-quantum cryptography is a different approach: new mathematical algorithms that run on normal computers but are believed to resist quantum attacks. The trial used QNu Labs' QKD device 'Armos' together with BISAG-N's post-quantum platform 'Vedic Kavach', so that security does not depend on a single method.
The policy frame
The National Quantum Mission, approved on 19 April 2023 with ₹6,003.65 crore for 2023-24 to 2030-31, aims at satellite-based quantum communication over 2,000 km, inter-city QKD over 2,000 km and quantum computers of 50 to 1,000 physical qubits. Free-space links are the bridge from campus tests to satellites.
Go deeper
In one line: An Indian team has sent quantum-secured encryption keys through 5.56 km of open air in Gandhinagar, a step towards satellite-based quantum communication.
Why it matters for UPSC
Quantum technology is a GS3 science and security topic, and Prelims has asked about qubits. This story connects the physics, the National Quantum Mission and cyber security.
The core idea
Quantum key distribution lets two parties share a key whose secrecy rests on physics: interception shows up as errors. The Gandhinagar test used Free-space optical communication, the method a satellite link would need. It was paired with Post-quantum cryptography, a software defence against future quantum computers. Both serve the goals of the National Quantum Mission.
Numbers and dates to remember
- 5.56 km: link length; BISAG-N to IIT Gandhinagar.
- Night of 27 to 28 September 2026: field trial; 3 October 2026: MeitY release.
- QBER below 5%; key rate 230 to 260 bits per second.
- About 1 km: DRDO and IIT Delhi free-space link, 2025.
- ₹6,003.65 crore; 2023-24 to 2030-31; 2,000 km satellite target.
Where to go next
- Quantum key distribution: how physics exposes an eavesdropper.
- Free-space optical communication: why air is harder than fibre.
- Post-quantum cryptography: the mathematical shield that complements QKD.
- National Quantum Mission: India's plan and targets.
Go deeper: promise and limits of quantum-secure links
The promise. Public-key encryption protects banking, government and defence traffic today. A large quantum computer could break some of these schemes, and data intercepted now could be decrypted later. Quantum key distribution answers this by making key sharing secure on physical grounds. Free-space optical communication extends it beyond fibre, towards satellites that could link distant ground stations.
Why combine with post-quantum methods. QKD secures key exchange but needs special hardware and line of sight. Post-quantum cryptography runs on existing computers and networks. Using both, as the Gandhinagar test did with 'Armos' and 'Vedic Kavach', gives defence in depth: if one layer fails, the other still protects the data.
The limits. Key rates of a few hundred bits per second are enough to refresh encryption keys, not to carry data directly. Free-space links suffer from sunlight, fog, rain and turbulence, which is why trials are often run at night. Long fibre networks need trusted relay points. Costs and certification standards are still evolving.
India's position. The National Quantum Mission set clear targets: satellite and inter-city QKD over 2,000 km, and quantum computers of 50 to 1,000 physical qubits by 2030-31. Demonstrations by DRDO and IIT Delhi (about 1 km, 2025) and now QNu Labs, BISAG-N and IIT Gandhinagar (5.56 km, 2026) show steady progress, with a start-up, a government institute and an IIT working together. The challenge ahead is moving from campus trials to operational networks.
Quantum key distribution
How physics, not mathematics, keeps the key secret.
In one line: Quantum key distribution (QKD) is a method of sharing a secret encryption key using quantum states of light, so that any eavesdropping can be detected.
The principle
Each bit of the key is encoded in a property of a single photon. Measuring a quantum state generally disturbs it. If an eavesdropper intercepts and measures photons, the receiver sees a higher quantum bit error rate (QBER). The two parties compare a sample of their results; if the QBER is low, they keep the rest as the key.
In the news
The Gandhinagar link kept QBER below 5% and generated 230 to 260 secure key bits per second over 5.56 km. Entanglement-based QKD, used by DRDO and IIT Delhi in 2025, is a variant where pairs of linked photons carry the key.
Where to go next
Free-space optical communication
Why sending photons through air is the harder, but necessary, route.
In one line: Free-space optical communication sends light signals through the air or space between two telescopes instead of through optical fibre.
Why use it
Fibre is not available everywhere, and a satellite cannot be connected by fibre. A free-space link only needs a clear line of sight between a transmitter and a receiver.
The difficulties
Sunlight adds background photons that look like signal, so many trials run at night; the Gandhinagar test was on the night of 27 to 28 September 2026. Fog, rain and air turbulence scatter the beam. The two ends must stay precisely aligned. For quantum links, where each bit rides on a single photon, every loss matters.
Where to go next
Post-quantum cryptography
The software defence that works alongside QKD.
In one line: Post-quantum cryptography (PQC) means encryption algorithms that run on ordinary computers but are designed to resist attacks by future quantum computers.
How it differs from QKD
QKD relies on physics and special optical hardware. PQC relies on mathematical problems that are believed to be hard even for quantum computers, and can be deployed as software on existing networks. The two are complementary.
In the news
BISAG-N's platform 'Vedic Kavach' provides PQC. In the Gandhinagar trial it was integrated with QNu Labs' QKD device 'Armos', so that messages were protected by both a physics-based key and quantum-resistant algorithms.
Where to go next
National Quantum Mission
India's funded plan for quantum computing, communication and sensing.
In one line: The National Quantum Mission (NQM), approved by the Union Cabinet on 19 April 2023, is India's programme to build quantum technologies, with ₹6,003.65 crore for 2023-24 to 2030-31.
Targets
- Intermediate-scale quantum computers with 50 to 1,000 physical qubits in eight years.
- Satellite-based secure quantum communication over 2,000 km between ground stations in India.
- Inter-city QKD over 2,000 km and multi-node quantum networks with quantum memories.
- Four thematic hubs: quantum computing; quantum communication; quantum sensing and metrology; quantum materials and devices.
Why it is in the news
Free-space QKD links, like the 5.56 km Gandhinagar test, are building blocks for the satellite communication target.
Where to go next
National Quantum Mission: every story that connects to it (2)
Prelims-style quiz
Consider the following statements about quantum key distribution (QKD):
1. It uses quantum states of light to share encryption keys.
2. An eavesdropping attempt tends to raise the quantum bit error rate.
3. It works only over optical fibre and cannot be used through free space.
How many of the statements given above are correct?- Only one
- Only two
- All three
- None
Show answer
Answer: (b) Only two. 1 and 2 are correct. 3 is wrong: free-space QKD has been demonstrated, including the 5.56 km Gandhinagar link and a DRDO and IIT Delhi link of about 1 km.
Consider the following statements:
Statement-I: Free-space QKD links are seen as a stepping stone to satellite-based quantum communication.
Statement-II: Satellite-based quantum communication must send photons through the atmosphere rather than through optical fibre.
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 and 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
Show answer
Answer: (a) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I. A satellite link has no fibre; photons travel through air and space. Free-space tests on the ground solve the same problems of alignment, noise and atmospheric loss, which is why they lead towards satellite QKD.
Consider the following statements about the National Quantum Mission:
1. It was approved by the Union Cabinet in April 2023.
2. Its outlay is ₹6,003.65 crore.
3. It runs from 2023-24 to 2030-31.
4. It targets satellite-based secure quantum communication over 2,000 km.
How many of the statements given above are correct?- Only one
- Only two
- Only three
- All four
Show answer
Answer: (d) All four. All four are correct: approved on 19 April 2023, outlay ₹6,003.65 crore, period 2023-24 to 2030-31, and a 2,000 km satellite-based quantum communication target between ground stations.
Post-quantum cryptography refers to:
- Encryption keys carried by entangled photons
- Mathematical algorithms run on classical computers that are designed to resist attacks by quantum computers
- Cryptography that becomes possible only after a quantum computer is built
- Hardware that destroys data when tampered with
Show answer
Answer: (b) Mathematical algorithms run on classical computers that are designed to resist attacks by quantum computers. Post-quantum cryptography is software-based: new algorithms on ordinary computers that are believed to withstand quantum attacks. QKD, by contrast, uses quantum physics to share keys.
Consider the following statements:
1. The Gandhinagar QKD field trial was conducted during daytime to test performance in sunlight.
2. QNu Labs, BISAG-N and IIT Gandhinagar carried out the trial.
Which of the statements given above is/are correct?- 1 only
- 2 only
- Both 1 and 2
- Neither 1 nor 2
Show answer
Answer: (b) 2 only. 1 is wrong: the trial was on the night of 27 to 28 September 2026. 2 is correct.