India has demonstrated a 5.56-kilometre quantum key distribution link through open air, establishing a new domestic benchmark for secure optical communications and advancing preparations for satellite-based quantum networks.
The successful field trial, conducted by QNu Labs, the Bhaskaracharya National Institute for Space Applications and Geo-informatics (BISAG-N) and IIT Gandhinagar, established a quantum communication channel between two facilities in Gandhinagar, Gujarat.
The Ministry of Electronics and Information Technology announced the achievement on October 3, confirming that the experiment took place overnight on September 27–28. The system generated secure cryptographic keys at 230–260 bits per second while maintaining a quantum bit error rate below five per cent.
The participating institutions also demonstrated successful encryption and decryption of test messages using the generated keys, establishing that the experimental quantum channel could operate alongside conventional communications infrastructure.
The achievement represents India’s first publicly announced free-space quantum key distribution demonstration at this distance. Unlike fibre-based systems, the technology transmits quantum signals through the atmosphere, allowing secure key exchange without a continuous physical cable between communicating locations.
QNu Labs deployed its Armos quantum key distribution equipment alongside a pointing, acquisition and tracking system designed to maintain optical alignment between transmitting and receiving terminals.
The experiment used a 1,550-nanometre optical channel and a differential phase shift decoy protocol. Precise alignment was essential because atmospheric disturbances and small movements can disrupt the transmission of weak quantum signals across extended distances.
The reported error rate provided an important indication of transmission quality, while the secure key generation rate demonstrated the system’s ability to produce cryptographic material for practical encryption applications.
The generated keys were integrated into BISAG-N’s Vedic Kavach platform, which incorporates post-quantum cryptography and quantum random number generation. This arrangement combined hardware-based quantum key distribution with software-based cryptographic protection.
Researchers demonstrated the transmission of 256-bit encryption keys through an interface conforming to the ETSI GS QKD 014 specification, enabling a test message to be encrypted, transmitted and decrypted successfully.
The hybrid architecture is intended to maintain cryptographic protection when the quantum channel becomes temporarily unavailable. Post-quantum cryptography uses mathematical algorithms designed to resist attacks from sufficiently powerful quantum computers, while quantum key distribution relies on the properties of quantum states to reveal potential interception.
The two approaches address different security requirements and can operate together, although neither eliminates every vulnerability associated with communication networks, including compromised devices or implementation weaknesses.
Sunil Gupta, co-founder and chief executive of QNu Labs, said quantum security would become meaningful at scale only when technologies moved beyond controlled laboratories and operated across actual communications infrastructure.
He said the field trial demonstrated that quantum key distribution, supported by precise optical tracking, could function across a multi-kilometre atmospheric link while integrating with a post-quantum security layer.
Vinay Thakur, director-general of BISAG-N, highlighted the integration of Vedic Kavach with quantum key distribution as evidence that complementary security technologies could address evolving protection requirements.
The demonstration also has implications for India’s proposed satellite quantum communication capabilities. Satellite-to-ground systems require quantum signals to pass through atmospheric conditions, making terrestrial free-space experiments useful for evaluating optical transmission and tracking technologies.
However, the Gandhinagar experiment did not establish a satellite connection or demonstrate operational performance across orbital distances. Such applications require additional testing involving moving platforms, longer optical paths and changing atmospheric conditions.
The achievement contributes to technical work associated with India’s National Quantum Mission, which includes developing secure quantum communications and supporting technologies for terrestrial and space applications.
Manish Tripathi, who oversees the Interdisciplinary School of Technology and Future at IIT Gandhinagar, described the experiment as a valuable field environment bringing together academic research, domestic technology development and practical testing.
The participating organisations have not announced a timetable for commercial deployment or a subsequent satellite demonstration based on the trial.
The reported performance figures describe the conditions achieved during the September experiment rather than guaranteed operating rates under different weather conditions or across other locations.
BISAG-N contributed its Vedic Kavach encryption environment, IIT Gandhinagar provided the academic testing setting, and QNu Labs supplied the quantum distribution equipment and optical tracking technology used in the demonstration.
