IIT-Delhi and the Defence Research and Development Organization (DRDO) successfully demonstrated free-space quantum secure communication using quantum entanglement on the IIT-Delhi campus on June 16, 2025, over a distance of more than one kilometer. This accomplishment shows that atmospheric quantum key distribution is feasible and could potentially allow satellite-based quantum networks throughout India, marking a substantial advancement over conventional fiber-optic quantum communication techniques.
A significant departure from traditional encryption techniques, quantum communication uses the unique characteristics of quantum physics rather than the intricacy of mathematics to provide security. Quantum communication offers theoretically unbreakable security based on the principles of physics itself, as contrast to classical cryptography, which depends on computational difficulties and may be cracked by sufficiently powerful computers. The security comes from quantum entanglement, in which two photon pairs become so coupled that, regardless of their distance from one another, measuring one photon immediately impacts its partner.
The ability of quantum communication to recognize eavesdropping attempts is what makes it revolutionary. The act of measuring itself disrupts the quantum states of the photons when an unauthorized person tries to intercept quantum-encrypted data, instantly warning the parties involved in the communication that an intruder is present. An essentially secure communication channel is produced by this characteristic in conjunction with the quantum no-cloning theorem, which forbids exact replication of unknown quantum states.
The main use of quantum communication technology is Quantum Key Distribution (QKD), which allows two parties to create shared cryptographic keys with assured security. It’s crucial to remember that QKD encrypts the encryption keys, which are subsequently utilized with conventional methods like AES to secure the sent data, rather than the actual message content. This strategy combines the useful effectiveness of traditional encryption techniques with the impenetrable security of quantum mechanics.
Entanglement-based QKD, which has several advantages over conventional prepare-and-measure quantum communication techniques, was used in the IIT-Delhi demonstration. A source generates pairs of entangled photons and distributes them to the communicating parties in entanglement-based systems, guaranteeing that the quantum entanglement itself upholds the security of the key distribution procedure even in the event that the devices are corrupted or flawed. This method preserves security even under less-than-ideal circumstances and offers increased resistance against device-specific assaults.
The system’s practical applicability for real-world applications is demonstrated by the achieved performance metrics. Even if it is slow when compared to traditional communication speeds, the safe key rate of 240 bits per second is a noteworthy accomplishment for free-space quantum communication over kilometers. Excellent system performance is indicated by a quantum bit error rate of less than 7%, which is significantly lower than the theoretical threshold of 11% that delineates the line separating secure and potentially compromised quantum communication channels.
In free-space quantum communication, atmospheric turbulence, detector noise, and artificial lighting interference are common sources of mistake. The resilience of the IIT-Delhi team’s experimental setup and the possibility of expanding the technology to larger distances and more difficult climatic circumstances are demonstrated by their ability to sustain such low error rates in spite of these difficulties.
Over the past few years, a number of more ambitious experiments have shown steady development in the IIT-Delhi quantum communication program. The researchers used commercial-grade underground dark optical fiber to establish India’s first intercity quantum communication link in 2022, spanning over 100 kilometers between Vindhyachal and Prayagraj in Uttar Pradesh. The feasibility of quantum key distribution over the current telecommunications infrastructure was demonstrated in this first demonstration, which established filtered key rates of up to 10 kHz.
The team built on this foundation in 2023 when they demonstrated safe quantum communication over 380 kilometers using normal telecom fiber, setting a world record for the Differential Phase Shift (DPS) Quantum Key Distribution protocol. This was the longest distance ever accomplished internationally. This accomplishment demonstrated the team’s growing proficiency in preserving quantum coherence across long distances while maintaining an exceptionally low quantum bit error rate of 1.48%. The study’s worldwide significance was highlighted by its publication in Nature Scientific Reports.
In 2024, the group improved its methods and got ready for the shift to free-space quantum communication by successfully distributing quantum keys via entanglement across a 100-kilometer spool of telecom-grade optical fiber. Since free-space systems do not require costly optical fiber infrastructure and allow quantum communication to satellites and remote locations, the shift from fiber-based to free-space quantum communication is an important technological achievement.
It is impossible to overestimate the military and strategic ramifications of quantum communication technology, especially in light of the growing prevalence of cyberwarfare and electronic surveillance. The fact that Defense Minister Rajnath Singh called this accomplishment a “game-changer in future warfare” illustrates how revolutionary quantum-secured communications could be for military operations. Current classical encryption techniques are seriously threatened by future quantum computers, while quantum communication offers encryption that is essentially unbreakable and secure.
For military applications, the IIT-Delhi demonstration’s free-space design is especially important since it removes reliance on delicate fiber-optic infrastructure that could be physically damaged or cut off during hostilities. Secure communications in border regions, distant military stations, and mobile platforms where installing optical fiber would be costly, challenging, or strategically unwise are made possible by free-space quantum communication. In contested areas where conventional communication routes may be blocked or corrupted, this feature is essential for preserving command and control communications.
The technology also supports the development of quantum networks with multiple nodes, enabling secure communication across entire military command structures. Such networks could revolutionize military communications by providing guaranteed secure channels for intelligence sharing, operational planning, and real-time battlefield coordination. The ability to detect any eavesdropping attempt instantly provides an additional layer of security assurance that is impossible to achieve with classical communication methods.
The IIT-Delhi quantum communication program’s ultimate objective goes much beyond the current 1-kilometer demonstration to include the distribution of quantum keys via satellite, which might cover the whole Indian subcontinent. Satellite-based quantum communication would use orbiting satellites to broadcast entangled photons through the atmosphere, allowing for the safe dissemination of keys to any site in India. This feature would be especially helpful for protecting communications to mobile platforms, distant areas, and places where terrestrial infrastructure is insecure or nonexistent.
In order to launch specialized quantum communication satellites, India intends to further up its efforts in satellite quantum communication during the course of the next six to twelve months. A constellation of four to seven satellites would probably be needed to maintain continuous coverage due to the difficulties of satellite-based quantum communication, especially with Low Earth Orbit satellites that only offer 15 to 20 minutes of coverage each day. It is anticipated that the Indian Space Research Organization (ISRO) will be instrumental in the creation and implementation of these quantum communication satellites.
India’s larger quantum technology goals, as stated in the National Quantum Mission, are further supported by the advancement of quantum communication technology. These goals include building multi-node quantum networks with quantum memory, establishing satellite-based secure quantum communications beyond 2000 kilometers, and producing intermediate-scale quantum computers with 50–1000 physical qubits. Applications of quantum sensing, such as magnetometers and atomic clocks for accurate timing and navigation, are also included in the mission.
A turning point in India’s scientific progress, the quantum communications discovery from IIT-Delhi shows the nation’s increasing proficiency in one of the most strategically significant new technologies of the twenty-first century. In addition to advancing the field of quantum communication, the successful demonstration of free-space quantum key distribution over a kilometer positions India as a major player in the global race to create useful quantum technology.
Beyond its technical qualities, the accomplishment has strategic, economic, and scientific implications that could change India’s place in the world of technology. India is in a strong position to create satellite-based quantum communication networks that could offer unbreakable security for both military and civilian purposes, thanks to the National Quantum Mission’s ongoing investment and the dedication of organizations like DRDO and IIT-Delhi.
India’s breakthrough in quantum communications lays the groundwork for future advancements that could have significant effects on cybersecurity, national defense, and economic growth as the world approaches a time when quantum technologies will determine national competitiveness and security. The development from lab tests to real-world examples indicates that quantum-secured communications might materialize sooner than most people thought, which could revolutionize the way private data is safeguarded and shared in the digital era.
