Dr. Kalpana Bora
(Professor, Physics Department, Gauhati University)
After PM Modi congratulated Indian Armed Forces for their stellar showcase of military victory of Bharat in Operation Sindoor in early May 2025, Defence Minister Rajnath Singh now congratulates scientists from DRDO (Defence Research Development Organisation) and IIT-Delhi in June 2025 for the successful demonstration of quantum communication, a landmark achievement. Bharat has thus entered a new quantum era of secured communication, which will be a ‘game-changer’ in future warfare, as stated by the defence minister. This research was carried out under the project “Design and development of photonic technologies for free space QKD” of the Directorate of Futuristic Technology Management (DFTM), DRDO. Here, QKD stands for Quantum Key Distribution. This successful experiment has made prospects of quantum communication practically viable.
Developed through DRDO-industry-Academia – Centre of Excellence (DIA-CoEs), achieved via a free-space optical link established on the IIT-Delhi campus, Quantum Entanglement (QE)-based Quantum Secure Communication has been demonstrated over a distance of 1 kilometre range, which heralds a breakthrough in quantum cybersecurity and secure communications. This experimental advancement has paved the way for real-time applications in quantum cybersecurity, long-distance QKD, the development of quantum networks and the future quantum internet.
In QKD, encryption (the process of converting information or data into a code) keys between two parties are securely shared using principles of quantum mechanics. This shared key is known only to the sender and receiver to decode the messages, ensuring data security. It differs from classical cryptography (secure communication), where security relies on computational complexity, making it vulnerable to future advancements in computing power.
A Bit of Quantum Physics
Quantum physics is one of the most remarkable developments of the 20th century, which holds true for subatomic particles like electrons, photons (particles or quanta of light), etc. Since they are very tiny, it was observed that they cease to obey Newtonian laws of classical physics. Everyday objects like cars, human beings, etc., obey laws of classical mechanics. In quantum mechanics, all physical variables like velocity, position, and momentum become uncertain, and the trajectories of subatomic particles like electrons are fuzzy paths, not well-defined sharp trajectories. There are uncertainties in all physical quantities. A particle can behave as a wave as well as a particle, but it will behave as any one at a given time. If it is behaving as a particle, at that moment it cannot manifest itself as a wave, and vice versa. In an experiment, when we try to measure the wave nature of a particle, this process collapses its wave function; it loses its wave nature and behaves as a particle. This is called wave-particle duality. Thus, measurement disturbs the system. The wave function of a quantum particle represents the probability density to find a particle in space, and the total probability to find a given particle in space should be one. Heisenberg’s uncertainty principle puts an upper limit on the value of the product of uncertainties in the position and momentum of the particle. This principle is closely related to wave-particle duality. It states that there is a fundamental limit to how precisely certain pairs of physical properties of a particle, like position and momentum, can be known simultaneously. Measuring one with high accuracy inevitably reduces the accuracy with which the other can be known.
Quantum particles manifest themselves as a wave packet – when the particles become very tiny, their presence can be felt in a broad region, not only at a certain point in space. A quantum particle thus appears as a fuzzy cloud. Western scientists like Heisenberg, Bohr, and Schrödinger contributed immensely to the development of modern physics; however, interestingly, many of them were deeply inspired by Bharatiya philosophy and the knowledge treasure of ancient Bharatiya scriptures.
Quantum Entanglement
Quantum Entanglement (QE) is a fascinating phenomenon where two tiny (quantum) particles, like photons, become linked in such a way that whatever happens to one instantly affects the other, even if they are very far apart. They share the same combined quantum state, and measurement of one particle instantly influences the state of the other. This can be thought of like a pair of magical twins — no matter how far apart they are, if one twin sneezes, the other twin instantly knows it! Using QE, a secret communication key can be created that is truly secure. And how does it work? First, a pair of entangled photons is created. Thereafter, one photon is sent to the sender, and the other to the receiver, through open air (free space). Both parties measure the states of their photons. As the photons are entangled, their results are always linked. Unlike sending a physical object, you are sending the state or condition of a particle. If they are measured to be the same, it means the message has not been hacked or tampered with.
Quantum Physics in Upanishads
Bharat has a rich legacy of science and knowledge systems dating back several thousands of years, much earlier than the Ramayana (which happened at least 7000 years ago, in an astronomical context) and the Mahabharata (which happened at least 3500 years ago, in an archaeological context). This treasure of knowledge is proudly and gracefully contained in our ancient scriptures like the Vedas, Upanishads, Puranas, Ramayana, Bhagavad Gita, etc. The Upanishads are a collection of Sanskrit texts transmitted orally from guru to shishya over several thousand years and are concerned with the nature of reality, mind and the self. Schrödinger was first exposed to Indian philosophy around 1918 AD through the writings of the German philosopher Arthur Schopenhauer (an ardent student of the Upanishads).
According to the Upanishads, Brahman alone exists. Everything we see around us is Maya, a distortion of the Brahman caused by our ignorance and imperfect senses. On this, Schrödinger wrote,
“… there is only one thing, and what seems to be a plurality is merely a series of different aspects of this one thing, produced by a deception (the Indian Maya)”
Quantum physics insists that reality exists as waves, and wave-particle duality arises due to our observation. Since we cannot perceive the true wave nature of reality, our observation reduces it to the incomplete reality we see. This reduction is what we know as the collapse of the wave function, and the emergence of Maya thus maps to this collapse. Niels Bohr had famously said, “I go to the Upanishad to toask questions.” In The Tao of Physics (1975), Fritjof Capra wrote of the time Heisenberg met Gurudev Rabindranath Tagore and that “introduction to Indian thought brought Heisenberg great comfort.”
Quantum communication
and its advantage
Quantum communication involves sending information using quantum entanglement, where information is encoded in qubits. Qubits are superpositions of quantum states of photons. Quantum key distribution is used to produce and distribute a key only, not to transmit any message data.
The technology of QE-based QKD offers several significant advantages over traditional methods, as it enhances both security and functionality. The use of QE ensures security of key distribution even if the devices are compromised or imperfect. Though someone may have advanced hacking tools, they can’t secretly intercept the message without being detected because the moment a hacker tries to intercept or measure the photons, the link is disturbed. The sender and receiver will notice this right away and know that the communication isn’t secure. Thus, quantum communication provides fundamentally unbreakable encryption. Moreover, there is no need to lay optical fibres in free-space QKD, and this is a technical edge over the traditional optical fibre method, which is both disruptive and expensive, particularly in dense urban areas and challenging terrains. In traditional secure messaging, secret codes or keys are used, which can sometimes be stolen or cracked.
Strategic boon
Quantum communication has applications in securing data in strategic sectors such as defence and finance and telecommunications, protecting national security-related communications – i.e., in defence as well as civilian applications. These initiatives will provide cutting-edge defence technologies that promise to put aspiring Bharat at the forefront of the global platform. Scientists are using this to create the most secure communication ever – like spy-level secret messages!
Global context
This achievement has strengthened India’s position globally, placing her among the elite group of nations at the forefront of revolutionary quantum technologies. The United States, China, and European nations are investing heavily in quantum research for both civilian and military applications. China has previously demonstrated satellite-based quantum communication over much longer distances, while the US and EU have established quantum network initiatives connecting research institutions. This experimental success of Bharat represents a complementary approach that could prove crucial for national security applications, particularly in border regions where traditional communication infrastructure may be vulnerable.
It will also provide gratifying, excellent, promising career opportunities for our students and youth, who can join DRDO and contribute their bit in nation building by becoming part of cutting-edge research teams.