Everything You Need To Know About Quantum Satellites And Will ISRO Ever Launch One

Quantum communication is set to provide next-gen unhackable type of communication. China, in 2016, with its satellite Micius acquired the first ever quantum communication satellite, testing quantum communications technology which is likely to become the cornerstone of unhackable communications systems of the future. India has also put a step forward in launching a quantum communication satellite, and join a clutch of countries with this capability. Raman Research Institute (RRI) has joined hands with ISRO to establish a quantum network to help with ISRO’s vision of developing a quantum communication network for its satellite. Only few nations worldwide have contributed to quantum network.

What Is Quantum Satellite?

Entanglement: The basic idea is to create a long-distance communication quantum channel between space and earth. The process is based on the idea of entanglement in quantum mechanics. In such a phenomenon, two or more particles interact with each other in such a way that their individual quantum states cannot be described, but instead, a quantum state of the whole system is described. This feature of QM is a bizarre offshoot of quantum mechanics, which is one of the many intriguing facts of QM, and Einstein had described it as ‘spooky action at a distance’. Although these entangled particles are not physically connected, they still are able to share information with each other instantaneously, breaking one of the most fundamental rules of classical physics which says no information can travel faster than light.

Image source: Sciencemag

Working Principle: The basic working principle revolves around a crystal that generates pairs of entangled photons whose properties remain coupled to one another however far apart they are. A high-fidelity optical communications system is then responsible for delivering the partners of the entangled pairs to optical ground stations at different locations, where their polarization properties will be used to generate a secret encryption key.

Technology Behind: In order to establish a quantum communication, quantum entanglement has to be established, and for that, long strings of entangled photons, shared between distant locations, acting as quantum keys, are sent. But these entangled photons degrade rapidly if they are passed through the modes of our normal communication today like optical fibres, or even air. A device called quantum repeater is used where they extend the range of such communication between a sender and a receiver. What is required is satellite distributing quantum signals that obtain a secure quantum network for communication.

Schematic block diagram of a quantum repeater. Image source: Australian Research Council Centre of Excellence

The satellite has a light alternating crystal on the satellite. A laser beam on sending into this crystal from earth, emits pairs of photons entangled, so that their polarisation states will be opposite when measured. These pairs of photons split and sent to two different receiving stations on earth. For this to happen, the beams of photons had to be focused on the ground stations as the satellite moves through space and that is a big challenge.

The Chinese team measured more than 1000 photon pairs and the photons had opposite polarisations, thereby confirming the spooky action over a distance, making Micius the first mission to put to the test whether entanglement can indeed exist between particles separated by very large distances as the laws of quantum mechanics propose.

India’s Contributions To Quantum Satellite

Only few nations across the world have contributed to quantum network and RRI and ISRO collaboration to establish a quantum network makes India one of these few countries, under a project called Quantum Experiments Using Satellite Technology (QUEST). According to the memorandum of understanding signed recently between RRI and ISRO Space Applications Centre (ISAC), the latter will fund the Quantum Information and Computing (QuiC) laboratory at RRI for developing the quantum technology tools. It was during a five-day conference on Quantum Frontiers and Fundamentals at RRI, that schemes for making India a major contributor in quantum technologies was deliberated.

“This is India’s first step towards quantum communications between ground and satellites,” Urbasi Sinha, who heads the QuiC laboratory and has been pioneering fundamental quantum experiments “using single and entangled photons”, had said. Although Sinha’s lab at RRI has been engaged since 2013 in “manufacture, manipulation and application of single and entangled photons,” experimental validation of the tools it had developed for quantum communications had to wait for payload space in an ISRO satellite.

“ISRO’s move to join the race is welcome indeed,” Arun Kumar Pati, who heads the quantum information and communication group at The Harish-Chandra Research Institute, said. “But this has to be some kind of mega-project involving scientists with theoretical, experimental and computational background as well as engineers.”

Already many proposals have been received from researchers from different parts of the country. ISRO is geared to launch the payload on board one of their satellite missions, once RRI is ready with it.


Since the technology is going to provide an extreme level of security in communications, it can very well be used for security purposes and in the defence. National security and intelligence agencies can make the best use of it. Governments worldwide face a problem of attacks on protected information on several occasions.

Apart from secure communication, which is the major purpose of these communication satellites, it will also serve its use in the field of medicine, clock synchronization, extending the baseline of telescopes, secure identification, achieving efficient agreement on distributed data, exponential savings in communication, quantum sensor networks.

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