India Demonstrates First 5.56 km Free-Space Quantum Key Link

The correct answer is 5.56 km. That is the span over which the country's first free-space Quantum Key Distribution link was established, between the BISAG-N campus and IIT Gandhinagar, in a field trial run on the night of 27 and 28 September. Options A, C and D are wrong because each names a distance other than the one achieved, and in a question of this type the figure itself is the whole answer. The distance matters for a reason worth understanding rather than merely memorising: sending single photons through open air means fighting turbulence, scattering and the problem of keeping a narrow beam locked on a receiver kilometres away, which is why a Pointing, Acquisition and Tracking system was needed. The team described the result as a step towards longer-distance quantum-secure networks and towards quantum communication by satellite, so later figures may well be larger.

The correct answer is QNu Labs, BISAG-N and IIT Gandhinagar. QNu Labs supplied the hardware QKD device Armos, BISAG-N contributed the post-quantum cryptography platform Vedic Kavach along with one end of the link, and IIT Gandhinagar hosted the other end and provided the field setting. Option A is wrong because neither the space agency nor the defence research organisation is named in this demonstration, although both work on allied technologies. Option C is wrong because the telecom research centre, the public sector electronics firm and the Bengaluru institute named there had no part in this particular trial. Option D is wrong on the same ground. The partnership is worth remembering as a shape as much as a list: a private quantum technology firm, an autonomous scientific society under the Ministry of Electronics and Information Technology, and an IIT supplying the academic and field component.

The correct answer is 230 to 260 bits per second, with the Quantum Bit Error Rate held below 5%. Both numbers describe the quality of the link: the key rate is how fast fresh secret material can be produced for encryption, and the error rate measures how often a photon is read wrongly, which in quantum key distribution also signals whether anyone has interfered with the channel. Options B, C and D each pair figures that were not those recorded, and a candidate who remembers only one of the two values can still be caught by a mismatched pair, so the two should be learnt together. The keys produced at this rate were handed to the Vedic Kavach platform, where post-quantum cryptography completed the encryption and decryption of test messages from end to end.

The correct answer is Vedic Kavach, the post-quantum cryptography platform built by BISAG-N. The keys produced by the quantum link were integrated with it, and test messages were then encrypted and decrypted from end to end. Option A is a trap worth noticing: Armos is also part of this story, but it is QNu Labs' hardware QKD device that generates the keys over the free-space optical channel, not the software platform that consumes them. Keeping the two names apart is the main thing this question tests. Option C is wrong because no platform of that name features in the demonstration. Option D is wrong as well and is simply a plausible sounding invention. Remember the division of labour: Armos is hardware and makes the keys, Vedic Kavach is software, adds post-quantum cryptography and quantum random number generation, and uses them.