The free-space quantum secure communication was demonstrated over a distance of ~1 km via a free-space optical link.
- ISRO demonstrated 1st free-space QKD over 300m in 2021.
 
About the experiment
- It was part of the ‘Design and development of photonic technologies for free space Quantum Key Distribution (QKD)’ of DRDO.
 - The experiment exhibited a very low quantum bit error rate (QBER) of less than 7%.
- QBER is the error between the information sent and received and an indicator of the probability of eavesdropping.
 
 - It paves the way for real-time applications in quantum cybersecurity, long-distance QKD, and the future quantum internet.
 
What is QKD?
- Communication Technology: It is a Quantum Communication technology based on quantum mechanics, that is, quantum entanglement and cryptography.
- Quantum mechanics explains how extremely small objects simultaneously have the characteristics of both particles and waves (a disturbance or variation that transfers energy). 
- Physicists call this the “Wave-Particle Duality.”
 
 
 - Quantum mechanics explains how extremely small objects simultaneously have the characteristics of both particles and waves (a disturbance or variation that transfers energy). 
 - Key Principles: 
- Quantum entanglement: Particles of the same origin, which were once connected, always stay connected, even when separated by vast distances.
 - Quantum cryptography: encryption to secure and transmit data in a way that cannot be hacked.
 
 
Benefits of Entanglement-Based QKD
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