India has successfully demonstrated a free-space quantum secure communication using quantum entanglement over 1 km recently via an optical link.

About the Experiment

• The experiment was conducted through the DRDO-Industry-Academia Centre of Excellence (DIA-CoE), IIT Delhi. 
• Project: The experiment was conducted under the project ‘Design and development of photonic technologies for free space QKD’, sanctioned by Directorate of Futuristic Technology Management (DFTM), DRDO.
• The Experiment: 
  • A free-space quantum secure communication was established using quantum entanglement via a free-space optical link at the IIT Delhi campus for more than 1 km distance.
  • The experiment attained a secure key rate of nearly 240 bits per second with a quantum bit error rate (QBER) of less than 7%.
    • QBER is a metric which represents the percentage of bits that are incorrectly received due to noise or potential eavesdropping.
• Applications:
  • Cybersecurity: The entanglement-assisted quantum secure communication will assist real-time applications in quantum cyber security including long-distance Quantum Key Distribution (QKD)
  • The experiment will also assist in the development of quantum networks, and the future quantum internet.
  • National Security: Using Quantum Key Distribution in various real-world scenarios, includes secure communication channels for sensitive information in finance, government, and military sectors.

About Quantum Key Distribution (QKD)

• QKD It is a secure communication method based on quantum physics for exchanging encryption keys only known between shared parties and to prevent leakage and eavesdropping.
  • QKD works by transmitting many light particles (photons) over fiber optic cables or in a free state between parties.
  • Qubits: Each photon has a random quantum state, and collectively, the photons sent make up a stream of ones and zeros. This stream of ones and zeros are called qubits
• Quantum Physics: The Quantum Key Distribution (QKD) technology is a part of the Quantum Communication technology ensuring unconditional data security and is based on the principles of quantum mechanics.
• Origin: The concept of Quantum Key Distribution (QKD) originated from the concept of quantum cryptography, first proposed by Stephen Wiesner in the early 1970s with his “quantum conjugate coding” idea. 
  • This concept was later built upon by Artur Ekert in 1991, by linking it with the use of quantum entanglement.
• Types: 
  • Prepare-and-Measure Protocols: These protocols involve one party preparing quantum states and sending them to the other party for measurement and are designed to detect eavesdropping attempts during the transmission of quantum states. 
    • Examples: The BB84 protocol, where photons are encoded with polarization states, and the sifting process is used to establish a shared key. 
  • Entanglement-Based Protocols: Here two parties share entangled quantum states where measurement of one part of the entangled state instantaneously affects the other part, allowing for key generation. 
    • These protocols can also detect eavesdropping if an attacker attempts to interfere with the entangled particles.
• Significance:
  • Security Against Quantum Computers: Future evolution of quantum computers pose a threat to the traditional encryption methods. QKD offers a solution by using quantum mechanics, making it secure even against attacks from future quantum computers.
  • Detecting Eavesdropping: Any attempt to intercept the quantum signals will be detected, alerting the communicating parties to the potential eavesdropping. 
  • Unconditional Security: QKD offers a level of security that is not based on computational assumptions but rather on the fundamental laws of physics, making it more robust and reliable. 
  • Future Proof Secure Communication: As quantum computing becomes more advanced, the need for quantum-safe encryption methods like QKD will become increasingly vital since no future advancements in computational power can break the quantum-cryptosystem.
  • Interoperability: QKD solutions can be integrated with existing encryption systems, providing a seamless upgrade path to quantum-safe security.
• Limitations of QKD: 
• • QKD does not provide a means to authenticate the QKD transmission source.
  • Distance Limits: QKD systems like the single-photon detection, suffer from significant signal attenuation over longer distances, limiting their practical range.
  • Cost Intensive: QKD requires specialized equipment as it is hardware-based like  single-photon detectors and potentially repeaters, which can significantly increase the cost of deployment compared to classical cryptography.
    • Also QKD networks can’t be upgraded or patched easily.
  • Infrastructure: QKD often requires dedicated fiber optic cables, which can be costly and difficult to integrate with existing communication networks.
  • Security Vulnerabilities: QKD is perfectly secure in theory, but in practice, imperfections in tools such as single photon detectors create security vulnerabilities.
  • A Denial-of-Service Attack: Since eavesdroppers can cause a transmission to stop, they can deny the use of a transmission by its intended users.

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