Quantum Communication

GS3 – Science & Technology

Context:

In a significant advancement, IIT-Delhi and DRDO jointly demonstrated Quantum Key Distribution (QKD) in free-space communication across a distance exceeding 1 km. The system achieved a secure key rate of 240 bits per second with a Quantum Bit Error Rate (QBER) of less than 7%.

• Secure Key Rate: Number of secure bits generated per second.
• QBER: Indicates errors in the measurement of photon states, expressed as a percentage.

Global Benchmark:

In 2021, China established the world’s first large-scale quantum communication network, a 4,600 km space-to-ground link, using the Micius satellite.

Understanding Quantum Communication:

Quantum communication leverages quantum physics principles—notably entanglement and superposition—to ensure extremely secure data transmission.

• Photon-Based Encoding: Information is encoded in the quantum states of photons, unlike binary bits in classical communication.
• Entanglement-Driven Security: Utilizes pairs of entangled photons whose states are interlinked, ensuring secure, real-time coordination between parties.
• Quantum Key Distribution (QKD): A core technique to generate tamper-proof encryption keys.
• Superposition Principle: Allows photons to exist in multiple states until measured, adding complexity to interception.

Core Concepts in Quantum Mechanics:

• Quantum Entanglement:
  When two photons are entangled, measuring one instantly determines the state of the other, regardless of distance. This phenomenon violates classical physics norms (non-locality).
  • Created by: Parametric down-conversion, using crystals to produce entangled pairs.
  • Property Shared: Usually polarisation.
• Quantum Superposition:
  A quantum particle can exist in more than one state simultaneously until an observation collapses it into one.

Quantum Key Distribution (QKD):

A specialized method to exchange secure encryption keys, QKD doesn’t encrypt data directly but protects the key exchange, enabling secure systems like AES.

• Mechanism: Qubits (quantum bits) are transmitted via photons, encoding information in their quantum states such as polarisation.
• Encryption Standard Used: Advanced Encryption Standard (AES), a symmetric cryptographic method used in secure platforms like UPI.

Types of QKD:

Feature	Prepare-and-Measure QKD	Entanglement-Based QKD
Photon Source	Sender sends individually prepared photons	Uses entangled photon pairs
Security Basis	Trust-based on device reliability	Device-independent, stronger security
Complexity	Simpler, easier to implement	More complex due to entanglement
Error Resistance	More prone to device-related errors	Better resistance to side-channel attacks
Scalability	Compatible with current systems	Limited scalability due to entanglement

Applications of Quantum Communication:

• Military: Ensures secure transmission for precision strikes, UAVs, and surveillance systems.
• Banking & Digital Payments: Safeguards platforms like UPI against cyber theft.
• Healthcare: Secures digital health records and telemedicine data.
• Smart Infrastructure: Protects data in smart grids and urban IoT systems.
• E-Governance: Shields citizen data in platforms like Digital India.

Advantages:

• Unhackable Systems: Instantly detects interception attempts.
• Satellite-Enabled Security: Supports global, space-based secure communication.
• Future-Proof: Immune to hacking by future quantum computers.
• Integrity Protection: Ensures that transmitted data remains intact.
• Supports Quantum Internet: Paves the way for next-generation secure networks.

Challenges:

• Range Constraints: Photon loss reduces effective communication distance.
• Cost Barriers: High cost of quantum detectors and infrastructure.
• Infrastructure Compatibility: Not compatible with conventional telecom networks.
• Lack of Global Standards: Absence of uniform international protocols—e.g., India vs China systems.
• Error Management: High Quantum Bit Error Rate can degrade security and efficiency.