Introduction
Quantum Entanglement is a fundamental phenomenon of quantum mechanics in which two or more particles become so closely correlated that the quantum state of one particle is intrinsically linked to the state of the other(s), regardless of the distance separating them.
When entangled particles are measured, the outcome of one particle is correlated with the outcome of the other. This phenomenon, which has no equivalent in classical physics, is one of the foundational principles of quantum computing, quantum communication, and quantum cryptography.
How Quantum Entanglement Works
When two particles (such as photons or electrons) interact under suitable conditions, they can become entangled, meaning they share a single quantum state.
- The properties of the particles become correlated.
- Measuring one particle immediately determines the corresponding state of the other, even if they are separated by large distances.
- The measurement outcomes are correlated in a way that cannot be explained by classical physics.
Important: Entanglement does not allow information to travel faster than the speed of light. Although the correlations appear instantaneous, they cannot be used for faster-than-light communication, and therefore do not violate Einstein’s theory of relativity.
Key Characteristics
Strong Quantum Correlation
Entangled particles exhibit correlations that are stronger than those predicted by classical physics.
Non-Classical Behaviour
The properties of entangled particles cannot be described independently; the quantum system must be treated as a whole.
Fragility
Entanglement is highly sensitive to interactions with the environment. External disturbances can destroy the entangled state, a process known as decoherence.
Einstein’s View
Albert Einstein, along with Boris Podolsky and Nathan Rosen, questioned the completeness of quantum mechanics in the famous EPR (Einstein–Podolsky–Rosen) Paradox (1935).
Einstein referred to entanglement as “spooky action at a distance”, expressing skepticism about the seemingly instantaneous correlations.
Later experiments, particularly those testing Bell’s Theorem, confirmed the predictions of quantum mechanics and demonstrated that entanglement is a real physical phenomenon.
Applications
Quantum Computing
Entanglement enables qubits to work together in ways impossible for classical bits, allowing quantum computers to solve certain complex problems much faster than classical computers.
Quantum Communication
Entangled particles are used to develop highly secure communication systems, including Quantum Key Distribution (QKD), where any attempt to intercept the communication disturbs the quantum state and can be detected.
Quantum Teleportation
Quantum entanglement enables the transfer of the quantum state of a particle from one location to another without physically moving the particle itself. It is important to note that this is the transfer of quantum information, not the teleportation of matter.
Quantum Networks
Entanglement is a key resource for building future quantum internet infrastructure, enabling secure communication and distributed quantum computing.
Precision Measurement
Entangled states improve the sensitivity of measurements in:
- Atomic clocks.
- Gravitational wave detectors.
- Quantum sensors.
- Navigation systems.
Challenges
- Decoherence: Loss of entanglement due to interaction with the environment.
- Scalability: Maintaining entanglement across many qubits is technically challenging.
- Error Correction: Quantum systems are highly susceptible to noise and errors.
- Transmission Losses: Long-distance quantum communication requires quantum repeaters to preserve entanglement.
Quantum Entanglement in India
Under the National Quantum Mission (NQM), India is promoting research in:
- Quantum communication.
- Quantum computing.
- Quantum cryptography.
- Quantum sensing.
One of the mission’s objectives is to develop secure quantum communication networks based on entanglement and related quantum technologies.
Significance
Quantum entanglement has transformative potential in:
- Secure communications.
- Cybersecurity.
- Quantum computing.
- Defence technologies.
- Financial security.
- Healthcare and scientific research.
- Space-based quantum communication.
It is regarded as one of the most important resources in modern quantum technologies.
Conclusion
Quantum entanglement is one of the most remarkable and experimentally verified phenomena in quantum physics. By creating strong correlations between particles that cannot be explained by classical mechanics, it forms the foundation of quantum computing, quantum communication and the emerging quantum internet. Continued advances in entanglement-based technologies are expected to play a pivotal role in the next generation of computing, secure communications and precision measurement systems.
