What is 'Quantum Entanglement'?

In 2022, Alain Aspect, John F. Clauser, and Anton Zeilinger got a Noble prize in physics for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science, in short, quantum entanglement. But what is this 'Quantum Entanglement'?

'Quantum Entanglement' is a fascinating and mysterious phenomenon in quantum mechanics that occurs when two particles become connected in such a way that the state of one particle is dependent on the state of the other, regardless of the distance between them. What does this mean? It means a group of particles that are linked with one another and the quantum state of each particle of the group can't be described independently. Their state depends on the state of other particles that are connected with that particle. This connection doesn't depend on the distance between them.

The idea of quantum entanglement was first proposed by Albert Einstein, Boris Podolsky, and Nathan Rosen in 1935. However, even Einstein couldn't believe in the theory of quantum entanglement because it violates his 'Theory of General Relativity'. According to the general relativity theory, the speed of light is the highest speed in our universe. But the information between two entangled particles transfers without any time delay, which means this information travels through the universe faster than light and it doesn't follow the relativity theory. However, the theory of quantum entanglement was later proven through experiments in the 1960s by physicist John Bell.

But how does this quantum entanglement work? When two particles become entangled, they form a single quantum system, and their properties, such as spin or polarization, become correlated. This means that if one particle is measured to have a certain spin or polarization, the other particle will also have the same spin or polarization, even if it is located on the other side of the universe.

This correlation occurs instantaneously, meaning that the state of one particle is affected as soon as the state of the other particle is measured, regardless of the distance between them. This is known as "Spooky Action at a Distance," and it is a fundamental principle of quantum mechanics.

But what is the importance of this theory? Is it just a theory to reveal the hidden truths of the universe or will it help us to make ourselves more developed and civilized? Well, it is a much-needed theory for many inventions.

Quantum entanglement has important implications for the field of quantum computing, as entangled particles can be used to create quantum bits, or qubits, which can exist in multiple states at the same time. This allows for much more powerful and efficient computing than traditional binary bits. I will discuss 'Quantum Computer' in some other blog.

Entanglement also plays a key role in quantum cryptography and quantum teleportation. In quantum cryptography, entangled particles can be used to create a secure communication channel that cannot be intercepted or hacked. In quantum teleportation, the state of one particle can be transferred to another particle instantaneously, whatever may the distance between them.

Despite its importance, quantum entanglement is still not well understood. Quantum entanglement is a mysterious and wonderful phenomenon in quantum mechanics. But the phenomenon seems to violate the principles of classical physics and it is still a subject of ongoing research.

Written by: Tasnim Ferdous