Definition of Quantum Entanglement
Quantum entanglement is a fundamental phenomenon in quantum mechanics where two or more particles become interconnected such that the quantum state of each particle cannot be described independently of the others, even if they are separated by vast distances. This correlation arises from their shared quantum state, and measuring the property of one particle instantaneously determines the corresponding property of the other, defying classical intuitions of locality.
Key Principles of Quantum Entanglement
Entanglement stems from the principles of quantum superposition and the collapse of the wave function. Particles in an entangled system exist in a superposition of states until measured, at which point the wave function collapses, fixing the states of all entangled particles simultaneously. This process, first highlighted in the Einstein-Podolsky-Rosen (EPR) paradox, demonstrates non-locality without violating the speed of light, as no information is transferred faster than light.
A Practical Example of Entanglement
Consider two entangled electrons created in a process that pairs their spins oppositely. If one electron is measured and found to have an upward spin, the other, even if located light-years away, will instantly have a downward spin. This was experimentally verified through Bell's inequality tests, which rule out local hidden variables and confirm quantum predictions, as demonstrated in experiments by Alain Aspect in the 1980s.
Importance and Applications in Physics
Quantum entanglement is crucial because it underpins the non-local nature of quantum reality, challenging classical physics and enabling advancements in quantum information science. It is essential for quantum computing, where entangled qubits allow parallel processing for complex calculations; quantum cryptography, providing secure key distribution via protocols like BB84; and quantum teleportation, which transfers quantum states without physical movement of particles, paving the way for future technologies in secure communication and simulation of quantum systems.