Entanglement is a fundamental concept in quantum mechanics that describes a strong correlation between quantum particles, such as electrons, photons, or atoms. When particles become entangled, their states become interdependent, regardless of the distance between them. This correlation persists even if the particles are spatially separated.
The key feature of entanglement is that the quantum states of the entangled particles are described by a joint wavefunction, rather than individual wavefunctions for each particle. This joint wavefunction cannot be factorized into separate wavefunctions for the individual particles, meaning that the states of the entangled particles are intertwined and cannot be described independently.
Regarding the transmission of quantum information over long distances using entanglement, it is important to note that entanglement itself does not transmit information instantaneously. Instead, it enables the possibility of transmitting information in a way that exhibits non-local correlations.
One method that exploits entanglement for long-distance quantum communication is known as quantum teleportation. In quantum teleportation, the quantum state of a particle (referred to as the "quantum information" to be transmitted) is transferred from one location to another by utilizing the entanglement between two distant particles.
The basic process of quantum teleportation involves the following steps:
Generation of Entanglement: A pair of particles, often referred to as an entangled pair, is created and shared between the sender and the receiver.
Bell Measurement: The sender performs a joint measurement, known as a Bell measurement, on the particle to be teleported and one of the entangled particles. This measurement extracts correlations between the two particles.
Classical Communication: The sender communicates the measurement outcomes to the receiver using classical communication channels. This information is essential for the receiver to reconstruct the original quantum state.
State Reconstruction: The receiver utilizes the measurement results and performs appropriate operations on the remaining entangled particle to reconstruct the teleported quantum state.
Through this process, the quantum information carried by the initial particle is effectively transferred to the distant particle at the receiver's location, using the entanglement as a resource. However, it is important to note that the actual transmission of classical information (i.e., the measurement results) is limited by the speed of light, so no instantaneous communication of information is achieved.
Entanglement and quantum teleportation offer intriguing possibilities for secure communication and quantum information processing, but they do not violate the principle of causality or allow for faster-than-light communication.