Entanglement typically arises as a result of interaction between particles or systems. However, there are scenarios where entanglement can occur without direct interaction. One such example is through a process known as quantum measurement or quantum correlation.
Consider a pair of particles that were previously entangled through an interaction but have since been separated. If one of the particles is measured, its quantum state collapses into a particular value for the measured property. Due to the entanglement, this measurement instantaneously affects the state of the other particle, regardless of the spatial separation between them.
This phenomenon, known as quantum non-locality or Einstein-Podolsky-Rosen (EPR) steering, demonstrates entanglement without the need for ongoing interaction. It showcases how the measurement of one particle can instantaneously determine the state of the other, even if they are widely separated in space.
It's important to note that although the particles may appear to be non-locally connected, information cannot be transmitted faster than the speed of light using entanglement alone. The entanglement does not allow for direct communication but rather establishes a correlation between the measured properties of the entangled particles.
This type of entanglement without ongoing interaction has been experimentally verified and plays a crucial role in various applications, including quantum cryptography and quantum teleportation.