Quantum entanglement experiments can be performed with both individual particles and ensembles of indistinguishable particles, depending on the specific experimental setup and goals.
Individual Particles: In some experiments, researchers work with individual particles to study their entangled states and properties. For example, entangled photons can be generated using certain types of crystals or nonlinear optical processes. These individual entangled particles can be manipulated, measured, and used to demonstrate various quantum phenomena, such as quantum teleportation or quantum key distribution.
Ensembles of Indistinguishable Particles: Many experiments in quantum optics and quantum information involve ensembles of indistinguishable particles, such as a collection of atoms or photons. These ensembles are prepared in a specific quantum state, which can exhibit entanglement among the constituent particles. The measurements and observations made on the ensemble provide statistical information about the entangled state and its properties.
It's worth noting that experiments with individual particles allow for a more direct and precise control of the entangled states, enabling researchers to investigate phenomena at the single-particle level. On the other hand, experiments with ensembles provide statistical information and are often more practical for certain applications, such as quantum communication or quantum cryptography, where the statistical properties of the entangled states are sufficient for achieving the desired functionality.
In both cases, the entanglement between particles is a fundamental aspect of quantum mechanics, and experimentalists employ various techniques and setups to generate, manipulate, and measure entangled states to investigate their properties and potential applications.