In quantum mechanics, when two particles are entangled, their properties become correlated in such a way that the state of one particle is dependent on the state of the other. However, the detection of the state of particle A does not automatically reveal the state of particle B.
When the entangled state of particle A is measured, it "collapses" into a specific state, but the state of particle B remains undetermined until it is also measured. The measurement on particle A provides information about its own state but does not instantaneously determine the state of particle B. Instead, the state of particle B becomes determined only when it is measured independently.
This characteristic of entangled particles is known as quantum non-locality or quantum correlation. The measurements made on entangled particles are statistically correlated, but the specific outcome of each measurement is uncertain until it is observed. It is only when both particle A and particle B are measured that their individual states become known.
This phenomenon has been experimentally confirmed through various tests of Bell's inequalities, which provide a way to quantify the correlations between the entangled particles. These experiments have consistently shown that the measurement outcomes on entangled particles are probabilistically correlated but still allow for independent measurement results for each particle.
In summary, the detection of the state of particle A in an entangled system does not automatically reveal the state of particle B. Both particles need to be independently measured to determine their individual states. The correlation between the measurement outcomes of entangled particles arises due to their shared entangled state, but each particle's state is only determined upon measurement.