The discussion centers on the concept of decoherence and its relationship with classical states, particularly in the context of Environment-Induced Superselection (Einselection). Participants clarify that classical states are robust against decoherence due to their entanglement properties with the environment, which leads to the emergence of pointer states. The conversation also explores the implications of decoherence on macroscopic objects, using the example of the Buckingham Palace windows to illustrate how quantum effects could theoretically alter perceptions of reality if Einselection were suppressed. Key references include Zurek's work on Quantum Darwinism and a specific book detailing the nature of decoherence.
PREREQUISITESQuantum physicists, students of quantum mechanics, and anyone interested in the foundational aspects of quantum theory and its implications for classical reality.
bhobba said:Its simple. It's got to do with the difference between a proper and an improper mixed state. The mixed state is Σ pu |u><u| + pd |d><d|. If you observe that with the up-down observable you will get |u><u| with probability pu and |d><d| with probability pd. Now is that because it was in state |u><u| with probability pd and similarly for |d><d|? If so the observation did nothing - no change. In interpretations like BM or GRW that actually is the case and is how they resolve the measurement problem. But they may not be true - the observation may have changed the mixed state to a pure one - there is no way of telling. Remember this is a mixed state - not a superposition - interference terms have been suppressed.
Thanks
Bill
lucas_ said:is the "state |u><u| with probability pd and similarly for |d><d|" the improper mixed state in the example (noting that entangled electron with spin up and spin down are entangled so you can't use proper mixed state).. but why did you use proper mixed state in Σ pu |u><u| + pd |d><d|?