This discussion clarifies the distinctions between pure and mixed quantum states. A pure state, such as a superposition of |0> and |1>, represents a coherent combination of states, while a mixed state is a statistical mixture where the system is definitely in one of the states, but the observer lacks complete knowledge of which one. The conversation emphasizes that mixed states cannot be represented as a statistical combination of pure states and arise from incomplete knowledge or entangled systems. Understanding these concepts is crucial for interpreting quantum mechanics accurately.
PREREQUISITESStudents and professionals in quantum physics, particularly those studying quantum mechanics, quantum information theory, and anyone interested in the foundational concepts of quantum states.
vanhees71 said:Well, can you prove that the measurement devices used to measure the polarization of photons or the spin of particles etc. etc. are not described by quantum statistics of macroscopic "very-many-body systems"
If so, then you'd be right in saying that there is a division of the world in microscopic and macroscopic behavior.
Physics is defined as describing preparation procedures, measurements, quantitative observations of Nature. All theories of physics are right about this way to investigate what's objectively going on. If you want something else, it's not physics!stevendaryl said:I'm calling your approach schizophrenic. If the only meaning of the quantum state is to give probabilities for measurement outcomes (or other macroscopic quantities such as mean values) in terms of preparation procedures, then that's necessarily schizophrenic. A non-schizophrenic theory would not mention macroscopic quantities such as measurements or preparation procedures in the fundamental laws, but would be able to derive whatever is being claimed about those things.
This is your very individual idea about what the natural sciences should provide. Nature doesn't care about our feelings and expectations how she should behaves. She is just is she is.stevendaryl said:Absolutely, I can't prove that, and I don't believe it. I believe that there should be a non-schizophrenic formulation of quantum theory, but the current formulation is schizophrenic.
vanhees71 said:This is your very individual idea about what the natural sciences should provide. Nature doesn't care about our feelings and expectations how she should behaves. She is just is she is.
vanhees71 said:Physics is defined as describing preparation procedures, measurements, quantitative observations of Nature. All theories of physics are right about this way to investigate what's objectively going on. If you want something else, it's not physics!