3 ms·

Superposition is easy to understand: when you are looking at a rotating wheel, it looks like it is in a superposition of Up and Down, because it rotating so fas

by drran 5y ago

Superposition is easy to understand: when you are looking at a rotating wheel, it looks like it is in a superposition of Up and Down, because it rotating so fast. In quantum world, situation changes so fast and so fragile, than you cannot predict a state in a next moment of time, so it's much easier to use superposition in calculations. For example, when somebody need to predict trajectory of a car, he will not try to predict position of car tires in the every moment of the trajectory, because it's too complex. He will just assume that tires are "rotating" (i.e. in superposition of all tire states), unless tire state is important for the calculation, e.g. when braking. PS. Sorry for my English.

QuantumAnon1 5y ago
Hey ! No worries your English is totally fine. I disagree with your vision, and I don't think the evolution allegory works with the rotating wheel. The complexity to me comes from the fact that in QM you describe evolution through the Schrodinger's equation (or for mixed system where you indeed lack understanding on the possible outcomes of the system, either Lindblad or Von-Neumann eqs), those are deterministic equations describing random processes and mostly the source of many unresolved problems in the interpretation of QM. You can take two approaches : either in the Schrodinger's picture states are moving and operators (hence, measurable quantities) are static, or in the Heisenberg picture operators are moving but states are described as static. Defining trajectories themselves in QM is a daunting task (but can be done, through quantum trajectories, which can be interpreted as the ensemble of realizations of all possible outcomes of the system). When you are dealing with superposition, in pure states, you might be in actuality in a stationary case and can only rely on measurements, which by themselves pose ontological problems (see the measurement paradox for more info). The determining factor of selection of the next outcome is philosophically unresolved and at the time I don't know if it can be explained through any case of quantum fluctuations. At the moment for example I am working with arbitrary qubit selection with Ramsey interferences, the experimental setup can make by interferating one photon to another any superposition of two frequency states (thus manipulating the probability to be in a frequence or in other over an average of realizations of the experiment), thus an arbitrary Qubit. In our case, we could freeze time and the outcome would be the same, in fact, time poses absolutely no role in any part in our description. I know some top physicists who lose sleep over this question of being able to describe past, present and future of quantum states in dynamical context all at once, without even considering time. To put it simply, there's two sources of probabilities in QM : intrinsic to the random nature of QM (pure states) and probabilities due to our lack of knowledge (mixed states). When dealing with highly controlled system we can assume we are in pure states conditions, selection is automatic, and not due to any lack of description, at least to our current understanding.

by drran 5y ago

QuantumAnon1 5y ago

Hey ! No worries your English is totally fine. I disagree with your vision, and I don't think the evolution allegory works with the rotating wheel. The complexity to me comes from the fact that in QM you describe evolution through the Schrodinger's equation (or for mixed system where you indeed lack understanding on the possible outcomes of the system, either Lindblad or Von-Neumann eqs), those are deterministic equations describing random processes and mostly the source of many unresolved problems in the interpretation of QM. You can take two approaches : either in the Schrodinger's picture states are moving and operators (hence, measurable quantities) are static, or in the Heisenberg picture operators are moving but states are described as static. Defining trajectories themselves in QM is a daunting task (but can be done, through quantum trajectories, which can be interpreted as the ensemble of realizations of all possible outcomes of the system). When you are dealing with superposition, in pure states, you might be in actuality in a stationary case and can only rely on measurements, which by themselves pose ontological problems (see the measurement paradox for more info). The determining factor of selection of the next outcome is philosophically unresolved and at the time I don't know if it can be explained through any case of quantum fluctuations. At the moment for example I am working with arbitrary qubit selection with Ramsey interferences, the experimental setup can make by interferating one photon to another any superposition of two frequency states (thus manipulating the probability to be in a frequence or in other over an average of realizations of the experiment), thus an arbitrary Qubit. In our case, we could freeze time and the outcome would be the same, in fact, time poses absolutely no role in any part in our description. I know some top physicists who lose sleep over this question of being able to describe past, present and future of quantum states in dynamical context all at once, without even considering time. To put it simply, there's two sources of probabilities in QM : intrinsic to the random nature of QM (pure states) and probabilities due to our lack of knowledge (mixed states). When dealing with highly controlled system we can assume we are in pure states conditions, selection is automatic, and not due to any lack of description, at least to our current understanding.