Two examples illustrating the differences between classical and quantum mechanics

Mixing Quantum and Classical Mechanics

Using a group theoretical approach we derive an equation of motion for a mixed quantum-classical system. The quantum-classical bracket entering the equation preserves the Lie algebra structure of quantum and classical mechanics: The bracket is antisymmetric and satisfies the Jacobi identity, and, therefore, leads to a natural description of interaction between quantum and classical degrees of f...

I. the Differences between Quantum and Classical States

Now that you have learned the basic quantum formalism from an axiomatic point of view and are skilled in manipulating the mathematical objects we need, I want to loop back and ask what exactly the quantities you have been manipulating mean. You’ve probably heard that there are some “weird” aspects to quantum mechanics and its historically been somewhat of a nonintuitive theory. Maybe you have a...

The equivalence principle in classical mechanics and quantum mechanics ∗

We discuss our understanding of the equivalence principle in both classical mechanics and quantum mechanics. We show that not only does the equivalence principle hold for the trajectories of quantum particles in a background gravitational field, but also that it is only because of this that the equivalence principle is even to be expected to hold for classical particles at all. While the equiva...

Classical Limit of Quantum Mechanics

para o valor esperado de uma dada observável fı́sica A = A(p, q, t) representada pelo operador Â. As equações (1) e (2) são válidas desde que o potencial externo V varie vagarosamente dentro de um pacote de onda bem localizadoψPE (Pacote de Ehrenfest). Assim, de acordo com os livros-texto [1], as equações de Newton são obtidas como limite clássico da equação de Schrödinger. No entanto, Ballentin...

Classical models of quantum mechanics