Sheldon: How would you determine the ground state of a quantum system with no exact solution?
Howard: I would guess a wave-function and then vary its parameters until I found the lowest energy solution.
A wave function or wavefunction (also named a state function) in quantum mechanics describes the quantum state of a system of one or more particles, and contains all the information about the system considered in isolation.
... entanglement also may enable pigeons and robins to navigate. These birds detect the Earth’s magnetic field, apparently due to quantum entanglement in their eyes. Light coming into the eye boosts the energy of electrons. A property of the electrons called ‘spin’ is then influenced by tiny variations in the Earth’s magnetic field, and it is thought that quantum entanglement makes it possible for the bird to build a picture by linking different electrons.