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Hamurabi, I assume you are asking for the order of the wave equation. Try thinking about intramolecular vs. intermolecular forces. A wave equation is necessary to describe the energy of any quantum occurrence, so far as I recall. It may take an approximation for any non-ideal system, but exact or not the wave equation describes the moment in time when the ...

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BEC qubits are set up by splitting one harmonic condensate trap into a double-well trap by means of a suitable laser or microwave field. See for instance pg.6 on these LANL slides: Quantum dynamics, measurement and decoherence in Bose-Einstein condensates. Under strong enough separation the overall ground state becomes two-fold degenerate and the two ...

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Superfluid helium finds an application as a coolant in superconducting systems (http://link.springer.com/chapter/10.1007%2F3-540-45542-6_4#page-1 )

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I will try to address the first point raised by the OP, i.e. the occurrence of spontaneous symmetry breaking in Bose-Einstein condensation. The free boson gas is described by the hamiltonian: $$H_V=\int_V\frac{d^sx}{2m}\big|\nabla\phi(x)\big|^2.$$ The ground state satisfies $H_V\Psi_0 = 0,\ \forall V$ and hence $\nabla \phi(x)\Psi_0=0,\ \forall x.$ ...

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In the Bogoliubov transformation, it is the case that $$u_{-p} = u^*_p,$$ and $$v_{-p} = v^*_p,$$ so your result is correct. In fact, if you move on to basically the next equation, they assume that both $u$ and $v$ are real, in which case $$u_{-p} = u^*_p = u_p,$$ as mentioned by Mark Mitchison in a comment below this answer. And incidentally, yes it is ...

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I dug around in the literature a bit and found that this formulation (semiclassical Bose-Hubbard plus Langevin-type dissipation) has been studied before. Here is the relevant reference: http://arxiv.org/abs/1304.5071. What you are trying to do is derive their equation (9). You probably missed it because they refer to their model as the discrete nonlinear ...

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The Gross-Pitaevskii's equation is obtained from the Heisenberg equations-of-motion for the normal and anomalous bosonic Green's functions in the ordered (superfluid) phase. For a detailed account, see Chp. 14, Section 55 of Fetter, A. L., and J. D. Walecka. “Quantum theory of many-particle systems”. New York: McGraw-Hill (1971).

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