Dynamical Casimir effect for magnons in a spinor Bose-Einstein condensate

Magnon excitation in a spinor Bose-Einstein condensate by a driven magnetic field is shown to have a close analogy with the dynamical Casimir effect. A time-dependent external magnetic field amplifies quantum fluctuations in the magnetic ground state of the condensate, leading to magnetization of the system. The magnetization occurs in a direction perpendicular to the magnetic field breaking the rotation symmetry. This phenomenon is numerically demonstrated and the excited quantum field is shown to be squeezed.Comment: 8 pages, 3 figure

Optical Aharonov-Bohm Effect on Wigner Molecules in Type-II Semiconductor Quantum Dots

We theoretically examine the magnetoluminescence from a trion and a biexciton in a type-II semiconductor quantum dot, in which holes are confined inside the quantum dot and electrons are in a ring-shaped region surrounding the quantum dot. First, we show that two electrons in the trion and biexciton are strongly correlated to each other, forming a Wigner molecule: Since the relative motion of electrons is frozen, they behave as a composite particle whose mass and charge are twice those of a single electron. As a result, the energy of the trion and biexciton oscillates as a function of magnetic field with half the period of the single-electron Aharonov-Bohm oscillation. Next, we evaluate the photoluminescence. Both the peak position and peak height change discontinuously at the transition of the many-body ground state, implying a possible observation of the Wigner molecule by the optical experiment.Comment: 10 pages, 10 figures, accepted for publication in Phys. Rev.

Local gauge invariance implies Siegert's hypothesis

The nonrelativistic Ward-Takahashi identity, a consequence of local gauge invariance in quantum mechanics, shows the necessity of exchange current contributions in case of nonlocal and/or isospin-dependent potentials. It also implies Siegert's hypothesis: in the nonrelativistic limit, two-body charge densities identically vanish. Neither current conservation, which follows from global gauge invariance, nor the constraints of (lowest order) relativity are sufficient to arrive at this result. Furthermore, a low-energy theorem for exchange contributions is established.Comment: 5 pages, REVTE

Dynamical Casimir effect without boundary conditions

The moving-mirror problem is microscopically formulated without invoking the external boundary conditions. The moving mirrors are described by the quantized matter field interacting with the photon field, forming dynamical cavity polaritons: photons in the cavity are dressed by electrons in the moving mirrors. The effective Hamiltonian for the polariton is derived, and corrections to the results based on the external boundary conditions are discussed.Comment: 12 pages, 2 figure