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Collective Quantum Phenomena

Nicholas d'Ambrumenil, Boris Mouzykantskii

A central problem in many-body systems is that the particles cannot always be treated as if they moved in the average potential of all the other particles. Such systems have been the source of some of the most unexpected discoveries in physics - superconductivity and superfluidity, the quantum Hall effect, Bose-Einstein condensation in cold atom and non-equilibrium excitonic systems. Although each of these phenomena presents its own tough theoretical challenges, they have something in common. Loosely speaking, the system condenses into a state with low-lying coherent collective excitations, which cannot be mapped onto those of the corresponding free particle system. Finding the correct description of these excitations is a major component of what we do.

In free Fermi gases we are looking at protocols for exciting small numbers of excitations. Voltage pulses tend to generate noise by exciting large numbers of particle-hole excitations as well as driving charge (information) from one point to another. We are looking at the quantum theory of this noise.

Water droplets as a model for noisy excitation
Water droplets as a model for noisy excitation