Theory of 2δ-kicked quantum rotors

We examine the quantum dynamics of cold atoms subjected to pairs of closely spaced δ kicks from standing waves of light and find behavior quite unlike the well-studied quantum kicked rotor (QKR). We show that the quantum phase space has a periodic, cellular structure arising from a unitary matrix with oscillating bandwidth. The corresponding eigenstates are exponentially localized, but scale with a fractional power L∼(ℎ/2π)-0.75, in contrast to the QKR for which L∼(ℎ/2π)-1. The effect of intercell (and intracell) transport is investigated by studying the spectral fluctuations with both periodic as well as 'open' boundary conditions