quasi1D

Quasi-one-dimensional (quasi-1D) systems are physical systems in which motion is confined strongly in two transverse directions, so that the low-energy dynamics are effectively one-dimensional, although the system retains a finite transverse extent. The confinement leads to a set of discrete transverse modes (subbands), separated by an energy scale set by the transverse confinement frequency. When the temperature and chemical potential are well below this energy spacing, only the lowest transverse mode is occupied and the system behaves as a true 1D gas or conductor; if several subbands are populated, the system is described as quasi-1D rather than strictly 1D.

Common realizations include semiconductor quantum wires and other nanoscale conductors, carbon nanotubes, and ultracold atomic gases trapped in highly elongated optical or magnetic traps, or loaded into optical lattices that produce arrays of tubes. In solid-state devices, transport is often described in terms of conductance quantization, G = (2e^2/h) M, where M is the number of occupied subbands. In ultracold atoms, quasi-1D geometries realize exactly solvable or near-solvable models such as the Lieb-Liniger gas for bosons or the Gaudin-Yang model for fermions; strongly interacting 1D Bose gases can enter the Tonks-Girardeau regime.

Theoretically, quasi-1D systems probe the crossover between higher-dimensional behavior and true 1D physics. When multiple subbands are populated, inter-subband coupling and transverse excitations can modify correlation functions and transport, while in the truly 1D limit, correlations are enhanced and conventional long-range order is suppressed. Experimental studies probe Luttinger liquid behavior, density correlations, and collective modes, among other phenomena.