Topological properties of Berry’s phase
Kazuo Fujikawa
Abstract
By using a second quantized formulation of level crossing, which does not assume adiabatic approximation, the exact formula for geometric terms including off-diagonal terms is derived. If one diagonalizes the geometric terms in the infinitesimal neighborhood of level crossing, the geometric phases become trivial for any finite time interval T. The topological interpretation of Berry’s phase such as the topological proof of phase-change rule thus fails for any finite T. The geometric phases are mostly defined in the framework of adiabatic approximation [1]-[6], though a non-adiabatic treatment has been considered in, for example, [7]. One may then wonder if some of the characteristic properties generally attributed to the geometric phases are the artifacts of the approximation. We here show that the topological properties of the geometric phases associated with level crossing are the artifacts of the approximation which assumes the infinite time interval T → ∞. To substantiate this statement, we start with the exact definition of geometric terms associated with level crossing. The level crossing problem is formulated by using the second quantization technique