nLab geometrical formulation of quantum mechanics



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Symplectic geometry



What is called the “geometrization of quantum mechanics” by Kibble (1979) who introduced the idea, or “geometrical formulation of quantum mechanics” [Ashtekar & Schilling (1999)] or just “geometric quantum mechanics” [Brody & Hughston (2001)], but which ought to be called the “symplectic formulation”, is the observation that, in standard quantum mechanics:

  1. the complex projective space PP \mathscr{H} of the Hilbert space of pure quantum states \mathscr{H} is canonically a Kähler manifold (via the Fubini-Study metric) and so in particular a symplectic manifold,

  2. the curves in PP \mathscr{H} which correspond to solutions of the Schrödinger equation are Hamiltonian flows with respect to this symplectic structure.

This is fairly immediate to see from mathematical inspection, but the perspective is somewhat surprising from the point of view of standard accounts of classical/quantum physics, which tend to frame symplectic geometry and its Hamiltonian flows as the hallmark of classical phase spaces and classical physics, and to highlight quantization as a deformation of this symplectic structure (whence: “deformation quantization”).

Now, the standard perspective is certainly not wrong, but various authors have inevitably suggested that the “geometrical formulation” (more descriptive would be: “symplectic formulation”) of quantum mechanics may point to some deeper truth, and if only to show some kind of conceptual unity where one is used to amplifying the dichotomy.


The observation is due to:

The idea was picked up in:

Further discussion:

Discussion of dynamics of mixed states (density matrices), now via Poisson geometry:

  • Pritish Sinha, Ankit Yadav, Poisson Geometric Formulation of Quantum Mechanics [arXiv:2312.05615]

Last revised on December 12, 2023 at 11:30:50. See the history of this page for a list of all contributions to it.