Mechanics is developed over a differentiable manifold as space of possible positions. Time is considered to fill a one-dimensional Riemannian manifold, so having the metric as lapse. Then the system is quantized with covariant instead of partial derivatives in the Schrödinger operator.
In this paper we show what seems to be the (very simple) key for quantization of classical systems. Given a manifold M , each pair given by a riemannian metric (nondegenerate, of arbitrary signature) and a linear connection, canonically determine a quantization rule or 'Correspondence Principle', which assigns to each classical magnitude (function in TM , subject to certain conditions) a differential operator in . The issue about the order in which the p ' and q ' are to be taken in quantization loses all meaning, when the general rule has been fixed. Once specified the Correspondence Principle, each 'classical state' of the system, understood as a vector field on M , determines a wave equation for each magnitude. The Schrödinger equation is a particular example of these wave equations.
Using extended Schwinger's quantization approach quantum mechanics on a Riemannian manifold M with a given action of an intransitive group of isometries is developed. It was shown that quantum mechanics can be determined unequivocally only on submanifolds of M where G acts simply transitively (orbits of G-action). The remaining part of degrees of freedom can be described unequivocally after introducing some additional assumptions. Being logically unmotivated, these assumptions are similar to canonical quantization postulates. Besides this ambiguity that has a geometrical nature there is undetermined gauge field of hbar (or higher) order, vanishing in the classical limit hbarto0.
We investigate algorithms for the quantum simulation of the Schrödinger equation on a Riemannian manifold, where the kinetic operator is defined by the Laplace--Beltrami operator corresponding to the metric. Our first algorithms are based on a global spectral method based on the identification of an efficient transform to the eigenbasis of the Laplace--Beltrami operator. We use this method to provide explicit, efficient, quantum simulation algorithms for the Riemannian Schrödinger equation on tori and spheres with their standard metrics, simplices with the Wright--Fisher metric, truncated positive orthants and their invertible affine images with the log-barrier Hessian metric, and ℓp balls with a metric induced by the Duffy map. Our second algorithm is based on a coherent simulation of local spectral methods on multiple charts, and is in principle applicable to any compact manifold. We first analyze this algorithm in the continuum and derive conditions under which a polynomial spectral cutoff suffices. We also provide a discretization analysis of a polynomial spectral cutoff for tensor-products of constant-dimensional manifolds. Finally, we consider applications of these methods to optimization and physical simulation. For optimization, we provide results including a generalization and convergence analysis of Quantum Hamiltonian Descent for geodesically convex functions that leads to explicit algorithms on the sphere and simplex, and a Riemannian generalization of the Real-Space Adiabatic Algorithm. For physical simulation, we show that our algorithms can simulate certain spatially discretized field theories, including a variant of the nonlinear sigma model.