Cirelli, Manià and Pizzocchero generalized quantum mechanics by Kähler geometry. Furthermore they proved that any unital C
∗-algebra is represented as a function algebra on the set of pure states with a noncommutative
∗-product as an application. The ordinary quantum mechanics is regarded as a dynamical system of the projective Hilbert space
P(H) of a Hilbert space
H. The space
P(H) is an infinite dimensional Kähler manifold of positive constant holomorphic sectional curvature. In general, such dynamical system is constructed for a general Kähler manifold of nonzero constant holomorphic sectional curvature
c. The Hilbert ball
BH is defined by the open unit ball in
H and it is a Kähler manifold with
c<0. We introduce the quantum mechanics on
BH. As an application, we show the structure of the noncommutative function algebra on
BH.
In a recent paper it was shown that all the Hilbert space formulas for quantum probabilities can be realized as functions of geometric properties of the associated projective space, but those functions were expressed using the structures of the associated Hilbert space. In this paper a direct description of all these probabilities is given as formulas involving only the geometric properties of the projective space itself without referring to the associated Hilbert space theory. In large part this depends on a projection theorem for complex projective space which is analogous to the projection theorem for Hilbert spaces. The importance of this is that this exhibits quantum probability in terms of the geometry of a Riemannian metric in a non-linear Kähler manifold without any reference to a linear Hilbert space. As such this is a part of a larger program of the geometrization of physics. This opens the possibility of generalizations of quantum theory in other similar geometric settings. The theory presented includes projective spaces of both finite and infinite dimension. Some comments explain how quantum theory based on a von Neumann algebra is compatible with this approach.
We develop a geometrical approach to Schrödinger quantum mechanics, alternative to the usual one, which is based on linear and algebraic structures such as Hilbert spaces, operator algebras, etc. The starting point of this approach is the Kähler structure possessed by the set of the pure states of a quantum system. The Kähler manifold of the pure states is regarded as a “quantum phase space”, conceptually analogous to the phase space of a classical hamiltonian system, and all the constituents of the conventional formulation, in particular the algebraic structure of the observables, are reproduced using a suitable “Kähler formalism”. We also show that the probabilistic character of the measurement process in quantum mechanics and the uncertainty principle are contained in the geometrical structure of the quantum phase space. Finally, we obtain a characterization for quantum phase spaces which can be interpreted as a statement of uniqueness for Schrödinger quantum mechanics.
We review the geometry of the space of quantum states
S(H) of a finite-level quantum system with Hilbert space
H from a group-theoretical point of view. This space carries two stratifications generated by the action of two different Lie groups: the special unitary group
SU(H) and its complexification
SL(H), the complex special linear group. A stratum of the stratification generated by
SU(H) is composed of isospectral states, that is, density operators with the same spectrum, A stratum of the stratification generated by
SL(H) is composed of quantum states with the same rank. We prove that on every submanifold of isospectral quantum states there is also a canonical left action of
SL(H) which is related with the canonical Kähler structure on isospectral quantum states. The fundamental vector fields of this
SL(H)-action are divided into Hamiltonian and gradient vector fields. The former give rise to invertible maps on
S(H) that preserve the von Neumann entropy and the convex structure of
S(H), while the latter give rise to invertible maps on
S(H) that preserve the von Neumann entropy but not the convex structure of
S(H). A similar decomposition is given for the
SL(H)-action generating the stratification of
S(H) into manifolds of quantum states with the same rank, where gradient vector fields preserve the rank but do not preserve entropy. Some comments on multipartite quantum systems are made. It is proved that the sets of product states of a multipartite quantum system are homogeneous manifolds for the action of the complex special linear group associated with the partition.
Chapter 6 Von Neumann algebras 6.1 The algebras l (X) In this chapter we discuss quantum measure theory. This is formally rather similar to quantum topology; in both cases we treat the given structure (topological or measure theoretic) in terms of the algebra of complex-valued functions which are compatible with that structure. The algebras which arise in the latter case are actually a special case of the former: every von Neumann algebra is a C*-algebra (although this is not always the best way to think about them).
Entanglement for pure bipartite states is most commonly quantified in a state-by-state manner to each pure state of a bipartite system a scalar quantity, such as the von Neumann entropy of a reduced density matrix. This provides a precise local characterization of how entangled a given state is. At the same time, this local description naturally invites a set of complementary, more global questions about the structure of the space of pure states: How abundant are the states with a given amount of entanglement within the full state space? Do the manifolds of constant entanglement exhibit distinct geometric regimes? These questions shift the focus from assigning an entanglement value to a single state to understanding the global organization and geometry of entanglement across the entire manifold of pure states.
In this work, we develop a geometric framework in which these questions become natural. We regard the projective Hilbert space of pure states, endowed with the Fubini-Study metric, as a Riemannian manifold and promote bipartite entanglement to a macroscopic functional on this manifold. Its level sets stratify the space of pure states into hypersurfaces of constant entanglement, and we define a geometric entanglement entropy as the log-volume of these hypersurfaces, weighted by the Fubini-Study gradient of entanglement. This quantity plays the role of a microcanonical entropy in entanglement space: it measures the degeneracy of a given entanglement value in the natural quantum geometry.
The framework is illustrated first in the simplest case of a single spin-1/2 and then for bipartite entanglement of spin systems, including a two-qubit example where explicit calculations can be carried out, along with a sketch of the extension to spin chains.