The Berry connection of a smoothly varying family of Hermitian operators is conventionally defined through the differentiation of instantaneous eigenvectors, a construction that introduces local gauge choices and becomes singular at energy degeneracies. In this paper we show that the Berry connection admits an intrinsic, gauge-independent reconstruction through the Moore-Penrose pseudoinverse of the adjoint action. By defining the connection directly on the operator level via the spectral adjoint, we eliminate the need to track eigenbases or construct local coordinates. This provides a unified operator formulation that applies equally to non-degenerate and degenerate spectral subspaces.
The Berry connection of a smoothly varying family of Hermitian operators is conventionally defined through the differentiation of instantaneous eigenvectors, a construction that introduces local gauge choices and becomes singular at energy degeneracies. In this paper we show that the Berry connection admits an intrinsic, gauge-independent reconstruction through the Moore-Penrose pseudoinverse of the adjoint action. By defining the connection directly on the operator level via the spectral adjoint, we eliminate the need to track eigenbases or construct local coordinates. This provides a unified operator formulation that applies equally to non-degenerate and degenerate spectral subspaces.
In a companion paper we showed that the Berry connection of a smoothly varying family of Hermitian operators can be reconstructed intrinsically from the Moore-Penrose pseudoinverse of the adjoint action. In the present work we show that the same operator also determines the quantum geometric tensor. For a smooth non-degenerate family H(lambda), we define the spectrally normalised deformation operators X_mu as the pseudoinverse of the adjoint action applied to the parameter derivatives of H. We prove that the band quantum geometric tensor admits an intrinsic operator representation given by the inner product of these spectrally normalised Hamiltonian deformations. This demonstrates that the quantum geometric tensor is precisely the Gram matrix of these operator deformations. Consequently, positivity of the quantum geometric tensor follows immediately from Hilbert-space geometry rather than perturbation theory.
Non-Hermitian systems exhibit spectral and topological phenomena absent in Hermitian physics; however, their geometric characterization remains subtle due to the intrinsic ambiguity of biorthogonal eigenspaces. Since left and right eigenvectors are not related by Hermitian conjugation, the associated Berry connection is generally nonunique, leading to complex geometric phases and ambiguously defined holonomies. Here, we formulate a covariant geometric framework for non-Hermitian quantum systems based on the metric structure of the underlying Hilbert space. We show that, in the quantum regime with continuous state evolution, the conventional Berry connection and the associated Berry holonomy over closed parameter-space loops can be consistently defined only in the pseudo-Hermitian limit, where the spectrum is real. For generic non-Hermitian Hamiltonians with complex spectra, the relevant geometric object is instead the Aharonov-Anandan holonomy associated with cyclic evolution in projective Hilbert space. Within the pseudo-Hermitian regime, we construct a unique Hermitian Berry connection that is covariant under arbitrary GL(N,C) frame transformations and reduces to the standard Berry connection in the Hermitian limit. The resulting formalism separates the intrinsic geometry of the Hamiltonian eigenspace from contributions arising from the parameter dependence of the Hilbert-space metric, revealing that the conventional biorthogonal formulation generally mixes these distinct geometric effects. Consequently, geometric phases, synthetic gauge fields, and topological characteristics commonly attributed to non-Hermitian eigenspace geometry may, in part, originate from the underlying metric structure. Our framework therefore provides a consistent geometric foundation for Berry phases, non-Abelian holonomies, and topological invariants in non-Hermitian quantum systems.
Non-Hermitian systems exhibit spectral and topological phenomena absent in Hermitian physics; however, their geometric characterization remains subtle due to the intrinsic ambiguity of biorthogonal eigenspaces. Since left and right eigenvectors are not related by Hermitian conjugation, the associated Berry connection is generally nonunique, leading to complex geometric phases and ambiguously defined holonomies. Here we formulate a covariant geometric framework for non-Hermitian quantum systems based on the metric structure of the underlying Hilbert space. We show that, in the quantum regime with continuous state evolution, the conventional Berry connection and the associated Berry holonomy over closed parameter-space loops can be consistently defined only in the pseudo-Hermitian limit, where the spectrum is real. For generic non-Hermitian Hamiltonians with complex spectra, the relevant geometric object is instead the Aharonov--Anandan holonomy associated with cyclic evolution in projective Hilbert space. Within the pseudo-Hermitian regime, we construct a unique Hermitian Berry connection that is covariant under arbitrary GL(N,C) frame transformations and reduces to the standard Berry connection in the Hermitian limit. The resulting formalism separates the intrinsic geometry of the Hamiltonian eigenspace from contributions arising from the parameter dependence of the Hilbert-space metric, revealing that the conventional biorthogonal formulation generally mixes these distinct geometric effects. Consequently, geometric phases, synthetic gauge fields, and topological characteristics commonly attributed to non-Hermitian eigenspace geometry may, in part, originate from the underlying metric structure. Our framework therefore provides a consistent geometric foundation for Berry phases, non-Abelian holonomies, and topological invariants in non-Hermitian quantum systems.
Non-Hermitian systems exhibit spectral and topological phenomena absent in Hermitian physics; however, their geometric characterization remains subtle due to the intrinsic ambiguity of biorthogonal eigenspaces. Since left and right eigenvectors are not related by Hermitian conjugation, the associated Berry connection is generally nonunique, leading to complex geometric phases and ambiguously defined holonomies. Here, we formulate a covariant geometric framework for non-Hermitian quantum systems based on the metric structure of the underlying Hilbert space. We show that, in the quantum regime with continuous state evolution, the conventional Berry connection and the associated Berry holonomy over closed parameter-space loops can be consistently defined only in the pseudo-Hermitian limit, where the spectrum is real. For generic non-Hermitian Hamiltonians with complex spectra, the relevant geometric object is instead the Aharonov-Anandan holonomy associated with cyclic evolution in projective Hilbert space. Within the pseudo-Hermitian regime, we construct a unique Hermitian Berry connection that is covariant under arbitrary GL(N,C) frame transformations and reduces to the standard Berry connection in the Hermitian limit. The resulting formalism separates the intrinsic geometry of the Hamiltonian eigenspace from contributions arising from the parameter dependence of the Hilbert-space metric, revealing that the conventional biorthogonal formulation generally mixes these distinct geometric effects. Consequently, geometric phases, synthetic gauge fields, and topological characteristics commonly attributed to non-Hermitian eigenspace geometry may, in part, originate from the underlying metric structure. Our framework therefore provides a consistent geometric foundation for Berry phases, non-Abelian holonomies, and topological invariants in non-Hermitian quantum systems.
We introduce a spinor differential operator whose expectation value reproduces the Berry connection exactly. We derive its transformation under local U(1) gauge transformations and show that the conventional Berry gauge transformation follows directly through projection onto the normalized spinor. The proposed formulation provides an operator-level formulation of Berry geometry whose projection reproduces the conventional Berry connection and its gauge transformation.
We present a spectral formulation of unitary propagation in which the dynamics is characterized directly by the resolvent structure of a self-adjoint operator. A propagation operator defined by the Cayley transform is considered, whose form allows expressing the evolution in terms of the resolvent of the structural operator, without direct reference to continuous differential equations. It is shown that the bilocal propagation kernel is completely determined by the resolvent, implying that the dynamic connectivity does not reduce, in general, to the local support of the structural operator. In the perturbative regime, a controlled expansion is obtained that characterizes an effective notion of locality, while in the homogeneous regime the evolution is organized by a nonlinear spectral phase associated with the eigenvalues of the operator. From this structure, dynamical quantities such as frequency and group velocity are defined, which emerge as well-defined spectral functions, modulated by nonlinear factors arising from the unitarity of the evolution. Additionally, it is demonstrated that the spectrum responds in a controlled manner to internal perturbations associated with phase parameters, establishing a general mechanism of spectral response. The obtained results are strictly structural and independent of external phenomenological hypotheses. It is concluded that unitary propagation admits a consistent formulation in terms of the resolvent of a self-adjoint operator and its spectral decomposition, providing a minimal level at which connectivity, modal evolution, and response to perturbations are determined internally by the structure of the operator.