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arXiv:2308.12977 · International Journal of Geometric Methods in Modern Physics

Equivalent quantum systems

M. Caruso

Published Jun 10, 2023• 0 citations
arXivHTMLPDF

Abstract

We have studied quantum systems on finite-dimensional Hilbert spaces and found that all these systems are connected through local transformations. Actually, we have shown that these transformations give rise to a gauge group that connects the Hamiltonian operators associated with each quantum system. This bridge allows us to connect different quantum systems, in such a way that studying one of them allows to understand the other through a gauge transformation. Furthermore, we included the case where the Hamiltonian operator can be time-dependent. An application for this construction will be achieved in the theory of control quantum systems.

DOI
10.1142/s0219887823502092

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We have studied quantum systems on finite-dimensional Hilbert spaces and found that all these systems are connected through local transformations. Actually, we have shown that these transformations give rise to a gauge group that connects the Hamiltonian operators associated with each quantum system. This bridge allows us to connect different quantum systems, in such a way that studying one of them allows to understand the other through a gauge transformation. Furthermore, we included the case where the Hamiltonian operator can be time-dependent. An application for this construction will be achieved in the theory of control quantum systems.
We construct and study lattice realizations of finite 2-group symmetries in 2+1{2+1}2+1d quantum lattice systems with finite-dimensional tensor-product Hilbert spaces. We focus on two broad classes of 2-groups with 0-form symmetry group GGG and 1-form symmetry group AAA: split 2-groups with trivial Postnikov class [β]∈H3(G,A){[β]\in\mathcal{H}^3(G,A)}[β]∈H3(G,A), and central 2-groups with trivial action ρ ⁣:G→Aut(A){ρ\colon G\to\text{Aut}(A)}ρ:G→Aut(A). In both cases, we construct symmetry operators on the full tensor-product Hilbert space that become 2-group symmetry operators when restricted to the topological subspace of the lattice AAA 1-form symmetry. While the lattice split 2-group symmetry operators are onsite, the lattice central 2-group symmetry operators are not, and can only be made onsite after introducing ancillae. We extensively explore various manifestations of ρρρ and [β][β][β] for these lattice 2-group symmetry operators and demonstrate their agreement with expectations from quantum field theory. These manifestations arise in the transformation of operators carrying symmetry charge, the structure of lattice 2-group symmetry defects, and the dual fusion 2-category symmetries obtained by gauging the lattice 2-group symmetries. We further propose families of local symmetric Hamiltonians for both classes of lattice 2-group symmetries and identify exactly solvable limits lying in phases with spontaneous 2-group symmetry breaking and nontrivial symmetry-enriched topological order. In one such limit, the gauged Hamiltonians are exactly solvable lattice realizations of the corresponding 2-group gauge theories, whose ground-state degeneracies we calculate.
In this thesis, we lay out the goal, and a broad outline, for a program that takes quantum mechanics in its minimal form to be the fundamental ontology of the universe. Everything else, including features like space-time, matter and gravity associated with classical reality, are emergent from these minimal quantum elements. We argue that the Hilbert space of quantum gravity is locally finite-dimensional, in sharp contrast to that of conventional field theory, which could have observable consequences for gravity. We also treat time and space on an equal footing in Hilbert space in a reparametrization invariant setting and show how symmetry transformations, both global and local, can be treated as unitary basis changes. Motivated by the finite-dimensional context, we use Generalized Pauli Operators as finite-dimensional conjugate variables and define a purely Hilbert space notion of locality based on the spread induced by conjugate operators which we call "Operator Collimation." We study deviations in the spectrum of physical theories, particularly the quantum harmonic oscillator, induced by finite-dimensional effects, and show that by including a black hole-based bound in a lattice field theory, the quantum contribution to the vacuum energy can be suppressed by multiple orders of magnitude. We then show how one can recover subsystem structure in Hilbert space which exhibits emergent quasi-classical dynamics. We explicitly connect classical features (such as pointer states of the system being relatively robust to entanglement production under environmental monitoring and the existence of approximately classical trajectories) with features of the Hamiltonian. We develop an in-principle algorithm based on extremization of an entropic quantity that can sift through different factorizations of Hilbert space to pick out the one with manifest classical dynamics. This discussion is then extended to include direct sum decompositions and their compatibility with Hamiltonian evolution. Following this, we study quantum coarse-graining and state-reduction maps in a broad context. In addition to developing a first-principle quantum coarse-graining algorithm based on principle component analysis, we construct more general state-reduction maps specified by a restricted set of observables which do not span the full algebra (as could be the case of limited access in a laboratory or in various situations in quantum gravity). We also present a general, not inherently numeric, algorithm for finding irreducible representations of matrix algebras. Throughout the thesis, we discuss implications of our work in the broader goal of understanding quantum gravity from minimal elements in quantum mechanics.
Abstract We present DLST Ver.11.0.0, a compact recurrence-classification framework for exact physical histories, relational time, and relativistic closure. Ver.11 explicitly corrects the earlier interpretation of DLST: finite signal speed, microscopic length, compactness, finite entropy, finite Hilbert dimension, or a discrete evolution label do not by themselves establish a fundamental discrete clock or exact recurrence. The central objects are instead the physical identity space, the stabilizer of an individual state, and the common global kernel of the evolution. This separates state-specific recurrence, universal recurrence, gauge stationarity, and observational indistinguishability. For autonomous discrete quantum evolution, we prove that a common exact projective return for all pure-state rays and density operators exists if and only if the one-step projective update [U] is a torsion element of PU(H), equivalently U^N = exp(i phi) I for some finite N. Membership in a finite projective unitary subgroup is therefore a sufficient special case. Finite-volume exact Clifford dynamics on finitely many prime-dimensional qudits provides an explicit conditional realization: the projective Clifford group is finite, so an exact Clifford quantum cellular automaton has a nonzero common recurrence period. This bridge does not require a finite quantum-state cardinality. Its scope is exact and finite-volume; infinite-lattice Clifford QCA or arbitrarily small irrational non-Clifford phases need not recur globally. Complementary positive criteria are given by finite same-law closure and spectral commensurability. For unitary evolution, exact recurrence of an occupied state requires its active eigenphase or energy differences to lie on a common arithmetic lattice. These results clarify why finite-dimensional Hilbert space alone is insufficient: exact recurrence is controlled by projective order and spectral arithmetic rather than vector-space dimension. The relativistic obstruction side is strengthened. In 1+d-dimensional Poincare-covariant quantum dynamics with d >= 2, if the scalar/projective translation kernel contains any nonzero translation—timelike, spacelike, or null—Lorentz covariance and additivity force the entire translation subgroup into the kernel. Hence a nontrivial translation representation cannot possess a nonzero universal spacetime period. A related connected simple-group obstruction excludes noncentral universal projective periods under the stated representation hypotheses. For relativistic scattering sectors, Haag-Ruelle wave-operator equivalence transfers the asymptotic energy spectral measure to the interacting sector. A nonzero non-atomic energy component is incompatible with the affine spectral lattice required for exact projective return, yielding an exact nonreturn criterion without assuming that every state belongs to the scattering sector. Independently, any strictly monotone extensional physical witness along the complete admitted history forbids exact recurrence. Ver.11 also proves a finite-window nonidentifiability result: for any finite observation horizon and tolerance, one can construct finite-dimensional Hamiltonians whose propagators remain arbitrarily close throughout the observed interval while belonging to different global recurrence classes. Finite measurement precision therefore cannot replace an exact structural bridge from observed dynamics to all-history recurrence. Related audits show that finite Hilbert dimension, Type II_1 finite-entropy language, gauge stationarity, and cosmological labels are not exact recurrence classifiers by themselves. Finite-dimensional completeness is also incompatible with a nontrivial exact continuous unitary representation of the standard connected de Sitter group under the stated assumptions. The resulting classification contains both positive and negative bridges. Positive exact routes include finite same-law closure, projective torsion, finite-volume exact Clifford QCA, and affine spectral lattices. Obstruction and nonreturn routes include Poincare symmetry, non-atomic scattering spectra, and strict extensional monotonicity. Gauge equivalence, compactness, finite observational windows, and coarse finiteness statements remain nonclassifying without additional physical input. The principal methodological change is therefore a shift from presumed temporal discreteness to fail-closed actuality promotion: a recurrence or nonrecurrence claim is promoted only after the physical identity relation, complete evolution law, and exact all-history bridge have been independently specified. DLST Ver.11.0.0 does not establish that the actual universe is periodic, aperiodic, fundamentally discrete in time, a finite Clifford automaton, or governed by a universal microscopic tick. C4 Ver.1.0.0 and OUROBOROS Ver.2.0.0 remain separate downstream research programs rather than premises of DLST. Deterministic reproducibility checks accompany the release for the finite-projective, Clifford-group, spectral, permutation, and finite-window constructions. These computational audits verify explicit finite examples and implementation details; the analytic theorems remain the scientific basis of the classification. DLST Ver.11.0.0 thus provides a compact framework connecting exact recurrence, dynamical stabilizers, projective unitary torsion, Clifford quantum cellular automata, Poincare symmetry, Haag-Ruelle scattering, operator-algebraic finiteness, de Sitter representation theory, and relational physical time under an explicit claim boundary.