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Remarks on entanglement entropy for gauge fields (1312.1183v1)

Published 4 Dec 2013 in hep-th, cond-mat.stat-mech, and quant-ph

Abstract: In gauge theories the presence of constraints can obstruct expressing the global Hilbert space as a tensor product of the Hilbert spaces corresponding to degrees of freedom localized in complementary regions. In algebraic terms, this is due to the presence of a center --- a set of operators which commute with all others --- in the gauge invariant operator algebra corresponding to finite region. A unique entropy can be assigned to algebras with center, giving place to a local entropy in lattice gauge theories. However, ambiguities arise on the correspondence between algebras and regions. In particular, it is always possible to choose (in many different ways) local algebras with trivial center, and hence a genuine entanglement entropy, for any region. These choices are in correspondence with maximal trees of links on the boundary, which can be interpreted as partial gauge fixings. This interpretation entails a gauge fixing dependence of the entanglement entropy. In the continuum limit however, ambiguities in the entropy are given by terms local on the boundary of the region, in such a way relative entropy and mutual information are finite, universal, and gauge independent quantities.

Citations (328)

Summary

  • The paper demonstrates that gauge constraints prevent a natural tensor product decomposition of the Hilbert space, complicating entropy definitions.
  • It introduces maximal boundary link trees to construct localized algebras with trivial centers, enabling calculable entanglement entropy in lattice gauge theories.
  • The study shows that while entanglement entropy may be gauge-dependent, relative entropy and mutual information remain gauge-independent in the continuum limit.

An Examination of Entanglement Entropy in Gauge Fields

The paper discusses the intricate topic of entanglement entropy in the context of gauge fields by examining how constraints affect the partitioning of the Hilbert space. The key challenge is the inability to naturally express the global Hilbert space as a tensor product in regions separated by boundaries due to gauge constraints, which pose a significant difficulty in defining localized degrees of freedom. Instead of a straightforward decomposition, regions are marred by centers within their operator algebras — a collective of operators that commute universally within specified regions.

Entanglement entropy — a pivotal concept in gauge theories — traditionally required unique entropy definitions to articulate localized entropy on lattice gauge theories. Peculiarities, however, stem from ambiguities inherent in associating algebras with spatial regions. Problematically, ordinary algebra choices may possess centers, thereby obstructing genuine entanglement entropy characterizations. Notably, every region can be associated with localized algebras possessing trivial centers through well-reasoned algebra assignments, essentially by adopting maximal boundary link trees which emulate partial gauge fixings.

The intricacy of these algebraic constructions yields gauge dependency within defined entanglement entropy, though in the continuum limit, entropy ambiguities localize to regional boundaries, rendering relative entropy and mutual information as gauge-independent — outcomes of profound significance. These concepts remain finite and universal, particularly when scrutinizing information exchange between systems.

Lattice gauge fields underpin the formulation, with gauge transformation algebra characterized by link-associated group elements that uphold gauge invariance. This framing reveals peculiarities, such as non-trivial centers arising in localized operators due to inherent constraints.

To explore localized entropy within these systems, examining set operator algebras elucidates the multipart allegations between scalar fields and constrained systems. Notably, scalar fields allow for canonical operator constructions that connect spaces naturally, unlike their gauge-bound counterparts. The insight leads to observing the non-uniqueness of algebra choices. Although typical formulations imply non-trivial centers, entanglement entropy remains calculable.

Consequentially, the framework permits in-depth theoretical explorations of scenarios absent of straightforward tensor product factorization. Providing a mechanism by which entropy can be calculated in gauge theories, this work suggests new avenues for practical applications across higher-energy theoretical fields and quantum computing contexts.

Benchmarking outcomes against previously established topological models highlights entropy's gauge-dependency alongside potentially mutable entropies under reclassification of algebraic boundaries. Indicative examples demonstrate significant numerical variability attributable to model-specific interpretations.

Practically, advancing towards a comprehensive understanding entails selecting strategic local algebras that account for emergent quantum structures and classical entropic components. Theoretical implications envisage improved comprehension of entropic constraints within physical models and speculation evolves around the flexibility of entropy definitions requisite for envisioning more abstract gauge theory applications, especially as models venture towards continuum field theories.

Finally, while formulating effective representations to gauge field states in different selections — via mechanical or other abstractions — harmonious equivocations with past results reconcile synthesized positions suitable for continual exploitation within fundamental physics, hinting at broader ramifications within computational quantum and condensed matter paradigms.