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We study the ground-state entanglement of gapped domain walls between topologically ordered systems in two spatial dimensions. We derive a universal correction to the ground-state entanglement entropy, which is equal to the logarithm of the total quantum dimension of a set of superselection sectors localized on the domain wall. This expression is derived from the recently proposed entanglement bootstrap method., Comment: 5 pages, 5 figures

We show how lattice gauge theories can display many-body localization dynamics in the absence of disorder. Our starting point is the observation that, for some generic translationally invariant states, Gauss law effectively induces a dynamics which can be described as a disorder average over gauge super-selection sectors. We carry out extensive exact simulations on the real-time dynamics of a lattice Schwinger model, describing the coupling between U(1) gauge fields and staggered fermions. Our results show how memory effects and slow entanglement growth are present in a broad regime of parameters - in particular, for sufficiently large interactions. These findings are immediately relevant to cold atoms and trapped ions experiments realizing dynamical gauge fields, and suggest a new and universal link between confinement and entanglement dynamics in the many-body localized phase of lattice models., Comment: 5Pages + appendices; V2: updated discussion in page 2, more numerical results, added references

We investigate decoherence in the limit where the interaction with the environment is weak and the evolution is dominated by the self Hamiltonian of the system. We show that in this case quantized eigenstates of energy emerge as pointer states selected through the predictability sieve., Comment: 4 pages, no figures

It is proposed that an unconstrained quantum system is completely specified by its configuration space C and its group of symmetries G . It is then shown that the theory of projective unitary representations of G on a certain Hilbert space determined by C and G leads to a definitive resolution of supposed ambiguities relating to superselection rules, choice of wave functions, topological properties of G and C , anomalies, etc. {copyright} {ital 1997} {ital The American Physical Society}

We develop a theory of charge-parity-time ($CPT$) frameness resources to circumvent $CPT$ superselection. We construct and quantify such resources for spin-0, $1/2$, 1, and Majorana particles and show that quantum information processing is possible even with $CPT$ superselection. Our method employs a unitary representation of $CPT$ inversion by considering the aggregate action of $CPT$ rather than the composition of separate $C$, $P$, and $T$ operations, as some of these operations involve problematic antiunitary representations.

Natural particle-number entanglement resides between spatial modes in coherent ultra-cold atomic gases. However, operations on the modes are restricted by a superselection rule that forbids coherent superpositions of different particle numbers. This seemingly prevents mode entanglement being used as a resource for quantum communication. In this paper, we demonstrate that mode entanglement of a single massive particle can be used for dense coding and quantum teleportation despite the superselection rule. In particular, we provide schemes where the dense coding linear photonic channel capacity is reached without a shared reservoir and where the full quantum channel capacity is achieved if both parties share a coherent particle reservoir., Comment: 4 pages, 1 figure

Bipartite entanglement may be reduced if there are restrictions on allowed local operations. We introduce the concept of a generalized superselection rule (SSR) to describe such restrictions, and quantify the entanglement constrained by it. We show that ensemble quantum information processing, where elements in the ensemble are not individually addressable, is subject to the SSR associated with the symmetric group (the group of permutations of elements). We prove that even for an ensemble comprising many pairs of qubits, each pair described by a pure Bell state, the entanglement per element constrained by this SSR goes to zero for a large number of elements., 4 pages, published version

We show that the superselection rule in the Galilean transformation, forbidding the superposition of states of different mass, in inconsistent with the nonrelativistic limit of the Lorentz transformation. We also point out that the extra Galilean phase is merely the residue of the "twin-paradox" effect, which does not vanish nonrelativistically. In general, there are phase effects due to proper time differences, and effects due to mass-energy equivalence, that do not vanish nonrelativistically but that are not handled adequately by the Galilean transformation.

This is a reply to the above comment (hep-th/9509028). We argue that QED displays a class of symmetries which may be used to select out the various velocity dependent superselection sectors.