SciPost Phys. 14, 097 (2023) ·
published 8 May 2023

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We give a bit thread prescription that is equivalent to the quantum extremal surface prescription for holographic entanglement entropy. Our proposal is inspired by considerations of bit threads in doubly holographic models, and equivalence is established by proving a generalisation of the Riemannian maxflow mincut theorem. We explore our proposal's properties and discuss ways in which islands and spacetime are emergent phenomena from the quantum bit thread perspective.
Ammanamanchi Ramesh Chandra, Jan de Boer, Mario Flory, Michal P. Heller, Sergio HÃ¶rtner, Andrew Rolph
SciPost Phys. 14, 061 (2023) ·
published 5 April 2023

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We consider proposals for the cost of holographic path integrals. Gravitational path integrals within finite radial cutoff surfaces have a precise map to path integrals in $T\overline{T}$ deformed holographic CFTs. In Nielsen's geometric formulation cost is the length of a notnecessarilygeodesic path in a metric space of operators. Our cost proposals differ from holographic state complexity proposals in that (1) the boundary dual is cost, a quantity that can be 'optimised' to state complexity, (2) the set of proposals is large: all functions on all bulk subregions of any codimension which satisfy the physical properties of cost, and (3) the proposals are by construction UVfinite. The optimal path integral that prepares a given state is that with minimal cost, and cost proposals which reduce to the CV and CV2.0 complexity conjectures when the path integral is optimised are found, while bounded cost proposals based on gravitational action are not found. Related to our analysis of gravitational actionbased proposals, we study bulk hypersurfaces with a constant intrinsic curvature of a specific value and give a Lorentzian version of the GaussBonnet theorem valid in the presence of conical singularities.
SciPost Phys. 12, 079 (2022) ·
published 1 March 2022

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We study the structure and dynamics of entanglement in CFTs and black holes.
We use a local entanglement measure, the entanglement contour, which is a
spatial density function for von Neumann entropy with some additional
properties. The entanglement contour can be calculated in many 1+1d condensed
matter systems and simple models of black hole evaporation. We calculate the
entanglement contour of a state excited by a splitting quench, and find
universal results for the entanglement contours of low energy nonequilibrium
states in 2d CFTs. We also calculate the contour of a nongravitational bath
coupled to an extremal AdS$_2$ black hole, and find that the contour only has
finite support within the bath, due to an island phase transition. The
particular entanglement contour proposal we use quantifies how well the bath's
state can be reconstructed from its marginals, through its connection to
conditional mutual information, and the vanishing contour is a reflection of
the protection of bulk island regions against erasures of the boundary state.
Dr Rolph: "I would like to thank the refe..."
in Submissions  report on Quantum bit threads