# Condensed matter physics, area laws & LQG?

1. Nov 14, 2016

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https://arxiv.org/abs/1611.00360
de Sitter as a Resonance
Jonathan Maltz, Leonard Susskind
(Submitted on 1 Nov 2016)
A quantum mechanical formulation of de Sitter cosmological spacetimes still eludes string theory. In this paper we conjecture a potentially rigorous framework in which the status of de Sitter space is the same as that of a resonance in a scattering process. We conjecture that transition amplitudes between certain states with asymptotically supersymmetric flat vacua contain resonant poles characteristic meta-stable intermediate states. A calculation employing constrained instantons illustrates this idea.

https://arxiv.org/abs/1611.03491
de Sitter Harmonies: Cosmological Spacetimes as Resonances
Jonathan Maltz
(Submitted on 10 Nov 2016)
The aim of this work is to provided the details of a calculation summarized in the recent paper by Maltz and Susskind which conjectured a potentially rigorous framework where the status of de Sitter space is the same as that of a resonance in a scattering process. The conjecture being that transition amplitudes between certain states with asymptotically supersymmetric flat vacua contain resonant poles characteristic meta-stable intermediate states. A calculation employing constrained instantons is presented that illustrates this idea.

2. Nov 28, 2016

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https://arxiv.org/abs/1611.08581
Towards a dS/MERA correspondence
Raj Sinai Kunkolienkar, Kinjal Banerjee
(Submitted on 25 Nov 2016)
Recent advances have suggested that spacetime itself emerges from the entanglement of the quantum degrees of freedom living on the boundary. In the case of the AdS spacetimes, a particular class of tensor networks has been shown to realize the same via Multi-Scale Entanglement Renormalization Ansatz (MERA). In this paper we suggest a prescription for the dS/MERA correspondence and recover a discrete version of de Sitter Penrose diagram by using the MERA on conformal theories identified with the future/past conformal boundaries of the de Sitter spacetime. As anticipated, time appears as the emergent direction. We comment on the possible interpretation that the de Sitter cosmological horizon entropy involves entanglement with degrees of freedom across the cosmological horizon as well as the implications of our construction for cosmology.

https://arxiv.org/abs/1611.08613
Tensor Network Models of Unitary Black Hole Evaporation
Samuel Leutheusser, Mark Van Raamsdonk
(Submitted on 25 Nov 2016)
We introduce a general class of toy models to study the quantum information-theoretic properties of black hole radiation. The models are governed by a set of isometries that specify how microstates of the black hole at a given energy evolve to entangled states of a tensor product black-hole/radiation Hilbert space. The final state of the black hole radiation is conveniently summarized by a tensor network built from these isometries. We introduce a set of quantities generalizing the Renyi entropies that provide a complete set of bipartite/multipartite entanglement measures, and give a general formula for the average of these over initial black hole states in terms of the isometries defining the model. For models where the dimension of the final tensor product radiation Hilbert space is the same as that of the space of initial black hole microstates, the entanglement structure is universal, independent of the choice of isometries. In the more general case, we find that models which best capture the "information-free" property of black hole horizons are those whose isometries are tensors corresponding to states of tripartite systems with maximally mixed subsystems.

3. Dec 2, 2016

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https://arxiv.org/abs/1612.00433
Dean Carmi, Robert C. Myers, Pratik Rath
(Submitted on 1 Dec 2016)
We study two recent conjectures for holographic complexity: the complexity=action conjecture and the complexity=volume conjecture. In particular, we examine the structure of the UV divergences appearing in these quantities, and show that the coefficients can be written as local integrals of geometric quantities in the boundary. We also consider extending these conjectures to evaluate the complexity of the mixed state produced by reducing the pure global state to a specific subregion of the boundary time slice. The UV divergences in this subregion complexity have a similar geometric structure, but there are also new divergences associated with the geometry of the surface enclosing the boundary region of interest. We discuss possible implications arising from the geometric nature of these UV divergences.

4. Dec 9, 2016

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https://arxiv.org/abs/1612.02427
cMERA for Interacting Fields
Jordan S. Cotler, Javier Molina-Vilaplana, Mark T. Mueller
(Submitted on 7 Dec 2016)
We upgrade cMERA to a systematic variational ansatz and develop techniques for its application to interacting quantum field theories in arbitrary spacetime dimensions. By establishing a correspondence between the first two terms in the variational expansion and the Gaussian Effective Potential, we can exactly solve for a variational approximation to the cMERA entangler. As examples, we treat scalar $φ^{4}$ theory and the Gross-Neveu model and extract non-perturbative behavior. We also comment on the connection between generalized squeezed coherent states and more generic entanglers.

5. Dec 19, 2016

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https://arxiv.org/abs/1612.05698
A defect in holographic interpretations of tensor networks
Bartlomiej Czech, Phuc H. Nguyen, Sivaramakrishnan Swaminathan
(Submitted on 17 Dec 2016)
We initiate the study of how tensor networks reproduce properties of static holographic space-times, which are not locally pure anti-de Sitter. We consider geometries that are holographically dual to ground states of defect, interface and boundary CFTs and compare them to the structure of the requisite MERA networks predicted by the theory of minimal updates. When the CFT is deformed, certain tensors require updating. On the other hand, even identical tensors can contribute differently to estimates of entanglement entropies. We interpret these facts holographically by associating tensor updates to turning on non-normalizable modes in the bulk. In passing, we also clarify and complement existing arguments in support of the theory of minimal updates, propose a novel ansatz called rayed MERA that applies to a class of generalized interface CFTs, and analyze the kinematic spaces of the thin wall and AdS3-Janus geometries.

6. Jan 1, 2017

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https://arxiv.org/abs/1612.09513
Holographic Bell Inequality
Jiunn-Wei Chen, Sichun Sun, Yun-Long Zhang
(Submitted on 30 Dec 2016)
We study the Bell inequality in a holographic model of a casually disconnected Einstein-Podolsky-Rosen (EPR) pair. The CHSH form of Bell inequality are computed using holographic Schwinger-Keldysh(SK) correlators. We show that the manifestation of quantum entanglement in Bell inequality can be reproduced from the classical gravitation theory in the bulk, which lends support to the ER=EPR conjecture.

7. Jan 4, 2017

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https://arxiv.org/abs/1701.01107
The Second Law of Quantum Complexity
(Submitted on 4 Jan 2017)
We give arguments for the existence of a thermodynamics of quantum complexity that includes a "Second Law of Complexity". To guide us, we derive a correspondence between the computational (circuit) complexity of a quantum system of K qubits, and the positional entropy of a related classical system with 2K degrees of freedom. We also argue that the kinetic entropy of the classical system is equivalent to the Kolmogorov complexity of the quantum Hamiltonian. We observe that the expected pattern of growth of the complexity of the quantum system parallels the growth of entropy of the classical system. We argue that the property of having less-than-maximal complexity (uncomplexity) is a resource that can be expended to perform directed quantum computation.
Although this paper is not primarily about black holes, we find a surprising interpretation of the uncomplexity-resource as the accessible volume of spacetime behind a black hole horizon.

8. Jan 7, 2017

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https://arxiv.org/abs/1701.01383
Group Field theory and Tensor Networks: towards a Ryu-Takayanagi formula in full quantum gravity
Goffredo Chirco, Daniele Oriti, Mingyi Zhang
(Submitted on 5 Jan 2017)
We establish a dictionary between group field theory (thus, spin networks and random tensors) states and generalized random tensor networks. Then, we use this dictionary to compute the R\'{e}nyi entropy of such states and recover the Ryu-Takayanagi formula, in three different cases corresponding to three different truncations/approximations, suggested by the established correspondence.

9. Jan 11, 2017

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https://arxiv.org/abs/1701.02319
Connecting Fisher information to bulk entanglement in holography
Souvik Banerjee, Johanna Erdmenger, Debajyoti Sarkar
(Submitted on 9 Jan 2017)
In the context of relating AdS/CFT to quantum information theory, we propose a holographic dual of Fisher information metric for mixed states in the boundary field theory. This amounts to a holographic measure for the distance between two mixed quantum states. For a spherical subregion in the boundary we show that this is related to a particularly regularized volume enclosed by the Ryu-Takayanagi surface. We further argue that the quantum correction to the proposed Fisher information metric is related to the quantum correction to the boundary entanglement entropy. We discuss consequences of this connection.