Search Talks

I describe a class of non-perturbative renormalization group (RG) transformations which, when applied to the (discrete time) Euclidean path integrals of a quantum systems on the lattice, can give results consistent with conformal transformations of quantum field theories. In particular, this class of transformation, which we call Tensor Network Renormalization (TNR), is shown to generate a scale-invariant RG flow for quantum systems at a critical point. Applications of TNR towards study of quantum critical systems, and its relationship to the multi-scale-entanglement renormalization ansatz (MERA) for ground and thermal states of quantum systems, will be discussed.

Of course not, but if one believes that information cannot be destroyed in a theory of quantum gravity, then we run into apparent contradictions with quantum theory when we consider evaporating black holes. Namely that the no-cloning theorem or the principle of entanglement monogamy is violated. Here, we show that neither violation need hold, since, in arguing that black holes lead to cloning or non-monogamy, one needs to assume a tensor product structure between two points in space-time that could instead be viewed as causally connected. In the latter case, one is violating the semi-classical causal structure of space, which is a strictly weaker implication than cloning or non-monogamy. We show that the lack of monogamy that can emerge in evaporating space times is one that is allowed in quantum mechanics, and is very naturally related to a lack of monogamy of correlations of outputs of measurements performed at subsequent instances of time of a single system. A particular example of this is the Horowitz-Maldacena proposal, and we argue that it needn't lead to cloning or violations of entanglement monogamy. In the case of the AMPS firewall experiment we find that the entanglement structure is modified, and one must have entanglement between the infalling Hawking partners and early time outgoing Hawking radiation which surprisingly tame violation of entanglement monogamy. http://arxiv.org/abs/1506.07133

The Ryu-Takayanagi proposal (and generalizations) for holographic entanglement makes predictions for geometric CFT entanglement entropy (EE) that continue to hold for any CFT, regardless of existence of large-N limit or strong coupling. We establish this using a direct field theory calculation, thus providing a non-trivial check of the holographic proposal. This universality emerges for small perturbations of the EE of a ball shaped region. Einstein’s equations arise from the field theory calculation as a way to efficiently encode this perturbative CFT entanglement holographically in the geometry of a dual space-time.

We will present a reformulation of the Ryu-Takayanagi holographic entanglement entropy formula which does not involve the areas of surfaces. The reformulation leads to a picture of entanglement entropy of boundary regions being carried by Planck-thickness "bit threads" in the bulk. We will argue that this picture resolves a number of conceptual difficulties surrounding the RT formula.

We study a quantum information metric (or fidelity susceptibility) in conformal field theories with respect to a small perturbation by a primary operator. We argue that its gravity dual is approximately given by a volume of maximal time slice in an AdS spacetime when the perturbation is exactly marginal. We confirm our claim in several examples.

Due to the linearity of the field equations and the resulting bilinear structure of the Hamiltonian, quantum radiation effects such as black hole evaporation or particle creation in an expanding universe are typically described as (squeezing) processes where particles are created in pairs. Here, we address the following question: given a mode (e.g., wave-packet) corresponding to a created particle (e.g., as part of Hawking radiation), what is its partner, i.e., the other particle of the pair? After a general derivation of this partner mode, we will discuss some examples such as moving mirror radiation and speculate about possible implications for the black hole information puzzle.

Can high energy physics can be simulated by low-energy, nonrelativistic, many-body systems, such as ultracold atoms? Ultracold atomic systems lack the type of symmetries and dynamical properties of high energy physics models: in particular, they do not manifest local gauge invariance nor Lorentz invariance, which are crucial properties of the quantum field theories which are the building blocks of the standard model of elementary particles. However, it will be shown that there are ways to configure atomic system to manifest both local gauge invariance and Lorentz invariance. In particular, local gauge invariance can arise either as an effective, low energy, symmetry, or as an "exact" symmetry, following from the conservation laws in atomic interactions. Such quantum simulators may lead to new type of (table-top) experiments, to test various QCD phenomena, as the confinement of dynamical quarks, phase transitions, and other effects.

I will sketch a few interesting phenomena involving ideal plasmas, including helicity conservation, frozen flux, the Blandford-Znajek mechanism, and self-confined Poynting jets, using the language of differential forms.

This year marks the 40’th anniversary of the Unruh effect as described at the first Marcel Grossmann meeting in 1975. We revisit it with emphasis on the observability issue which might be a concern at first sight, since the linear acceleration needed to reach a temperature 1 K is of order 10^20 m/s^2 . We close the talk by emphasizing that the Unruh effect does not require any verification beyond that of relativistic free field theory itself. The Unruh effect lives among us.