Scientific Series

We introduce a technique for applying quantum expanders in a distributed fashion, and use it to solve two basic questions: testing whether a bipartite quantum state shared by two parties is the maximally entangled state and disproving a generalized area law. In the process these two questions which appear completely unrelated turn out to be two sides of the same coin. Strikingly in both cases a constant amount of resources are used to verify a global property.

The AdS/CFT correspondence from string theory provides a quantum theory of gravity in which spacetime and gravitational physics emerge from an ordinary non-gravitational system with many degrees of freedom. In this talk, I will explain how quantum entanglement between these degrees of freedom is crucial for the emergence of a classical spacetime, and describe progress in understanding how spacetime dynamics (gravitation) arises from the physics of quantum entanglement."

The moduli space of k G instantons on C^2, where G is a classical gauge group, has a well known HyperKahler quotient formulation known as the ADHM construction. The extension to exceptional groups is an open problem.
In string theory this is realized using a system of branes, and the moduli space of instantons is identified with the Higgs branch of a particular supersymmetric gauge theory with 8 supercharges.
A less known, and less studied aspect of moduli spaces of instantons is that they can be realized as the Coulomb branch of a supersymmetric gauge theory in 2+1 dimensions.
Recent developments on the understanding of the Coulomb branch gives us a nice solution to the problem where G is an exceptional group, thus allowing a systematic study of these moduli spaces which was unavailable so far.
I will discuss these developments, and present the corresponding quivers, and the Coulomb branch Hilbert Series - the main tool which lead to the recent progress.

The Higgs couplings to fermions are known parameters within the Standard Model. Deviations from these
expectations would be clear signals of new physics and are thus important target measurements for the LHC program. 
In this talk I shall discuss ways to extra information about the coupling of the Higgs boson to the charm quark with
emphasis on methods applicable with the available LHC data set. A novel method based on the current ATLAS and CMS
Hbb measurement will be presented and compared to our knowledge so far.  Future projections and the even more
challenging case of light-quark Yukawa couplings will be discussed.

It is well known that S-matrix Analyticity, Lorentz invariance and Unitarity place strong constraints on whether Effective Field Theories can be UV completed. A large class of gravitational field theories such as Massive Gravity and DGP inspired braneworld models contain as limits Galileon theories which in the past have been argued to violate the conditions necessary for a UV completion. I will present arguments that imply quite the opposite, although Galileons do not admit a standard Wilsonian UV completion, I will use the recently discovered Galileon duality to argue that these theories can exhibit a non-Wilsonian completion consistent with the `Classicalization’ proposal. These theories have quintessentially gravitational properties such as non-polynomially bounded scattering amplitudes, absence of local off-shell observables and an exponentially soft 2-2 scattering amplitude. These properties show up in a violation of the standard Wightman axioms and are consistent with many of the known properties of UV completions of gravity. I will argue that the superluminal solutions found in the low energy EFT are absent in the UV completion.

Gravitational waves (GW) imprint apparent Doppler shifts on the frequency of photons propagating between an emitter and detector of light. This forms the basis of a method to detect mHz GW using Doppler velocimetry between pairs of satellites [1]. The crucial component in such GW detectors is the frequency standard on board the emitting and receiving satellites. I will discuss how recent developments in atomic clock technology have led to devices that could be sufficiently sensitive to probe astrophysically interesting sources. I will present a design for a robust, space-capable optical frequency standard [2], that is being developed at York.

References

[1] JW Armstrong, Living Rev. Relativity 9, (2006), 1 [2] AC Vutha, arXiv:1501.01733 (2015)

In this talk I will outline the process of institutional change begun at the University of Michigan in 2001 and continuing today. This will include discussion of a range of institutional efforts to improve hiring, recruitment, climate and leadership that was focused on creating a more diverse and inclusive faculty.  I will close with brief discussion of two studies: one assessing changes in the workplace climate for faculty in 2001, 2006 and 2012; and one examining the characteristics of departments that made the most change in contrast to those that made the least.  I will conclude with some observations about the change process.

The last years have seen a renewed interest in theories of massive gravity. They represent an infra-red modification of gravity where the gravitational force weakens at very large scales. Heuristically, they provide the playground to understand a possible modification of GR which could potentially provide a dynamical solution to the cosmological constant problem. In this talk I will discuss a number of theoretical aspects of massive gravity theories, focusing on the relevance of the so-called Vainstein mechanism, both at the classical and the quantum level. I will also discuss how we can use cosmology from the early and late universe to constrain these theories. For example, what does the Cosmic Microwave Background Radiation know about the graviton mass?

The Elitzur-Vaidman bomb tester allows the detection of a photon-triggered bomb with a photon, without setting the bomb off. This seemingly impossible task can be tackled using the quantum Zeno effect. Inspired by the EV bomb tester, we define the notion of "bomb query complexity". This model modifies the standard quantum query model by measuring each query immediately after its application, and ends the algorithm if a 1 is measured.

We show that the bomb query complexity is asymptotically the square of the quantum query complexity. Moreover, we will show how this characterization inspires a general theorem relating classical and quantum query complexity, and derive new algorithms from this theorem.

The entanglement spectrum, i.e. the logarithm of the eigenvalues of reduced density matrices of
quantum many body wave functions, has been the focus of a rapidly expanding research endeavor recently.
Initially introduced by Li & Haldane in the context of the fractional quantum Hall effect, its usefulness has been
shown to extend to many more fields, such as topological insulators, fractional Chern insulators, spin liquids,
continuous symmetry breaking states, etc.
After a general introduction to the field we review some of our own contributions to the field, in particular the
perturbative structure of the entanglement spectrum in gapped phases, the entanglement spectrum across the
Mott-insulator transition in the Bose-Hubbard model, and the relation of the entanglement spectrum of
(1+1) dimensional quantum critical systems to the operator content of their underlying CFT.

Recent research has suggested deep connections between geometry and entropy. This connection was first seen in black hole thermodynamics, but has been more fully realized in the Ryu-Takayanagi proposal for calculating entanglement entropies in AdS/CFT. We suggest that this connection is even broader: entropy, and in particular compression, are the fundamental building blocks of emergent geometry. We demonstrate how spatial geometry can be derived from the properties of a recursive compression algorithm for the boundary CFT. We propose a general algorithm for constructing MERA-like tensor networks and elucidate connections to the mathematical field of integral geometry.