Talks

It is commonly believed that quantum information is not lost in a black hole. Instead, it is encoded into non-local degrees of freedom in some clever way; like a quantum error-correcting code. In this talk, I will discuss recent attempts to resolve some paradoxes in quantum gravity by using the theory of quantum error-correction. First, I will introduce a simple toy model of the AdS/CFT correspondence based on tensor networks and demonstrate that the correspondence between the AdS gravity and CFT is indeed a realization of quantum codes. I will then show that the butterfly effect in black holes can be interpreted as non-local encoding of quantum information and can be quantitatively measured by out-of-time ordered correlations. Finally, I will discuss how out-of-time ordered correlations, measured outside the black hole horizon, may probe smoothness of the geometry across the horizon.

Laser-cooled trapped ions are among the most versatile experimental platforms for exploring quantum information. In this talk, I will give a brief overview of this system and its capabilities to simulate non-trivial interacting quantum models. Internal states of these ions, such as hyperfine states, constitute well isolated qubit (or spin-1/2) states, with quantum coherence demonstrated up to fifteen minutes. Individual qubits states can be detected by laser beams with near perfection. Quantum logic gates and interacting spin Hamiltonians are engineered by coupling internal states of multiple ions to their collective vibrational modes using optical forces. By suitably tailoring these spin-phonon couplings, interactions between ion-spins can be tuned in magnitude, range, and sign. The laboratory for Quantum Information with Trapped Ions at IQC aims to build a highly flexible quantum simulator with dozens of spins, and explore problems in quantum information and many-body physics in a regime that is intractable with classical computers.

Trine State discrimation solution, Quantum Money, Computing classical functions, Black and White boxes, Reversible circuits and cleaning the 'garbage', Quantum Key Distribution, One-time pad, BB84 Protocol.

The scattering amplitude of string perturbation theory as an integral over intrinsic geometry of the world sheet and a path integral over all possible emeddings of world-sheet in space-time; Nambu-Goto action and Polyakov action.

In this talk we propose a Hamiltonian approach to 2+1D gapped topological phases on an open surface with boundary. The bulk part is

(Levin-Wen) string-net models arising from a unitary fusion category (can be viewed as Hamiltonian approach to extended Turaev-Viro TQFT), while the boundary Hamiltonian is constructed using any Frobenius algebra in the input category. The combined Hamiltonian is exactly solvable and gives rise to a gapped energy spectrum which is topologically protected.

Our boundary Hamiltonians can be used to characterize and classify boundary conditions that give rise to gapped topological phase. We study the ground states and boundary excitations. Particularly, we show a correspondence between elementary excitations and the ground states on a cylinder system. Both are characterized by the category of bimodules over the Frobenius algebra that defines the  boundary Hamiltonian.

The fact that in physics concepts such as space, time, mass and energy are considered to be foundational has been conveniently serving a set of higher-level physical theories.

However, this keeps us from gaining a deeper understanding of such concepts which can in turn help us build a theory based on truly foundational concepts.

In this talk I introduce an alternate description of physical reality based on a simple foundational concept that there exist things that influence one another.

A network of objects that influence one another form a partially-ordered set (poset) that is called the influence network is considered. By consistently quantifying such a network with respect to a distinguished chain of events that is called an embedded observer, I demonstrate in relevant special cases that influence events can only be quantified by the familiar mathematics of space-time (Minkowski metric and Lorentz transformations), influence gives rise to basic concepts in Euclidean geometry such as direction, dimension and subspaces as well as the Pythagorean theorem, the dot product and geometrical figures. Thus a discrete version of some of the Euclidean geometry’s fundamental concepts is derived in this picture. Finally I talk about the concept of influence in quantum mechanics and how the case of a free particle is identical to the Feynman checkerboard problem for the electron which is known to give rise to the Dirac equation.

In this talk I will discuss a new use for conformal field theory crossing equation in the context of AdS/CFT:  the computation of loop amplitudes in AdS, dual to non-planar correlators in holographic CFTs. I will revisit this problem and the dual 1/N expansion of CFTs, in two independent ways. The first is to show how to explicitly solve the crossing equations to the first subleading order in 1/N^2, given a leading order solution. This is done as a systematic expansion in inverse powers of the spin, to all orders. These expansions can be resummed, leading to the CFT data for finite values of the spin. The second approach involves Mellin space. As an example, I’ll show how the polar part of the four-point, loop-level Mellin amplitudes can be fully reconstructed from the leading-order data. The anomalous dimensions computed with both methods agree. In the case of \phi^4 theory in AdS, the crossing solution reproduces a previous computation of the one-loop bubble diagram. I will end with a discussion on open problems and new developments.

We are currently entering the era of precision CMB polarization observations. The most exciting scientific targets are a possible detection of primordial gravitational waves and a measurement of the sum of the neutrino masses. The former depends on the extensive landscape of early Universe models, while the latter has been forecasted to present a clear, and reachable, scientific target. First, if large angular B modes are detected, we should firmly establish that these are sourced by primordial gravitational waves. I will discuss that cross correlating the B-mode signal with the curl-lensing field could help establish the nature of the detected B-modes. Second, I will propose to look beyond Gaussianity in the tensor sector. Scalar non-Gaussianities are tightly constrained by Planck, but couplings between tensors and scalars are currently not constrained and future CMB polarization surveys could open a new window into the early Universe, by searching for tensor non-Gaussianites. Finally, a detection of the normal hierarchy of the neutrino mass requires an excellent measurement of the amplitude of primordial fluctuations. The required measurement can only be achieved if we are able to measure the large angle E-mode polarization spectrum, which currently lies beyond reach, at least within the foreseeable future. I will present a possible solution and show how this simple methodology can be used to constrain exotic primordial physics at the same time.