Scientific Series

The exact boundary states for the rolling D-brane solution in two-dimensional black hole systems will be presented.I will study the physical significance of the solution in relation to the ``tachyon-radion correspondence\" and the ``black hole - string transition\". When the alpha\' corrections become larger, when at the same time the Hawking temperature coincide with the Hagedorn temperature, the phase transition occurs and the physics changes drastically. It also suggests the universal feature of the decaying D-brane and its failure in the strong quantum regime. The talk is based on my series of works hep-th/0605013, hep-th/0507040 in collaboration with Soo-jong Rey (SNU) and Yuji Sugawara (Tokyo).

We have previously isolated and characterized a multipotent precursor cell (termed SKPs for SKin-derived Precursors) from both rodent and human skin, and have shown that these stem cells share many characteristics with a multipotent stem cell that is found in the embryo termed a neural crest stem cell. Here I will discuss our current work with regard to the basic biology of these stem cells, with a focus on the “what, where and why”, and on their therapeutic potential with specific regard to the nervous system.

Most modern discussions of Bell's theorem take microscopic causality (the arrow of time) for granted, and raise serious doubts concerning realism and/or relativity. Alternatively, one may allow a weak form of backwards-in-time causation, by considering "causes" to have not only "effects" at later times but also "influences" at earlier times. These "influences" generate the correlations of quantum entanglement, but do not enable information to be transmitted to the past. Can one realize this scenario in a mathematical model? If macroscopic time-asymmetry is introduced by imposing initial conditions, such a model can not be deterministic. Stochastic Quantization (Parisi and Wu,1981) is a non-deterministic approach known to reproduce quantum field theory. Based on this, a search for models displaying quantum nonlocal correlations, while maintaining the principles of realism, relativity and macroscopic causality, is proposed.

It will be shown that eternal inflation of the random walk type is generically absent in the brane inflationary scenario. Eternal inflation will be analysed both in the context of KKLMMT and the DBI inflationary models. A Langevin analysis will be employed for a more careful treatment. The DBI action, and the relativistic nature of the brane motion in DBI inflationary model, leads to new subtleties in formulating a Langevin approach.

I will discuss some ambiguities involved in using the AdS/CFT correspondence to calculate the ultra-relativistic jet quenching parameter for quarks moving in an N=4 super Yang-Mills thermal bath. Along the way, I will investigate the behavior of various string configurations on a five-dimensional AdS black hole background.

In this talk, I will show how to efficiently generate graph states based on realistic linear optics (with imperfect photon detectors and source), how to do scalable quantum computation with probabilistic atom photon interactions, and how to simulate strongly correlated many-body physics with ultracold atomic gas.

I will explain how a quantum circuit together with measurement apparatuses and EPR sources can be fully verified without any reference to some other trusted set of quantum devices. Our main assumption is that the physical system we are working with consists of several identifiable sub-systems, on which we can apply some given gates locally. To achieve our goal we define the notions of simulation and equivalence. The concept of simulation refers to producing the correct probabilities when measuring physical systems. The notion of equivalence is used to enable the efficient testing of the composition of quantum operations. Unlike simulation, which refers to measured quantities (i.e., probabilities of outcomes), equivalence relates mathematical objects like states, subspaces or gates. Using these two concepts, we prove that if a system satisfies some simulation conditions, then it is equivalent to the one it is supposed to implement. In addition, with our formalism, we can show that these statements are robust, and the degree of robustness can be made explicit. Finally, we design a test for any quantum circuit whose complexity is linear in the number of gates and qubits, and polynomial in the required precision. Joint work with Frederic Magniez, Dominic Mayers and Harold Ollivier.

Complexity class MA is a class of yes/no problems for which the answer `yes\' has a short certificate that can be efficiently checked by a classical randomized algorithm. We prove that MA has a natural complete problem: stoquastic k-SAT. This is a quantum-mechanical analogue of the satisfiability problem such that k-bit clauses are replaced by k-qubit projectors with non-negative matrix elements. Complexity class AM is a generalization of MA in which the certificate may include a short conversation between Prover and Verifier. We prove that AM also has a natural complete problem: stoquastic Local Hamiltonian with a quenched disorder. The problem is to evaluate expectation value of the ground state energy of disordered local Hamiltonian with non-positive matrix elements.

The nature of an unusual class of cosmic X-ray source, dubbed "Anomalous X-ray Pulsars," was a mystery since 1982 when the first example was discovered. In this talk, I will show the recent observational evidence that unambiguously links them with another equally exotic class of object, the explosive "Soft Gamma Repeaters." The evidence todate strongly supports the picture that both are "magnetars:" isolated young neutron stars having surface magnetic fields ~1000 times greater than those in conventional neutron stars.