Talks

One of the most significant questions in quantum information is about the origin of the computational power of the quantum computer; namely, from which feature of quantum mechanics and how does the quantum computer obtain its superior computational potential compared with the classical computer? In my talk, I address this open question more concisely through the study of measurement-based quantum computer, in which all the quantum resource is attributed to entanglement since computation is carried through its consumption by local measurements. I also show a simple model of the phase transition of quantum computer occurring at some threshold, below which the quantum computer comes to allow an efficient classical simulation in accordance with an exponential drop in the amount of entanglement.

Quantum fields in the Minkowski vacuum are entangled with respect to local field modes. This entanglement can be swapped to spatially separated quantum systems using standard local couplings. A single, inertial field detector in the exponentially expanding (de Sitter) vacuum responds as if it were bathed in thermal radiation in a Minkowski universe. Using two inertial detectors, interactions with the field in the thermal case will entangle certain detector pairs that would not become entangled in the corresponding de Sitter case.The two universes can thus be distinguished by their entangling power.

We demonstrate a number of effective field theory constructions developed to capture the effects of new physics on the Higgs sector of the standard model. We demonstrate that as the self couplings of the Higgs could be significantly effected by new physics, novel phenomenology such as a two Higgs bound state (Higgsium) may be possible. We also demonstrate that the effects of new physics on the Higgs fermion couplings, and thus the Higgs width, could be significant. We show that it is possible this could happen while the new physics cannot be directly detected at LHC. This could lead to an early Higgs discovery or a missing Higgs in the first 100 fb^(-1) of data at LHC.

Cosmic strings are non-trivial configurations of scalar (and vector) fields that are stable on account of a topological conservation law. They can be formed in the early universe as it cools after the Big Bang. The scalar fields required to form cosmic strings arise naturally if Nature is supersymmetric at high energies. A common feature of supersymmetric theories are directions in the scalar potential that are extremely flat. Combining these two ingredients, the cosmic strings associated with supersymmetric flat directions are qualitatively different from ordinary cosmic strings. In particular, flat-direction strings have very stable higher-winding modes, and are very wide relative to the scale of their energy density. These novel features have important implications for the formation and evolution of a network of flat-direction cosmic strings in the early universe. They also affect the observational signatures of the strings, which include gravity waves, dark matter, and modifications to the nuclear abundances and the blackbody spectrum of the microwave background radiation

Strong gauge dynamics can be given a holographic description in terms of a warped extra dimension. In particular, Randall-Sundrum models with bulk fields are dual to Standard Model partial compositeness. We identify a holographic basis of 4D fields that allows for a quantitative description of the elementary/composite mixing in these theories.

We highlight the unexpected impact of nucleosynthesis on the detectability of tracking quintessence dynamics at late times, showing that dynamics may be invisible until Stage-IV dark energy experiments (DUNE, JDEM, LSST, SKA). Nucleosynthesis forces |wŒ(0)| <0.2 for the models we consider and strongly limits potential deviations from _LCDM . Surprisingly, the standard CPL parametrisation, w(z) = w0 +waz/(1+z), cannot match the nucleosynthesis bound for minimally coupled tracking scalar fields. Given that such models are arguably the best-motivated alternatives to a cosmological constant these results may significantly impact future cosmological survey design and imply that dark energy may be dynamical even if we do not detect any dynamics in the next decade.

First, a brief description of Bell\'s theorem will be given. It states states that there is no classical-like (local realistic) description of all quantum predictions. Next, a plausible class of non-local realistic models will be presented which is incompatible with quantum mechanics, as first shown by Leggett. Experiments confirming the incompatibility will be described. Finally, it will be argued that quantum mechanics can be seen as a theory of systems with limited information resources.