Search Talks

In the future it may be possible to observe the CMB radiation at very low frequencies. I review the origin of the signal from 21cm absorption by dark-age gas and explain the huge potential for observational cosmology. I summarise recent work on theoretical expectations for the observable power spectrum, including discussion of Hubble-scale perturbations, the effects of perturbed recombination and non-linear evolution.

Sensitive information can be valuable to others - from your personal credit card numbers to state and military secrets. Throughout history, sophisticated codes have been developed in an attempt to keep important data from prying eyes. But now, new technologies are emerging based on the surprising laws of quantum physics that govern the atomic scale. These powerful techniques threaten to crack some secret codes in widespread use today and, at the same time, offer new quantum cryptographic protocols which could one day profoundly alter the way we safeguard critical information. Quantum cryptography, quantum physics, Daniel Gottesman, cryptography, one-time pad, RSA, encryption, public key, decryption, private key, quantum computer, qubit, shor\'s algorithm, quantum key distribution, QKD

Consider a discrete quantum system with a d-dimensional state space. For certain values of d, there is an elegant information-theoretic uncertainty principle expressing the limitation on one's ability to simultaneously predict the outcome of each of d+1 mutually unbiased--or mutually conjugate--orthogonal measurements. (The allowed values of d include all powers of primes, and at present it is not known whether any value of d is excluded.) In this talk I show how states that minimize uncertainty in this sense can be generated via a discrete phase space based on finite fields. I also discuss some numerically observed features of these minimum-uncertainty states as the dimension d gets very large.

Shear viscosity is a transport coefficient in the hydrodynamic description of liquids, gases and plasmas. The ratio of the shear viscosity and the volume density of the entropy has the dimension of the ratio of two fundamental constants - the Planck constant and the Boltzmann constant - and characterizes how close a given fluid is to a perfect fluid. Transport coefficients are notoriously difficult to compute from first principles. Recent progress in string theory, in particular the development of the gauge-gravity duality, has enabled one to approach this problem from a totally unexpected perspective. In my talk, I will describe the connection between the dynamics of black hole horizons (encoded in their quasinormal spectra) and the hydrodynamics of certain strongly coupled plasmas. I will comment on the relevance of this approach for the interpretation of data obtained in experiments on heavy ion collisions.