Talks

This talk is concerned with the existence of spectral triples in quantum gravity. I will review the construction of a spectral triple over a functional space of connections. Here, the *-algebra is generated by holonomy loops and the Dirac type operator has the form of a global functional derivation operator. The spectral triple encodes the Poisson structure of General Relativity when formulated in terms of Ashtekars variables. Finally I will argue that the Hamiltonian of General Relativity may emerge from the construction via the requirement that inner automorphisms vanish on the vacuum sector.

A recent breakthrough in quantum computing has been the realization that quantum computation can proceed solely through single-qubit measurements on an appropriate quantum state - for example, the ground state of an interacting many-body system. It would be unfortunate, however, if the usefulness of a ground state for quantum computation was critically dependent on the details of the system\'s Hamiltonian; a much more powerful result would be the existence of a robust ordered phase which is characterized by the ability to perform measurement-based quantum computation (MBQC). To identify such phases, we propose to use nonlocal correlation functions that quantify the fidelity of quantum gates performed between distant qubits. We investigate a simple spin-lattice system based on the cluster-state model for MBQC, and demonstrate that it possesses a zero temperature phase transition between a disordered phase and an ordered \'cluster phase\' in which it is possible to perform a universal set of quantum gates.

The last years have seen tremendous progress in simulations of inspiral and coalescence of binary black holes. I will present recent results of the Caltech/Cornell collaboration simulating inspiral and collision of two black holes. Furthermore, while currently no talk on numerical relativity seems to be complete without a discussion of binary black hole coalescence, there are many more aspects of Einstein\'s equations that can be probed numerically. I will discuss some of these unexpected and intriguing features, among them black holes with five horizons and super-extremal black holes.