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Timetable (QISW05)

Focus Week: Quantum Gravity and Quantum Information

Tuesday 14th December 2004 to Friday 17th December 2004

Tuesday 14th December 2004
10:00 to 11:00 Model of a big crunch/big bang transition
Session: Quantum Gravity and Quantum Information
INI 1
11:30 to 12:30 Black hole analogues and the universality of the Hawking effect
Session: Quantum Gravity and Quantum Information
INI 1
16:30 to 17:30 Bohr, Penrose and Hawking
Session: Quantum Gravity and Quantum Information

No Phenomenon is a phenomenon until it is an observed phenomenon. What limits does quantum measurement theory place on black hole physics?

INI 1
Wednesday 15th December 2004
10:00 to 11:00 Information loss, determinism and quantum mechanics
Session: Quantum Gravity and Quantum Information

Since the probabilistic interpretation of Quantum Mechanics requires unitarity, conventional Quantum Mechanics does not allow for a notion such as information loss. However, it is possible to interpret Quantum Mechanics in terms of an underlying deterministic theory, and it is here, in the classical sense, that information loss can be introduced. We argue that information loss then indeed may be an essential ingredient of the theory, helping us to understand how the notion of holography can be reconciled with locality. Thus, determinism and information loss may become crucial ingredients of Planck Scale Physics, and we explain why exactly this should lead to the unitary quantum mechanical framework of the Standard Model of the subatomic world.

INI 1
11:30 to 12:30 Limits of quantum mechanics from general relativity: a clash of principles
Session: Quantum Gravity and Quantum Information

The subject of "quantum gravity" is generally studied from the point of view of how our classical space-time picture might become modified when it is made subject to the principles of quantum (field) theory. Yet there are several good reasons to believe that, conversely, the very principles of quantum mechanics are also limited in their scope, and that Einstein's principle of equivalence may supply a limitation to the basic quantum principle of linear superposition. Such a limitation is suggested from a study of the Galilean limit of the Unruh effect, and appears to be accessible to forseeable experimental test.

INI 1
16:00 to 17:00 Universe from sub-Planckian bits
Session: Quantum Gravity and Quantum Information
INI 1
Thursday 16th December 2004
10:00 to 11:00 D Gottesman ([Perimeter Institute])
Black hole evaporation, unitarity and final state projection
Session: Quantum Gravity and Quantum Information

What happens when a black hole evaporates? Does it leave behind anything more than a spray of Hawking radiation, and perhaps more importantly, how is the state of that radiation related to objects that fell into the black hole? In particular, is the overall behavior of the system unitary, or is information about the system's initial state irrevocably lost? I will give an overview of proposed resolutions to the black hole information-loss problem aimed towards those studying quantum information. I will then focus on a recent proposal by Horowitz and Maldacena to solve the problem by introducing a final state projection at the black hole singularity, and an objection to this solution by Preskill and myself.

INI 1
11:30 to 12:30 C Galfard ([CMS])
The path integral approach to the black hole information problem
Session: Quantum Gravity and Quantum Information

The black hole information loss problem has been the focus of much debate for the past thirty years. I will review the path integral approach to the problem: how it can be seen that black holes evaporate (Hartle-Hawking) thus apparently destroying information and how the sum over (Euclidean) space-time topologies may lead to a recovery of the information (Maldacena, Hawking). I will also point out why this may not be the end of the story (Barbon-Rabinovici) and, time permitting, mention a related holographic black hole non-formation argument to solve the problem which I am working on with Germani and Ishibashi.

INI 1
16:30 to 17:30 When entanglement met black hole...
Session: Quantum Gravity and Quantum Information

There are two ways of doing quantum information theory beyond qubits. One task is to investigate its basic notions in the new situations. The familiar entities there acquire some unusual properties. Entropy is observer-dependent, but not always so. Entanglement measures may be observer-dependent as well. We discuss the reasons for this dependence and the implications of both invariance and non-invariance, illustrating by the geometric entropy in quantum field theory and black hole entropy.

On the other hand, we may apply quantum information to the problems in other areas. For example, the logarithmic corrections for the black hole entropy may be related to the entanglement between parts of the spin network that describes its horizon. We also speculate that the entropy production during the black hole creation and evaporation is actually an expression of entanglement between gravity and matter.

INI 1
17:30 to 18:30 Quantum information theory and the low energy problem of quantum gravity INI 1
Friday 17th December 2004
10:00 to 11:00 S Lloyd ([MIT])
Quantum gravity and quantum computation
Session: Quantum Gravity and Quantum Information

This talk proposes a theory of quantum gravity and elementary particle physics based on quantum computation. In this theory, fundamental processes are described in terms of quantum information processing: the structure of space-time and of quantum fields are constructs, derived from the underlying quantum computation.

INI 1
11:30 to 11:50 Entanglement and area
Session: Quantum Gravity and Quantum Information
INI 1
11:50 to 12:10 Locked information and the black hole information loss problem
Session: Quantum Gravity and Quantum Information

Recently, a new and purely quantum effect has been discovered in which a small amount of information acts as a key that can unlock a much larger amount of information. Classically, the accessible mutual information about a random variable is never less than the total amount of entropy in the random variable minus the size of the key. Quantum-mechanically, the accessible information without the key can vanishing compared to the total entropy available when the key is known.

This effect may help resolve the black hole infomration loss problem: If the information leaks out of an evaporating black hole while appearing random until the hole is of Plank size, then the plank scale black hole must someone "encrypt" all the information that has radiated away so far while itself having very small entropy. This was thought to be impossible but is precisely the case in the locking effect.

INI 1
12:10 to 12:30 Black holes, simulated time travel and the scalability of complexity
Session: Quantum Gravity and Quantum Information
INI 1
University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons