Forthcoming events in this series
Quantum information processing in spacetime
Abstract
Cutting-edge experiments in quantum communications are reaching regimes
where relativistic effects can no longer be neglected. For example, there
are advanced plans to use satellites to implement teleportation and quantum
cryptographic protocols. Relativistic effects can be expected at these
regimes: the Global Positioning System (GPS), which is a system of
satellites that is used for time dissemination and navigation, requires
relativistic corrections to determine time and positions accurately.
Therefore, it is timely to understand what are the effects of gravity and
motion on entanglement and other quantum properties exploited in quantum
information.
In this talk I will show that entanglement can be created or degraded by
gravity and non-uniform motion. While relativistic effects can degrade the
efficiency of teleportation between moving observers, the effects can also
be exploited in quantum information. I will show that the relativistic
motion of a quantum system can be used to perform quantum gates. Our
results, which will inform future space-based experiments, can be
demonstrated in table-top experiments using superconducting circuits.
Moduli spaces of instantons - stringy and combinatorial perspectives
The search for Intrinsic Decoherence
Abstract
Conventional decoherence (usually called 'Environmental
Decoherence') is supposed to be a result of correlations
established between some quantum system and the environment.
'Intrinsic decoherence' is hypothesized as being an essential
feature of Nature - its existence would entail a breakdown of
quantum mechanics. A specific mechanism of some interest is
'gravitational decoherence', whereby gravity causes intrinsic
decoherence.
I will begin by discussing what is now known about the mechanisms of
environmental decoherence, noting in particular that they can and do
involve decoherence without dissipation (ie., pure phase decoherence).
I will then briefly review the fundamental conflict between Quantum
Mechanics and General Relativity, and several arguments that suggest
how this might be resolved by the existence of some sort of 'gravitational
decoherence'. I then outline a theory of gravitational decoherence
(the 'GR-Psi' theory) which attempts to give a quantitative discussion of
gravitational decoherence, and which makes predictions for
experiments.
The weak field regime of this theory (relevant to experimental
predictions) is discussed in detail, along with a more speculative
discussion of the strong field regime.
Supersymmetric loop space
Abstract
We will first review the construction of N =1
supersymmetric Yang-Mills theory in three dimensions. Then we will
construct a superloop space formulation for this super-Yang-Mills
theory in three dimensions.Thus, we will obtain expressions for loop
connection and loop curvature in this superloop space. We will also
show that curvature will vanish, unless there is a monopole in the
spacetime. We will also construct a quantity which will give the
monopole charge in this formalism. Finally, we will show how these
results hold even in case of deformed superspace.
Generic string/M theory Predictions for Particle Physics and Dark Matter
Protecting Topological Encodings Against Local Perturbations
Abstract
Topological quantum error correcting codes, such as the Toric code, are
ideal candidates for protecting a logical quantum bit against local noise.
How are we to get the best performance from these codes when an unknown
local perturbation is applied? This talk will discuss how knowledge, or lack
thereof, about the error affects the error correcting threshold, and how
thresholds can be improved by introducing randomness to the system. These
studies are directed at trying to understand how quantum information can be
encoded and passively protected in order to maximise the span of time between successive rounds of error correction, and what properties are
required of a topological system to induce a survival time that grows
sufficiently rapidly with system size. The talk is based on the following
papers: arXiv:1208.4924 and Phys. Rev. Lett. 107, 270502 (2011).
Conformal Cyclic Cosmology: Its Current Status, and its Role in the Emergence of Rest-Mass
BPS state counting on singular varieties
Abstract
This is a report of joint work with T. Koppe, P. Majumdar, and K.
Ray.
I will define new partition functions for theories with targets on toric
singularities via
products of old partition functions on crepant resolutions. I will
present explicit examples
and show that the new partition functions turn out to be homogeneous on
MacMahon factors.
N=2 Gauge Theories: Congruence Subgroups, Coset Graphs and Modular Surfaces
An Update on Dark Matter
Abstract
We still don't know what dark matter is but a class of leading candidates
are weakly interacting massive particles or WIMPs. These WIMP models are
falsifiable, which is why we like them. However, the epoch of their
falsifiability is upon us and a slew of data from different directions is
placing models for WIMPs under pressure. I will try and present an updated
overview of the different pieces of evidence, false (?) alarms and
controversies that are making this such an active area of research at the
moment.
Quantum Field Theory: Where do we come from? What are we? Where are we going?
Abstract
In recent decades, quantum field theory (QFT) has become the framework for
several basic and outstandingly successful physical theories. Indeed, it has
become the lingua franca of entire branches of physics and even mathematics.
The universal scope of QFT opens fascinating opportunities for philosophy.
Accordingly, although the philosophy of physics has been dominated by the
analysis of quantum mechanics, relativity and thermo-statistical physics,
several philosophers have recently undertaken conceptual analyses of QFT.
One common feature of these analyses is the emphasis on rigorous approaches,
such as algebraic and constructive QFT; as against the more heuristic and
physical formulations of QFT in terms of functional (also knows as: path)
integrals.
However, I will follow the example of some recent mathematicians such as
Atiyah, Connes and Kontsevich, who have adopted a remarkable pragmatism and
opportunism with regard to heuristic QFT, not corseted by rigor (as Connes
remarks). I will conceptually discuss the advances that have marked
heuristic QFT, by analysing some of the key ideas that accompanied its
development. I will also discuss the interactions between these concepts in
the various relevant fields, such as particle physics, statistical
mechanics, gravity and geometry.
Review on Lifshitz type quantum field theories in Particle Physics
Abstract
Attractive features of Lifshitz type theories are described with different
examples,
as the improvement of graphs convergence, the introduction of new
renormalizable
interactions, dynamical mass generation, asymptotic freedom, and other
features
related to more specific models. On the other hand, problems with the
expected
emergence of Lorentz symmetry in the IR are discussed, related to the
different
effective light cones seen by different particles when they interact.
Six-dimensional space-time from quaternionic quantum mechanics
Abstract
Quaternionic quantum Hamiltonians describing nonrelativistic spin particles
require the ambient physical space to have five dimensions. The quantum
dynamics of a spin-1/2 particle system characterised by a generic such
Hamiltonian is described. There exists, within the structure of quaternionic
quantum mechanics, a canonical reduction to three spatial dimensions upon
which standard quantum theory is retrieved. In this dimensional reduction,
three of the five dynamical variables oscillate around a cylinder, thus
behaving in a quasi one-dimensional manner at large distances. An analogous
mechanism exists in the case of octavic Hamiltonians, where the ambient
physical space has nine dimensions. Possible experimental tests in search
for the signature of extra dimensions at low energies are briefly discussed.
(Talk based on joint work with Eva-Maria Graefe, Imperial.)