This meeting will be held at the Rm431/4.33 Informatics Forum, University of Edinburgh.

Abstracts

Practical quantum coin flipping, Eleni Diamanti
Coin flipping is a fundamental cryptographic primitive with numerous applications. In this talk we show that quantum coin flipping with security guarantees that are strictly better than in any classical protocol is possible to implement with current technology. In particular, our protocol can tolerate both losses and noise in the communication channel and the detection system, and takes into account common experimental practices such as the use of attenuated laser sources. Under these conditions, we show that a quantum advantage can be achieved for a channel length of up to 21 km. Quantum coin flipping joins in this way quantum key distribution as a powerful and easily implementable application of quantum information processing. Work towards the experimental implementation of this protocol is underway in our lab. In addition to this work, we will also briefly present other experimental activities of the Quantum Information Group in Telecom ParisTech.

Entanglement and Flow and what they say about universality and simulateability of Quantum Computation, Damian Markham
Flow is a sufficient condition for a graph state to facilitate a unitary computation across it in the measurement based model. We relate this to known and presented entanglement conditions for a graph state to be a universal resource for measurement based quantum computation, and the ability to simulate any computation on it (again in the measurement based model). We then present new conditions based on the Flow structure. We further discuss the relation to similar conditions in the circuit model through a known translation between the two. Joint work with Elham Kashefi.

N-party Hardy proofs for symmetric states, Zizhu Wang
Nonlocality tests in quantum mechanics range from expectation value based CHSH test to the all-versus-nothing Mermin test. In between these two extremities lie the almost probability-free Hardy test. In the original Hardy test, the nonlocality manifests as a paradox when some suitably chosen local projective measurements are made on almost any bipartite entangled state. In Hardy's words, the test works because of "a certain lack of symmetry". We extended this result to n-party permutation symmetric states by exploiting both the original symmetry and the remaining symmetry the system has when part of the system has been measured. In addition to the Hardy test, we also have a CH-type inequality that can potentially be violated experimentally. Joint work with Damian Markham.

A brief introdcution to Quantum Formal Methods, Process Calculus, Model-checking, Simon Gay

Experimenting with Entangled Photons: life in the lab
For the last decade our group has used technology found in data projectors to control light. These devices act as re-programable holograms which although not good enough to make a 3D TV can shape standard laser beams into exotic shapes. We use these shaped beams to move microscopic objects (Tweezers with a twist, Nature Photon. 5, 343-348 (2011)), and create complex optical fields with embedded topological features (Isolated optical vortex knots, Nature Phys. 6, 118-121 (2010)).
Over the last five years we have realised that in addition to creating shapes in light, the same technology can be used to measure the spatial properties of individual photons. We have used two separated holograms to observe and quantify the quantum entanglement of the spatial modes of photon pairs produced by parametric down-conversion. Our particular interest are helical phasefronts which gives the light beam a twist and a mechanically observable angular momentum. Together with our collaborators, within the quantum regime we have used this approach to demonstrate the EPR paradox for angles (Quantum Correlations in Optical Angle-Orbital Angular Momentum Variables, Science 329, 662-665 (2010)) and tests of Bell type inequalities in high dimensions (Experimental high-dimensional two-photon entanglement and violations of generalized Bell inequalities, Nature Physics 7 (2011)).
Rather than trying to describe the underlying quantum science, in this talk I will try and outline the experimental realities perhaps identifying new opportunities.

Further Details to come. Enquiries to Elham Kashefi.