Quantum Amplitudes, Classical Ignorance & Quantum Information Processing

Quantum Amplitudes, Classical Ignorance & Quantum Information Processing

Date: Saturday, June 30, 2018 - 10:30

Venue: Martin Wood Lecture Theatre, Clarendon Laboratory

A major theme in current theoretical physics is understanding the implications of quantum mechanics for the dynamics of composite systems. When sub-systems interact, they naturally become correlated. In the 1980s it was realised that by exploiting the correlations between quantum sub-systems it should be possible to (i) break current cryptographic systems by rapidly decomposing large numbers into their prime factors, and (ii) exchange confidential information in the secure knowledge that messages have not been intercepted. As we have become ever more dependent on the internet these explosive implications of quantum mechanics for cryptography have driven efforts to build quantum communication channels and quantum computers.

On June 30, to mark the completion of the Beecroft Building, the members of the Rudolf Peierls Centre for Theoretical Physics, who occupy the building above ground, and the members of the Quantum Information Technology hub (NQIT), who are installing kit in many of its subterranean laboratories, will join forces to explain the basic principles underlying the quantum dynamics of composite systems and to describe the challenge of implementing quantum computation and cryptography practically.

In the afternoon there will be three talks from NQIT, which is led by Oxford University. A general introduction to the programme will be followed by two talks about using ion traps and photonics to build a quantum computer. There will also have a chance to see the new labs via exclusive video and an opportunity to questions NQIT researchers.

You will have an opportunity to explore the Beecroft Building (above ground) between 09.00-10.30.


Quantum Systems from Group up
The first talk will review the modern formulation of the basic ideas of quantum mechanics. We start by explaining what quantum amplitudes are, how they lead to the idea of a quantum state and how these states evolve in time. We then discuss what happens when a measurement is made before describing correlated ('entangled') systems. Applying these ideas to two-state systems ('qubits') we point out that the complexity of computing the evolution of an N qubit system grows like exp(N).



“Open” Quantum Systems
The second talk will review how to deal with quantum systems that are coupled to the outside world, as in reality all systems are. We first introduce density operators and explain how quantum states give rise to them. We then turn to measures of entanglement that can be computed from a density operator, and show that entanglement grows with time. Finally, we show how the interaction with the environment gives rise to the phenomenon of decoherence.

Networked Quantum Information Technologies (NQIT)