This week Alastair Abbott is visiting from Geneva. Tomorrow he'll tell us about "Quantum Circuits with Classical and Quantum Control of Causal Orders". See below for the abstract. 

Best,

-joe

Abstract: 

The standard approach to quantum information processing, including the quantum circuit framework, implicitly assumes that operations are applied in a well defined causal order. However, quantum mechanics allows the order in which operations are applied to itself be in a quantum superposition. This observation has led to the process matrix formalism describing quantum processes without any global causal order. 

I will review a simple such process, the "quantum switch", that enables several advantages in quantum information. In fact, the quantum switch and its generalisation are thus far the only known "causally indefinite" processes for which a physical implementation is known to be possible. With this motivation, I will present two generalisations of standard quantum circuits: quantum circuits with classical and quantum control of causal order. These can be nicely characterised and the latter provides a concrete way of pursuing new noncausal processes that are, by construction, physically implementable.