Hi all,

today we're meeting a little bit early so that those interested can also make it to the Robert Wald lecture downtown later (see here: http://www.eth-its.ethz.ch/activities/its-science-colloquium/Robert%20Wald.html). Christa Zoufal will present the results of her master's thesis. See below for title and abstract.

Best,

-joe

Title:
The quantum SWITCH and its causal simulations

Abstract:
Quantum mechanics challenges our intuition in a wide range of areas. In particular, the superposition principle leads to a large number of counterintuitive phenomena. Recently, it was found that it allows for scenarios where the order of the events can be in a quantum superposition. The first example of this situation is the quantum SWITCH, a higher-order operation that combines two gates in an order that is determined by the state of a quantum system. It has been shown that the SWITCH offers advantages in communication and computation. However, to achieve these advantages, one has to implement the quantum SWITCH in a real physical system. Since in standard quantum mechanics the order of events is well-defined, it is natural to ask in which sense an experimental implementation realizes an indefinite causal order. The aim of this thesis is to determine the resources needed for the simulation of the quantum SWITCH in a definite causal order, analyzing different types of simulations and showing that every simulation of the quantum SWITCH on generic boxes requires extra resources, such as the addition of quantum control and communication channels, and the use of multiple copies of the controlled boxes.