Multi-party involvement: When everything is connected

Understanding is a ubiquitous concept in modern physical research: it occurs in subjects ranging from quantum gravity to quantum calculus. In a publication published in Physical review letters Last week, UvA-IoP physicist Michael Walter and his collaborator Sepehr Nezami shed new light on the properties of quantum entanglement – especially when many particles are involved.

In the quantum world, physical phenomena appear that we never observe in our everyday world on a large scale. One of these phenomena is the entanglement of quantities, in which two or more quantum systems share certain properties in a way that affects the measurements on the systems. The famous example is that of two electrons that can be tangled in such a way that – even when they are very far away – they can be seen rotating in the same direction, say clockwise or counterclockwise. , despite the fact that the direction of rotation of any of the individual electrons can be predicted in advance.

Multi-stakeholder involvement

This example is somewhat limited: the violation does not necessarily have to be between two-quantum systems. Multi-particle systems can also be tangled, even in such an extreme way that if a certain property is observed for one of them (think about “turning clockwise again”), the same property will be observed for all other systems. This multiparty entanglement is known as the state GHZ, after physicists Daniel Greenberger, Michael Horne and Anton Zeilinger.

In general, multiparty entanglement is poorly understood, and physicists do not have a systematic perspective on how it works. In a new paper that was published in Physical review letters this week, UvA physicist Michael Walter and his collaborator Sepehr Nezami of Caltech begin filling this gap, theoretically investigating a rich class of multi-body states and their tangling properties. For this purpose, they use a mathematical technique known as the “tensor network.” The researchers point out that the geometric properties of this network provide a wealth of useful information about the confusing properties of the states under investigation.

A more detailed understanding of obtaining authors could have many future applications. The research was initially motivated by questions seeking a better understanding of the quantum properties of gravity, but the technical tools that have been developed are also very useful in the theory of quantum information that is used to develop quantum computers and quantum software. .