Pearls on a quantum necklace: modeling and analyzing spin systems

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Lea Lenke

by Max Gmelch (SAOT)

Theoretical physics aims at describing observable phenomena and predicting possible effects using a huge mathematical toolbox. A powerful approach is considering the system as a so-called Hermitian system. This theoretical approach results in observable numbers like the position, the momentum or energy values that can be measured in real-world experiments. Regarding quantum optics, an example for a simple Hermitian system is a simple waveguide like an optical fiber. Light can travel both ways in this fiber, the two directions are fully equivalent.

This is not always the case, as for example in specially manufactured waveguide systems. By including gain and loss elements, it is possible to create an asymmetry in the propagation of light. Here, considering the system as so-called non-Hermitian systems may be beneficial.

Lea Lenke used this approach to describe quantum spin models. She investigated linear spin chains, similar to pearls on a necklace, as well as a so-called toric code. The latter may play a role in future quantum computers, as it enables error correction resulting from e.g. quantum noise. She published her results in her article High-order series expansion of non-Hermitian quantum spin models.

Lea works at the Institute of Theoretical Physics I at FAU Erlangen-Nürnberg, her supervisor is Kai Phillip Schmidt. Her work is part of QuCoLiMa Area D: Pushing the limits of quantum cooperativity. The original publication can be found in Physical Review B.

The spins in the quantum necklace show wave-like interaction similar to the spheres in Newton‘s cradle.