# Realizing and manipulating space-time inversion symmetric topological semimetal bands with superconducting quantum circuits

## TL;DR

This paper experimentally realizes and manipulates space-time inversion symmetric topological semimetal bands using superconducting quantum circuits, demonstrating topological phase transitions, robustness, and the effects of symmetry-breaking perturbations.

## Contribution

It introduces a novel experimental approach to realize and control Z2-type topological semimetal bands in superconducting circuits, revealing topological phase transitions and robustness under symmetry perturbations.

## Key findings

- Successfully imaged tunable gapless band structures.
- Observed topological phase transitions between semimetals and insulators.
- Demonstrated robustness of topological features under specific symmetry-breaking perturbations.

## Abstract

We have experimentally realized novel space-time inversion (P-T) invariant Z2-type topological semimetal-bands, via an analogy between the momentum space and a controllable parameter space in superconducting quantum circuits. By measuring the whole energy spectrum of system, we imaged clearly an exotic tunable gapless band structure of topological semimetals. Two topological quantum phase transitions from a topological semimetal to two kinds of insulators can be manipulated by continuously tuning the different parameters in the experimental setup, one of which captures the Z2 topology of the PT semimetal via merging a pair of nontrivial Z2 Dirac points. Remarkably, the topological robustness was demonstrated unambiguously, by adding a perturbation that breaks only the individual T and P symmetries but keeps the joint PT symmetry. In contrast, when another kind of PT -violated perturbation is introduced, a topologically trivial insulator gap is fully opened.