Quantum topology in the ultrastrong coupling regime

Area of Science:

• Quantum Physics
• Condensed Matter Physics
• Quantum Information Science

Background:

• Coupling between quantum objects is categorized as strong or weak based on interaction strength relative to loss rates.
• Ultrastrong coupling (USC), where interaction energy is comparable to bare energies, introduces profound changes, including non-empty ground states with virtual excitations.
• The implications of USC for topological systems, which typically conserve excitation numbers, are largely unexplored.

Purpose of the Study:

• To investigate the interplay between ultrastrong coupling and topological states in a one-dimensional system.
• To reveal novel phenomena arising from USC in quantum topological systems.
• To provide a framework for experimental exploration of ultrastrong quantum topology.

Main Methods:

• Theoretical study of a dimerized chain of two-level systems in the ultrastrong coupling regime.
• Analysis of the Hamiltonian, including saturation and counter-rotating terms.
• Investigation of the multi-excitation effective bandstructure and topological properties.

Main Results:

• Demonstration of rich, multi-excitation effective bandstructures driven by combined saturation and counter-rotating terms in USC.
• Discovery of unusual topological edge states and a new class of states termed 'anti-edge states'.
• Observation of remarkable geometric-dependent renormalizations of the quantum vacuum.

Conclusions:

• Ultrastrong coupling significantly alters topological properties, leading to novel quantum states.
• The theoretical framework provides a roadmap for experimentalists to explore ultrastrong quantum topology.
• This research opens new avenues in quantum physics and topological matter.