2014/08/31 by K. W. Plumb, Kyusung Hwang, Yunfeng Qiu +12 · 3 citations
Physics and Astronomy · #Advanced Condensed Matter Physics #Condensed matter physics #Magnetic properties of thin films #Physics #Physics of Superconductivity and Magnetism #Quantum #Quantum electrodynamics #Quantum mechanics #Quasiparticle #Superconductivity #cond-mat.str-el
paper · pdf · doi:10.1038/nphys3566
published as Nature Physics 12, 224-229 (2016) · main text - 16 pages, 4 figures; supplementary information - 3 pages, 1 figure
openalex publication_date 2015/11/23 · arxiv created 2015/12/02 · arxiv updated 2016/03/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. However, little is known about the level repulsion when more than two quasiparticles are present; for example, in an open quantum system where a quasiparticle can spontaneously decay into many particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. In our fine resolution neutron spectroscopy study of magnetic quasiparticles in a frustrated quantum magnet BiCu2PO6, we observe a renormalization of quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states. Our results have a broadimplication for understanding open quantum systems described by non-hermitian Hamiltonian.