A bound state in the continuum (BIC) is a symmetry-protected topological state that, despite lying in the continuum radiation spectrum of a system, is unable to radiate in the far field. When supported by a photonic crystal, it is characterized by a supposedly infinite lifetime and a remarkable ability to enhance non-linear effects.
Now, researchers in Italy, the US and France have utilized these properties to demonstrate polariton Bose-Einstein condensation in a planar waveguide in which semiconductor quantum wells are strongly coupled to a BIC. The particularly low excitation threshold of the system shows promise for creating easily-integrable hybrid light-matter optical circuits and quantum information processing systems. The full study is described in Nature.
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