QUANTUM OPTICS

Into the valley

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Science  09 Jul 2021:
Vol. 373, Issue 6551, pp. 176-177
DOI: 10.1126/science.373.6551.176-c

The topological features of band structures provide robust propagation paths for classical and quantum states of light. Another ingredient of band structure is the valley degree of freedom, in which the propagation path of light is dependent on its polarization state. Chen et al. used both topology and valley-dependent transport to design and fabricate a photonic crystal structure capable of forming the basis of optical quantum circuits. The authors demonstrate the input of left- and right-circularly polarized states of quantum light, their separation into different paths, and controlled interference as the single photons are brought back together again. The results provide a route for developing complex optical quantum circuits for on-chip quantum information processing.

Phys. Rev. Lett. 126, 230503 (2021).

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