One of the goals of photonics is to implement photonic quantum computation. Quantum interference of single photons at a 50:50 beamsplitter is a key phenomenon in quantum physics and lies at the heart of linear optical quantum computation.
Researchers have implemented high-visibility quantum interference of two single-photon topological boundary states in a photonic waveguide array. They engineered a time-varying Hamiltonian, controlling the band structure of the device and the spatial isolation of the topological states to implement a 50:50 beamsplitter.
They showed that single photons localized to topological boundary states can undergo high-visibility quantum interference. They used a laser-written photonic circuit that represents one of the most complex examples of a continuous waveguide array with engineered coupling coefficients varying along the propagation direction. This technology enables future studies of quantum effects in topological materials that are challenging or impossible to probe due to, for example, large magnetic field requirements or excessive noise. The topological beam splitter (TBS) could be extended to other topological models. The TBS presented in this work will combine with other leading work in topological photonics to help solve challenges currently faced in quantum photonics, including pump filtering for photon generation and robust photon transport.
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