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Optical circuit

Spin–photon interface


Phys. Rev. Lett. 110, 037402 (2013)

An in-plane spin–photon interface is essential for integrating quantum dot spins with optical circuits. This is difficult to achieve because the circularly polarized light emitted from a quantum dot is reduced to a linear-polarization component in a planar optical circuit, which inhibits the in-plane transfer of spin information. Isaac Luxmoore and co-workers in the UK and India have now demonstrated a spin–photon interface based on two orthogonal waveguides, where the polarization emitted by a quantum dot is mapped to a path-encoded photon. The device consists of two orthogonal freestanding waveguides (about 200 nm wide) connected to four out-couplers. The waveguides were fabricated from a 140-nm-thick GaAs layer containing a single layer of InGaAs quantum dots. The photoluminescence observed vertically from the intersection of the waveguides showed two peaks corresponding to right and left circularly polarized transitions. Both peaks were also observed from the edges of the orthogonal waveguides. The interference of the photoluminescence from both peaks was simultaneously measured from the orthogonal waveguides, and it showed that the relative phase between the two peaks was close to π, confirming that the spin-up or -down state of the quantum dot is encoded in the relative phase between the waveguides.


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Horiuchi, N. Spin–photon interface. Nature Photon 7, 263 (2013).

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