Fig. 1: Deterministic GHZ state generation from a QD embedded in a PCW.
From: Deterministic photon source of genuine three-qubit entanglement
A three-qubit GHZ state is realized by entangling the QD (yellow dot) electron spin and two QD-emitted single photons (red wavepackets). We collect the single photons through the PCW and couple them to free space via a grating outcoupler. The QD electron spin (dark green arrow) is subjected to the Overhauser field induced by nearby nuclear spins (purple arrows). To improve \({T}_{2}^{*}\) of the electron spin, we reduce fluctuations of the Overhauser field by employing nuclear spin narrowing. The QD is operated in the Voigt geometry with an in-plane magnetic field of 4 T along the x-axis. The energy level scheme of the QD is presented in the inset. The Raman laser Ωr (blue) is used for coherent spin manipulation of two Zeeman ground states \(\left\vert \uparrow \right\rangle\) and \(\left\vert \downarrow \right\rangle\). To generate single photons, a picosecond pulsed laser Ωp (red) drives photon emissions on the diagonal cycling transition \(\left\vert \downarrow \right\rangle \to \left\vert \uparrow \downarrow \Uparrow \right\rangle\). The same transition is used for the spin readout. Spin initialization is realized through optical pumping on the non-cycling transition \(\left\vert \downarrow \right\rangle \to \left\vert \downarrow \uparrow \Downarrow \right\rangle\).
