Figure 1: Outline and setup of the spin–photon entanglement experiment.
From: Complete tomography of a high-fidelity solid-state entangled spin–photon qubit pair
(a) Level structure of an electron-doped quantum dot, with the magnetic field in-plane (Voigt geometry, see inset). V and H refer to linear polarizations, either perpendicular to (V) or parallel (H) to the magnetic field. (b) Excitation and manipulation used in the experiment. See text for details. CW: continuous-wave laser, used for spin initialization and read-out. 100 ps: 100 ps laser pulse used for trion excitation. δω: Zeeman energy splitting (2π × 17.6 GHz). Ωeff: effective spin-Rabi frequency of the detuned coherent-spin rotation laser. (c) Schematic overview of the time-resolved conversion process. A few-ps, 2.2-μm gate pulse converts a single 910-nm photon to a 1560-nm photon with picosecond timing resolution in a periodically poled lithium niobate waveguide. The resulting timing resolution acts as a quantum eraser for frequency-which-path information present in the spontaneous emission decay from the Λ-system, permitting high-fidelity spin-polarization entanglement to be measured. (d) Timing and pulse scheme used for generating and verifying spin–photon entanglement. (e) Schematic overview of the experimental apparatus. EOM: electro-optic modulator; VR: variable retarder; H(Q)WP: half-(quarter-)waveplate; (N)PBS: (non-)polarizing beamsplitter; PPLN: periodically poled lithium niobate; QD: quantum dot; SM: single-mode; BPF: bandpass filter.
