Figure 1

Experimental arrangement combing a quantum-dot single-photon source and the Sun. The InAs/GaAs QD-micropillar system lies in a cryostat at 4 K and is resonantly excited by a pulsed picosecond laser (not shown) to emit single photons in pulses which are collected by a confocal setup. The single photons then go through a polarization beam splitter (PBS) and spectrally filtering by a 1 GHz FWHM etalon. In precedence of the beam splitter (BS) for two photon interference lies a half-wave-plate (HWP) which determines whether parallel polarization (indistinguishable) case or cross polarization (distinguishable) case it is in. The upper right panel shows the scanning electron microscope image of the quantum dot in a micropillar. The sunlight is collected by a simple optical setup fixed to an equatorial mount, in precedence of which a grating is placed to select out infrared band near 893 nm. These photons from the Sun are polarized at a PBS and filtered by a 1 GHz FWHM etalon. A superconducting nanowire single-photon detector (SNSPD) with time resolution of 20 ps is used to register the arrival of single photons. Detection signals are led to a time-to-digital converter (not shown) where electrically gating and coincident analysis are performed. For correlation measurement in entanglement establishment and Bell experiment, between the beam splitter and SNSPDs two polarizers are inserted (not shown).