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Register a new userEntanglement swapping with energy-polarization entangled photons from quantum dot cascade decay
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Authors
F. Troiani
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We theoretically investigate the efficiency of an entanglement swapping procedure based on the use of quantum dots as sources of entangled photon pairs. The four-photon interference that affects such efficiency is potentially limited by the fine-structure splitting and by the time correlation between cascaded photons, which provide which-path information. The effect of spectral inhomogeneity is also considered, and a possible quantum eraser experiment is discussed for the case of identical dots.
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Polarized cross-correlation spectroscopy on a quantum dot charged with a single hole shows the sequential emission of photons with common circular polarization. This effect is visible without magnetic field, but becomes more pronounced as the field along the quantization axis is increased. We interpret the data in terms of electron dephasing in the X+ state caused by the Overhauser field of nuclei in the dot. We predict the correlation timescale can be increased by accelerating the emission rate with cavity-QED.
A quantum dot can be used as a source of one- and two-photon states and of polarisation entangled photon pairs. The emission of such states is investigated from the point of view of frequency-resolved two-photon correlations. These follow from a spectral filtering of the dot emission, which can be achieved either by using a cavity or by placing a number of interference filters before the detectors. The combination of these various options is used to iteratively refine the emission in a distillation process and arrive at highly correlated states with a high purity. So-called leapfrog processes where the system undergoes a direct transition from the biexciton state to the ground state by direct emission of two photons, are shown to be central to the quantum features of such sources. Optimum configurations are singled out in a global theoretical picture that unifies the various regimes of operation.
Photonic entanglement swapping, the procedure of entangling photons without any direct interaction, is a fundamental test of quantum mechanics and an essential resource to the realization of quantum networks. Probabilistic sources of non-classical light can be used for entanglement swapping, but quantum communication technologies with device-independent functionalities demand for push-button operation that, in principle, can be implemented using single quantum emitters. This, however, turned out to be an extraordinary challenge due to the stringent requirements on the efficiency and purity of generation of entangled states. Here we tackle this challenge and show that pairs of polarization-entangled photons generated on-demand by a GaAs quantum dot can be used to successfully demonstrate all-photonic entanglement swapping. Moreover, we develop a theoretical model that provides quantitative insight on the critical figures of merit for the performance of the swapping procedure. This work shows that solid-state quantum emitters are mature for quantum networking and indicates a path for scaling up.
We report entanglement swapping with time-bin entangled photon pairs, each constituted of a 795 nm photon and a 1533 nm photon, that are created via spontaneous parametric down conversion in a non-linear crystal. After projecting the two 1533 nm photons onto a Bell state, entanglement between the two 795 nm photons is verified by means of quantum state tomography. As an important feature, the wavelength and bandwidth of the 795 nm photons is compatible with Tm:LiNbO3-based quantum memories, making our experiment an important step towards the realization of a quantum repeater.
We show that with a new family of pyramidal site-controlled InGaAsN quantum dots it is possible to obtain areas containing as much as 15% of polarization-entangled photon emitters - a major improvement if compared to the small fraction achievable by other quantum dot systems. Entanglement is attested by a two-photon polarization state density matrix and the parameters obtained from it. Emitters showing fidelities up to 0.721+-0.043 were found.
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