We report the generation of frequency-bin entangled narrowband biphotons from spontaneous four-wave mixing (SFWM). Making use of time-resolved detection, we observe violation of the CHSH Bell inequality and confirm the genuine entanglement.
Entanglement, describing the inseparability of a quantum multiparty system, is one of the most intriguing features of quantum mechanics. Violation of Bell inequality, for ruling out the possibility of local hidden variable theories, is commonly used as a strong witness for quantum entanglement. In previous Bell test experiments with photonic entanglement based on two-photon coincidence measurement, the photon temporal wave packets are absorbed completely by the detectors. That is, the photon coherence time is much shorter than the detection time window. Here we demonstrate generation of frequency-bin entangled narrowband biphotons, and for the first time, test the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality |S|<= 2 for their nonlocal temporal correlations with time-resolved detection. We obtain a maximum |S| value of 2.52+/-0.48 that violates the CHSH inequality. Our result will have applications in quantum information processing involving time-frequency entanglement.
We demonstrate the generation of narrowband biphotons with polarization-frequency-coupled entanglement from spontaneous four-wave mixing in cold atoms. The coupling between polarization and frequency is realized through a frequency shifter and linear optics. When the polarization-frequency degrees of freedom are decoupled, it is robust to create polarization and frequency Bell states, confirmed by the polarization quantum-state tomography and the two-photon temporal quantum beating. Making use of the polarization-frequency coupling to transfer polarization phase retardation to the entangled frequency modes, we produce a frequency Bell state with tunable phase difference between its two bases.
We demonstrate a robust scheme to produce narrowband biphotons with polarization-frequency-coupled entanglement from spontaneous four-wave mixing (SFWM) in laser cooled atoms with a right-angle geometry. Making use of an acousto-optic modulator and polarization-dependent two-photon interference, we create a coupled hyperentanglement between the polarization and frequency domains from unentangled SFWM photon pairs. We further demonstrate that, making use of the coupling effect, we can transfer the phase of a complex polarizer into the frequency entanglement and create a tunable two-mode frequency entangled Bell state.
We demonstrate the generation of narrowband biphotons with polarization-frequency coupled hy- perentanglement from spontaneous four-wave mixing in cold atoms. The coupling between polariza- tion and frequency is realized through a frequency shifter and linear optics. When the polarization- frequency degrees of freedom are decoupled, it is robust to create polarization and frequency Bell states, confirmed by the polarization quantum-state tomography and the two-photon temporal quan- tum beating. Making use of the polarization-frequency coupling to transfer polarization phase retard to the entangled frequency modes, we produce a frequency Bell state with tunable phase difference between its two bases.