Efficient quantum memory for photonic polarization qubits generated by cavity-enhanced spontaneous parametric downconversion.

Quantum memories, for storing then retrieving photonic quantum states on demand, are crucial components for scalable quantum technologies. Spontaneous parametric downconversion (SPDC) with a nonlinear crystal is the most widely used process for generating entangled photon pairs or heralded single photons. Despite the desirability of efficient quantum memories for SPDC-generated single photons, the storage and retrieval efficiencies achieved with this approach still fall below 50%, a threshold value for practical applications. Here, we report an efficiency of > 70% for the storage of heralded single photons generated by cavity-enhanced SPDC using atomic quantum memories based on electromagnetically induced transparency (EIT). In addition, we demonstrate the quantum memory for single-photon polarization qubits with a fidelity of ∼96%. This result paves the way towards the development of large-scale quantum networks.

Memory-based optical polarization conversion in a double-[Formula: see text] atomic system with degenerate Zeeman states.

Optical memory based on the electromagnetically induced transparency (EIT) in a double-[Formula: see text] atomic system provides a convenient way to convert the frequency, bandwidth or polarization of an optical pulse by storing it in one [Formula: see text] channel and retrieving it from another. This memory-based optical converter can be used to bridge the quantum nodes which have different physical properties in a quantum network. However, in real atoms, each energy level usually contains degenerate Zeeman states, which may lead to additional energy loss, as has been discussed in our recent theoretical paper (Tsai et al. in Phys. Rev. A 100, 063843). Here, we present an experimental study on the efficiency variation in the EIT-memory-based optical polarization conversion in cold cesium atoms under Zeeman-state optical pumping. The experimental results support the theoretical predictions. Our study provides quantitative knowledge and physical insight useful for practical implementation of an EIT-memory-based optical converter.

Neurodevelopmental outcomes of extremely preterm infants in southern China: A multicenter study.

OBJECTIVE: To assess treatment outcomes and associated factors of extremely preterm infants (EPIs) in GuangXi, China. METHODS: This was a retrospective study consisting of 131 eligible cases with gestational age (GA) between 22 and 28 weeks, and infants were followed until 18-24 months. Data including clinical characteristics, perinatal factors and after-birth conditions were collected from the neonatal intensive care unit in 10 hospitals in Guangxi from January 1st 2010 until May 31st 2016. RESULTS: During that period, 307 EPIs were born in the hospitals. 137 infants died in hospital after their parents decided to withdraw clinical treatment, and 11 infants died despite full resuscitation was provided. Of the 159 surviving infants, 28 infants were lost to follow-up. In total, 131 infants who survived and were presented to follow-up at 18-24 months of age were enrolled into this study. Of the 131 infants evaluated at 18-24 months follow-up, 47 (35.9%) were diagnosed with neurodevelopmental disability (ND), and 84 (64%) demonstrated on tract motor and language skills. The incidence of chorioamnionitis, early onset sepsis (EOS), bronchopulmonary dysplasia (BPD) were all higher in the group of infants who were diagnosed with ND compared to those with normal motor language development (NML), the duration of mechanical ventilation (MV) was longer in ND group, and the higher incidence of ND was seen in the smaller GA babies (p < 0.05). Adjusted the BPD severity, GA was a protective factor of neurodevelopmental outcome (combined OR = 0.338, 95% CI: 0.145-0.791). In EPIs with moderate BPD and severe BPD, chorioamnionitis was a risk factor of ND (OR = 10.313 and 5.778，respectively, 95% CI: 1.389-6.486 and 1.444-23.119, respectively). The Logistic regression analysis showed that GA (OR = 0.207, 95%CI = 0.047-0.917) was a protective factor for ND, and chorioamnionitis (OR = 6.010, 95%CI: 1.331-27.138), moderate-to-severe BPD (OR = 4.285, 95%CI: 1.495-12.287), the duration of MV (OR = 3.508, 95%CI: 2.077-5.926) were independent risk factors for ND in EPIs. CONCLUSIONS: Chorioamnionitis, moderate-to-severe BPD, and the duration of MV were associated with neurodevelopmental disability in EPIs. The smaller the GA, the higher incidence of neurodevelopmental disability.