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We propose an asymmetric double AlGaAs/GaAs quantum well structure with a common continuum to generate a large cross-phase modulation (XPM). It is found, owing to resonant tunneling, that a large XPM can be achieved with vanishing linear and two-photon absorptions.

Using a data sample corresponding to an integrated luminosity of 2.93 fb −1 collected at a centerof-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider, we search for a scalar partner of the X(3872), denoted as X(3700), via ψ(3770) → γηη and γπ + π − J/ψ processes. No significant signals are observed and the upper limits of the product branching fractions B(ψ(3770) → γX(3700))•B(X(3700) → ηη ) and B(ψ(3770) → γX(3700))•B(X(3700) → π + π − J/ψ) are determined at the 90% confidence level, for the narrow X(3700) with a mass ranging from 3710 to 3740 MeV/c 2 , which are from 0.8 to 1.8 (×10 −5 ) and 0.9 to 3.4 (×10 −5 ), respectively.

We investigate an enhancement of the Kerr nonlinearity in phase-dependent double electromagnetically induced transparency (EIT) media. We find, by changing the relative phase of the driven fields, that the properties of EIT and the Kerr nonlinearity can be modified significantly. Choosing the relative phase appropriately, a giant Kerr nonlinearity can be achieved with vanishing absorptions.