Ultrathin optical fibres integrated into cold atom setups are proving to be ideal building blocks for atom-photon hybrid quantum networks. Such optical nanofibres (ONFs) can be used for the demonstration of nonlinear optics and quantum interference phenomena in atomic media. Here, we report on the observation of multilevel cascaded electromagnetically induced transparency (EIT) using an optical nanofibre to interface cold 87Rb atoms. Intense evanescent fields can be achieved at ultralow probe (780 nm) and coupling (776 nm) powers when the beams propagate through the nanofibre. The observed multipeak transparency spectra of the probe beam could offer a method for simultaneously slowing down multiple wavelengths in an optical nanofibre or for generating ONF-guided entangled beams, showing the potential of such an atom-nanofibre system for quantum information. We also demonstrate all-optical-switching in the all-fibred system using the obtained EIT effect.

https://iopscience.iop.org/article/10.1088/1367-2630/17/12/123012/pdf

Multi-level cascaded electromagnetically induced transparency in cold atoms using an optical nanofibre interface

Electromagnetically induced transparency in five-level cascade scheme of 85Rb atoms: An analytical approach

We demonstrate high-contrast electromagnetically induced absorption (EIA) bright resonances on the D1 line of K39 with characteristics comparable to those of the electromagnetically induced transparency (EIT) dark resonances observed in the same conditions. EIA is produced by the interaction of a weak probe beam with the atomic ground state driven in a degenerate coherent superposition by either a co- or counter-propagating pump beam. We have obtained an order of magnitude increase of the EIA’s contrast with respect to previous similar experiments, performed with other alkalis, without compromising its linewidth. Furthermore, we show that the magneto-optic resonances can be continuously tuned from EIT to EIA by changing the relative handedness of circular polarizations of pump and probe beams, or depending on whether they co- or counter-propagate. This opens new perspectives in the use of EIA in a broad range of physical domains and in a large wealth of potential applications in optics and photonics.

/pdf/tunable-and-polarization-controlled-high-contrast-bright-and-4yongyo027.pdf

Tunable and polarization-controlled high-contrast bright and dark coherent resonances in potassium.

Ultrathin optical fibres integrated into cold atom setups are proving to be ideal building blocks for atom-photon hybrid quantum networks. Such optical nanofibres (ONF) can be used for the demonstration of nonlinear optics and quantum interference phenomena in atomic media. Here, we report on the observation of multilevel cascaded electromagnetically induced transparency (EIT) using an optical nanofibre to interface cold $^{87}$Rb atoms through the intense evanescent fields that can be achieved at ultralow probe and coupling powers. Both the probe (at 780 nm) and the coupling (at 776 nm) beams propagate through the nanofibre. The observed multipeak transparency spectra of the probe beam could offer a method for simultaneously slowing down multiple wavelengths in an optical nanofibre or for generating ONF-guided entangled beams, showing the potential of such an atom-nanofibre system for quantum information. We also demonstrate all-optical-switching in the all fibred system using the obtained EIT effect.

Using density-matrix theory, an analytical expression of the self-Kerr nonlinear coefficient of a three-level lambda EIT medium for a weak probe light is derived. Influences of the coupling light and Doppler broadening on the self-Kerr coefficient are investigated and compared to experimental observation with a good agreement. The self-Kerr nonlinearity of the medium is modified and greatly enhanced in the spectral region of EIT window. Furthermore, sign, slope, and magnitude of the self-Kerr coefficient can be controlled with frequency and intensity of the coupling light and temperature of the medium. In particular, for a given set of fixed values of the parameter coupling and probe lights, it is possible to choose an optimized temperature with which to obtain the largest magnitude of the self-Kerr coefficient. Such a controllable Kerr nonlinearity can find interesting applications in optoelectronic devices working with low-light intensity at various temperature conditions.

http://iopscience.iop.org/article/10.1088/0031-8949/90/4/045502/pdf

EIT enhanced self-Kerr nonlinearity in the three-level lambda system under Doppler broadening

We propose to use a five-level cascade system to enhance self-Kerr nonlinearity under an electromagnetically induced transparency (EIT) condition. Using density-matrix theory, an expression of the self-Kerr nonlinear coefficient for a weak probe light is derived. Variations of the self-Kerr coefficient with respect to the frequency and intensity of a strong coupling light are investigated. The Kerr nonlinearity is basically modified and enhanced greatly in the spectral regions corresponding to EIT transparent windows. Furthermore, the sign, slope, and magnitude of the self-Kerr coefficient can be controlled with the frequency and intensity of the coupling light. Such a controllable Kerr nonlinearity can find interesting applications in optoelectronic devices working with low light intensity at multiple frequencies.

Enhancement of self-Kerr nonlinearity via electromagnetically induced transparency in a five-level cascade system: an analytical approach

We propose an optical bistability (OB) model consisting of a five-level cascade electromagnetically induced transparency (EIT) medium placed in a unidirectional ring cavity. An input-output intensity relationship for a weak probe light field is derived as a function of parameters of a strong coupling light and cooperation C. The OB behaviors of the system are investigated with variation of the parameters. It has been shown that the OB behaviors occur simultaneously in three EIT windows. Furthermore, switching thresholds and the hysteresis loop can be controlled by the parameters of the coupling light and/or a cooperation of atomic medium. Such controllable OB behaviors can find interesting applications in bistable photonic devices working at low light intensity and multiple frequencies.

Nguyen Huy Bang

Papers

Enhancement of self-Kerr nonlinearity via electromagnetically induced transparency in a five-level cascade system: an analytical approach

Electromagnetically induced transparency in five-level cascade scheme of 85Rb atoms: An analytical approach

EIT enhanced self-Kerr nonlinearity in the three-level lambda system under Doppler broadening

Optical bistability in a five-level cascade EIT medium: an analytical approach

Propagation of laser pulse in a three-level cascade inhomogeneously broadened medium under electromagnetically induced transparency conditions