Multichannel nonreciprocal amplifications using cesium vapor

Multichannel synchronous amplifications are an inevitable key problem in quantum communication process, which can broaden the bandwidth of transmitted signals and establish correlation among different optical channels. Here we study a nonreciprocal system with four concurrent amplification channels using hot cesium atoms, both theoretically and experimentally. For the forward probe field, the double--electromagnetically induced transparency structure is formed and the phase-matching condition of the multiwave mixing process is satisfied, which are both destroyed when the probe field is reversed. In addition, the four-channel nonreciprocal amplifications are formed in the Zeeman sublevels of the system with special selection of light field polarization, which will also dramatically enhance the signal-to-noise ratio by suppressing the spontaneous emission noise of the system. In our experiment, the quadruple nonreciprocal amplifications are achieved with the maximum forward gain reaching 30 dB and the reverse suppression reaching--23 dB. The gain adjustability allows the construction of a gain-loss balanced system, providing a scheme for an atomic system to engineer a parity-time-symmetric (or -antisymmetric) structure.