We present a robust method of single-photon modulation by directly modulating the single photons and observe its fre- quency spectrum. Compared with conventional photon counting technique, the single-photon modulation spectrum shows that the method could not only realize high-frequency modulation but also obtain higher signal-to-noise ratio. Moreover, the theoretical calculations show good agreement with the experimental results.
Nonlinear tunneling is investigated by analytically solving the one-dimensional Gross–Pitaevskii equation（GPE）with a strong rectangular potential barrier. With the help of analytical solutions of the GPE, which can be reduced to the solution of the linear case, we find that only the supersonic solution in the downstream has a linear counterpart. A critical nonlinearity is explored as an up limit, above which no nonlinear tunneling solution exists. Furthermore, the density solution of the critical nonlinearity as a function of the position has a step-like structure.
Single photon modulation has been proposed to overcome the defects of the low signal-to-noise ratio(SNR)and slow process rate of photon counting. In this paper, we present the quantum theory of single photon modulation, and then experimentally investigate the modulation spectroscopy both in the time domain and frequency domain. It is found that the SNR reached 150 in approximately the MHz modulation bandwidth.
The high-resolution photoassociation spectrum of the ultracold cesium molecular 0＋ state below the 6S1/2 ＋ 6PI/2 limit is presented in this paper. The saturation of the photoassociation scattering probability is observed from the depen dence of the trap-loss probability on the photoassociation laser intensity. The corresponding resonant line width is also demonstrated to increase linearly with increasing photoassociation laser intensity. Our experimental data have good con sistency with the theoretical saturation model of Bohn and Julienne [Bohn J L and Julienne P S 1999 Phys. Rev. A 60 1].
We propose a new transparency mechanism,which is based on photoassociation(PA)laser intensity induced transitional frequency shift for ultracold cesium molecules formed in PA scheme.The PA laser intensity is supposed to change before the atom-molecule resonance.Thus,a remarkable transparent effect for PA laser is expected to appear in the vicinity of original resonant transitional line,where the variation of PA laser intensity induces the shift of the excited molecular levels.The mechanism is different from electromagnetically induced transparency effect and interesting for further research on the scattering length for cesium atomic condensate.
Quantum secure direct communication is an important mode of quantum communication in which secret messages are securely communicated directly over a quantum channel.Quantum secure direct communication is also a basic cryptographic primitive for constructing other quantum communication tasks,such as quantum authentication and quantum dialog.Here,we report the first experimental demonstration of quantum secure direct communication based on the DL04 protocol and equipped with single-photon frequency coding that explicitly demonstrated block transmission.In our experiment,we provided 16 different frequency channels,equivalent to a nibble of four-bit binary numbers for direct information transmission.The experiment firmly demonstrated the feasibility of quantum secure direct communication in the presence of noise and loss.
Jian-Yong HuBo YuMing-Yong JingLian-Tuan XiaoSuo-Tang JiaGuo-Qing QinGui-Lu Long
