Light-shift induced by two unbalanced spontaneous decay rates in EIT (CPT) spectroscopies under Ramsey pulse excitation

Light shift is important and inevitably affects the long-term stability of an atomic clock. In this work, considering two unbalanced branches of the spontaneous decay rate in a three-level system, we studied the frequency shifts of electromagnetically induced transparency (EIT) and coherent population trapping (CPT) clocks operating under the pulse sequence regime by numerically solving the Liouville density matrix equations. The results show that the frequency shifts are larger when the two branches of spontaneous emission rate are not equal compared to the equal case. In addition, in EIT-Ramsey, the effect of the unbalanced branches of the spontaneous decay rate and relaxations of low-energy states on the frequency shift is greater than that of Rabi frequency. In CPT-Ramsey, the relaxations of low-energy states play a dominant role in frequency shift.     

Temperature Dependence of Dark Lines in Coherent Population Trapping

We measure the signal amplitude and linewidth of a dark line in coherent population trapping in the Rb vapour cell filled with mixed buffer gas N2 and Ar as a function of cell temperature. We find that the dark line signal amplitude increases with temperature up to a maximum at 49℃ and then drops at higher temperatures due to quenching effects of N2. The linewidth of the dark line remains basically constant, at 1080 Hz. We also measure the linewidth of the dark line as a function of laser intensity. The linewidth increases linearly with laser intensity. An intrinsic linewidth （FWHM=896 Hz at 3.4 GHz） of the Rb cell is obtained.     

Bichromatic Coherent Population Trapping Under Hanle Configuration

We report the observation of bichromatic coherent population trapping under the transition ^87 RbFg = 1 → Fc = 0 with two linearly polarized laser beams by means of a Hanle effect configuration. The mechanism behind this effect is identified, and numerical solutions for the pump rates equations are presented.     

超冷玻色气体中电磁感应透明和慢光现象中的原子相互作用效应

我们研究了原子之间的相互作用对超冷玻色原子气体中电磁感应透明性质和光的群速的影响.我们考虑Λ型的原子结构.最初原子凝聚在其中的一个基态上,凝聚体原子用平均场理论来描述,原子之间的相互作用近似为两体的s-波散射长度,原子之间的碰撞不引起原子的电子跃迁.     

Transparency and Strong Gain Without Population Inversion in Photonic Bandgap Crystals

Without using the weak-field approximation,we investigate the transient properties of a Λ-type atom with one transition near resonant with a photonic bandgap edge.Whatever the initial state of the atom is,the atom can become transparent to a probe field,and strong gain without population inversion is also possible if the atom has been pre-excited.The defect mode formed by atomic doping can have a strong effect on the absorption properties of the atom.     

Saturation of biphoton generation near atomic resonance

We have numerically investigated the biphoton generation rate as a function of several parameters in the spontaneous four-wave mixing in cold atoms.It has been found that the biphoton generation rate can easily reach saturation with the intensity of the coupling laser increasing.The saturation intensity is mainly dependent on the dephasing rate of the ground states,unrelated to the pumping laser.It implies that though the biphoton waveform can be manipulated by the coupling laser,the generation rate of the biphoton cannot increase markedly after the saturation.The saturation effect also suggests that there is an optimal coupling laser for obtaining the largest biphoton generation rate with a sufficiently long coherence time.     

Measuring Transmittance in Rubidium Vapour Cells Using an Extremely Weak Coherent Field of Light

The absorptive properties of the atomic transition in the Rb^85 D2 (A) line (5S1/2-5P3/2) at 780.Onm are measured by using a continuous tunable diode laser and a CCD detector in Rb vapour cell under the condition of extremely weak incident intensity. When the intensity of incident light decreases from 420pW/cm^2 to 0.03pW/cm^2, the transmittance is found to be independent of the incident intensity within our experimental accuracy.     

Stimulated Raman Adiabatic Population Transfer of Two Bose—Einstein Condensates

Considering all the ground-state atom interactions,we investigate the population transfer of two Bose-Einstein condensate (BEC) states,which are trapped in diffecent potential wells,or two ground states of the BEC in the same trap using the stimulated Raman adiabatic process.With a proper choice of pulsed geometric parameters,the dark state exists.By simply choosing ground-state detunings,the effects of the interatomic interaction can be suppressed and a high population transfer rate can be obtained.     

An effective pumping method for increasing atomic utilization in a compact cold atom clock

We propose a simple pumping method to increase the effective population of cold atoms in the clock state and investigate the factors which affect the pumping efficiency in cold atom systems. We report the theory and demonstrate the corresponding experiment in an ⁸⁷Rb integrating sphere cold atom clock. The experimental results show that the population of cold atoms in the Zeeman sublevel |F=2, m_F=0> is approximately 1.62 times that of the result using optical pumping alone. This method can also be applied to increase the effective population in any one of the target Zeeman sublevels in other cold atom systems.     

The dispersive properties of an excited-doubletfour-level atomic system

We have investigated the dispersive properties of excited-doublet four-level atoms interacting with a weak probe field and an intense coupling laser field. We have derived an analytical expression of the dispersion relation for a general excited-doublet four-level atomic system subject to a one-photon detuning. The numerical results demonstrate that for a typical rubidium D1 line configuration, due to the unequal dipole moments for the transitions of each ground state to double excited states, generally there exists no exact dark state in the system. Close to the two-photon resonance, the probe light can be absorbed or gained and propagate in the so-called superluminal form. This system may be used as an optical switch.