Effects of squeezed vacuum on transient optical response in a ∧ system

The effects of the squeezed vacuum (SV) on the transient optical properties in a ∧-type three-level atomic medium with or without the vacuum-induced coherence (VIC) are investigated in this paper. We find that the oscillatory amplitude of the optical spectra, the transient absorption (gain), and the response time from the transient to the steady situation are remarkably dependent on the SV. When including the VIC, the transient and steady optical properties display a reverse variation with the SV. Additionally, it is interesting to find that the steady population distribution is kept at the same value for different initial conditions in the presence of SV.     

Quantum interference effect on absorption-dispersion spectra in Λ-type three-level EIT medium interacting with a squeezed bath

A Λ-type three-level atomic system in the electromagnetically induced transparency (EIT) configuration interacting with a broadband squeezed vacuum (SV) bath is studied with quantum interference (QI) between decay channels taken into account. We formulate two sufficient critical conditions for the medium to be dispersionless or absorptionless. Computational results for the dispersion and absorption spectra show that presence of both QI and SV offers more avenues to manipulate the group velocity of probe pulse for its variation from sub-luminal to super-luminal regimes. The relative phase between the two external fields is found to act as a control knob of the atomic medium.     

Transient response in a three-level system with the squeezed vacuum

In this paper, the effects of the squeezed vacuum (SV) on the transient response in a ??-type three-level atomic medium are investigated. We find that the properties of transient process can be greatly affected by the SV whether the vacuum-induced coherence (VIC) exists or not. The combined influence of the SV and the VIC can dramatically modify the transient absorption and gain. Especially, the transient gain can be almost eliminated in the absence of VIC. And the response time from the transient to the steady situation is dependent on the SV. When including the VIC, the transient and steady optical properties display a reverse variation with the SV. Besides, it is shown that the considerable steady state population without inversion can be always induced by the SV.     

Quantum nondemolition measurement of transverse atomic position in Kapitza-Dirac atomic beam scattering

It is demonstrated that one can measure the distribution of the transverse position of an atom crossing one or more optical cavities by monitoring the phase of the standing wave fields in the cavities. For the atom-field interaction the Kapitza-Dirac regime is assumed; it is shown that in this regime the method represents a quantum nondemolition measurement of the atomic position. On the other hand it can be applied to prepare narrow distributions of the transverse atomic position. In order to show this, a numerical simulation is performed, which illustrates the collapse of a broad initial Gaussian wavepacket, which can be coherent or incoherent, to a distribution with narrow peaks. Preparing the cavity fields in a squeezed state, one can greatly enhance the impact of the cavity field measurements on the atomic density matrix.     

频率变化的压缩态光场与原子的相互作用

研究了频率随时间变化的压缩态光场与二能级原子的相互作用，主要讨论了光场频率随时间作正弦调制和脉冲调制两种典型情况下原子布居数反转随时间的演化特性.当光场频率随时间作正弦调制时，不仅光场频率调制，而且压缩态的压缩系数和压缩相位均对原子布居数反转的崩塌-回复过程有影响.当光场频率随时间作脉冲调制时，脉冲调制的突变使各拉比振荡之间的相干性发生改变，并在原子布居数反转随时间演化过程中诱导出新的崩塌-回复过程，尤其在脉冲出现的区间内，原子布居数反转表现出持续的小幅快速振荡，这与压缩态的压缩系数无关. 关键词： Jaynes-Cummings模型 压缩态 原子布居数反转     

Effect of spontaneously generated coherence on probe response in an open system

The effect of spontaneously generated coherence on the probe response in an open ladder atomic system with equispaced levels is studied. The result shows that by adjusting the strength of spontaneously generated coherence (SGC), electromagnetically induced transparency (EIT) and high dispersion (index of refraction) with zero absorption can be realized, a much larger gain without inversion (GWI) than that without SGC can be obtained. Moreover, in the open system and for some strength of SGC, GWI without the incoherent pumping is much larger than that with the incoherent pumping; however, in the corresponding closed system, when the incoherent pumping is absent, we cannot obtain any gain (with or without inversion) for any strength of SGC. In addition, the manipulation role of the atomic exit and injection rates on SGC-dependent absorption property is analyzed for the case when the incoherence pumping does not exist.     

Interactions of a two-level atom and a field with a time-varying frequency without rotating-wave approximation

The interactions between a two-level atom and a field with a time-varying frequency without rotating-wave approximation have been investigated. The frequency of the field varies in the form of rectangle. The dynamic behaviors of the atomic population inversion, photon anti-bunching and atomic dipole squeezing are investigated numerically as function of time. A number of novel phenomena are discovered and discussed.     

Entanglement dynamics and quasiprobability distribution for the degenerate Raman process

In this paper, we consider the model which consists of a degenerate Raman process involving two degenerate Rydberg energy levels of an atom interacting with a single-mode cavity field. The influence of the atomic coherence on the von Neumann entropy of the atom and the atomic inversion is investigated. It is shown that the atomic coherence decreases the amount of atom-field entanglement. It is also found that the collapse and revival times are independent of the atomic coherence, while the amplitude of the revivals is sensitive to this coherence. Moreover, the Q function and the entropy squeezing of the field are examined. Some new conclusions can be obtained.     

Laser cooling force in noisy quadrature of squeezed light

The laser cooling of atoms is a result of the combined effect of Doppler shift, light shift and polarization gradient. These are the phenomena which generally introduce frequency shift and uncertainty. However, they combine gainfully in realizing laser cooling and trapping of the atoms. In this paper we discuss the laser cooling of atoms in the presence of the squeezed light with the decay of atomic dipole moment into noisy quadrature. We show that the higher decay rate of the atomic dipole moment into the noisy quadrature, which leads to decrease in the signal to noise ratio, may contribute in realizing larger cooling force vis-à-vis with coherent laser light.     

Squeezing properties of light field in the process preparing Raman atom laser

In this paper, the squeezing properties of the probe light field in the process preparing Raman-type atom laser via stimulated Raman transition of the sodium atom Bose-Einstein condensate (BEC) interacting with two light beam of a weaker squeezed coherent probe light and a stronger classical pump light are studied. The results show that the probe light can be periodically squeezed. The squeezing period is related to the mean number of atoms in trap, the strength of interaction between squeezed light and BEC atoms, and the detuning of the light, and the squeezing depth is determined by the initial squeezing factor of the probe light.     

Complete entanglement transfer between light and qubits

Using the two-mode two-photon Jaynes-Cummings model, entanglement transfer between atoms and field is studied. It is found that when the field is in state constructed from the two-mode photon number states |00〉,|11〉 or the two-mode squeezed vacuum states, full entanglement exchange can be attained no matter the atoms are initially in pure or mixed states. These investigations show that CV entangled states can act as perfectly as the entangled number states in entangling initially separable atoms. The two-mode two-photon atom-field interaction also provides a simple way for the quantum teleportation of atomic or field states.     

Wigner function and tomogram of the excited squeezed vacuum state

The excited squeezed light (ESL) can be the outcome of interaction between squeezed light probe and excited atom, which can explore the status and the structure of the atom. We calculate the Wigner function and tomogram of ESL that may be comparable to the experimental measurement of quadrature-amplitude distribution for the light field obtained using balanced homodyne detection. The method of calculation seems new.     

Amplification without population inversion in molecules

We have studied the feasibility of amplification without population inversion (AWI) in LiH molecule for three-level ladder, V, and Λ schemes. We have shown the salient features of AWI in a molecular system in comparison to that in an atomic system, viz. the dependence of gain profile on the choice of different rotational and vibrational transitions. Under different three-level schemes, the effect of homogeneous and inhomogeneous broadening on the gain profile has been studied. We have also studied the dependence of gain on different external parameters. The temporal evolution of gain has been analyzed and it was found that AWI is achievable in both the transient and the steady state regime. For all the three-level schemes and in particular for the ladder scheme, amplification of the weak probe was obtained using a coupling laser of smaller frequency.     

Squeezed displaced Wigner operator and its applications

In this paper, we introduce the squeezed displaced Wigner operator. We proved that the squeezed displaced Wigner operator can bring more convenience to calculate the Wigner functions of squeezed states. Finally, we give some new applications of such squeezed displaced Wigner operator.     

Collective atomic spin squeezing and control

Using a quantum theory for an ensemble of two- or three-level atoms driven by electromagnetic fields in an optical cavity, we show that the various spins associated with the atomic ensemble can be squeezed. Two kinds of squeezing are obtained: on the one hand self-spin squeezing when the input fields are coherent ones and the atomic ensemble exhibits a large non-linearity; on the other hand squeezing transfer when one of the incoming fields is squeezed. Received 14 August 2001 and Received in final form 7 November 2001     

Gain without population inversion in a two-level atom damped by a broadband squeezed vacuum

We study the absorption spectrum of a two-level atom driven by a resonant laser field and damped by a broadband squeezed vacuum. We show that for some values of the Rabi frequency of the driving field the central component of the absorption spectrum can switch from absorption to amplification. We find that the presence of the squeezed vacuum field is essential for the gain at the central component. Moreover, the gain is not attributed to any population inversion in both the atomic bare states and in the dressed atomic states. We show that the gain originates from the coherent population oscillations, which are significantly enhanced when the atom is damped by a broadband squeezed vacuum.     

Quantum state transfer from light beams to atomic ensembles

We show the equivalence between an ensemble of two-level atoms driven by a squeezed vacuum field, and a harmonic oscillator coupled to a squeezed field. We give the conditions for optimal squeezing transfer from the field to the atomic ensemble. We show that EPR-type correlations are created between the atomic ensemble and the incoming field. Received 23 January 2001     

Dynamics of optical switching phenomena in dense media

The ultrafast optical switching phenomena in a dense medium of two-level atoms induced by arbitrary varying pulses are explained in terms of the adiabatic cancellation of the pulse by the induced polarization. The final population inversion of the medium after the passage of the pulse is found to depend on the number of oscillations the inversion exhibits during the time interval when the normalized pulse amplitude exceeds the maximum allowed value of the atomic polarization. If the inversion undergoes an integer number of oscillations in this region, then the final state of the system returns to the ground state. On the other hand, if the inversion undergoes a half integer number of oscillations in this region, the final state of the system is fully inverted. This behavior is explored analytically and illustrated numerically for the constant, sine and secant pulse shapes.     

Enhanced squeezing and entanglement in a non-degenerate three-level cascade laser with injected squeezed light

We consider a non-degenerate three-level cascade laser coupled to a two-mode squeezed vacuum reservoir via the lossy single-port mirror. Applying the pertinent master equation, we analyze the effects of the injected squeezed light on the quadrature squeezing, entanglement and normalized intensity difference fluctuations. We show that the injected squeezed light considerably enhances the degree of squeezing and entanglement in the two-mode light for certain initial conditions. Moreover, the injected squeezed light increases the mean photon number where the squeezing and entanglement is significant. We also show that the presence of the injected squeezed light greatly reduces the noise in the intensity difference.     

Entanglement and nonclassicality evolution of the atom in a squeezed vacuum

As an important parameter, von Neumann entropy has been used to characterize the entanglement between atom and light field. We discussed the entanglement and nonclassicality evolution of an atom in a squeezed vacuum—a typical nonclassical field, and compare it with that of the coherent state. It shows that the atom-field entanglement in squeezed vacuum is much stronger and stabler than that in coherent state, whereas the nonclassicality of the light field depends on its initial status. This investigation is trying to find a new insight into the relation between entanglement of atom-field system and nonclassicality of light fields. The result shows that the entanglement between the atom and the field can be maintained well in the squeezed vacuum and this implies better control of atom and photon mutually.