Recoil-induced resonances in pump-probe spectroscopy.

We propose a multifunction phase-shifting manipulator with low noise at a single-photon level,by using a threelevel atomic scheme.This three-level system interacts with a strong pumping field and a weak probe field with a large detuning.Due to this large detuning,two lower states can be coherently prepared prior to the injection of the pump and probe fields.In our configuration,the duration of the pumping field is much longer than that of the probe field. By solving the Heisenberg-Langevin equations of our system under the steady state approximation,we calculate the linear susceptibility of the system and examine the quantum noise properties of the probe field in detail.We show that this scheme,which rests on the process of two-wave mixing with initial atomic coherence,exhibits many interesting properties that neither typical electromagnetically induced transparency (EIT) schemes nor active Raman gain (ARG) schemes possess.Although both EIT-and ARG-based schemes have been widely investigated in atomic medium,the direct generalizations of these schemes to the single/few photon limit prove to be more problematic.The low fidelity due to the significant probe-field attenuation in EIT medium and the large quantum noise due to the amplification of the probe field in an active Raman gain medium are the main obstacles that prohibit a high-fidelity,low-noise phase shifter from being realized in the single/few photon limit.Physically,this scheme can be viewed as a hybrid scheme in which two processes of different physical principles are allowed to interfere with each other to achieve many desired functionalities. For instance,it can be used as a lossless two-photon-broadband phase-shifter with suitable system parameters.It can also be used as an attenuator/amplifier and a total transparency with a zero phase shift.In particular,we show that by locking the pump field intensity and the two-photon detuning simultaneously a flat constant π-phase shift can be realized with unit probe fidelity in a broad probe field frequency range.Applying the quantum regression theorem,we calculate the noise spectrum of the outgoing probe field as a large phase shift is achieved,and show that this two-photon-insensitive π-phase shift may significantly reduce the quantum noise fluctuations associated with a Raman gain process,and have a lot of potential applications for quantum information processing and optical telecommunication.The realization of this broadband π-phase-shift with significantly reduced quantum noise fluctuations makes this scheme attractive for the realization of low-noise phase-gate/polarization-gate at single-photon level.

We study the directional amplification of an optical probe field in a three-mode optomechanical system, where the mechanical resonator interacts with two linearly-coupled optical cavities and the cavities are driven by strong optical pump fields. The optical probe field is injected into one of the cavity modes, and at the same time, the mechanical resonator is subject to a mechanical drive with the driving frequency equal to the frequency difference between the optical probe and pump fields. We show that the transmission of the probe field can be amplified in one direction and de-amplified in the opposite direction. This directional amplification or de-amplification results from the constructive or destruction interference between different transmission paths in this three-mode optomechanical system.

We present an optical resonator with modified properties due to a nonabsorbing highly dispersive medium. The steep nonabsorbing dispersion is created with an additional pump field in an atomic beam using the effect of coherent population trapping. The linewidth of such a resonator depends on the slope of the dispersion line, which in turn depends on the atomic density and the intensity of pump and probe field. In the experiments presented here, the cavity linewidth is reduced by a factor of more than 50 relative to the linewidth of the empty resonator. We have studied the influence of the relative intensities of pump and probe field on the line profile. Due to the dispersion of the medium, the resonance frequency is nearly independent of the geometrical length of the resonator.

We have studied the stimulated hyper-Raman scattering process in the presence of two strong electromagnetic fields whose frequency modes are initially populated and are near resonance with the two atomic transition frequencies. Using the Green's-function formalism, the excitation spectra are calculated in the limit of high photon densities of both laser fields. Expressions are derived for the relative intensities describing the following processes when (i) both pump fields are at resonance, (ii) the detunings take opposite values corresponding to the cooperative two-photon resonance, and (iii) both laser fields are off resonance. In processes (i) and (ii), the spectra consist of a single peak describing the stimulated hyper-Raman scattering and two pairs of sidebands induced by the laser fields. A new peak appears in process (iii) in addition to those appearing in processes (i) and (ii). The induced spectra are symmetric at resonance but asymmetric in the off-resonance processes, and the extent of the asymmetry depends strongly on the numerical values of the detunings. It is shown that when the two laser fields are treated classically, the derived results are identical to those obtained when the fields are quantized only when photon-photon correlations arising from each laser field are discarded. Numerical calculations for selected values of Rabi frequencies and detunings are graphically presented and discussed.

Theories unifying gravity with other interactions suggest spatial and temporal variation of fundamental “constants” in the Universe. A change in the fine structure constant, $$\alpha = {e}^{2}/\hslash c$$ , could be detected via shifts in the frequencies of atomic transitions in quasar absorption systems. Recent studies using 140 absorption systems from the Keck telescope and 153 from the Very Large Telescope, suggest that α varies spatially (61). That is, in one direction on the sky α seems to have been smaller at the time of absorption, while in the opposite direction it seems to have been larger. To continue this study we need accurate laboratory measurements of atomic transition frequencies. The aim of this paper is to provide a compilation of transitions of importance to the search for α variation. They are E1 transitions to the ground state in several different atoms and ions, with wavelengths ranging from around 900–6000 Å, and require an accuracy of better than 10 − 4 Å. We discuss isotope shift measurements that are needed in order to resolve systematic effects in the study. The coefficients of sensitivity to α-variation (q) are also presented.

Motivated by a recent experiment, the author presents a theoretical study on optical absorption in a semiconductor subjected to pump and probe radiation fields. The electron and hole interactions with midinfrared pump and probe fields are considered and the absorption coefficient is calculated on the basis of a Boltzmann equation approach. It is found that the results obtained theoretically are in line with those observed experimentally and can be used to understand important experimental findings such as the optical absorption in the forbidden zone and the dependence of the absorption of the probe field on intensity and frequency of the pump field.

We present a convenient and efficient scheme to generate arbitrarily multipartite continuous-variable entanglement via mechanical oscillator displacement induced by two strong input pump fields in the conventional single-cavity optomechanical system. It is shown that multipartite entanglement among the outputs of the two pump fields and any number of relatively weak probe fields can be realized and optimized when the two pump fields with suitable amplitude ratio and relative initial phase are, respectively, tuned to the red and blue mechanical sidebands of a single cavity mode and each probe field is red-detuned by the mechanical frequency with respect to a different neighboring cavity mode. This method can, in principle, be extended to flexibly and conveniently generate arbitrarily multiple nondegenerate bright entangled fields by using only coherent laser fields, and may find promising applications in realistic quantum communication and networks.

Tunable high-order sideband generation has important applications in the realization of the optical frequency comb with a varying spectral region (corresponding to the sideband range) and frequency resolution (corresponding to the sideband interval). In this paper, we propose a theoretical scheme to tune both the range and the interval of the high-order sidebands in a coupled double-cavity optomechanical system, which consists of an optomechanical cavity and an auxiliary cavity. Our proposal can be realized by driving the optomechanical cavity with a control field and a probe field simultaneously, driving the auxiliary cavity with a pump field. Furthermore, we assume that the frequency detuning between the control field and the probe field (the pump field) equals ωb/n (ωb/m), where ωb is the mechanical frequency, m and n are integers. When n = m = 1, we find that the sideband range can be effectively enlarged by increasing the pump amplitude or the photon-hopping coupling rate, or by decreasing the auxiliary cavity damping rate. When n = 1 and m > 1, the output spectrum consists of a series of integer-order sidebands, fraction-order sidebands, and the sum and difference sidebands, and the sideband interval becomes ωb/m and can be diminished by simultaneously increasing m and the pump amplitude.

A theory of pump-probe spectroscopy is developed in which optical fields drive two-quantum, Raman-like transitions between ground state sublevels. Three fields are incident on an ensemble of atoms. Two of the fields act as the pump field for the two-quantum transitions. The absorption or gain of an additional probe field is monitored as a function of its detuning from one of the fields which constitutes the pump field. Although the probe absorption spectrum displays features common to those found in pump-probe spectroscopy of single-quantum transitions, new interference effects are found to modify the spectrum. Many of these features can be explained within the context of a dressed atom picture.

We investigate the change in width of transparency windows and the amplification of the probe output spectra in an optomechanical system with multiple mechanical resonators. Each mechanical resonator is driven by a mechanical driving field, and the phases of these mechanical driving fields are different. Via exhibiting the probe output spectra of the system, we find that the number of transparency windows is explicitly decided by the number of mechanical resonators with different frequencies. Meanwhile, we discuss the effect of cavity decay rate on the width of the transparency windows. Moreover, we also investigate the absorption and amplification phenomena with the different phase differences among the pump field, probe field, and mechanical driving fields. By adjusting the phase differences, the fast–slow light transitions can occur. These interesting phenomena can also be exploited to investigate the optical switch and frequency comb generation.

Simultaneous strong coherent pumping of the two transitions of a V-level atom with very different decay rates has been predicted to create almost perfect inversion on the narrower transition. Using the example of the blue and red transitions in Strontium we show that for suitable operating conditions the corresponding resonant gain can be used to continuously operate a laser on the narrow transition. In particular, for a strong detuning of the pump field with respect to the narrow transition, coherent laser emission occurs close to the bare atomic transition frequency exhibiting only a negligible contribution from coherent pump light scattered into the lasing mode. Calculations of the cavity output spectrum show that the resulting laser linewidth can get much smaller than the bandwidth of the pump light and even the natural linewidth of the narrow atomic transition. Its frequency is closely tied to the atomic transition frequency for properly chosen atom numbers. Simulations including atomic motion show Doppler cooling on the strong transition with minor motion heating on the lasing transition, so that continuous laser operation in the presence of a magneto-optical trap should be possible with current experimental technology.

A three-level lambda system driven by multicolor control, pump, and probe fields is investigated. The pump and probe fields are derived from the same laser with opposite propagating directions. Due to the Doppler effect, the zero group-velocity atoms face bichromatic fields, while other atoms face trichromatic fields. The atomic medium shows distinct characteristics and exhibits simultaneous electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) at two frequencies. EIT and EIA peaks have a fixed relationship with frequency, which is determined by the Doppler shifts.

We have measured the absorption from a weak time-delayed probe field by a two-level atomic system [Na 3[ital s][sub 1/2]([ital F]=2,[ital m][sub [ital F]]=2)[r arrow]3[ital p][sub 3/2]([ital F]=3,[ital m][sub [ital F]]=3)] saturated by a phase-diffusing pump field. The pump and probe, derived from the same artificially-noise-modulated phase-diffusing laser beam, are frequency degenerate and resonant with the atomic transition. The probe is a time-delayed replica of the pump. Our results, carried out in a regime where the field bandwidth and the Rabi frequency are comparable, provide confirmation of recent theoretical predictions [K. Gheri, M. A. M. Marte, and P. Zoller, J. Opt. Soc. Am. B 5, 1559 (1991)] for the atomic response to the non-Markovian composite of a pump and time-delayed probe, valid for arbitrary bandwidths and intensities. Amplification of the probe field is observed for delays comparable to the lifetime of the upper level and again for very long delays, if the bandwidth is less than the decay rate of the upper state.

We demonstrate an approach to create a stable erbium-fiber-based frequency comb at communication band by directly locking the combs to two rubidium atomic transitions resonances (electromagnetically induced transparency absorption and two-photon absorption), respectively. This approach directly transfers the precision and stability of the atomic transitions to the comb. With its distinguishing feature of compactness by removing the conventional octave-spanning spectrum and f-to-2f beating facilities and the ability to directly control the comb's frequency at the atomic transition frequency, this stable optical comb can be widely used in optical communication, frequency standard, and optical spectroscopy and microscopy.

We study the electromagnetically induced transparency in dispersive band gap materials when an ensemble of non-interacting four-level atoms is doped. The system is interacting with a pump field, a probe field and a reservoir. The method of master equation and Lap lace transform has been used in calculating the expression for the susceptibility. Numerical simulations are performed on the susceptibility in dispersive band gap material (i.e. SiC). The phenomenon of electromagnetically induced transparency has been predicted in SiC. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)