Linewidth of electromagnetically induced transparency under motional averaging in coated vapor cell

The linewidth of electromagnetically induced transparency (EIT) in a coated Rb vapor cell was studied under a magnetic field gradient. The nonlinear broadening of the EIT linewidth with the magnetic field gradient was observed. It was found that the motional averaging of the field gradient was more pronounced at higher laser intensities and larger beam sizes. In the same regime, there was a small linewidth decrease with the increasing magnetic field gradient. We have established a Monte-Carlo model, which gave results in good qualitative agreement with our experiment. Physics pictures for the above phenomena were also suggested. These results provide an understanding of the EIT linewidth behavior under the motional averaging, and should be useful for applications in quantum optics and metrology based on coated vapor cells.     

Cavity linewidth narrowing by means of electromagnetically induced transparency in Rb with a longitudinal magnetic field

We demonstrate a method for further reducing the cavity linewidth by the application of a small longitudinal magnetic field on the Rb cell. Because of the magnetic field multiple electromagnetically induced transparen- cies （EITs） are observed. The center EIT linewidth is measured as a function of the magnetic field. By utilizing the center EIT we narrow the cavity linewidth to 2 MHz which is half of the cavity linewidth without magnetic field.     

Coherent population trapping and strong electromagnetically induced transparency resonances on the D<Subscript>1</Subscript> line of potassium

In this paper we report the first experimental observation of coherent population trapping (CPT) in thermal potassium vapor in a three levels Λ scheme. We demonstrate that K presents the advantage of a reduced modulation frequency with a large resonance contrast (up to 40%), in comparison to similar approaches with other alkalis. We report also the first evidence of electromagnetically induced transparency (EIT) resonances in K in the so called Hanle configuration. We tested different kinds of cells, demonstrating strong enhancement of the resonance contrast and amplitude for antirelaxation coated and buffered cells containing K vapor: resonance contrast up to 90% (for coated cells) and 65% (for buffered cells) is achieved with a linewidth of about 13 mG, while under similar conditions, the EIT resonance contrast in Cs vapor buffered by Ar gas is about 1%. Such relevant improvement is due to the reduced optical pumping in K, because of the overlapping of the hyperfine levels Doppler profiles, which does not occur in the case of Rb and Cs vapor. For this reason, K can be considered very promising for further CPT and EIT applications, especially for those where optical pumping losses represent a major limiting factor, such as light slowing and magnetometry.     

Cavity-linewidth narrowing by means of electromagnetically induced transparency

Cavity-linewidth narrowing in a ring cavity that is due to the high dispersion and reduced absorption produced by electromagnetically induced transparency (EIT) in rubidium-atom vapor has been experimentally observed. The cavity linewidth with rubidium atoms under EIT conditions can be significantly narrowed. Cavity-linewidth narrowing was measured as a function of coupling beam power.     

Decoherence of electromagnetically induced transparency in atomic vapor

We report characterization of electromagnetically induced transparency (EIT) resonances in the D1 line of (87)Rb under various experimental conditions. The dependence of the EIT linewidth on the power of the pump field was investigated at various temperatures for the ground states of the lambda system associated with different hyperfine levels of the atomic 5S(1/2) state as well as magnetic sublevels of the same hyperfine level. Strictly linear behavior was observed in all cases. A theoretical analysis of our results shows that dephasing in the ground state is the main source of decoherence, with population exchange playing a minor role.     

High resolution spectroscopy of Rb in magnetic field by far-detuning electromagnetically induced transparency

We have presented a high resolution spectroscopy of Rb in magnetic field by far-detuning electromagnetically induced transparency (EIT). The EIT spectrum in the $\Xi$-type configuration is usually companied by a double resonance optical pumping (DROP) due to the strong optical coupling between the two upper states, leading to the spectral lines seriously deformed and widely broadened for complex relaxation processes in DROP. Here we demonstrate a high resolution spectroscopy by far-detuning EIT for $^{87}\rm{Rb}$ $\rm{5S_{1/2}\rightarrow5P_{3/2}\rightarrow5D_{5/2}}$ in magnetic fields. The method of far-detuning eliminates the relaxation in DROP to the most extent and decreases the spectral linewidth from more than 20 MHz down to its natural linewidth limit (6 MHz). The deformation of the spectral lines also disappears and the observed spectra are well in accordance with the theoretical calculation. Our work shows that far-detuning EIT is a reliable high resolution spectroscopic method when the relaxation in DROP cannot be neglected, especially for the case of transition to low excited states.     

High quality electromagnetically induced transparency spectroscopy of ~(87)Rb in a buffer gas cell with a magnetic field

We have studied the phenomenon of electromagnetically induced transparency(EIT) of ~(87)Rb vapor with a buffer gas in a magnetic field at room temperature. It is found that the spectral lines caused by the velocity selective optical pump effects get much weaker and wider when the sample cell is mixed with a 5-Torr N_2 gas while the EIT signal is kept almost unchanged. A weighted least-square fit is also developed to remove the Doppler broadening completely. This spectral method provides a way to measure the Zeeman splitting with high resolution, for example, the Λ-type EIT resonance splits into four peaks on the D_2 line of ~(87)Rb in the thermal 2-cm vapor cell with a magnetic field along the electric field of the linearly polarized coupling laser. The high-resolution spectrum can be used to lock the laser to a given frequency by tuning the magnetic field.     

利用微波场抑制电磁感应透明的功率展宽

电磁感应透明的重要参量之一是透明窗口的光谱线宽。在Λ-型三能级原子系统中,电磁感应透明的光谱线宽由两低能级间的相干失相速率决定,若两低能级同属于原子基态的精细结构,则电磁感应透明窗口的极限线宽很窄。但较强的耦合场作用往往会导致电磁感应透明窗口的功率展宽,而减弱耦合场又会影响电磁感应透明的对比度和深度。为此,通过引入微波控制场共振作用于基态精细能级间构成三场作用下的准Λ-型四能级系统,利用微波控制场来抑制耦合场所引起的电磁感应透明窗口的功率展宽。结果表明,引入微波控制场不仅得到了双窗口电磁感应透明,而且在保持较好对比度的条件下,使得电磁感应透明的光谱线宽明显小于不加微波场的情况。     

Absorption resonances in A-type three-level system in cesium vapor cell with buffer gas

We report experimentally the transformation from the electromagnetically induced transparency (EIT) resonance to a dispersion-like signal and eventually to a nearly symmetric absorption resonance as coupling detuning increases in A-type three-level system in the cesium vapor cell with buffer gas at room temperature. The observed absorption resonance occupies some remarkable properties of the strong amplitude and the narrow linewidth in comparison with the case without buffer gas. The relation between linewidth of the enhanced absorption resonance and buffer gas pressure is studied. With pressure increasing, linewidth of the absorption resonance becomes narrow. The sub-natural linewidth is observed in Doppler-broadened cesium vapor cell in our experiment. The experimental results are in qualitative agreement with the numerical simulations.     

Electromagnetically induced transparency and electromagnetically induced absorption in Y-type system

The propagation of a probe field through a four-level Y-type atomic system is described in the presence of two additional coherent radiation fields, namely, the control field and the coupling field. An expression for the probe response is derived analytically from the optical Bloch equations under steady state condition to study the absorptive properties of the system under probe field propagation through an ensemble of stationary atoms as well as in a Doppler broadened atomic vapor medium. The most striking result is the conversion of electromagnetically induced transparency(EIT) into electromagnetically induced absorption(EIA) as we start switching from weak probe regime to strong probe regime. The dependence of this conversion on residual Doppler averaging due to wavelength mismatch is also shown by choosing the coupling transition as a Rydberg transition.     

Splitting of the electromagnetically induced transparency resonance on 85Rb atoms in strong magnetic fields up to the Paschen-Back regime

Electromagnetically induced transparency (EIT) resonance in strong magnetic fields of up to 1.7 kG has been investigated with the use of a 30-??m cell filled with an atomic rubidium vapor and neon as a buffer gas. The EIT resonance in the ?? system of the D₁ line of ⁸⁵Rb atoms has been formed with the use of two narrowband (??1 MHz) 795-nm diode lasers. The EIT resonance in a longitudinal magnetic field is split into five components. It has been demonstrated that the frequencies of the five EIT components are either blue- or red-shifted with an increase in the magnetic field, depending on the frequency ??_P of the probe laser. In has been shown that in both cases the ⁸⁵Rb atoms enter the hyperfine Paschen-Back regime in magnetic fields of >1 kG. The hyperfine Paschen-Back regime is manifested by the frequency slopes of all five EIT components asymptotically approaching the same fixed value. The experiment agrees well with the theory.     

Uniaxial Diffusional Narrowing of NMR Lineshapes for Membrane Proteins Reconstituted in Magnetically Aligned Bicelles and Macrodiscs

Structure and dynamics of membrane proteins can be effectively studied by oriented-sample solid-state nuclear magnetic resonance (NMR) techniques when the lipid bilayers are macroscopically aligned with respect to the main magnetic field. Magnetic alignment of the protein-containing membrane bilayer results from the negative susceptibility anisotropy of the lipid hydrocarbon interior yielding perpendicular sample alignment. At this orientation, while the uniformity of alignment represents an essential prerequisite for obtaining high-quality NMR spectra, further line narrowing is obtained by uniaxial motional averaging of the azimuthal parts of the chemical shift anisotropies and dipolar couplings. The motional averaging is brought about by uniaxial rotational diffusion of the protein molecules about the normal to the membrane surface, which is perpendicular to the magnetic field. Uniaxial averaging is efficient when the motion about the axis of alignment becomes sufficiently fast (on the timescale of the dipolar couplings and chemical shift anisotropies). Line narrowing under uniaxial rotation can be theoretically modeled using the stochastic Liouville equation. In this mini-review, we illustrate the method of uniaxial averaging for the relatively small Pf1 coat protein which exhibits excellent resolution in magnetically aligned bicelles due to its fast uniaxial diffusion and even superior resolution in large (30 nm) nanodiscs (macrodiscs) stabilized by a belt peptide. Spectra of Pf1 coat protein in polymer-stabilized macrodiscs, an alternative and more robust alignment media, are presented. We also report on preliminary spectra of a much larger protein—uniformly ¹⁵N labeled M1-M4 domain for the human acetylcholine receptor. While some spectral resolution is apparent, significantly broader linewidths emphasize the need for creating fast rotating discoidal membrane mimetics.     

Subnatural linewidth in a strongly-driven degenerate two-level system

We observe linewidths below the natural linewidth for a probe laser on a degenerate two-level F → F′ transition, when the same transition is driven by a strong control laser. We take advantage of the fact that each level of the transition is made of multiple magnetic sublevels, and use the phenomenon of electromagnetically induced transparency (EIT) or absorption (EIA) in multilevel systems. Optical pumping by the control laser redistributes the population so that only a few sublevels contribute to the probe absorption, an explanation which is verified by a density-matrix analysis of the relevant sublevels. We observe more than a factor of 3 reduction in linewidth in the D₂ line of Rb in room-temperature vapor. Such subnatural features vastly increase the scope of applications of EIT, such as high-resolution spectroscopy and tighter locking of lasers to atomic transitions, since it is not always possible to find a suitable third level.     

EIT as a tool to observe dual wavelength operation of a semiconductor laser

We propose a simplified technique for dual wavelength operation of an extended cavity semiconductor laser, and its characterization using electromagnetically induced transparency (EIT). In this laser cavity scheme light beam is made converging before it incidences on the cavity grating. The converging angle of the beam creates two longitudinal oscillating modes of resonating cavity. Frequency separation between the longitudinal modes are measured with the help of beat frequency generation in a photodiode and creating pair of EIT spectra in Rb vapor. The pair of EIT dips that are generated due to dual wavelength of this laser (that is used as control laser) can be used to estimate frequency difference between the generated wavelengths. Width of EIT spectra can be used to estimate linewidth of individual wavelength components.     

Temperature dependence of the quadrupole interaction in potassium heptafluohafnate

The quadrupole interaction between the tantalum nucleus and its environment in potassium heptafluohafnate incorporating radioactive¹⁸¹Hf has been studied over the temperature range from 77 K to 318 K. A discontinuity in the field gradient tensor is observed at 250 K together with a more gradual alteration with midpoint temperature of approximately 210 K. Below 250 K, the data indicate two inequivalent sites for the tantalum nuclei. The values obtained for the electric field gradient tensor suggest that motional averaging may be significant in this compound.     

Muon-hydrogen correlation in nickel-titanium metallic glass

Measurements of muon spin rotation in a transverse magnetic field in the Ni₃₅Ti₆₅ metallic glass saturated with hydrogen are reported. The experiment was carried out on the μSR facility at ISIS/RAL. Chilton, UK. The decay of the muon precession has a gaussian form below 150 K. Above this temperature motional narrowing occurs, the linewidth falling to the background value at about 300 K. The linewidth is almost entirely determined by the dipolar interaction between the muon and proton spins and the line narrowing is due to the correlated motion of the muon-hydrogen system. The activation energies and jump rates deduced from these measurements and from nuclear magnetic dipolar relaxation are compared.     

Cavity linewidth narrowing with dark-state polaritons

We present a quantum-theoretical treatment of cavity linewidth narrowing with intracavity electromagnetically induced transparency(EIT). By means of intracavity EIT, the photons in the cavity are in the form of cavity polaritons:bright-state polariton and dark-state polariton. Strong coupling of the bright-state polariton to the excited state induces an effect known as vacuum Rabi splitting, whereas the dark-state polariton decoupled from the excited state induces a narrow cavity transmission window. Our analysis would provide a quantum theory of linewidth narrowing with a quantum field pulse.     

Electromagnetically induced transparency resonances inverted in magnetic field

The phenomenon of electromagnetically induced transparency (EIT) is investigated in a Λ-system of the ⁸⁷Rb D ₁ line in an external transverse magnetic field. Two spectroscopic cells having strongly different values of the relaxation rates γ_rel are used: an Rb cell with antirelaxation coating (L ~ 1 cm) and an Rb nanometric- thin cell (nanocell) with a thickness of the atomic vapor column L = 795 nm. For the EIT in the nanocell, we have the usual EIT resonances characterized by a reduction in the absorption (dark resonance (DR)), whereas for the EIT in the Rb cell with an antirelaxation coating, the resonances demonstrate an increase in the absorption (bright resonances (BR)). We suppose that such an unusual behavior of the EIT resonances (i.e., the reversal of the sign from DR to BR) is caused by the influence of an alignment process. The influence of alignment strongly depends on the configuration of the coupling and probe frequencies as well as on the configuration of the magnetic field.     

Coherent effect of triple-resonant optical parametric amplification inside a cavity with injection of a squeezed vacuum field

In theory, we study the quantum tluctuatlons ot tlae suDllarmonlc renecteu nela Irom a ulplc-rc~ulltUtt IdU~ClIClatC optical parametric amplifier （OPA） inside an optical cavity. We discuss two cases, where the linewidth of the harmonic field is either much narrower or broader than the subharmonic field. Since an electromagnetically-induced-transparency （EIT）-like effect can be simulated in a triple-resonant OPA, the output spectra from a triple-resonant OPA with a squeezed vacuum input may simulate the phenomenon of the response of an EIT medium for squeezed states. This scheme can be implemented with present experimental setups.     

激光线宽对原子相干效应的影响

该文在λ型三能级原子系统中分别讨论了耦合场和探针场线宽对电磁诱导透明(EIT)的影响,通过实验观测探针光和耦合光线宽变化时EIT的透明窗口的变化,得出耦合光对EIT的影响大于探针光线宽的影响,这一结果将为原子存储时间的提高具有一定意义.