Hot Atomic Vapor Research Articles

Storage and retrieval of ghost images in hot atomic vapor

Ghost imaging is an imaging technique in which the image of an object is revealed only in the correlation measurement between two beams of light, whereas the individual measurements contain no imaging information. Here, we experimentally demonstrate storage and retrieval of ghost images in hot atomic rubidium vapor. Since ghost imaging requires (quantum or classical) multimode spatial correlation between two beams of light, our experiment shows that the spatially multimode correlation, a second-order correlation property of light, can indeed be preserved during the storage-retrieval process. Our work, thus, opens up new possibilities for quantum and classical two-photon imaging, all-optical image processing, and quantum communication.

GHz Rabi Flopping to Rydberg States in Hot Atomic Vapor Cells

We report on the observation of Rabi oscillations to a Rydberg state on a time scale below 1ns in thermal rubidium vapor. We use a bandwidth-limited pulsed excitation and observe up to 6 full Rabi cycles within a pulse duration of ∼4 ns. We find good agreement between the experiment and numerical simulations based on a surprisingly simple model. This result shows that fully coherent dynamics with Rydberg states can be achieved even in thermal atomic vapor, thus suggesting small vapor cells as a platform for room-temperature quantum devices. Furthermore, the result implies that previous coherent dynamics in single-atom Rydberg gates can be accelerated by 3 orders of magnitude.

Interference between electromagnetically induced transparency and two-step excitation in three-level ladder systems

We have performed electromagnetically induced transparency (EIT) and two-photon absorption experiments in ladder-type three-level systems in a hot sodium atomic vapor, using the 3S1/2-3P1/2-4D3/2, 3S1/2-3P3/2-4D3/2,5/2, 3S1/2-3P1/2-5S1/2, and 3S1/2-3P3/2-5S1/2 transitions. In particular, in the most pronounced 3S1/2-3P1/2-4D3/2 system, we have observed quite unique spectral line shapes that are superpositions of sharp dips and peaks, in contrast to ordinary EIT spectra. The peaks and dips have apparently different physical origins, and the line shape can be interpreted as the interference between EIT and two-step excitation.

Analysis of electromagnetically induced transparency and slow light in a hot vapor of atoms undergoing collisions

We present a realistic theoretical treatment of a three-level $\Lambda$ system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths, leading to electromagnetically-induced transparency and slow light under the two-photon resonance condition. We take into account all the relevant decoherence processes including col5Blisions. Velocity-changing collisions (VCCs) are modeled in the strong collision limit effectively, which helps in achieving optical pumping by the coupling beam across the entire Doppler profile. The steady-state expressions for the atomic density-matrix elements are numerically evaluated to yield the experimentally measured response characteristics. The predictions, taking into account a dynamic rate of influx of atoms in the two lower levels of the $\Lambda$, are in excellent agreement with the reported experimental results for $^4$He*. The role played by the VCC parameter is seen to be distinct from that by the transit time or Raman coherence decay rate.

Four-wave-mixing stopped light in hot atomic rubidium vapour

Digital signal processing, holography, and quantum and classical information processing rely heavily upon recording the amplitude and phase of coherent optical signals. One method for achieving coherent information storage makes use of electromagnetically induced transparency. Storage is achieved by compressing the optical pulse using the steep dispersion of the electromagnetically induced transparency medium and then mapping the electric field to local atomic quantum-state superpositions. Here we show that nonlinear optical processes may enhance pulse compression and storage, and that information about the nonlinear process itself may be stored coherently. We report on a pulse storage scheme in hot atomic rubidium vapour, in which a four-wave-mixing normal mode is stored using a double- configuration. The entire (broadened) waveform of the input signal is recovered after several hundred microseconds (1/e time of about 120 s), as well as a new optical mode (idler) generated from the four-wave-mixing process.

Delocalized Correlations in Twin Light Beams with Orbital Angular Momentum

We generate intensity-difference-squeezed Laguerre-Gauss twin beams of light carrying orbital angular momentum by using four-wave mixing in a hot atomic vapor. The conservation of orbital angular momentum in the four-wave mixing process is studied as well as the spatial distribution of the quantum correlations obtained with different configurations of orbital angular momentum. Intensity-difference squeezing of up to -6.7 dB is demonstrated with beams carrying orbital angular momentum. Delocalized spatial correlations between the twin beams are observed.

Image storage in hot vapors

We theoretically investigate image storage in hot atomic vapor. A so-called $4f$ system is adopted for imaging and an atomic vapor cell is placed over the transform plane. The Fraunhofer diffraction pattern of an object in the object plane can thus be transformed into atomic Raman coherence according to the idea of ``light storage.'' We investigate how the stored diffraction pattern evolves under diffusion and discuss the essence of the stability of its dark spots. Our result indicates, under appropriate conditions, that an image can be reconstructed with high fidelity. The main reason for this procedure is the fact that diffusion of opposite-phase components of the diffraction pattern interferes destructively.

Generation of Spatially Broadband Twin Beams for Quantum Imaging

We generate spatially multimode twin beams using 4-wave mixing in a hot atomic vapor in a phase-insensitive traveling-wave amplifier configuration. The far-field coherence area measured at 3.5 MHz is shown to be much smaller than the angular bandwidth of the process and bright twin images with independently quantum-correlated subareas can be generated with little distortion. The available transverse degrees of freedom form a high-dimensional Hilbert space that we use to produce quantum-correlated twin beams with finite orbital angular momentum.

Experimental study on laser pattern formation by strong nonlinear effects in rubidium atomic hot vapor

There are abundant nonlinear effects in atomic vapor. In this paper, the phenomenon of laser breaking up into filaments is studied in the near-resonant rubidium atomic vapor，which is induced by the strong nonlinear Kerr effect. When the continuous-wave laser beam with transverse Gaussian distribution passes through the atomic vapor, the pattern arising from the coherent superposition of the diffraction patterns of filaments is observed. We also investigated the influence on the mode pattern by input power of laser, the temperature of the vapor cell and the frequency detuning of pump light. Due to the hyperfine structure of rubidium atoms, the four-wave mixing effect exists in hot rubidium atomic vapor, which is related to the third-order nonlinear effect closely. The Raman gain of the Stokes and anti-Stokes photons is observed by scanning the frequency of the probe beam.

Ultraslow Propagation of Matched Pulses by Four-Wave Mixing in an Atomic Vapor

We have observed the ultraslow propagation of matched pulses in nondegenerate four-wave mixing in a hot atomic vapor. Probe pulses as short as 70 ns can be delayed by a tunable time of up to 40 ns with little broadening or distortion. During the propagation, a probe pulse is amplified and generates a conjugate pulse which is faster and separates from the probe pulse before getting locked to it at a fixed delay. The precise timing of this process allows us to determine the key coefficients of the susceptibility tensor. The fact that the same configuration has been shown to generate quantum correlations makes this system very promising in the context of quantum information processing.

Spontaneously generated coherence in a Doppler broadened atomic system

We investigate the spontaneously generated coherence (SGC) in a Doppler broadened four-level atomic system driven by two coherent fields. We plot the spontaneous emission spectra with different parameters and discuss how the initial atomic conditions and parameters of both fields change the number of peaks and dark lines of spontaneous emission spectra. Furthermore, we also show how the spontaneous emission spectrum is modified by Doppler effects in the viewed direction. Our results have important references to the experimental observation of SGC in hot atomic vapors.

Sub-Doppler absorption narrowing in atomic vapor at two intense laser fields

We have experimentally studied electromagnetically induced transparency (EIT) and absorption (EIA) in hot 85Rb atomic vapor using probe and coupling light with comparable power levels. We have shown that strong-probe EIT has different linewidth and appears in fewer configurations than does usual, weak probe EIT. In V-scheme, where optical pumping and saturation are dominant mechanisms, narrow EIT is possible only when a probe is tuned to a closed transition. The width of the EIT resonance increases with laser intensity with non-linear dependence, similar to the weak-probe EIT in Lambda- scheme. The EIT in Lambda- scheme was observed when two transitions had balanced population losses. The EIA was modified for the case of a strong probe as well: in four-level N-scheme with Zeeman sublevels the EIA was observed only for a cycling transition when F'=F+1, where F and F' are the angular momenta of the 5 2S1/2 (ground) and 5 2P3/2 (excited) state hyper-fine levels, respectively. The combination of strong probe and strong coupling laser beam intensities allows observation of an absorption dip due to three-photon resonance in a four-level scheme that involves the Raman transitions via virtual level.

Saturable nonlinear refraction in hot atomic vapor

Atomic vapors make flexible and useful nonlinear optical media when light is detuned far from resonances. However, few direct measurements of their nonlinear coefficients have been performed to date. We present a measurement of the Kerr coefficient for various detunings to both the red and blue of the $D2$ line in hot atomic rubidium vapor. Saturation effects complicate the interpretation of the standard z-scan method, but a simple saturation model agrees well with our data. We find values of ${n}_{2}\ensuremath{\approx}\ifmmode\pm\else\textpm\fi{}{10}^{\ensuremath{-}7}{\mathrm{cm}}^{2}/\mathrm{W}$ for 1 GHz detunings from the $D2$ line.

Stabilizing an optoelectronic microwave oscillator with photonic filters

This paper compares methods of active stabilization of an optoelectronic microwave oscillator (OEO) based on insertion of a source of optical group delay into an OEO loop. The performance of an OEO stabilized with either a high-Q optical cavity or an atomic cell is analyzed. We show that the elements play a role of narrow-band microwave filters improving an OEO stability. An atomic cell also allows for locking the oscillation frequency to particular atomic clock transitions. This reports a proof-of-principle experiment on an OEO stabilization using the effect of electromagnetically induced transparency in a hot rubidium atomic vapor cell.

Nonlinear absorption and refraction in near-detuned rubidium vapor

Using the z-scan technique, we have measured the self-induced absorptive and refractive nonlinear behavior of hot atomic rubidium vapor within the Doppler profile of the D2 line. We observe large nonlinear amplitude and phase effects with only tens of microwatts of incident power. Our results are in good agreement with numerical calculations based on an analytic model of a Doppler-broadened two-level system.

Observation of a three-photon electromagnetically induced transparency in hot atomic vapor

We demonstrate experimentally the effect of a three-photon electromagnetically induced transparency in hot ${}^{85}\mathrm{Rb}$ atomic vapor driven by two coherent electromagnetic fields. The narrow transparency window is observed on the background of high-contrast Doppler-free subnatural absorption resonance. Our analytical calculations and numerical simulations are in good agreement with the experimental data. Both the transparency and the absorption resonances can find applications in high-precision metrology.

Spontaneous Density Grating Formation in Hot Atomic Vapor

Spontaneous Density Grating Formation in Hot Atomic Vapor

Determination of the temperature of the atomic vapor produced by a mini-massmann carbon rod atomizer and by a west-type carbon filament atomizer using atomic absorption spectrometry

The temperature of the atomic vapor produced by a nonflame mini-Massmann carbon rod atomizer and by a West-type carbon filament atomizer is measured by a two-line atomic absorption method. Temperatures are reported for atomic gallium and indium with argon and argon plus hydrogen as a sheath atmosphere. The carbon rod atomizer with only argon as sheath gas yielded the highest temperatures: 2770°K for gallium and 2080°K for indium. Because both elements yield different maximum temperatures, under similar conditions, equilibrium does not appear to be attained between the hot atomic vapor and the sheath gas, within the residence time of the atomic vapor in the optical path for both atomizer systems. The variation of temperature with height above the rod for the carbon filament atomizer, and with applied voltage for atomization for both atomizers was investigated. Recommendations are made for the improvement of the design of nonflame atomizers.