Cold Rb Atoms Research Articles

Lifetime Measurement of Cold Atoms in an Integrating Sphere

We present an experimental measurement of the lifetime of the cold 87Rb atoms in an integrating sphere. The atoms are cooled by the diffuse light which is generated by the diffuse reflection of laser beams in the integrating sphere. Our result shows that the lifetime is primarily determined by the free fall of the cold 87Rb atoms, and its half-life can reach 40 ms, which is suitable for many experiments, especially for a cold atom clock.

Efficient Multiparticle Entanglement via Asymmetric Rydberg Blockade

We present an efficient method for producing N particle entangled states using Rydberg blockade interactions. Optical excitation of Rydberg states that interact weakly, yet have a strong coupling to a second control state is used to achieve state dependent qubit rotations in small ensembles. On the basis of quantitative calculations, we predict that an entangled quantum superposition state of eight atoms can be produced with a fidelity of 84% in cold Rb atoms.

Simultaneous coupling of three hfs components in a cascade scheme of EIT in cold 85Rb atoms

Abstract We have investigated multiple windows of electromagnetically induced transparency (EIT) registered in a cascade scheme 5S 1/2 (F = 3) → 5P 3/2 (F′ = 3) ↔ 5D 5/2 (F″ = 4, 3, 2) of cold 85 Rb atoms in a magneto-optical trap (MOT), with a weak probe laser in the first step and with a strong coupling laser in the second step. A structure composed of up to three transparency windows is observed in the spectral profile of the probe absorption, due to a simultaneous coupling of three F″ components of a dense hfs structure of a 5D 5/2 state of the 85 Rb isotope. The experimental EIT features, as dependent on the coupling beam intensity or on the frequency detuning from the F′ = 3 ↔ F″ = 3 resonance are compared with those theoretically obtained from a five-level model. A coefficient characterizing a relative decrease of absorption at the center of the most prominent EIT peak, plotted versus the coupling beam intensity, is also presented for both the experimental and modeled spectra. A good agreement between theory and experiment is observed. As it is very simple to manipulate the positions, shapes and depths of the EIT features, the present scheme could be of interest, e.g ., for the quantum information science.

Light-pulse atom interferometry in microgravity

We describe the operation of a light pulse interferometer using cold 87Rb atoms in reduced gravity. Using a series of two Raman transitions induced by light pulses, we have obtained Ramsey fringes in the low gravity environment achieved during parabolic flights. With our compact apparatus, we have operated in a regime which is not accessible on ground. In the much lower gravity environment and lower vibration level of a satellite, our cold atom interferometer could measure accelerations with a sensitivity orders of magnitude better than the best ground based accelerometers and close to proven spaced-based ones.

Fluorescence weakening due to radiation trapping in a high density cold-atom cloud

We have measured the change of fluorescence from cold 87Rb atoms after magnetic field of the magneto-optic trap is turn off. A rise in fluorescence within several tens of milliseconds was observed. Analyzing this phenomenon in connection with the experimental conditions, we found that incoherent pumping field due to radiation trapping in the high density cold-atom cloud was the reason of fluorescence weakening under tight confinement by the magneto-optic trap. We have also performed a simple numerical simulation, which indicated that the calculations agree with experimental results only when the effect of frequency redistribution of scattered light is taken into account.

Fictitious magnetic resonance by quasielectrostatic field

We propose a new kind of spin manipulation method using a fictitious magnetic field generated by a quasielectrostatic field. The method can be applicable to every atom with electron spins and has distinct advantages of small photon scattering rate and local addressability. By using a CO2 laser as a quasielectrostatic field, we have experimentally demonstrated the proposed method by observing the Rabi oscillation of the ground state hyperfine spin F=1 of the cold 87Rb atoms and the Bose–Einstein condensate.

Optical switching mediated by quantum interference of Raman transitions

We report an experimental study of quantum interference between two-photon Raman transitions and demonstration of the phase control of light attenuation/transmission in cold Rb atoms. By varying the phase and frequency of a weak control laser, either constructive interference or destructive interference between the two-photon Raman transitions in a three-level Lambda system can be manipulated. The interference enables absorptive switching of one field by another field at low light levels.

Cold atoms observed for the first time at the Universidad de Santiago de Chile

A cloud of cold 85Rb atoms was recently observed for the first time in Chile in a magneto optical trap using a Rb getter. We also observed cooling and trapping of the 87Rb isotope. This experience represents a preliminary result for an ongoing effort to promote the experimental research in the field of quantum optics in Chile.

Atomic reflection off conductor walls as a tool in cold atom traps

We explain why a system of cold 85Rb atoms at temperatures of the order T≈ 7.78× 10-5 K and below, but not too low to lie in the quantum reflection regime, should be automatically repelled from the surface of a conductor without the need of an evanescent field, as in a typical atom mirror, to counteract the van der Waals attraction. The repulsive potential arises naturally outside the conductor and is effective at distances from the conductor surface of about 400 nm, intermediate between the van der Waals and the Casimir-Polder regions of variation. We propose that such a field-free reflection capability should be useful as a component in cold atom traps. It should be practically free of undesirable field fluctuations and would be operative at distances for which surface roughness, dissipative effects and other finite conductivity effects should be negligibly small.

Suppressing normal mode excitation by quantum interference in a cavity-atom system

Collective coupling of multiple atoms with a cavity mode produces two normal modes that are separated in energy by Vacuum Rabi splitting. We show that the normal mode excitation of the cavity-atom system can be suppressed by coupling a control laser to the atomic system from free space. The control laser splits the normal mode of the cavity-atoms system and opens two excitation channels. The destructive quantum interference between the two channels renders the cavity-atoms system opaque to the light coupled to the cavity-atom system. We demonstrate suppression of the normal mode excitation by the destructive quantum interference in an experiment using cold Rb atoms confined in an optical cavity.

Slow light with cavity electromagnetically induced transparency

We report an experimental observation of slow light propagation in cold Rb atoms exhibiting cavity electromagnetically induced transparency (EIT). The steep slope of the atomic dispersion manifested by EIT reduces the light group velocity. The cavity filtering and feedback further contribute to the slowdown and delay of the light pulse propagation. A combination of the cavity and the EIT atomic system significantly improves the performance of the slow light propagation. A propagation time delay of approximately 200 ns was observed in the cavity and Rb EIT system, which is approximately 70 times greater than the time delay calculated for the light pulse propagation through the same Rb EIT system without the cavity.

Vacuum Rabi splitting and intracavity dark state in a cavity-atom system

We report experimental measurements of the transmission spectrum of an optical cavity coupled with cold Rb atoms. We observe the multiatom vacuum Rabi splitting of a composite cavity and atom system. When a coupling field is applied to the atoms and induces the resonant two-photon Raman transition with the cavity field in a $\ensuremath{\Lambda}$-type system, we observe a cavity transmission spectrum with two vacuum Rabi sidebands and a central peak representing the intracavity dark state. The central peak linewidth is significantly narrowed by the dark-state resonance and its position is insensitive to the frequency change of the empty cavity.

Excited-state imaging of cold atoms

We have investigated state-selective diffraction contrast imaging (DCI) of cold 85Rb atoms in the first excited (52P3/2) state. Excited-state DCI requires knowledge of the complex refractive index of the atom cloud, which was calculated numerically using a semi-classical model. The Autler-Townes splitting predicted by the model was verified experimentally, showing excellent agreement.780 nm lasers were used to cool and excite atoms within a magneto-optical trap, and the atoms were then illuminated by a 776 nm imaging laser. Several excited-state imaging techniques, including blue cascade fluorescence, on-resonance absorption, and DCI have been demonstrated. Initial results show that improved signal-to-noise ratio (SNR) will be required to accurately determine the excited state fraction. We have demonstrated magnetic field gradient compression of the cold atom cloud, and expect that further progress on compression and additional cooling will achieve sufficient diffraction contrast for quantitative state-selective imaging.

Enhancement of Transfer Efficiency of Cold Atoms Using an OpticalGuiding Laser Beam

We transfer cold 87Rb atoms from a vapour cell chamber to aspatially separated UHV magneto-optical trap (MOT) with the assistanceof a red-detuned optical guiding beam and a normal push beam. Efficientoptical guiding of the cold atoms is observed within a small detuningwindow. A pulsed optical guiding beam enhances the transfer efficiencyand hence allows us to collect more atoms in UHV MOT in a shorter time,which is favourable for our experiment of achieving Bose–Einsteincondensates (BEC). Besides the easy operation, another advantage ofthis optical guiding technique is also demonstrated such that sloweratomic beams may be efficiently transferred along horizontal direction.This study is a direct application of the optical guiding technique asa powerful tool.

Versatile element for free-space dividing and redirecting neutral-atom clouds

We introduce a tunnel lock that can be exploited to divide, delay, and alter the direction of traveling clouds of cold atoms. This versatile free-space element is implemented by crossing two atom tunnels formed by low-intensity, blue-detuned dark-hollow (Bessel mode) laser beams. We show that clouds of cold Rb atoms initially moving within one tunnel can be transferred to the other without heating by gating the intensities of the two tunnels---a tunnel lock---with an efficiency limited by the overlap volume. The element also can be used to divide a single cloud into smaller clouds, each having a distinct momentum.

Acceleration of cold Rb atoms by frequency modulated light pulses

The displacement of Rb atoms in a magneto-optical trap (MOT) caused by the force of a finite time series of counter-propagating frequency modulated light pulse pairs is measured as a function of the chirp of the pulses. The frequency modulated light pulses induced 85Rb 52S1/2 F=3 ↔ 85Rb 52P3/2 F'=2, 3, 4 excitation and de-excitation of the atoms. The result of this excitation de-excitation process is a force causing the acceleration and, consequently, the displacement of the maximum of the spatial distribution of the trap atoms. The time dependence of the populations of the levels of the atom are calculated — including also the 85Rb 52S1/2 F=2 and F'=1 states — as the result of the interaction with the finite train of counter propagating frequency modulated light pulses by the solution of the Bloch equations. As the result of the measurement the interval of the chirp of the frequency modulated light of given intensity where the transitions take place, are determined. The results of the experiment and the expectation on the basis of model calculations are in qualitative agreement.

Polychromatic-field-induced transparency and absorption in a three-levelΛsystem

We report an experimental study of atomic coherence and interference in a three-level $\ensuremath{\Lambda}$ system of cold Rb atoms driven by multicolor coupling and probe fields. The multicolor coupling and probe fields open multiple channels for a two-photon Raman process. Interference between the open channels leads to rich spectral features in the $\ensuremath{\Lambda}$ system and can be controlled by the phase of the probe field. The constructive-interference-induced transparency or the destructive-interference-induced absorption with a subnatural linewidth can be selectively created near the atomic resonance.

Observation of electromagnetically induced transparency for a squeezed vacuum with the time domain method

A probe light in a squeezed vacuum state was injected into cold 87Rb atoms with an intense control light in a coherent state. A sub-MHz window was created due to electromagnetically induced transparency, and the incident squeezed vacuum could pass through the cold atoms without optical loss, as was successfully monitored using a time-domain homodyne method.

Stable fiber-based Fabry-Pérot cavity

The development of a fiber-based, tunable optical cavity with open access is reported. The cavity is of the Fabry-Pérot type and is formed with miniature spherical mirrors positioned on the end of single- or multimode optical fibers by a transfer technique, which involves lifting a high-quality mirror from a smooth convex substrate, either a ball lens or microlens. The cavities typically have a finesse of ∼1000 and a mode volume of 600μm3. The detection of small ensembles of cold Rb atoms guided through such a cavity on an atom chip is demonstrated.

Deflecting Atoms through a Submicron-Sized Slit with Near-Field Light

We report experiments on deflecting cold 87Rb atoms by repulsive near-field light induced in a 200-nm-wide slit. The spatial profile is measured with a two-step photoionization scan. The number of outputted atoms from the slit increases by the amount of 40 ± 7.2% at a 5.1 ± 2.0° angle for the blue detuning of +1 GHz. We discuss the spatial profile involving an image of the atomic cloud by means of the scattering cross section.