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An advanced undergraduate experiment to study the 5 P 3 / 2 → 6 P 3 / 2 electric quadrupole transition in rubidium atoms is presented. The experiment uses two external cavity diode lasers, one operating at the D2 rubidium resonance line and the other built with commercial parts to emit at 911 nm. The lasers produce the 5 s → 5 p → 6 p excitation sequence in which the second step is the forbidden transition. Production of atoms in the 6 P 3 / 2 state is observed by detection of the 420 nm fluorescence that results from electric dipole decay into the ground state. Lines whose widths are significantly narrower than the Doppler width are used to study the hyperfine structure of the 6 P 3 / 2 state in rubidium. The spectra illustrate characteristics unique to electric dipole forbidden transitions, like the electric quadrupole selection rules; they are also used to show general aspects of two-color laser spectroscopy such as velocity selection and hyperfine pumping.

The design and construction of an experimental system for studying two photon spectroscopy processes in atomic rubidium is presented. It is designed to measure absorption and polarization rotation induced by any of the two laser beams and also the visible fluorescence that results from decay of the excited states. Two home-built diode lasers are used to produce the optical fields that later interact with room temperature rubidium atoms. Using counterpropagating beams allows velocity selection of the groups of atoms that interact with both laser beams. The system was tested in the 5 S→5 P3/2 →5 Dj ladder energy level configuration of atomic rubidium. Blue fluorescence (420 nm) that results from decay of the intermediate 6Pj states is filtered and then measured with a photomultiplier tube. Absorption and fluorescence spectra provide mutually complementary information about the interaction between the rubidium atoms and the two optical fields. All Rights Reserved © 2015 Universidad Nacional Autonoma de Mexico, Centro de Ciencias Aplicadas y Desarrollo Tecnologico. This is an open access item distributed under the Creative Commons CC License BY-NC-ND 4.0.

Doppler-free optical double-resonance spectroscopy is used to study the 5S1/2 → 5P3/2 → 6Pj (j = 3/2,1/2) excitation sequence in room-temperature rubidium atoms. This involves a 5S1/2 → 5P3/2 electric dipole preparation step followed by the 5P3/2 → 6Pj electric quadrupole excitation. The electric dipole forbidden transitions occur at 911.0 nm (j = 3/2) and 917.5 nm (j = 1/2). Production of atoms in the 6Pj states is detected by observing their direct decay to the ground state through emission of blue photons (λ ≈ 420 nm). A detailed experimental and theoretical study of the dependence on the relative linear polarizations of excitation beams is made. It is shown that specific electric quadrupole selection rules over magnetic quantum numbers are directly related to the relative orientation of the linear polarization of the excitation beams.

We perform Ramsey spectroscopy on the ground state of ultracold 87Rb atoms magnetically trapped on a chip in the Knudsen regime. Field inhomogeneities over the sample should reduce the contrast of the Ramsey frindges by a factor of 5 for 5 s of interrogation. We measure hardly any decay, only a factor 1.08 corresponding to a coherence time of the order of one minute. This new effect allows us to increase the quality factor of the microwave atomic resonance. We explain this surprising result by a spin self-rephasing mechanism induced by the identical spin rotation effect. The study of decoherence under metrological condition is the key to this synchronisation regime where non-linear effects dominate the evolution of the cloud. We propose a theory of this synchronization mechanism and obtain good agreement with the experimental observations. The effect is general and may appear in other physical systems with trapped atoms. In particular, this effect will exist for fermions and could be exploited to enhance the stability of optical lattice clocks.

Direct evidence of excitation of the $5{p}_{3/2}\ensuremath{\rightarrow}6{p}_{3/2}$ electric-dipole-forbidden transition in atomic rubidium is presented. The experiments were performed in a room-temperature rubidium cell with continuous-wave external cavity diode lasers. Optical-optical double-resonance spectroscopy with counterpropagating beams allows the detection of the nondipole transition free of Doppler broadening. The $5{p}_{3/2}$ state is prepared by excitation with a laser locked to the maximum $F$ cyclic transition of the ${D}_{2}$ line, and the forbidden transition is produced by excitation with a 911 nm laser. Production of the forbidden transition is monitored by detection of the 420 nm fluorescence that results from decay of the $6{p}_{3/2}$ state. Spectra with three narrow lines ($\ensuremath{\approx}13$ MHz FWHM) with the characteristic $F\ensuremath{-}1, F$, and $F+1$ splitting of the $6{p}_{3/2}$ hyperfine structure in both rubidium isotopes were obtained. The results are in very good agreement with a direct calculation that takes into account the $5s\ensuremath{\rightarrow}5{p}_{3/2}$ preparation dynamics, the $5{p}_{3/2}\ensuremath{\rightarrow}6{p}_{3/2}$ nondipole excitation geometry, and the $6{p}_{3/2}\ensuremath{\rightarrow}5{s}_{1/2}$ decay. The comparison also shows that the electric-dipole-forbidden transition is a very sensitive probe of the preparation dynamics.

Doppler-free optical double-resonance spectroscopy is used to study the excitation sequence in room-temperature rubidium atoms. This involves a electric dipole preparation step followed by the electric quadrupole excitation. A detailed experimental and theoretical study of the dependance on the excitation beams polarization from the 420 nm decay fluorescence () is presented. When a circularly polarized preparation beam is used, it produces a strongly oriented intermediate state. In this case a linear quadrupole excitation beam transfers the oriented state to the hyperfine states. For linearly polarized preparation and quadrupole excitation beams the spectra of the hyperfine lines follow a cosine squared dependence on the angle between the polarization directions. As a consequence, it is shown that the choice of polarization configuration allows direct use of the electric quadrupole transition selection rules to control the populations of the hyperfine magnetic sublevels in the absence of external fields. This is achieved by independently enhancing or suppressing either or ±2 electric quadrupole transitions.

International audience; We investigate the operation of pyramidal magneto-optical traps (MOTs) microfabricated in silicon. Measurements of the loading and loss rates give insights into the role of the nearby surface in the MOT dynamics. Studies of the fluorescence versus laser frequency and intensity allow us to develop a simple theory of operation. The number of 85Rb atoms trapped in the pyramid is approximately L6, where Llsim6 is the size of the pyramid opening in mm. This follows quite naturally from the relation between capture velocity and size and differs from the L3.6 often used for describing larger MOTs. Our results represent substantial progress towards fully integrated atomic physics experiments and devices.

Optically trapped ensembles are of crucial importance for frequency measurements and quantum memories, but generally suffer from strong dephasing due to inhomogeneous density and light shifts. We demonstrate a drastic increase of the coherence time to 21 s on the magnetic field insensitive clock transition of Rb-87 by applying the recently discovered spin self-rephasing. This result confirms the general nature of this new mechanism and thus shows its applicability in atom clocks and quantum memories. A systematic investigation of all relevant frequency shifts and noise contributions yields a stability of 2.4E-11 x tau^(-1/2), where tau is the integration time in seconds. Based on a set of technical improvements, the presented frequency standard is predicted to rival the stability of microwave fountain clocks in a potentially much more compact setup., 5 pages, 4 figures

International audience; We present a compact atomic frequency standard based on the interrogation of magnetically trapped 87Rb atoms. Two photons, in the microwave and radiofrequency domain excite the atomic transition. At a magnetic field of 3.23 G this transition from |F = 1, mF = -1> to |F = 2, mF = 1> is 1st order insensitive to magnetic field variations. Long Ramsey interrogation times can thus be achieved, leading to a projected stability in the low 10-13 at 1 s. This makes this device a viable alternative to LITE and HORACE as a good candidate for replacing or complementing the rubidium frequency standards and passive hydrogen masers already on board of the GPS, GLONASS, and GALILEO satellites. Here we present preliminary results. We use an atom chip to cool and trap the atoms. A coplanar waveguide is integrated to the chip to carry the Ramsey interrogation signal, making the physics package potentially as small as (5 cm)3. We describe the experimental apparatus and show preliminary Ramsey fringes of 1.25 Hz linewidth. We also show a preliminary frequency stability sigmay = 1.5 × 10-12tau-1/2 for 10 < tau < 103 s. This represents one order of magnitude improvement with respect to previous experiments.

We perform Ramsey spectroscopy on the ground state of ultra-cold 87Rb atoms magnetically trapped on a chip in the Knudsen regime. Field inhomogeneities over the sample should limit the 1/e contrast decay time to about 3 s, while decay times of 58 s are actually observed. We explain this surprising result by a spin self-rephasing mechanism induced by the identical spin rotation effect originating from particle indistinguishability. We propose a theory of this synchronization mechanism and obtain good agreement with the experimental observations. The effect is general and susceptible to appear in other physical systems., Comment: Revised version; improved description of the theoretical treatment

We report on the realization of a 6.834-GHz synthesis chain for the trapped atom clock on a chip (TACC) that is being developed at LNE-SYRTE. The chain is based on the frequency multiplication of a 100-MHz reference signal to obtain a signal at 6.4 GHz. It uses a comb generator based on a monolithic GaAs nonlinear transmission line. This is a novelty in the fabrication of high-stability microwave synthesizers. Measurements give a low flicker phase noise of -85 dBrad(2)/Hz at 1-Hz offset frequency and a white phase noise floor-115 dBrad(2)/Hz. Based on these results, we estimate that the performance of the synthesizer is at least one order of magnitude better than the stability goal of TACC. This ensures that the synthesizer will not be limiting the clock performance.

Ultracold atoms can be manipulated using microfabricated devices known as atom chips. These have significant potential for applications in sensing, metrology, and quantum information processing. To date, the chips are loaded by transfer of atoms from an external macroscopic magnetooptical trap (MOT) into microscopic traps on the chip. This transfer involves a series of steps, which complicate the experimental procedure and lead to atom losses. In this paper, we present a design for integrating a MOT into a silicon wafer by combining a concave pyramidal mirror with a square wire loop. We describe how an array of such traps has been fabricated, and we present magnetic, thermal, and optical properties of the chip.

Polarized velocity selective spectra for rubidium atoms in a room temperature cell are presented. The experiments were performed in the lambda configuration (D2 manifold) and in the ladder configuration. For the lambda configuration the effect of the probe beam intensity in the absorption and polarization spectra are compared with results of a rate equation approximation. Good overall agreement between experiment and theory is found. The results indicate different saturation rates for each of the atomic transitions. Distinctive polarization signals with hyperfine-resolved components are found for the ladder and upper states. Fluorescence detection of the 420 nm that results from the second step in the cascade decay was used in the ladder experiments. This fluorescence was also used for the detection of the electric dipole forbidden transition in atomic rubidium that occurs at 911 nm. The hyperfine structure was resolved in this continuous wave, non-dipole excitation.

Concave pyramids are created in the (100) surface of a silicon wafer by anisotropic etching in potassium hydroxide. High quality micro-mirrors are then formed by sputtering gold onto the smooth silicon (111) faces of the pyramids. These mirrors show great promise as high quality optical devices suitable for integration into MOEMS and atom chips. We have shown that structures of this shape can be used to laser-cool and hold atoms in a magneto-optical trap., Comment: 4 pages, 5 figures

We have produced magnetic patterns suitable for trapping and manipulating neutral atoms on a $1 \mu$m length scale. The required patterns are made in Co/Pt thin films on a silicon substrate, using the heat from a focussed laser beam to induce controlled domain reversal. In this way we draw lines and "paint" shaped areas of reversed magnetization with sub-micron resolution. These structures produce magnetic microtraps above the surface that are suitable for holding rubidium atoms with trap frequencies as high as ~1 MHz., Comment: 6 pages, 7 figures

International audience; We present an atomic clock based on the interrogation of magnetically trapped 87Rb atoms. Two photons, in the microwave and radiofrequency domain, excite the clock transition. At a magnetic field of 3.23 G the clock transition from |F = 1, mF = -1¿ to |F = 2, mF = 1¿ is 1st-order insensitive to magnetic field variations. Ramsey interrogation times longer than 2 s can be achieved, leading to a projected clock stability in the low 10-13 at 1 s for a cloud of 105 atoms. We use an atom chip to cool and trap the atoms. A coplanar waveguide is integrated to the chip to carry the Ramsey interrogation signal, making the physics package as small as (5 cm)3. We describe the experimental setup and show preliminary Ramsey fringes of line width 1.25 Hz.