Standard Magneto-optical Trap Research Articles

Measurements of cesium PJ-series quantum defect with the microwave spectroscopy

High-precision microwave spectroscopy has been used to measure the transition frequency of nS1/2 → nPJ (n is the principle quantum number) and further the quantum defect of nPJ states in a standard cesium magneto-optical trap. A microwave field with 30-μs duration coupling the nS1/2 → nP1/2,3/2 transition yields a narrow linewidth microwave spectroscopy with the linewidth approaching the Fourier limit. After carefully compensating the stray electric and magnetic field and using the diluted atomic gas, we extract improved quantum defects of nPJ state, δ0(nP1/2) = 3.59159091(19), δ2(nP1/2) = 0.36092(35) and δ0(nP3/2) = 3.55907153(25), δ2(nP3/2) = 0.37344(47).

Sub-Doppler laser cooling and magnetic trapping of natural-abundance fermionic potassium

We demonstrate the largest number of 40K atoms that has ever been cooled to deeply sub-Doppler temperatures in a single-chamber apparatus without using an enriched source of potassium. With gray molasses cooling on the D 1-line following a standard D 2-line magneto-optical trap, we obtain 3×105 atoms at 10(2) µK. We reach densities high enough to measure the temperature via absorption imaging using the time-of-flight method. We magnetically trap a mixture of mF=−3/2,−5/2 and −7/2 Zeeman states of the F=7/2 hyperfine ground state confining 5×104 atoms with a lifetime of 0.6 s or ∼103 atoms with a lifetime of 2.8 s—depending on whether the temperature of the potassium dispensers was chosen to maximize the atom number or the lifetime. The background pressure-limited lifetime of 0.6 s is a reasonable starting point for proof-of-principle experiments with atoms and/or molecules in optical tweezers as well as for sympathetic cooling with another species if transport to a secondary chamber is implemented. Our results show that unenriched potassium can be used to optimize experimental setups containing 40K in the initial stages of their construction, which can effectively extend the lifetime of enriched sources. Moreover, the demonstration of sub-Doppler cooling and magnetic trapping of a relatively small number of potassium atoms might influence experiments with laser-cooled radioactive isotopes of potassium.

Superradiance of ultracold cesium Rydberg |65D5/2〉 → |66P3/2〉

We investigate Rydberg |65D5/2〉 → |66P3/2〉 superradiance in dense ultracold cesium atoms, where the ground atoms are excited to |65D5/2〉 Rydberg states via two-photon excitation in a standard magneto-optical trap. The superradiant spectrum of |65D5/2〉 → |66P3/2〉 is obtained using the state-selective field ionization technique. We observe its dynamic evolution process by varying the delay time of ionization field t d. The results show that the evolution process of |65D5/2〉 → |66P3/2〉 is much shorter than its radiation lifetime at room temperature, which verifies the superradiance effect. The dependence of the superradiance process on Rydberg atoms number N e and principal quantum number n is investigated. The results show that the superradiance becomes faster with increasing N e, while it is suppressed for stronger van der Waals (vdW) interactions. Superradiance has potential applications in quantum technologies, and the Rydberg atom is an ideal medium for superradiance. Our system is effective for studying the strong two-body interaction between Rydberg atoms.

Precise measurements of polarizabilities of cesium nS Rydberg states in an ultra-cold atomic ensemble

We present precise measurements of polarizabilities of cesium nS1/2 (n = 65–75) Rydberg states by Stark spectroscopies. In experiment, Rydberg atoms are excited via a two-photon scheme of a standard magneto-optical trap and detected by the field ionization technique. The Stark shift is measured by analysing the spectroscopy under an external electric field. The polarizability, α, is acquired by fitting the experimental data of Stark shifts with . The theoretical model is applied to numerically simulate the Stark map and corresponding level shifts, related deviation between the experimental measurements and calculations are less than 2%. The scaling law of polarizabilities, (n* is effective principal quantum number), is attained, that shows a good agreement with the measurements.

Characterisation of focused-beam trap: FORT loading optimisation

We investigate the properties of the focused-beam magneto-optical trap (FBT) of Rb85 atoms, which provides more optical accessibility in contrast to typical magneto-optical trap (MOT). We have characterised the relations between temperature, number and density of trapped atoms versus trap parameters. In this paper, we discuss some distinctive features of the FBT comparing to those of standard MOTs, and determine a suitable condition in which loading atoms into a far-off-resonance optical dipole trap (FORT) is possible. Although the trap can capture fewer atoms comparing to the standard MOTs, due to its asymmetric geometry, it may offer an alternative trap configuration for preparing single atom.

Optical focusing based on the planar metasurface reflector with application to trapping cold molecules

We demonstrate theoretically a 2D subwavelength silicon-grating reflector with strong focusing capability and the potential application to an optical dipole trap of cold molecules such as MgF. We study the dependence of the focusing properties of this reflector on its structural parameters, numerical aperture, and fabrication-error tolerance. Our study shows that the reflector delivers high reflectivity and strong focusing performances with the maximum intensity at the focal point over 200 times the incident one. Such a focusing field on the reflector can provide a deep potential to trap cold MgF molecules from a standard magneto-optical trap.

Comparison of an efficient implementation of gray molasses to narrow-line cooling for the all-optical production of a lithium quantum gas

We present an efficient scheme to implement a gray optical molasses for sub-Doppler cooling of $^{6}$Li atoms with minimum experimental overhead. To integrate the $D_1$ light for the gray molasses (GM) cooling into the same optical setup that is used for the $D_2$ light for a standard magneto-optical trap (MOT), we rapidly switch the injection seeding of a slave laser between the $D_2$ and $D_1$ light sources. Switching times as short as $30\,\mu\textrm{s}$ can be achieved, inferred from monitor optical beat signals. The resulting low-intensity molasses cools a sample of $N=9\times10^8$ atoms to about $60\,\mu\textrm{K}$. A maximum phase-space density of $\rho=1.2\times10^{-5}$ is observed. On the same setup, the performance of the GM is compared to that of narrow-line cooling in a UV MOT, following the procedure in Sebastian et al. (2014). Further, we compare the production of a degenerate Fermi gas using both methods. Loading an optical dipole trap from the gray molasses yields a quantum degenerate sample with $3.3\times10^5$ atoms, while loading from the denser UV MOT yields $2.4\times10^6$ atoms. Where the highest atom numbers are not a priority this implementation of the gray molasses technique yields sufficiently large samples at a comparatively low technical effort.

3D optical lattices cooling of ultracold Cs atoms

Laser cooling of atoms is the basis of researches on ultracold atoms and molecules. It is of great importance in the study of precision measurement and quantum simulation, etc. In order to obtain ultracold cesium atomic sample with a lower temperature and a higher density, as the starting point to create ultracold cesium ground state molecules, we demonstrate in this article a method which effectively overcomes the heating from the reabsorption of scattered light in magneto-optical trap to further reduce the ultracold atomic temperature by loading atoms into a 3D optical lattices. Based on obtaining the ultracold Cs atoms in a standard magneto-optical trap, we use the compressed magneto-optical trap technology to increase ultracold Cs atomic density. Efficient loading of ultracold Cs atoms is achieved by 3D optical lattices which constructed by four lasers; the temperature of the atoms is measured by time-of-flight method. We observed the cooling result that the temperature drops from ~60.0 μK to ~11.6 μK. We also explore the dependence of the atom numbers in the lattice on the frequency of lattice lasers, and lead to the conclusion that the loading rate of the optical lattices reaches its maximum when the lattices laser’s detuning is –15.5 GHz. In the meantime, this paper investigates the use of optical lattice to suppress the heating of the ultracold atoms due to the radiation photons, in this sense, our research has far-reaching significance. Our scheme is advantageous due to its relaxed starting temperature requirement, meaning that 3D DRSC can be directly accomplished in a standard single cell vapour-loaded MOT without reliance on any additional devices such as a Zeeman slower.

Direct loading of atoms from a macroscopic quadrupole magnetic trap into a microchip trap**Project supported by the National Natural Science Foundation of China (Grant No. 11604348).

We demonstrate the direct loading of cold atoms into a microchip 2-mm Z-trap, where the evaporative cooling can be performed efficiently, from a macroscopic quadrupole magnetic trap with a high loading efficiency. The macroscopic quadrupole magnetic trap potential is designed to be moveable by controlling the currents of the two pairs of anti-Helmholtz coils. The cold atoms are initially prepared in a standard six-beam magneto-optical trap and loaded into the macroscopic quadrupole magnetic trap, and then transported to the atom chip surface by moving the macroscopic trap potential. By means of a three-dimensional absorption imaging system, we are able to optimize the position alignment of the atom cloud in the macroscopic trap and the microchip Z-shaped wire. Consequently, with a proper magnetic transfer scheme, we load the cold atoms into the microchip Z-trap directly and efficiently. The loading efficiency is measured to be about 50%. This approach can be used to generate appropriate ultracold atoms sources, for example, for a magnetically guided atom interferometer based on atom chip.

Radiation-Pressure Effects in Cold-Atom Absorption Spectroscopy and Electromagnetically Induced Transparency

Radiation pressure due to the interaction between a probe light and cold atoms is investigated in a standard cesium magneto-optical trap. The radiation pressure alters the absorption spectroscopy of cold atoms, leading to line shapes and linewidths after resonant interaction that are different for positive and negative probe chirps. The difference is attributed to the radiation pressure of the probe laser, due to which atoms become accelerated at the resonance. The effect of the radiation pressure is also seen in electromagnetically induced transparency (EIT) involving an excited Rydberg level. The density matrix equation accounting for the radiation pressure is used to simulate the experiments. The simulations agree well with the measurements both for absorption and EIT spectra. We find that the effect of the radiation pressure is reduced at low probe intensities, and can be neglected when the probe intensity is smaller than Isat/2 .

Microtrap on a concave grating reflector for atom trapping**Project supported by the National Natural Science Foundation of China (Grant Nos. 11374100, 91536218, and 11274114) and the Natural Science Foundation of Shanghai Municipality, China (Grant No. 13ZR1412800).

We propose a novel scheme of optical confinement for atoms by using a concave grating reflector. The two-dimension grating structure with a concave surface shape exhibits strong focusing ability under radially polarized illumination. Especially, the light intensity at the focal point is about 100 times higher than that of the incident light. Such a focusing optical field reflected from the curved grating structure can provide a deep potential to trap cold atoms. We discuss the feasibility of the structure serving as an optical dipole trap. Our results are as follows. (i) Van der Waals attraction potential to the surface of the structure has a low effect on trapped atoms. (ii) The maximum trapping potential is ∼ 1.14 mK in the optical trap, which is high enough to trap cold 87Rb atoms from a standard magneto-optical trap with a temperature of 120 μK, and the maximum photon scattering rate is lower than 1/s. (iii) Such a microtrap array can also manipulate and control cold molecules, or microscopic particles.

Direct comparison between a two-dimensional magneto-optical trap and a Zeeman slower as sources of cold sodium atoms

The atom source is a relevant component in many atomic molecular optics experiments. The compactness and efficiency of the source are fundamental issues, acquiring more importance as the complexity of the experiments increases. Characterizing new techniques to produce high atom flux is necessary to know the efficiency and peculiarities of each one. This allows choosing the most suitable source for a specific experiment. In this work, we show a direct comparison between a two-dimensional magneto-optical trap (2D-MOT) and a Zeeman slower (ZS) as source of cold sodium atoms to load a standard three-dimensional magneto-optical trap. The optimum parameters for each case are obtained by observing the loading rate and the final number of atoms in the 3D-MOT. We conclude that the 2D-MOT provides a high flux of atoms comparable with that produced by the ZS, but with an enormous advantage with respect to the size of the apparatus.

Using experimental measurements of three-level avoided crossings to determine the quantum defect for the Stark map of highly excited cesium Rydberg atoms

The spectra of Rydberg atoms in the domain of three-level avoided crossings formed by the Rydberg $49{S}_{1/2}$ state and high-$l$ states in the $n=45$ manifold are observed in the standard magneto-optical trap of cesium. We develop a highly accurate method which uses the spectroscopic results in order to refine the quantum defect of the $49{S}_{1/2}$ state from the previous value $4.0495\ifmmode\pm\else\textpm\fi{}0.0001$ extrapolated from $n=6--30\phantom{\rule{0.16em}{0ex}}S$ states [K. H. Weber and C. J. Sansonetti, Phys. Rev. A 35, 4650 (1987)] to the new value $4.049\phantom{\rule{0.16em}{0ex}}78\ifmmode\pm\else\textpm\fi{}0.000\phantom{\rule{0.16em}{0ex}}03$. For this purpose, we determine two characteristic properties of the avoided crossings: (i) the minimum gap between the upper and the lower levels, and (ii) the value of equal gaps between the upper and the middle levels and between the middle and the lower levels. The experimental results for the avoided crossing near 4 V/cm are (i) $(111.7\ifmmode\pm\else\textpm\fi{}1.3)h\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$, and (ii) $(57.0\ifmmode\pm\else\textpm\fi{}2.1)h\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$. For comparison, quantum mechanical simulations based on the published quantum defect yield (i) $109.52h\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$, and (ii) $56.04h\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$. The refined quantum defect is adjusted such that it yields (i) $111.50h\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$, and (ii) $56.98h\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$, in even better agreement with the experimental results. The theoretical values of the electric fields for (i) and (ii) differ by 0.03 V/cm, in perfect agreement with the experimental results. The refinement also improves the agreement of their absolute values. The remaining \ensuremath{\sim}1.5% difference is attributed to effects of stray fields.

Measurement of the Spatial Distribution of Ultracold Cesium Rydberg Atoms by Time-of-Flight Spectroscopy

We prepare nS (n = 49) cesium Rydberg atoms by two-photon excitation in a standard magnetooptical trap to obtain the spatial distribution of the Rydberg atoms by measuring the time-of-flight (TOF) spectra in the case of a low Rydberg density. We analyze the time evolution of the ultracold nS Rydberg atoms distribution by changing the delay time of the pulsed ionization field, defined as the duration from the moment of switching off the excitation lasers to the time of switching on the ionization field. TOF spectra of Rydberg atoms are observed as a function of the delay time and initial Rydberg atomic density. The corresponding full widths at half maximum (FWHMs) are obtained by fitting the spectra with a Gaussian profile. The FWHM decreases with increasing delay time at a relatively high Rydberg atom density (>5 × 107/cm3) because of the decreasing Coulomb interaction between released charges during their flight to the detector. The temperature of the cold atoms is deduced from the dependence of the TOF ...

All-optical production of 6Li quantum gases

We report efficient production of quantum gases of 6Li using a sub-Doppler cooling scheme based on the D1 transition. After loading in a standard magneto-optical trap, an atomic sample of 109 atoms is cooled at a temperature of 40 μK by a bichromatic D1 gray-molasses. More than 2×107 atoms are then transferred into a high-intensity optical dipole trap, where a two-spin state mixture is evaporatively cooled down to quantum degeneracy. We observe that D1 cooling remains effective in the deep trapping potential, allowing an effective increase of the atomic phase-space density before starting the evaporation. In a total experimental cycle of 11 s, we produce weakly-interacting degenerate Fermi gases of 7×105 atoms at T/TF < 0.1 and molecular Bose-Einstein condensates of up 5×105 molecules. We further describe a simple and compact optical system both for high-resolution imaging and for imprinting a thin optical barrier on the atomic cloud; this represents a first step towards the study of quantum tunneling in strongly interacting superfluid Fermi gases.

Time Evolution of High-l Stark States in Cold Rydberg Atoms

The high-l Rydberg Stark states are populated by the state transfer from initial prepared nS Rydberg state via avoided crossings induced by a weak electric-field pulse, and investigated by the state selective field ionization method in a cesium standard magneto-optical trap. The dependences of the transfer rate, given by the ratio of the number of high-l Stark states to all atoms, on the strength and holding time of electric-field pulse are investigated and compared with those with additional ions. The results show that the time evolution of high-l Stark states strongly depends on the electric-field strength, and is affected by the additional ions at relatively weaker field (1.51 V/cm here). The density of Rydberg atoms has a minor effect on the characteristic time of evolution process.

Investigation of ultracold atoms and molecules in a dark magneto-optical trap

In this paper, ultracold atoms and molecules in a dark magneto-optical trap (MOT) are studied via depumping the cesium cold atoms into the dark hyperfine ground state. The collision rate is reduced to 0.45 s−1 and the density of the atoms is increased to 5.6 × 1011 cm−3 when the fractional population of the atoms in the bright hyperfine ground state is as low as 0.15. The vibrational spectra of the ultracold cesium molecules are also studied in a standard MOT and in a dark MOT separately. The experimental results are analyzed by using the perturbative quantum approach.

Direct measurement of laser-induced frequency shift rate of ultracold cesium molecules by analyzing losses of trapped atoms

We report on a quantitative experimental determination of the laser-induced frequency shift rate of the ultracold cesium molecules formed via photoassociation (PA) by means of the trap loss measurement of the losses of trapped atoms in a standard magneto-optical trap. The experiment was directly performed by varying the photoassociation laser intensity without any additional frequency monitor technologies. Our experimental method utilized dependences of the losses on the laser-induced frequency shift rate based on the conditions of the identified photoassociation spectral shape. We demonstrated that the method is sensitive enough to determine small frequency shifts of rovibrational levels of ultracold cesium molecules.

A controllable double-well optical trap for cold atoms (or molecules) using a binary π-phase plate: experimental demonstration and Monte Carlo simulation

We experimentally demonstrate a practical scheme to form a controllable double-well optical dipole trap for cold atoms (or cold molecules), and give some experimental results as well as the fabrication method of a binary π-phase plate. The dependence of the double-well characteristics on the phase etching error of the π-phase plate and the evolution of the double-well optical trap from two wells to a single one are studied both theoretically and experimentally, and the experimental results are consistent with the theoretical prediction. Furthermore, the dynamic process of loading and splitting of cold 87Rb atoms from a standard magneto-optical trap (MOT) into our controllable double-well one are studied by Monte Carlo simulations. Our study shows that the loading efficiency of cold atoms from the standard MOT into our single-well trap can reach 100%, and the relative atomic density will be reduced from 1.0 to ∼0.5 during the evolution of our double-well trap, in which the temperature of cold atoms is reduced from 20 μK to ∼15 μK. In final, some potential applications of our controllable double-well optical trap in atom and molecule optics are briefly discussed.

Multiphoton Magnetooptical Trap

We demonstrate a magnetooptical trap (MOT) configuration which employs optical forces due to light scattering between electronically excited states of the atom. With the standard MOT laser beams propagating along the x and y directions, the laser beams along the z direction are at a different wavelength that couples two sets of excited states. We demonstrate efficient cooling and trapping of cesium atoms in a vapor cell and sub-Doppler cooling on both the red and blue sides of the two-photon resonance. The technique demonstrated in this work may have applications in background-free detection of trapped atoms, and in assisting laser cooling and trapping of certain atomic species that require cooling lasers at inconvenient wavelengths.