Cold Sodium Atoms Research Articles

Fast loaded dual species magneto optical trap of cold sodium and potassium atoms with light-assisted inter-species interaction

We present the design, implementation, and detailed experimental characterization and comparison with numerical simulations of two-dimensional magneto-optical traps (MOTs) of bosonic 23Na and 39K atoms for loading the cold atomic mixture in a dual-species 3DMOT with a large number of atoms. We report our various measurements pertaining to the characterization of two 2D+MOTs via the capture rate in the 3DMOT and also present the optimized parameters for the best performance of the system of the cold atomic mixture. Under the optimized condition, we capture more than 3 × 101039K atoms and 5.8 × 10823Na atoms in the 3DMOT simultaneously from individual 2D+MOTs with a capture rate of 5 × 1010 and 3.5 × 108 atoms/sec for 39K and 23Na, respectively. We also demonstrate improvements of more than a factor of 5 in the capture rate in the 3DMOT from the cold atomic sources when a relatively high-power ultraviolet light is used to cause light-induced atomic desorption in the 2D+MOT glass cells. A detailed study of the light assisted interspecies cold collisions between the co-trapped atoms is presented, and interspecies loss coefficients have been determined to be βNaK ∼ 2 × 10−12 cm3/sec. The cold atomic mixture would be useful for further experiments on quantum simulation with ultra-cold quantum mixtures in optical potentials.

Resolving the puzzle of sound propagation in a dilute Bose–Einstein condensate

A unified model of a dilute Bose–Einstein condensate is proposed, combining the logarithmic and Gross–Pitaevskii (GP) nonlinear terms in a wave equation, where the GP term describes two-body interactions, as suggested by the standard perturbation theory; while the logarithmic term is essentially nonperturbative, and takes into account quantum vacuum effects. The model is shown to have excellent agreement with sound propagation data in the condensate of cold sodium atoms known since the now classic works by Andrews and collaborators. The data also allowed us to place constraints on two of the unified model’s parameters, which describe the strengths of the logarithmic and GP terms. Additionally, we suggest an experiment constraining the value of the third parameter (the characteristic density scale of the logarithmic part of the model), using the conjectured attraction–repulsion transition of many-body interaction inside the condensate.

Comparison of time profiles for the magnetic transport of cold atoms

We have compared different time profiles for the trajectory of the centre of a quadrupole magnetic trap designed for the transport of cold sodium atoms. Our experimental observations show that a smooth profile characterized by an analytical expression involving the error function minimizes the transport duration while limiting atom losses and heating of the trapped gas. Using numerical calculations of single atom classical trajectories within the trap, we show that this observation can be qualitatively interpreted as a trade-off between two types of losses: finite depth of the confinement and Majorana spin flips.

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.

Entropy Associated with Information Storage and Its Retrieval

We provide an entropy analysis for light storage and light retrieval. In this analysis, entropy extraction and reduction in a typical light storage experiment are identified. The spatiotemporal behavior of entropy is presented for D1 transition in cold sodium atoms. The governing equations are the reduced Maxwell field equations and the Liouville–von Neumann equation for the density matrix of the dressed atom.

A Simplified Method for Identification of the Vibrational Series of Long-Range States in Na2

We performed two-color photoassociative ionization experiments in cold sodium atoms in a dark MOT. We produce a sample where most of the atoms were in the ground hyperfine state F=1. Applying a laser with variable frequency, in the region of 0 to −32 GHz, we obtained a photoassociative spectra containing sequences of different long-range potentials. Using the scaling law for intermediate states, we identified the vibrational series of involved states, separating the sequences. In this way, we have identified the vibrational series for the $1_{g}, 0_{u}^{+}$ , and $0_{g}^{-}$ states contributions.

Dephasing in sodium Ramsey interferometry under a weak inhomogeneous magnetic field

In Ramsey interference of the clock transition of cold sodium atoms, we observed dephasing of the visibility, which was based on the frequency fluctuation due to the second-order Zeeman effect for inhomogeneity of the magnetic field within the atomic cloud. The frequency fluctuation was enhanced with increased strength of the quantization magnetic field, causing the dephasing of the visibility to become large. The theoretical dephasing function with frequency fluctuation was in good agreement with experimental values.

Compact high-flux source of cold sodium atoms

We present a compact source of cold sodium atoms suitable for the production of quantum degenerate gases and versatile for a multi-species experiment. The magnetic field produced by permanent magnets allows to simultaneously realize a Zeeman slower and a two-dimensional magneto-optical trap (MOT) within an order of magnitude smaller length than standard sodium sources. We achieve an atomic flux exceeding 4 × 10(9) atoms/s loaded in a MOT, with a most probable longitudinal velocity of 20 m/s, and a brightness larger than 2.5 × 10(12) atoms/s/sr. This atomic source allows us to produce pure Bose-Einstein condensates with more than 10(7) atoms and a background pressure limited lifetime of 5 min.

Quantum-fluctuation-driven coherent spin dynamics in small condensates

We have studied the quantum spin dynamics of small condensates of cold sodium atoms. For a condensate initially prepared in a mean-field ground state, we show that coherent spin dynamics is purely driven by quantum fluctuations of collective spin coordinates and can be tuned by quadratic Zeeman coupling and magnetization. This dynamics in small condensates can be probed in a high-finesse optical cavity where the temporal behaviors of the excitation spectra of a coupled condensate-photon system reveal the time evolution of populations of atoms at different hyperfine spin states.

Spin-polarizing cold sodium atoms in a strong magnetic field

The efficiency of evaporative cooling, which is used for the creation of a Bose Einstein condensate, depends strongly on the number of particles at the start of the evaporation. A high efficiency can be reached by filling the magneto-optical trap with a large number of atoms and subsequently transferring these atoms to the magnetic trap as efficiently as possible. In our case (for sodium) this efficiency is limited to 1/3, because the magnetic substates of the F = 1 state, which is used in the trapping process, are equally populated. This limit can be overcome by spin-polarizing the sample before the transfer. For sodium atoms, however, the improvement is very small when it is done in a small magnetic field due to the large number of optical transitions in combination with the high optical density. In this article we describe spin-polarizing sodium atoms in a high magnetic field. The transfer efficiency is increased by a factor of 2. The high magnetic field makes the process also more robust against variations in the magnetic field, the laser frequency and the polarization of the laser beam.

Beam-loss spectroscopy of cold collisions in a bright sodium beam

We report beam-loss photoassociation (PA) spectra of cold collisions within a slow, bright Na atom beam near the ${D}_{1}$ resonance line. The high collimation and brilliance of the atomic beam permits the detection of atomic fluorescence loss resulting from the photoassociation of cold sodium atoms. The results show that even at high PA laser intensities, where strong coupling of the colliding atoms to the optical field might obscure spectral features, vibrational and rotational progressions are surprisingly well resolved. We attribute the conservation of narrow spectral features to the properties of the saturated line shapes and to the unconventional collision energy distribution in one-dimensional (1D) single-beam collisions compared to 3D collisions in a gas cell.

Linear magneto-optic rotation in a cold gas

In this paper, we report on our first measurements of the linear magneto-optic rotation experienced by a linearly polarized weak probe field as it passes through a sample of cold sodium atoms. The results are compared with theory that does account for the residual Doppler broadening but that does not take into account the recoil experienced by the atoms. We compare the results of our theoretical model with our measurements and find that, at the time of this conference presentation, there still exists a discrepancy. Improvements for future experiments are outlined.

Observation of the quantum zeno and anti-zeno effects in an unstable system.

We report the first observation of the quantum Zeno and anti-Zeno effects in an unstable system. Cold sodium atoms are trapped in a far-detuned standing wave of light that is accelerated for a controlled duration. For a large acceleration the atoms can escape the trapping potential via tunneling. Initially the number of trapped atoms shows strong nonexponential decay features, evolving into the characteristic exponential decay behavior. We repeatedly measure the number of atoms remaining trapped during the initial period of nonexponential decay. Depending on the frequency of measurements we observe a decay that is suppressed or enhanced as compared to the unperturbed system.

Absorption imaging of electromagnetically induced transparency in cold sodium atoms

Transmissivity of up to 200% has been observed in an absorption imaging study of electromagnetically induced transparency in cold sodium atoms, when a focused coupling beam is applied near the edge of the atom cloud. The signal behavior strongly depends on the frequency difference between the probe beam and the coupling beam. Such high transmissivity can be attributed to the strong focusing effect of the probe beam, when it propagates in a medium with spatially inhomogeneous refractive index induced by the coupling beam. A detailed numerical analysis based upon the Maxwell propagation equations is presented.

Wannier-Stark ladders in driven optical lattices

The paper studies the effect of a weak periodic driving on metastable Wannier-Stark states. The decay rate of the ground Wannier-Stark states as a continuous function of the driving frequency is calculated numerically. The theoretical results are compared with the experimental data of Wilkinson et al. [Phys. Rev. Lett. 76, 4512 (1996)] obtained for cold sodium atoms in an accelerated optical lattice.

Observation of an electromagnetically induced grating in cold sodium atoms

We have observed diffraction signals by a grating originating from electromagnetically induced transparency (EIT) in a three-level \ensuremath{\Lambda} system of cold sodium atoms. Theoretical and experimental analyses of this phenomenon, called the electromagnetically induced grating (EIG), have revealed that EIG spectra exhibit background-free, Lorentzian signal profiles regardless of the pump frequencies, making a clear contrast to the case of ordinary EIT spectra.

Dynamical Bloch Band Suppression in an Optical Lattice

Dynamical Bloch band suppression is observed for the first time, using cold sodium atoms in a far detuned standing wave of light. This system has well-defined Bloch bands as its energy spectrum, which are modified dynamically by imposing a strong phase modulation of the standing wave. The atoms are prepared in the lowest band, and the spectrum is mapped out by introducing a weak spectroscopic probe that drives transitions between the modified bands. Dynamical suppression of the bands is observed at a critical value of the modulation strength, and is well supported by a full quantum mechanical analysis that goes beyond the single-band and tight-binding approximations.

Observation of Rabi oscillations between Bloch bands in an optical potential

We report an experimental study of atomic motion in the Bloch band of a periodic potential. Our system consists of cold sodium atoms in a far detuned standing wave of near resonant light. We prepare the atoms in the lowest motional band, and then impose phase modulation in order to drive interband transitions. We observe Rabi oscillations between the first and second band as a function of modulation intensity and frequency. We also observe damped oscillations of the population as a function of modulation frequency, which are primarily due to a spread in Rabi frequencies over the Bloch band.

Temperature diagnostics for cold sodium atoms by transient four-wave mixing

Transient four-wave mixing signals were observed in cold sodium atoms. This phenomenon is interpreted as Bragg diffraction of a probe pulse by a population grating of the ground-state hyperfine level induced by pump pulses. The decay time of this grating is directly related to the temperature of the cold atoms and can serve as a novel technique for temperature diagnostics.

Observation of atomic tunneling from an accelerating optical potential

We observe quantum tunneling of cold sodium atoms from an accelerating one-dimensional standing wave of light. Atoms are trapped in a far-detuned standing wave that is accelerated for a controlled duration. For sufficiently large values of the acceleration, we observe an exponential decay in the number of atoms that remain trapped as a function of the interaction time. We show that this loss is due to quantum tunneling, and compare the decay rates with Landau-Zener theory. We also observe oscillations in the tunneling rate as a function of the acceleration which are due to quantum interference effects.