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Atom Optics Laboratory (AOL)

Objective and relevance of the activity

Over more than two decades, there has been enormous progress in generation and manipulation of cold atoms for basic research and practical applications for various purposes. The development of precision atomic clocks, ultra-precise inertial sensors (accelerometer, gyroscope, gravimeter and gravity gradiometer etc.), nano-lithography, cold electrons and ions sources, etc. are few examples. In world scenario, work on cold atoms is at very advanced stage and several labs are actively involed in R & D work in this area of cutting-edge research and advanced technology.

The objective of laser atom cooling activity at RRCAT is to generate ultra-cold samples and Bose Condensates of atoms for study of basic science as well as for developing sensitive atom-optics devices. The scope of the work also includes the demonstration of new trapping geometries using static magnetic field, combination of radio-frequency field and static magnetic field, far detuned focused laser field, periodic/ structured laser intensity fields etc. With the objective of achieving atom trapping on miniaturized scale for compact atom optic devices, an experimental setup for the magnetic trapping of cold 87Rb atoms on the atom chip is being developed. In addition to this, the experimental setup for laser cooling of inert noble gas Kr atoms with bosonic (82Kr, 84Kr and 86Kr) as well as fermionic (83Kr) isotopes has been developed. The laser cooling of noble gas Krypton atoms have applications in cold atom collision and ionization physics, nanolithography, atom trap trace analysis (ATTA) etc.

Our future work is directed towards trapping cold atoms in optical traps, magnetic trapping on atom chip and the development of cold atom based precision sensors such as cold atom gravimeter.

Achievements and technological description of the project

(i) Achievement of Bose-Einstein condensation of 87Rb atoms in double MOT setup

The experimental setup to produce ultracold 87Rb atoms and their Bose-Einstein condensation (BEC) has a double magneto-optical trap (double-MOT) configuration. The double-MOT setup (Figure 1) consists of a vapor chamber MOT (VC-MOT) at ~1-2 x 10-8 Torr pressure and an ultrahigh vacuum MOT (UHV-MOT) at ~5x10-11 pressure. This setup involves magnetic trap for cold atoms, RF evaporative cooling system, detection and characterization system, and a PC-based controller system to implement various cooling stages in a desired sequence. Here the UHV-MOT atoms are subjected to magnetic trapping and evaporative cooling to achieves BEC. Figure 2 shows an image and spatial profile of optical density of cold atom cloud after evaporative cooling performed using this setup in the lab. The sharp peak at the center in this profile shows the presence of Bose-condensate in the cloud.

Figure1. (a) Schematic and (b) photograph of the double-MOT setup
Figure1. (a) Schematic and (b) photograph of the double-MOT setup
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Figure1. (a) Schematic and (b) photograph of the double-MOT setup


Figure 2: (a) An observed image and (b) spatial profile of optical density of an ultracold atom-cloud with Bose-Einstein condensate at the center.
Figure 2: (a) An observed image and (b) spatial profile of optical density of an ultracold atom-cloud with Bose-Einstein condensate at the center.
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Figure 2: (a) An observed image and (b) spatial profile of optical density of an ultracold atom-cloud with Bose-Einstein condensate at the center.

(ii) Trapping cold 87Rb atoms in a toroidal trap using an RF-dressed magnetic trap

The evaporatively cooled atom cloud was also trapped in a toroidal trap using an RF-dressed magnetic trap. The RF-dressed potential was generated by applying a strong RF-field in presence of a static quadrupole magnetic trap used for trapping of laser cooled 87Rb atoms. The picture of atom cloud trapped in toroidal geometry is shown in Figure. 3. Such toroidal trapping can be useful to study behaviour of ultra-cold gases in low dimensions. The potential landscapes generated using RF-dressing of magnetic traps can be easily manipulated by varying RF field parameters such as frequency, polarization, amplitude and phase.

Figure 3. Image of atom cloud in (a) quadrupole magnetic trap and (b) RF-dressed toroidal trap.
Figure 3. Image of atom cloud in (a) quadrupole magnetic trap and (b) RF-dressed toroidal trap.

(iii) Demonstration of mirror- MOT formation on atom chip

For trapping atoms on miniaturized scale for compact atom-optic devices, a setup for trappimg atoms on atom-chip is being developed. The Figure 4 shows the setup, atom chip, and atom-chip mount system. As shown in Figure 4, the atom-chip mount assembly is vertically placed inside the vacuum chamber. Atom chip (Figure 5) was fabricated using Si substrate of size 25 mm x 25 mm (700 µm thick) after depositing the gold (Au) layer of 2 µm. The chip also serves as a mirror surface for mirror-MOT formation. The optical layout for the formation of mirror magneto-optical trap (MOT) is shown in Figure 6. In the mirror-MOT on chip, 87Rb cold atom cloud is formed few mm below the atom chip surface. The cold atom cloud has ~ 8 x 106 atoms at temperature of ~300 µK.

Figure 4: Photographs of (a)  atom chip setup and (b) atom-chip mounting system.
Figure 4: Photographs of (a)  atom chip setup and (b) atom-chip mounting system.
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Figure 4: Photographs of (a) atom chip setup and (b) atom-chip mounting system.


Figure 5: Photograph of in-house developed atom chip having two U- and one Z-shaped gold wires.
Figure 5: Photograph of in-house developed atom chip having two U- and one Z-shaped gold wires.


Figure 6: (a) MOT laser beam delivery in vacuum chamber for mirror-MOT (b) CCD image of 87Rb cold atom cloud below the mirror surface.
Figure 6: (a) MOT laser beam delivery in vacuum chamber for mirror-MOT (b) CCD image of 87Rb cold atom cloud below the mirror surface.
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Figure 6: (a) MOT laser beam delivery in vacuum chamber for mirror-MOT (b) CCD image of 87Rb cold atom cloud below the mirror surface.


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iv) Laser cooling of various bosonic (82Kr,84Kr and 86Kr) and fermionic (83Kr) isotopes of Krypton atom

The experimental setup to cool and trap noble gas metastable Kr atoms along with the CCD image of the cold atom cloud (inset) is shown in the Figure 7. The Krypton gas first flows into RF discharge glass tube through the gas inlet chamber, where metastable atoms of Kr are prepared. These metastable atoms, after slowing down in a Zeeman slower device, are transported to MOT chamber (~10-8 Torr). In this MOT chamber, the Kr atoms are cooled and trapped using cooling and repumpig laser beams alongwith appropriate quadrupole magnetic field. The laser cooling of various bosonic (82Kr, 84Kr and 86Kr) as well as fermionic (83Kr) isotopes of Krypton has been successfully demonstrated. In addition, dual-isotope MOTs (Figure. 8) for cold bosonic-bosonic and bosonic-fermionic mixtures have been demonstrated. The dual-isotope MOTs are useful to study cold collisions among various species.

Figure 7: (a) Schematics of the experimental setup for laser cooling of <sup>83</sup>Kr* atoms. C1: Kr gas inlet chamber, C2: Analysis chamber, C3: pumping chamber, MOT: magneto-optical trap, C: cooling beams, R1 and R2: repumping beams. (b) CCD fluorescence image of cold atom cloud of <sup>83</sup>Kr* atoms.
Figure 7: (a) Schematics of the experimental setup for laser cooling of <sup>83</sup>Kr* atoms. C1: Kr gas inlet chamber, C2: Analysis chamber, C3: pumping chamber, MOT: magneto-optical trap, C: cooling beams, R1 and R2: repumping beams. (b) CCD fluorescence image of cold atom cloud of <sup>83</sup>Kr* atoms.
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Figure 7: (a) Schematics of the experimental setup for laser cooling of 83Kr* atoms. C1: Kr gas inlet chamber, C2: Analysis chamber, C3: pumping chamber, MOT: magneto-optical trap, C: cooling beams, R1 and R2: repumping beams. (b) CCD fluorescence image of cold atom cloud of 83Kr* atoms.


Figure 8: (a) Photograph of the experimental setup for laser cooling of Kr atoms. (b) CCD fluorescence images of separated and overlapped cold atom clouds of Kr* atoms in a dual-isotope MOT.
Figure 8: (a) Photograph of the experimental setup for laser cooling of Kr atoms. (b) CCD fluorescence images of separated and overlapped cold atom clouds of Kr* atoms in a dual-isotope MOT.
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Figure 8: (a) Photograph of the experimental setup for laser cooling of Kr atoms. (b) CCD fluorescence images of separated and overlapped cold atom clouds of Kr* atoms in a dual-isotope MOT.


Publications

Some recent publications
  1. "Generation of a variable diameter collimated hollow laser beam using metal axicon mirrors",
    S. K. Tiwari, S. R. Mishra and S. P. Ram,
    Opt. Eng.50, 014001, (2011).

  2. "Investigation of atom transfer using a red-detuned push beam in a double magneto-optical trap setup",
    S. P. Ram, S. R. Mishra, S. K. Tiwari, and S. C. Mehendale,
    Rev. Sci. Instrum., 82, 126108, (2011).

  3. "Generation of a Bessel beam of variable spot size",
    S. K. Tiwari, S. R. Mishra, S. P. Ram, H. S. Rawat,
    Appl. Opt., 51, 3718, (2012).

  4. "Push beam spot-size dependence of atom transfer in a double magneto-optical trap setup",
    S. P. Ram, S. K. Tiwari, S. R. Mishra, H. S. Rawat,
    Rev. Sci. Instrum., 84, 073102, (2013).

  5. "Optimization of transfer of laser-cooled atom cloud to a quadrupole magnetic trap",
    S. P. Ram, S. K. Tiwari, S. R. Mishra, H. S. Rawat,
    Pramana - J. Phys., 82, 419, (2014).

  6. "Temperature and phase-space density of a cold atom cloud in a quadrupole magnetic trap",
    S. P. Ram, S. R. Mishra, S. K. Tiwari, H. S. Rawat,
    J. Korean Phys. Soc., 65, 462, (2014).

  7. "Anisotropic two-dimensional RF-dressed potentials for ultracold atoms",
    A. Chakraborty, S. R. Mishra,
    J. Korean Phys. Soc., 65, 1324, (2014).

  8. "An atomic beam fluorescence locked magneto optical trap for Kr atoms",
    S. Singh, V. B. Tiwari, S. R. Mishra, H. S. Rawat,
    Laser Phys., 24, 025501, (2014).

  9. "The effect of laser beam size in a zig-zag collimator on transverse cooling of a krypton atomic beam ",
    V. Singh, V. B. Tiwari, S. Singh, S. R. Mishra, H. S. Rawat,
    Pramana-J. Phys., 83, 131, (2014).

  10. "Loading of a Krypton magneto-optical trap with two hollow laser beams in Zeeman slower",
    S. Singh, V. B. Tiwari, S. R. Mishra, H. S. Rawat,
    J. Exp. Theo. Phys., 146, 464, (2014).

  11. "Velocity selective bi-polarization spectroscopy for laser cooling of metastable Krypton atoms",
    Y. B. Kale, V. B. Tiwari, S. Singh, S. R. Mishra, H. S. Rawat,
    J. Opt. Soc. Am. B, 31, 2531, (2014).

  12. "Generation and focusing of a collimated hollow beam",
    S. K. Tiwari, S. P. Ram, K.H. Rao, S.R. Mishra, H. S. Rawat,
    Opt. Eng., 54, 115111, (2015).

  13. "Resolution of hyperfine transitions in metastable 83Kr using electromagnetically induced transparency",
    Y. B. Kale, S. R. Mishra, V. B. Tiwari, S. Singh and H. S. Rawat,
    Phys. Rev. A, 91, 053852, (2015).

  14. "Investigation of cold collision in a two-isotope Krypton magneto-optical trap",
    S. Singh, V. B. Tiwari, Y. B. Kale, S. R. Mishra and H. S. Rawat,
    J. Phys. B: At. Mol. Opt. Phys., 48, 175302, (2015).

  15. "A toroidal trap for the cold 87Rb atoms using a rf-dressed quadrupole trap",
    A. Chakraborty, S. R. Mishra, S. P. Ram, S. K. Tiwari, H. S. Rawat,
    J. Phys. B: At. Mol. Opt. Phys. 49, 075304, (2016).

  16. "Electromagnetically induced absorption and transparency in degenerate two level systems of metastable Kr atoms and measurement of Lande g-factor", 
    Y. B. Kale, V. B. Tiwari, S. R. Mishra, S. Singh, and H. S. Rawat,
    Opt. Commun. 380, 297 (2016).

  17. "A tunable Doppler-free dichroic lock for laser frequency stabilization",
    V. Singh, V. B. Tiwari, S. R. Mishra, and H. S. Rawat,
    Appl. Phys. B:Lasers and Optics, 122, 225, (2016).

  18. " Dependence of in-situ Bose condensate size on final frequency of RF-field in evaporative cooling",
    S. R. Mishra, S. P. Ram, S. K. Tiwari, H. S. Rawat,
    Pramana – J. Phys.,88:59, (2017).
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