Martin Teichmann Atomes de lithium-6 ultra froids dans la ... - TEL

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CHAPTER 3. EXPERIMENTAL SETUP 3.1 The vacuum chamber As Lithium is a metal with a negligible vapor pressure at room temperature, the first step to make an atomic gas of it is to heat it. We do this in an oven which consists of a vertical stainless steel tube into which we put a few grams of Lithium. The oven is connected via a small tube to the vacuum chamber to create a collimated gas jet. Figure 3.1 shows the setup. A small metal mesh is installed in this collimator to recycle lithium into the oven via capillary forces. The oven is heated with an electric heating wire soldered around the tube. Originally, this wire had been only installed in the center of the tube, where the collimator leaves to the vacuum chamber. In order to have a more uniform heat distribution, we changed this design to heat the whole oven tube. This was a bad idea, since now there is no cold point in the oven anymore where lithium condenses. Instead, it will close the collimator albeit the mentioned recycling mesh. The solution to this problem was to also heat the collimator with a second heating wire, to temperatures comparable to the oven’s temperature. The most important drawback in our old setup was the very slow loading of the MOT. During the reconstruction, an important part of our efforts was to improve on that aspect. The loading times were mostly limited by the low flux of atoms in the gas jet. The flux of atoms in turn was limited by the small differential pumping tube between the oven part of our vacuum chamber and the experimental chamber. The obvious way to increase the flux, which is to open this differential pumping tube a bit more, had shown to degrade the vacuum to a point that the magnetic trap had lifetimes too low to work with. A second differential pumping stage was the solution. A 6-way cross was introduced between the oven chamber and the Zeeman slower to install a 25 l/s ion pump. The 6-way cross has windows on all ends, very helpful when measuring the flux of the atomic beam. Let us estimate the efficiency of the differential pumping. The vapor pressure of Lithium in the oven can easily exceed 20 mbar, which means that we are in the transition region between viscous and molecular flow [80]. This region is very hard to calculate, so we trust the reading of the ion pump in the oven chamber which gives a current corresponding to a pressure of 10 −7 mbar. The conductance of the differential pumping tubes can be calculated as C = 0,26¯vd 3 /l, where ¯v is the average velocity of the particles, d is the diameter of the tube and l its length. The pressure ratio between the two ends of the tube that can be maintained is C/S if S is the pumping speed of the pump before the tube. Plugging in 42
3.1. THE VACUUM CHAMBER Figure 3.1: This is the beginning of the vacuum chamber, where the atomic jet gets collimated. A block of lithium is in the oven on the left, heated by the heating wire wound around the oven. The gas jet leaves the oven by the little tube between the oven and the chamber, in which we placed a metal mesh as described in the text. Afterwards the jet passes through two small collimation tubes, which also act as differential pumping stages. Here they are marked with their length and inner diameter. Each pumping stage has its own ion pump, one is shown and the other one is situated orthogonal to the represented plane, and indicated with the dashed circle. Between the oven chamber and the Zeeman slower is a 6-way cross with windows on all open ends and a valve to separate the oven from the main chamber in case we have to change the lithium. A bellow before the Zeeman slower allows for fine tuning of the gas jet’s direction. 43
Page 1 and 2: École Normale Supérieure Laborato
Page 3 and 4: Contents 1 Introduction 7 2 Theory
Page 5 and 6: Acknowledgments This thesis would n
Page 7 and 8: Chapter 1 Introduction “The inter
Page 9 and 10: T c / T F 1 10 -2 10 -4 cold Fe rm
Page 11 and 12: JILA, where they use magnetic field
Page 13 and 14: Chapter 2 Theory Da steh’ ich nun
Page 15 and 16: 2.2. A REMINDER ON SCATTERING THEOR
Page 17 and 18: 2.2. A REMINDER ON SCATTERING THEOR
Page 19 and 20: pote ntial e ne rgy or probability
Page 21 and 22: 2.3. FESHBACH RESONANCES a total an
Page 23 and 24: energy / mRy 2.0 1.5 1.0 0.5 0.0 -0
Page 25 and 26: E / GH z 0,0 -0,5 -1,0 -1,5 -2,0 0
Page 27 and 28: 2.3. FESHBACH RESONANCES relating t
Page 29 and 30: 2.3. FESHBACH RESONANCES to fit the
Page 31 and 32: second quantization, this is writte
Page 33 and 34: equation (2.30) can easily be calcu
Page 35 and 36: 2.4. BCS THEORY Using the substitut
Page 37 and 38: occupation probability 1.0 0.8 0.6
Page 39 and 40: 2.4. BCS THEORY loose the last smal
Page 41: Chapter 3 Experimental setup LASER,
Page 45 and 46: 3.2. THE ZEEMAN SLOWER Figure 3.2:
Page 47 and 48: 3.3 The laser system 3.3. THE LASER
Page 49 and 50: 2 2 P 3/2 10 GH z 2 2 P 1/2 671 nm
Page 51 and 52: input to Fabry- Pérot input non-po
Page 53 and 54: 7 P Am p to m agnetic trap im aging
Page 55 and 56: atom ic be am pinch coils M O T coi
Page 57 and 58: 3.5. THE OPTICAL DIPOLE TRAP The he
Page 59 and 60: heating time / s 10 4 10 3 10 2 10
Page 61 and 62: Physics laser for the vertical. 3.6
Page 63 and 64: frequency / MHz 1000 950 900 850 3.
Page 65 and 66: 3.6. THE COOLING STRATEGY atoms in
Page 67 and 68: 3.7 MOT imaging 3.7. MOT IMAGING Wh
Page 69 and 70: 3.8. COMPUTER CONTROL where the cod
Page 71 and 72: from scipy.special import erf from
Page 73 and 74: Chapter 4 Data analysis A correct d
Page 75 and 76: 4.1. DETERMINATION OF THE TEMPERATU
Page 77 and 78: optical density 14 12 10 4.1. DETER
Page 79 and 80: F T = T r o f e u l a v d e t t i f
Page 81 and 82: Chapter 5 Experimental results Well
Page 83 and 84: 5.1. MOMENTUM DISTRIBUTION Now we h
Page 85 and 86: 2 ¹h = ¹ 2 a m 2 6 5 4 3 2 1 0 -1
Page 87 and 88: 5.1. MOMENTUM DISTRIBUTION get na 3
Page 89 and 90: n( k) 3 F k 1.0 0.8 0.6 0.4 0.2 5.2
Page 91 and 92: n( k) 3 F k 1.0 0.8 0.6 0.4 0.2 0.0
Page 93 and 94:
5.3. HYDRODYNAMIC EXPANSION where A
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5.3. HYDRODYNAMIC EXPANSION The sit
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5.3. HYDRODYNAMIC EXPANSION and tak
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° 0.67 0.66 0.65 0.64 0.63 0.62 0.
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ellipticity 1.6 1.4 1.2 1.0 0.8 clo
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Ellipticity 1.55 1.50 1.45 1.40 1.3
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ellipticity 1.4 1.3 1.2 1.1 1.0 0.9
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5.4. MOLECULAR CONDENSATE last sect
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density (a. u.) 70 60 50 40 30 20 1
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E / GH z 0 -1 -2 |1,1〉 ⊗ |1/2,-
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number of atoms / 1000 25 20 15 10
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5.6. OTHER EXPERIMENTS AND OUTLOOK
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Tem perature T c 0 Sarm a Ph ase 5.
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5.6. OTHER EXPERIMENTS AND OUTLOOK
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Chapter 6 Conclusions In this thesi
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Cold fermions in optical lattices c
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Appendix A Articles A.1 Experimenta
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VOLUME 93, NUMBER 5 FIG. 1. Onset o
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VOLUME 93, NUMBER 5 gas. The platea
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P-wave Feshbach resonances of ultra
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P-WAVE FESHBACH RESONANCES OF ULTRA
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A.3 Expansion of a lithium gas in t
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Ry/Rx = 2.0(1) is consistent with t
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× ��
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Bth (G) Bexp (G) 218 not seen 230 2
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Resonant scattering properties clos
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RESONANT SCATTERING PROPERTIES CLOS
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Page 149 and 150:
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A.5 Expansion of an ultra-cold lith
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2 L. Tarruell, et al. to image the
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4 L. Tarruell, et al. of mean field
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6 L. Tarruell, et al. The starting
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8 L. Tarruell, et al. for 0.5 ms in
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10 L. Tarruell, et al. [11] M. H. A
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Appendix B Bibliography [1] H. VOGE
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[29] M. BARTENSTEIN, A. ALTMEYER, S
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[62] P. NOZIÈRES and S. SCHMITT-RI
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[98] M. MARINI, F. PISTOLESI, and G
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[131] S. STRINGARI, Collective Exci
Page 173 and 174:
173
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Martin Teichmann Atomes de lithium-6 ultra froids dans la ... - TEL

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