Experiments to Control Atom Number and Phase-Space Density in ...

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past y = 0.5 mm the signal starts to decrease again. This is due to two reasons: the total number of atoms affected by the CO2 laser decreases as the laser beam is moved away from the center of the MOT. In addition the effect of the disturbance of the CO2 focus is only local. This means that even though the atomic distribution is affected by the presence of the laser beam, the overall effect is limited to only one half of the MOT and thus does not lead to an imbalance in the scattered light between the two halves. The same phenomenon is visible if the focus is moved to the lower half of the MOT (y < 0 mm). However, the sign of the observed signal has changed, because this system detects the difference in the APD signals, not the absolute value. Figure 8.10 (d) shows that the method described is not very sensitive to the alignment of the focus along the beam propagation axis, as expected from the long Rayleigh length along this dimension. The Rayleigh lengths of the CO2 are 522 µm and 1102 µm respectively. 8.4 Loading of the Optical Dipole Trap After aligning the CO2 laser beam to the MOT and compressing the MOT to reduce the temperature, atoms are successfully loaded into the optical dipole trap. Once a first signal of the atoms is obtained it is possible to optimize the transfer into the trap in multiple ways. Before going into more details about this, it should be pointed out that one important step needs to happen after compressing the MOT and before turning the MOT beams off completely. Optical evaporation happens using atoms in the |F = 1/2,mF = ±1/2〉 states. It is therefore necessary to optically pump the atoms into the lower state. This is done by turning the repump beam off before the MOT beam is turned off. Typical optical pumping times are on the order of ten to hundred of µs. The location of the optical dipole trap is optimized first by moving the final focusing lens of the CO2 laser beam. Additionally, the way the power in the MOT beams is decreased during the MOT compression stages is varied and the different curves of beam power as a function of time is shown in figure 8.11. The standard shape that was used for measuring the compressed MOT temperatures is shown in blue. Curve 1 161
Figure 8.11: Different shapes of MOT compression curves. The detuning of the MOT beams is ramped linearly in all of these cases. (black) leads to the best atom number in the optical dipole trap. (The number of atoms in the MOT before loading, and the final MOT beam detuning is kept constant to ensure fair comparison.) Table 8.1 summarizes the different shapes of the compression curves used and the corresponding atom number loaded into the optical dipole trap. The atom number is determined after 1 second holding in the CO2 dipole trap. This ensures that all atoms not captured in the dipole trap are removed. This data was taken before the problem of the optical dipole trap lifetime was solved, see section 8.5, and thus the number loaded into the trap was actually larger than the numbers reported in table 8.1. Curve Fitted curve shape atom number 1 6.22−6.20·sin 2 (0.00115·(t+55.199) 2 ) (8.19±0.72)×10 5 2 5.80−0.340·exp( t 3.53 ) (3.38 ± 0.04)×105 3 0.0146+646·(1−exp(− (t+4.30) 2.51 )) 7.69 · exp(− (t+4.30) 1.32 ) (5.34±0.68)×10 5 4 −0.160+5.69·sin 2 (0.147(t+10.5)) (7.97± 0.60)×10 5 5 5.51−0.549·t (3.78±0.56)×10 5 Table 8.1: Transfer into optical dipole trap for different compression curves. The atom number is determined 1 second after the MOT has been turned off, to ensure that only atoms in the optical dipole trap are counted. 162
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Copyright by Kirsten Viering 2012
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Experiments to Control Atom Number
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Acknowledgments First of all, I wou
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Experiments to Control Atom Number
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Table of Contents Acknowledgments v
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Chapter 7. Lithium Apparatus 92 7.1
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List of Tables 2.1 Physical propert
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4.1 Vacuum chamber . . . . . . . .
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7.39 Future vertical axis optics .
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The development of techniques to la
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Ptorr 10 5 10 6 10 7 10 8 10 9 260
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Property Symbol Value Reference Ato
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2.3.2 Hyperfine Structure So far th
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The Wigner-Eckhart theorem can be u
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The total magnetic moment of an ato
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interaction. The shift in the energ
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(a) (b) scattering length a 0 Energ
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a laser field with frequency ω. Th
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Here ω0 is the resonance frequency
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Optical molasses do not provide a s
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J=1 J=0 -1 Δ σ + σ - σ - 0 +1 -
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phase-space density is defined as
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which maintains a constant η = U/k
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2.12.1 Saturated Absorption Spectro
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Figure 2.22: Saturation absorption
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Signal 0 Signal (a) (b) Signal Freq
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(a) (b) (c) (d) Figure 2.24: Absorp
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y more complex energy level structu
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ight side of the box. An irreversib
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time (a) (b) (c) Figure 3.3: Single
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them to move from B to A, but close
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Figure 4.1: Vacuum chamber. Photogr
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( ( Figure 4.3: Helicoflex seal. (a
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88 mm 4.2.3 Auxiliary Coils 62 mm Q
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5 2 P 3/2 5 2 S 1/2 384. 230 484 46
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distribution of the MOT master lase
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shifts. First a frequency shift of
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transition. However, the laser freq
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4.3.1.4 Upper MOT Horizontal Slave
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provides the beam for the upper MOT
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demon beam λ λ horizontal MOT bea
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scholar, Florian Schreck. It is wri
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Atoms are then optically pumped to
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ferred into the |F = 1,mF = 0〉 or
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5.2 Branching Ratios and Population
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effect of the reflected beam at zer
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y the repulsive trough beams, gaini
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Figure 5.9: Atom number as a functi
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Figure 5.10: Radius of the magnetic
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on the collision rate of atoms insi
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ferred via the single-photon coolin
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By comparison an atomic Fock state
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of atoms in the two hyperfine groun
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difference in the lifetimes is dete
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Chapter 7 Lithium Apparatus Creatin
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angle valve rotary feedthrough ion
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an ion gauge controller (Granville
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viewports (MDC, 450002) are attache
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not trapped by the MOT impinge on t
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Should contamination of the vacuum
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Figure 7.12: The assembled Zeeman s
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7.2.2 MOT Coils A second set of coi
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BGauss 250 200 150 100 50 30 20 10
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Page 131 and 132: + B A Figure 7.23: Feshbach coil H-
Page 133 and 134: ensure that no particulates build u
Page 135 and 136: 118 Figure 7.26: Optical layout of
Page 137 and 138: The error signal shows three lines,
Page 139 and 140: into the CO2 laser. The optical lay
Page 141 and 142: Thorlabs PDA10A Coupler ZDC-10-1 to
Page 143 and 144: Imaging ber Imaging ber from Imagin
Page 145 and 146: Table 7.4 summarizes the beam power
Page 147 and 148: CO2 laser 40 MHz AOM f=2 in f=2 in
Page 149 and 150: 132 Figure 7.38: Optical layout aro
Page 151 and 152: Feshbach coil objective lenses atom
Page 153 and 154: MOT beams are no longer traveling a
Page 155 and 156: The second card (NI6733) offers eig
Page 157 and 158: Averaging over the magnetic subleve
Page 159 and 160: 2 2 P 3/2 D 2=670.977nm 2 2 S 1/2 m
Page 161 and 162: The right hand side of equation 7.1
Page 163 and 164: = E0 1 −n2 √2 exp σ0 ± iE0
Page 165 and 166: esidual potentials besides gravitat
Page 167 and 168: Figure 8.1: MOT loading. Typical lo
Page 169 and 170: A linear ramp typically changes the
Page 171 and 172: A typical MOT is density-limited at
Page 173 and 174: ubidium [113-115] and cesium[116].
Page 175 and 176: that most of the noise is due to th
Page 177: (a) (c) y . x z X=0.0mm Z=2.5mm 1)
Page 181 and 182: ZnSe lens f=5 in knife edge ZnSe wi
Page 183 and 184: shown in figure 8.13. By matching t
Page 185 and 186: Figure 8.15: Atom number and temper
Page 187 and 188: 275 Hz. Using these values the beam
Page 189 and 190: system. Maybe the easiest way to ac
Page 191 and 192: Appendix A Magic Wavelength of Hydr
Page 193 and 194: transitions for the excited state p
Page 195 and 196: Bibliography [1] J.J. Thomson. Cath
Page 197 and 198: [22] C.J. Foot. Atomic Physics. Oxf
Page 199 and 200: [46] E.D. Black. An introduction to
Page 201 and 202: [67] J.L. Hanssen. Controlling Atom
Page 203 and 204: [88] D.S. Naik, C.G. Peterson, A.G.
Page 205 and 206: [110] J.W. Goodman. Introduction to
Page 207: [132] C. Degenhardt, H. Stoehr, U.
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