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

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large safety margin on the current is implemented by using 10 MOSFETs in parallel. Figure 7.22: MOSFET H-bridge setup. The electrical circuit for the switching of the current direction through one of the Feshbach coils is shown in figure 7.23. This design allows for switching from Helmholtz- to anti-Helmholtz-configuration in only a few ms. The current direction is controlled by a TTL input to the H-bridge driving circuit. The H-Bridge driver (HIP4081) opens either the MOSFET groups A and D (each MOSFET symbol figure 7.23 represents a group of 10 MOSFETs run in parallel), or B and C simultaneously, switching the current direction through Feshbach coil 2. To reduce switching and turn-off times the overall inductance of the setup is minimized. Therefore all current carrying wires run in pairs with minimal distance between them. Because of the ability to switch the Feshbach coils between Helmholtz- and anti- Helmholtz configuration it is possible to use the Feshbach coils to create the quadrupole field for the MOT. In contrast to the MOT coils, the Feshbach coils can be run continously at the current required to generate the MOT magnetic field gradients (20 A). The loading rate and the atom number in both situations is comparable. The speed at which the system can be aligned however, is greatly increased when the quadrupole fields can be run continously. The experiment therefore now typically uses the Feshbach coils to create the MOT magnetic field gradients. 113
+ B A Figure 7.23: Feshbach coil H-bridge circuit. Using the H-bridge driver either MOSFETs A and D, or MOSFETs B and C open simultaneously, allowing the reversal of the current through the second Feshbach coil. Each MOSFET symbol represents 10 MOSFETs wired in parallel. For safety reasons an interlock system is installed. As with all of the interlocks it is based on the Arduino micro-controller. This interlock ensures that the Feshbach coils are not continously run above a current of 50 A. Below this current no significant temperature increase was measured and it is therefore not necessary to limit the time the coils are running below 50 A. Above a current of 100 A the interlock turns off the current after 10 s. If the current is between 50 A and 100 A the interlock turns off the current after 20 s. The interlock also monitors the cooling water temperature and the water flow. Table 7.3 summarizes the properties of the Feshbach coils. Number of coils 2 Magnetic field strength 6.34 G/A Number of layers per coil 1 Coil separation 36.0 mm Number of turns per coil 26 Water flow through each coil >2 l/min Inner diameter of the coils 29.5 mm Axial gradient 1.9 G/cm/A Outer diameter of the coils 45.0 mm Radial gradient 1.1 G/cm/A D C Table 7.3: Properties of the Feshbach coils 114
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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
Page 79 and 80: provides the beam for the upper MOT
Page 81 and 82: demon beam λ λ horizontal MOT bea
Page 83 and 84: scholar, Florian Schreck. It is wri
Page 85 and 86: Atoms are then optically pumped to
Page 87 and 88: ferred into the |F = 1,mF = 0〉 or
Page 89 and 90: 5.2 Branching Ratios and Population
Page 91 and 92: effect of the reflected beam at zer
Page 93 and 94: y the repulsive trough beams, gaini
Page 95 and 96: Figure 5.9: Atom number as a functi
Page 97 and 98: Figure 5.10: Radius of the magnetic
Page 99 and 100: on the collision rate of atoms insi
Page 101 and 102: ferred via the single-photon coolin
Page 103 and 104: By comparison an atomic Fock state
Page 105 and 106: of atoms in the two hyperfine groun
Page 107 and 108: difference in the lifetimes is dete
Page 109 and 110: Chapter 7 Lithium Apparatus Creatin
Page 111 and 112: angle valve rotary feedthrough ion
Page 113 and 114: an ion gauge controller (Granville
Page 115 and 116: viewports (MDC, 450002) are attache
Page 117 and 118: not trapped by the MOT impinge on t
Page 119 and 120: Should contamination of the vacuum
Page 121 and 122: Figure 7.12: The assembled Zeeman s
Page 123 and 124: 7.2.2 MOT Coils A second set of coi
Page 125 and 126: BGauss 250 200 150 100 50 30 20 10
Page 127 and 128: are required to create the high mag
Page 129: The coils are then checked for shor
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 and 178: (a) (c) y . x z X=0.0mm Z=2.5mm 1)
Page 179 and 180: Figure 8.11: Different shapes of MO
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ZnSe lens f=5 in knife edge ZnSe wi
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shown in figure 8.13. By matching t
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Figure 8.15: Atom number and temper
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275 Hz. Using these values the beam
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system. Maybe the easiest way to ac
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Appendix A Magic Wavelength of Hydr
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transitions for the excited state p
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Bibliography [1] J.J. Thomson. Cath
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[22] C.J. Foot. Atomic Physics. Oxf
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[46] E.D. Black. An introduction to
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[67] J.L. Hanssen. Controlling Atom
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[88] D.S. Naik, C.G. Peterson, A.G.
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[110] J.W. Goodman. Introduction to
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[132] C. Degenhardt, H. Stoehr, U.
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