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

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4.2.1 Upper MOT Coils A pair of anti-Helmholtz coils creates the quadrupole field required to create a MOT in the upper chamber. The radius of these coils is 4 cm, spaced 6 cm apart. The coils consist of 91 windings of AWG 20 wire, creating a magnetic field gradient of 15 G/cm at a current of 2.5 A. To dissipate the generated heat, the coils are mounted to water-cooled copper blocks. The current in each coil is controlled individually, so that the location of the magnetic field minimum can be adjusted in space. 4.2.2 Magnetic Trap Coils A second pair of circular coils are mounted around the science chamber cell. At small currents they create the weak magnetic field gradient required for producing a MOT in the lower chamber, at large currents these coils are able to generate the magnetic field gradients required to produce a quadrupole magnetic trap. Up to 30 A are typically used for creating the magnetic trap. These coils are made from 176 windings of AWG 14 wire in three layers (layer A: 53 windings, layer B: 53 windings, layer C: 70 windings). They have an inner diameter of 34 mm, an outer diameter of 69 mm and a width of 42 mm. The separation between the centers of the coils is 75 mm. At large currents up to 261 W resistive heat is produced in these coils. In order to effectively cool the coils, they are surrounded by a PVC enclosure, through which a continous flow of water is directed. Figure 4.4 shows a schematic of the magnetic trap coils. Near the center of the magnetic trap, these coils produce a magnetic field gradient of Bz = 9.7 G/(cm A) in the axial direction and Br = 4.8 G/(cm A) in the radial direction. They are wired in series and powered by three power supplies (Lambda Gen80-19) that are wired in parallel. A home-built PID control circuit regulates the current flow using seven power op-amps (OPA549). 49
88 mm 4.2.3 Auxiliary Coils 62 mm Quadrupole coil 69 mm 34 mm 158 mm 1.5 mm gap science chamber 33 mm 75 mm Quadrupole coil Figure 4.4: Schematic of the magnetic trap coils. wire layer: C B A nylon spacers Three more coils are located around the science chamber. A pair of Helmholtz coils is aligned with the axis of the quadrupole field. The constant magnetic field off- set created by these coils moves the center of the magnetic trap along this axis. They are also used to provide a homogeneous reference field during the optical pumping se- quence. These Helmholtz coils consist of 30 turns of AWG 16 wire, creating a field of approximately 2.6 G/A near the trap center. A last coil near the science chamber is mounted vertically above the cell. 150 windings of AWG 20 wire generate a field of about 1 G/A near the trap center. This coil can be used to translate the magnetic field minimum, i.e. the magnetic trap center, in the vertical direction, when superimposed to the quadrupole magnetic field. The dependence of the magnetic trap center as a function of current through this coil is shown in figure 4.5. 50
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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
Page 15 and 16: 4.1 Vacuum chamber . . . . . . . .
Page 17 and 18: 7.39 Future vertical axis optics .
Page 19 and 20: The development of techniques to la
Page 21 and 22: Ptorr 10 5 10 6 10 7 10 8 10 9 260
Page 23 and 24: Property Symbol Value Reference Ato
Page 25 and 26: 2.3.2 Hyperfine Structure So far th
Page 27 and 28: The Wigner-Eckhart theorem can be u
Page 29 and 30: The total magnetic moment of an ato
Page 31 and 32: interaction. The shift in the energ
Page 33 and 34: (a) (b) scattering length a 0 Energ
Page 35 and 36: a laser field with frequency ω. Th
Page 37 and 38: Here ω0 is the resonance frequency
Page 39 and 40: Optical molasses do not provide a s
Page 41 and 42: J=1 J=0 -1 Δ σ + σ - σ - 0 +1 -
Page 43 and 44: phase-space density is defined as
Page 45 and 46: which maintains a constant η = U/k
Page 47 and 48: 2.12.1 Saturated Absorption Spectro
Page 49 and 50: Figure 2.22: Saturation absorption
Page 51 and 52: Signal 0 Signal (a) (b) Signal Freq
Page 53 and 54: (a) (b) (c) (d) Figure 2.24: Absorp
Page 55 and 56: y more complex energy level structu
Page 57 and 58: ight side of the box. An irreversib
Page 59 and 60: time (a) (b) (c) Figure 3.3: Single
Page 61 and 62: them to move from B to A, but close
Page 63 and 64: Figure 4.1: Vacuum chamber. Photogr
Page 65: ( ( Figure 4.3: Helicoflex seal. (a
Page 69 and 70: 5 2 P 3/2 5 2 S 1/2 384. 230 484 46
Page 71 and 72: distribution of the MOT master lase
Page 73 and 74: shifts. First a frequency shift of
Page 75 and 76: transition. However, the laser freq
Page 77 and 78: 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
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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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are required to create the high mag
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The coils are then checked for shor
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+ B A Figure 7.23: Feshbach coil H-
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ensure that no particulates build u
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118 Figure 7.26: Optical layout of
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The error signal shows three lines,
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into the CO2 laser. The optical lay
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Thorlabs PDA10A Coupler ZDC-10-1 to
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Imaging ber Imaging ber from Imagin
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Table 7.4 summarizes the beam power
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CO2 laser 40 MHz AOM f=2 in f=2 in
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132 Figure 7.38: Optical layout aro
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Feshbach coil objective lenses atom
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MOT beams are no longer traveling a
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The second card (NI6733) offers eig
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Averaging over the magnetic subleve
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2 2 P 3/2 D 2=670.977nm 2 2 S 1/2 m
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The right hand side of equation 7.1
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= E0 1 −n2 √2 exp σ0 ± iE0
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esidual potentials besides gravitat
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Figure 8.1: MOT loading. Typical lo
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A linear ramp typically changes the
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A typical MOT is density-limited at
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ubidium [113-115] and cesium[116].
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that most of the noise is due to th
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(a) (c) y . x z X=0.0mm Z=2.5mm 1)
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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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