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

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Figure 5.3: Incremental transfer of atoms into the gravito-optical trap. Below a current of 2.5A the magnetic potential does no longer support the atoms against gravity and the single-photon cooling sequence is complete. Figure 5.4 shows an absorption image of atoms transferred into the optical trough via the single-photon cooling process. In this false color image about 1.5 × 10 5 atoms are trapped inside the optical trough. Figure 5.4: Absorption image of about1.5×10 5 atoms transferred into the optical trough via the single-photon cooling process. 71
5.2 Branching Ratios and Population Distribution The irreversible step in the implementation of single-photon cooling in rubidium lies in the spontaneous scattering event that occurs after the atom has been excited to the |F ′ = 1〉 state. Because of the branching ratios it is impossible to transfer all the atoms from the |F = 2,mF = 2〉 state into one final trapped state in the gravito-optical trap. Instead they are evenly distributed between the |F = 1,mF = 1〉 and |F = 1,mF = 0〉 states. After completion of the single-photon cooling sequence, the distribution of atoms between the two final states is determined by applying a magnetic field gradient such that atoms in the |F = 1,mF = 1〉 state are ejected out of the gravito-optical trap, leaving only the magnetically decoupled atoms in the |F = 1,mF = 0〉 state in the trap. As expected about 50% of the total number of atoms are in this state. Only atoms in the |F = 1,mF = 0〉 state are considered when calculating phase-space density. About 10% of the atoms that encounter the demon will fall back into the |F = 2,mF = 2〉 state, and about 5% will fall into the |F = 2,mF = 1〉 state. These atoms are thus transferred back into the reservoir and can undergo another cycle of excitation and decay when encountering the demon beam. Only about 5% of the atoms decay into the untrapped |F = 2,mF = 0〉 state and are lost from the system. 5.3 Effect of the Demon Beam Detuning As mentioned before, the demon beam is slightly detuned from resonance. Naively one would assume that the beam should ideally be on resonance. This is not true, as figure 5.5 shows. The maximum number of atoms is transferred into the trough not at zero detuning, but rather at a power-dependent optimum value. There are two reasons for this phenomenon. First, consider the scattered photon. As the density of atoms in the trap increases, the probability of reabsorption of this photon by atoms in the optical trough increases as well. If this photon is absorbed by an atom inside the trap, this additional scattering event can lead to trap loss. If the demon beam detuning ∆ is away from resonance, the probability of reabsorption of this photon is dramatically decreased, as the scattering rate is roughly proportional to 1/∆. 72
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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
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 and 66: ( ( Figure 4.3: Helicoflex seal. (a
Page 67 and 68: 88 mm 4.2.3 Auxiliary Coils 62 mm Q
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: ferred into the |F = 1,mF = 0〉 or
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 and 130: The coils are then checked for shor
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,
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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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