Experiments with Supersonic Beams as a Source of Cold Atoms

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wall starts at the edge of the trap, and the atoms do not encounter the wall during their oscillations. To cool the atoms, the wall is slowly swept towards the center of the trap. By moving the wall slowly, each atom in the trap will encounter the one-way wall close to the classical limit of its trajectory in the trap. Since the atoms are near their classical turning points, they have very little kinetic energy when they interact with the barrier. Encountering the one-way barrier, the atoms pass through the wall and are trapped near the minimum of the potential formed by the one-way wall and the original trap. In this manner the atoms have been transferred from a high potential energy state in one trap, to a low potential energy state in a different trap. By sweeping the wall adiabatically, atoms trapped by the one-way barrier are not heated by the sweep, and the entire 1D trap can be cooled. The one-way wall only cools the atoms in one dimension, even when placed in a three dimensional trap, unless trap ergodicity mixes the degrees of freedom sufficiently for each atom to encounter the wall at nearly zero kinetic energy. The experimental technique used to create a one-way wall is a laser that switches the internal state of atoms that encounter it, such that the trapping potential in the new state is changed. One important point though is that the state change must involve spontaneous emission to make the process irreversible. Single- photon cooling takes its name from the fact that changing the state of the atoms, and thus the potential landscape they see, requires each atom to scatter just one photon. A closed two level system, as is required for traditional laser cooling, is not required for single-photon cooling, making the technique broadly applicable. In fact, single-photon cooling will not work in a true two level system, since the atom will return to its orignal state after scattering the photon, and the process will not be irreversible. Single-photon cooling is a physical realization of the “Maxwell’s Demon” thought 159
experiment, where a being is capable of observing the motion of each particle in an ensemble and, using these observations, is able to reduce the entropy of the ensemble with doing work on it, apparently violating the Second Law of Thermodynamics. The classic example of this is a trap door, operated by the observer, which separates two chambers of gas. If the observer opens the trap door when a particle approaches from the left side, but not the right, then the observer can create a one-way wall using the door, and atoms will accumulate in the chamber on the right. This increases the phase space density without doing work. The resolution to this apparent paradox lies in the fact that information carries entropy. To operate the trap door, the observer must store information about the ensemble, which must eventually be erased, increasing the entropy of the universe in accordance with Landauer’s erasure principle [136]. For single-photon cooling, the photon scattered each time an atom changes state provides information about that particular atom’s position in the trap, making a measurement of the original state of the ensemble possible. In this manner, the entropy removed from the atomic ensemble is accounted for in the increased entropy of the radiation field [133]. A one-way wall for atoms has been demonstrated for optically trapped rubidium, in analog to the situation illustrated in 5.25(a) [137]. This experiment com- pressed the sample, but due to the heating from spontaneous scattering, the phase space density of the sample was only increased by a factor of 1.07. A different scheme, in which rubidium atoms are transferred from a magnetic trap to a gravito-optical trap has also been used for single-photon cooling [138, 139]. Using laser excitation and spontaneous emission to affect the irreversible state change that creates the effect of a one-way wall, this method succeeded in increasing the phase space density of the trapped sample by a factor of 350. More details on these experiments can be found in [116, 140, 141]. 160
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Copyright by Adam Alexander Libson
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General Methods of Controlling Atom
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Acknowledgments First and foremost,
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to problems, and I frequently went
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General Methods of Controlling Atom
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Table of Contents Acknowledgments v
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Chapter 5. Towards Trapping and Coo
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List of Figures 2.1 Comparison of e
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5.12 Faraday Rotation Signal During
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producing a cold sample. Alternativ
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place inside a dilution refrigerato
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atoms or molecules are slowed using
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2.1 Thermodynamics of Ideal Gases F
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Since there will be no heat exchang
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Using equation 2.17 to modify equat
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Normalized Effusive Beam Flux Norma
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general method for producing cold a
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The gas throughput of the nozzle ca
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Chapter 3 Slowing Supersonic Beams
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3.1 Using Helium for Atom Optics Ex
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Figure 3.1: Calculated elastic scat
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that they can be prepared ex-situ a
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successful. Any water that remains
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Skimmer 300 l/s Turbo Pump Even-Lav
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Figure 3.5: A CAD image of the dete
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from tubular aluminum welded togeth
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Figure 3.7: A CAD image of the roto
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Figure 3.10: A CAD image of large c
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Figure 3.11: This plot shows the am
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approximations are made in this cal
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3.3.3 Detection An SRS [61] residua
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TTL pulse to the data acquisition c
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A comparison of the time-of-flight
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eceding crystal. Each curve is the
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calculated slow beam velocity is qu
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the RGA does have an effect on the
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Chapter 4 The Atomic and Molecular
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field. In the L − S coupling regi
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3 P2 E Figure 4.2: This graph gives
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For intermediate fields, the full p
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Figure 4.4: This figure illustrates
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The same effect is also responsible
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(a) (b) (c) Time Figure 4.5: A pict
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which the particles enter). The oth
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the coil can instead be switched be
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the magnitude of the field some dis
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nozzle front surface aluminum catho
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Figure 4.9: A CAD overview of the s
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258V 1MΩ 5V 1mF DC/DC Converter TT
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Figure 4.12: An oscilloscope trace
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(a) (b) Figure 4.14: A CAD image of
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-HV PS 4 M MCP Anode 10 M 1 M Trans
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Signal [V] 2.5 2.0 1.5 1.0 0.5 refe
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Figure 4.20: An exploded view of th
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(a) (b) (c) (e) Figure 4.21: A pict
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258V 1MΩ TTL 2.2mF 50Ω TTL 5V 5V
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closed. With the new thyristor gate
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HeNe M2 M1 BB /2 L BB PC coil PC PD
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Table 4.1: Peak magnetic fields mea
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Figure 4.28: A cut-away CAD image o
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ameters. The coilgun chamber consis
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Table 4.2: Final velocities (vf), s
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Page 127 and 128: viability for molecules essential.
Page 129 and 130: 8 Ω LN2 Liquid Nitrogen Dewar Nozz
Page 131 and 132: Figure 4.33: Molecular oxygen slowi
Page 133 and 134: Chapter 5 Towards Trapping and Cool
Page 135 and 136: Energy meV 0.05 0.00 0.05 0.0 0.2 0
Page 137 and 138: 10 mm 2.0 T 1.8 1.6 1.4 1.2 1.0 0.8
Page 139 and 140: 250V 1MΩ 3x 2.2mF TTL 5V feedback
Page 141 and 142: Magnetic Field (T) 1.9 1.7 1.5 1.3
Page 143 and 144: 5.2.2.1 Principle of Operation of t
Page 145 and 146: Figure 5.8: Photograph of the trapp
Page 147 and 148: 4.1.3. In an anti-Helmholtz trap, t
Page 149 and 150: Figure 5.11: Photograph of the hydr
Page 151 and 152: Photodiode Signal (V) Time (s) Figu
Page 153 and 154: Figure 5.13: Time of flight plot of
Page 155 and 156: 500 l/s Turbo Pump Supersonic Nozzl
Page 157 and 158: Ionizer 500 l/s Turbo Pump Ion Opti
Page 159 and 160: guided the design of the apparatus.
Page 161 and 162: Z − Velocity (m/s) 100 60 30 0
Page 163 and 164: Atom Number 60 50 40 30 20 10 0.6 0
Page 165 and 166: scattered photon to extract informa
Page 167 and 168: where k1 · pi = − k2 · pi, wh
Page 169 and 170: the electron g-factor which causes
Page 171 and 172: Figure 5.24: A schematic of the tel
Page 173 and 174: prevent the determination of the is
Page 175: (a) (b) time Figure 5.25: A 1D illu
Page 179 and 180: potential position 2 x 243 nm Lα |
Page 181 and 182: Appendix 164
Page 183 and 184: y x V i Figure A.1: The geometry us
Page 185 and 186: Bibliography [1] H.J.MetcalfandP.va
Page 187 and 188: [17] Brian C. Sawyer, Benjamin L. L
Page 189 and 190: [34] R. Campargue. Progress in over
Page 191 and 192: [51] O. Carnal, M. Sigel, T. Sleato
Page 193 and 194: [70] Edvardas Narevicius, Adam Libs
Page 195 and 196: [87] Willis E. Lamb and Robert C. R
Page 197 and 198: [96] G.Gabrielse,N.S.Bowden,P.Oxley
Page 199 and 200: [110] N. Kolachevsky, J. Alnis, S.
Page 201 and 202: [125] Andreas Osterwalder, Samuel A
Page 203 and 204: [142] C. Cohen-Tannoudji, B. Diu, a
Page 205 and 206: [161] Paulo F. Bedaque, Aurel Bulga
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Experiments with Supersonic Beams as a Source of Cold Atoms

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