Ph.D. Thesis - Physics

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The base pressure of the vacuum chamber was 2×10 −9 torr, but rose to 3×10 −9 torr when the ablation laser was fired 10 times in 10 seconds. This rise is less than the typical value when one is first using an oven, but somewhat larger than the pressure rise due to an oven after a long period of use. A number of different ablation targets were tested. These include Sr metal (99% pure random pieces from Sigma-Aldrich), Sr/Al alloy (10% Sr, 90% Al by mass from KB Alloys), single crystal SrTiO3 (〈100〉 crystal orientation from Sigma-Aldrich), and SrTiO3 powder in an epoxy resin (5 µm SrTiO3 powder from Sigma-Aldrich mixed with Loctite 5 min epoxy). Of all the targets only Sr metal oxidizes in air, so although it’s the most obvious choice of material, it may not be best. Results obtained with each of these targets are presented below. 6.5.2 Experimental results We now present data to answer each of the above research questions. We begin with studying the effects of the composition of the target material. The goal is to measure both the efficiency of the loading process and the number of times a single spot on the target may be ablated before the efficiency begins to decrease. This is known to happen due to a profile being formed in the material that modifies the ablation process [CH94]. This process is not a fundamental limitation, however, since the spot being ablated can be varied from shot to shot. We study this question by ablating a given spot on each target a number of times, and measuring the ion signal in each load. Since the electrons that short the trap during ablation remove the ions already in the trap, we measure after each shot only the number of ions loaded during that shot. We find that there is some variance in the number of ions loaded per pulse, which is not ideal. More is said on this later. The data for each target is presented in Fig. 6-14. In all, we find that the SrTiO3 crystal is the “best” target choice. It produces, overall much more consistent ion numbers than the other targets, and has the longest lifetime, as well. The overall lower number of ions loaded is not a problem, since we are interested mainly in loading small numbers of ions. It is somewhat odd that the ion loads from the alloy peak after around 100 loads, but it is possible that impurities on the surface must be removed before loading efficiency can reach its maximum potential. Next, we turn to the question of loading into low trap depths. As in all our other traps, the depth is calculated using CPO and the pseudopotential approximation. Here, ions are loaded into the trap at a series of decreasing rf voltages which correspond to decreasing trap depths. We use an ablation laser pulse energy of 1.1 mJ and a spot size of 680 µm for this experiment; these values were chosen to maximize the ion signal at low trap depth. Our results are presented in Fig. 6-15. We found that ions could be loaded into a minimum trap depth of 40 meV, comparable to the shallowest depths loaded with photoionizaton of 146
Figure 6-14: A plot of the trapped ion signal as a function of the number of ablation pulses fired on a single spot of each of several targets. Each point represents the signal due to a single ablation pulse of energy 8 mJ. The ablation laser was focused to a spot size of 300 µm for this experiment. For reference, a single ion scatters roughly 0.2 photons/ms into the PMT in this setup. a thermal atomic beam [SHO + 06]. The same trap loaded with electron impact ionization of a thermal beam had a minimum loading depth of 470 meV. Next, we wish to address the possibility of loading single ions on demand. As stated above, the number of ions loaded per pulse varies greatly. Is it possible to tune the laser power to obtain a single ion at a time? The study of ablation targets in Fig. 6-14 involved loading hundreds of ions per shot. For this experiment, the pulse power was set at 2 mJ and the width of the spot at 0.5 mm. We present in Fig. 6-16 a plot of the probability of loading a certain number of ions with this set of parameters. The experimental probability distribution fits well to a Poisson distribution with a mean ion number of 0.16. With these parameters, it takes on average seven pulses to load and the probability of loading more than one ion is 8%. This is a satisfactory result, as these ions can simply be removed and the trap reloaded if only one ion is desired. The probability of loading more than two ions could also be lowered by further reducing the pulse intensity. Finally, we turn to a somewhat more qualitative discussion of the final question above, that is, the buildup of stray charge and other material during the loading process. Indeed, this is an issue that is more unique to surface-electrode traps, compared to macroscopic 3-D traps. Not only can charged material alter the trap potentials, but even additional neutral metal deposited is thought to alter the heating rate of trapped ions by changing the the makeup of the surfaces to which the ions are exposed [DK02, RBKD + 02, TKK + 99]. After 5000 ablation pulses, we do not see any qualitative change in trap behavior. This 147
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An Investigation of Precision and S
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Acknowledgments What a long, strang
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should totally start a band. I also
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2.4 Conclusions and further questio
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7.6.1 Regular array of stationary q
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List of Figures 2-1 The CNOT gate i
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7-12 Magnetic fields due to a “tr
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Chapter 1 Introduction The growth o
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1.1 Quantum information The concept
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us whether the target system obeys
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Nevertheless, there are a number of
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Digital Analog Classical Quantum Sp
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electrodes [TKK + 99]. This heating
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Digital Analog Classical Quantum Sp
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2. Initialization to a simple fiduc
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qubits, and in Ref. [SGA + 05] in t
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the lattice architecture, we discov
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1.6 Contributions to this work In t
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5) Ref. [DLC + 09b] Wiring up trapp
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Chapter 2 Quantum simulation using
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µN the nuclear magneton, and B0 th
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⎡ ⎤ a 0 0 0 ⎢ ⎥ ⎢ ρ2 =
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The same effect as number 2 above i
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where V0 is the maximum signal stre
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actions that occur between nuclei i
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Figure 2-2: The 2,3-dibromothiophen
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detail how this was done with a sim
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and thus requires invocation of the
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Renormalization Group (DMRG), with
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3.3 The bounds on precision In this
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Figure 3-1: A schematic of a generi
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Figure 3-3: The 11.7 T, 500 MHz sup
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. Figure 3-4: The above probe is a
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Figure 3-5: The CHFBr2 molecule. Al
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Figure 3-6: Frequency-domain spectr
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used to extract the answer is irrel
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Chapter 4 Theory and history of qua
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GND RF r ENDCAP 0 z 0 ENDCAP Ring T
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where Q is the charge of the trappe
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angular momentum along the quantiza
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emission from the excited state |
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selection rule ∆m = ±1 is applie
Page 95 and 96: Figure 4-3: Schematic diagram of sp
Page 97 and 98: to address an ion in state |↑〉
Page 99 and 100: the vibrational temperature is low.
Page 101 and 102: to the design of the trap itself. M
Page 103 and 104: to the quantum-mechanical ground st
Page 105 and 106: Chapter 5 Lattice ion traps for qua
Page 107 and 108: Figure 5-1: Schematic of the lattic
Page 109 and 110: Figure 5-3: Fit to Eq. 5.2 of the C
Page 111 and 112: Figure 5-4: The vacuum chamber for
Page 113 and 114: weeks. Low pressures depend on choo
Page 115 and 116: Figure 5-5: Left: Level diagram for
Page 117 and 118: Figure 5-7: (a) Schematic of the cr
Page 119 and 120: (a) Lattice Trap Schematic TOP PLAT
Page 121 and 122: mix the microspheres evenly in the
Page 123 and 124: Using the expression for ωˆr deri
Page 125 and 126: Figure 5-15: Plot of the motional c
Page 127 and 128: Figure 5-17: Dependence of the trap
Page 129 and 130: Chapter 6 Surface-electrode PCB ion
Page 131 and 132: Figure 6-1: Schematic of a linear i
Page 133 and 134: Figure 6-2: Layout of the trap elec
Page 135 and 136: Figure 6-3: Above are the cross sec
Page 137 and 138: Figure 6-6: Photograph of the trap
Page 139 and 140: Figure 6-8: CCD image of a cloud of
Page 141 and 142: Figure 6-9: Measurement results sho
Page 143 and 144: Figure 6-11: Bastille mounted in th
Page 145: Figure 6-13: A diagram of the setup
Page 149 and 150: allows us to upper-bound the amount
Page 151 and 152: Chapter 7 Quantum simulation in sur
Page 153 and 154: Figure 7-1: Left: Uraniborg 1, as r
Page 155 and 156: Figure 7-3: Calculated secular freq
Page 157 and 158: Figure 7-5: Left: Structure of 2-D
Page 159 and 160: Figure 7-7: Scaling of the order of
Page 161 and 162: involved. Because ions near the cen
Page 163 and 164: Results Before presenting the numer
Page 165 and 166: Figure 7-10: Calculation results fo
Page 167 and 168: 7.3 Magnetic gradient forces Now th
Page 169 and 170: Figure 7-13: Scaling of the J-coupl
Page 171 and 172: how are single-ion operations to be
Page 173 and 174: 250 psi, which increases to around
Page 175 and 176: Figure 7-18: At the center of this
Page 177 and 178: Figure 7-19: The plastic socket tha
Page 179 and 180: Figure 7-21: The two internal lense
Page 181 and 182: Figure 7-22: Measured secular frequ
Page 183 and 184: Along ˆy, the spacing is dˆy = 28
Page 185 and 186: of O2 to 2 × 10 −12 torr. Decohe
Page 187 and 188: Part III Toward ion-ion coupling ov
Page 189 and 190: Chapter 8 Motivation for and theory
Page 191 and 192: Figure 8-1: Schematic of the experi
Page 193 and 194: are in close agreement in the case
Page 195 and 196: 8.2.3 Simulated coupling rates We n
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Johnson noise We begin our discussi
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should suffice. Note that the above
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Chapter 9 Measuring the interaction
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Figure 9-2: Left: Level diagram for
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Figure 9-5: Photograph of the micro
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A fit of the resulting curve return
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Figure 9-9: Linear fit of the ωˆy
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Figure 9-12: Heating rate as determ
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Chapter 10 Conclusions and outlook
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traps, linking ions using photons,
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Bibliography [ADM05] Paul M. Alsing
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[CGB + 94] J. I. Cirac, L. J. Garay
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[GME + 02] M. Greiner, O. Mandel, T
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[LCL + 07] D. R. Leibrandt, R. J. C
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[PC04a] D. Porras and J. I. Cirac.
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[TBZ05] L. Tian, R. Blatt, and P. Z
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Appendix A Matlab code for Ising mo
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err_result = mean(theerr) 231
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J = J0; Jt(1) = J; Bt(1) = B; for k
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A.3 Simulation with constant force
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Appendix B Mathematica code for ion
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2 crystal_shape_6uraniborg.nb Out[6
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Appendix C How to trap ions in a cl
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Finally, we note that the chilled w
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C.4 Laser alignment and imaging As
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