Ph.D. Thesis - Physics

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Figure 6-12: Measured pickup from the rf electrode during laser ablation. The rf begins recovering after about 15 µs, and during this time ions are trapped. Figure reproduced from Ref. [HMO + 06]. lowered, some ions enter the trap, which returns to full strength with some ions already inside it. This was first observed by Hashimoto et al. [HMO + 06], and the relevant plot from that paper is presented in Fig. 6-12. The loading of ions into a conservative trap potential requires a nonconservative step; normally, it is the conversion of neutral atoms into ions within the trap, but with ablation loading it is an induced time-dependence of the trapping potentials themselves. We note also that lower-energy ablation pulses have been used in lieu of an oven to produce neutral atoms that are then photoionized within the trap [HGH + 07]. Laser ablation has a number of possible advantages. For one, it requires only a single laser, and the process is not sensitive to its frequency. For instance, if one wished to load simultaneously atomic and molecular ions, an ablation pulse (or set of synchronized ablation pulses) might do the trick. As with e-gun loading, however, the lack of isotopic selection could potentially lead to unwanted trapped species. Second, it is very fast: carefully- calibrated ablation loading could thus be very useful for loading the many ions needed in a scalable quantum simulator. If an ion was lost during a simulation, one could envision a classical subroutine that pauses execution of the algorithm and then reloads an ion in the correct spot using a single ablation pulse. The ion could be trapped and re-cooled in much less than one second. Third, ablation loading does not create a large heat load. In a cryogenic environment, the heat generated by a resistive oven could be conducted to the trap electrodes, increasing decoherence rates. In our later work, we solve this problem by placing the oven in contact with the 40 K radiation shield, which has enough cooling power to handle the heat load. In the future, however, it may be advantageous to have very site-specific loading, as in the scenario described above. In this case, ablation loading may be a superb option. 144
Figure 6-13: A diagram of the setup showing the position and orientation of the ablation target relative to the ion trap. The surface of the ablation target is approximately 25 mm from the trap center and is orthogonal to the direction to the ion trap. Not to scale. Attractive as laser ablation loading is, there is much that is not well-understood about it, especially on a practical level. This motivates the following research questions: 1. How shallow a trap may be loaded with direct laser ablation, and how does that value compare to other techniques, including electron impact ionization and photoioniza- tion? 2. How does the loading efficiency depend upon the composition of the material that is ablated, and upon the ablation laser power? 3. How does the number of ions loaded depend on the ablation laser power? 4. Is the buildup of stray charge an issue when using this method, especially with a surface-electrode trap? In the remainder of this section we present an experimental study of the ablation loading of ion traps, focusing on our experimental setup and results, with a goal of evaluating the utility of the technique for loading ion traps in view of the above questions. 6.5.1 Experimental setup The trap is driven with an rf voltage with amplitude 200-600 V at 8 MHz. The dc voltages, not discussed here in detail, are chosen to provide sufficient ˆz confinement (with depth at least equal to that in the ˆx and ˆy directions) and rough compensation. The ablation laser is a frequency-tripled pulsed Nd:YAG laser (Continuum Minilite) at 355 nm. It produces pulses from 1-10 mJ at a duration of 4 ns. The 422 nm and 1092 nm lasers are directed in a direction along the ˆz and ˆx directions, while the ablation laser is along ˆz; this is depicted in Fig. 6-13. As in the last section, a CCD camera and PMT are used for ion detection. 145
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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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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: Figure 6-11: Bastille mounted in th
Page 147 and 148: Figure 6-14: A plot of the trapped
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
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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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