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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015., Cataloged from PDF version of thesis., Includes bibliographical references (pages [187]-214)., Quantum computers employ quantum mechanical effects, such as superposition and entanglement, to process information in a distinctive way, with advantages for simulation and for new, and in some cases more-efficient algorithms. A quantum bit is a two-level quantum system, such as the electronic or spin state of a trapped atomic ion. Physics experiments with single atomic ions acting as "quantum bits" have demonstrated many of the ingredients for a quantum computer. But to perform useful computations these experimental systems will need to be vastly scaled-up. Our goal is to engineer systems for large-scale quantum computation with trapped ions. Building on established techniques of microfabrication, we create ion traps incorporating exotic materials and devices, and we investigate how quantum algorithms can be efficiently mapped onto physical trap hardware. An existing apparatus built around a bath cryostat is modified for characterization of novel ion traps and devices at cryogenic temperatures (4 K and 77 K). We demonstrate an ion trap on a transparent chip with an integrated photodetector, which allows for scalable, efficient state detection of a quantum bit. To understand and better control electric field noise (which limits gate fidelities), we experiment with coating trap electrodes in graphene. We develop traps compatible with standard CMOS manufacturing to leverage the precision and scale of this platform, and we design a Single Instruction Multiple Data (SIMD) algorithm for implementing the QFT using a distributed array of ion chains. Lastly, we explore how to bring it all together to create an integrated trap module from which a scalable architecture can be assembled., by Amira M. Eltony., Ph. D.

We demonstrate trapping in a surface-electrode ion trap fabricated in a 90-nm CMOS (complementary metal-oxide-semiconductor) foundry process utilizing the top metal layer of the process for the trap electrodes. The process includes doped active regions and metal interconnect layers, allowing for co-fabrication of standard CMOS circuitry as well as devices for optical control and measurement. With one of the interconnect layers defining a ground plane between the trap electrode layer and the p-type doped silicon substrate, ion loading is robust and trapping is stable. We measure a motional heating rate comparable to those seen in surface-electrode traps of similar size. This demonstration of scalable quantum computing hardware utilizing a commercial CMOS process opens the door to integration and co-fabrication of electronics and photonics for large-scale quantum processing in trapped-ion arrays., United States. Defense Advanced Research Projects Agency. Microsystems Technology Office, National Science Foundation (U.S.). Interdisciplinary Quantum Information Science & Engineering (iQuiSE) Program, United States. Dept. of Energy (Science Graduate Fellowship), United States. Intelligence Advanced Research Projects Activity, United States. Dept. of Defense. Assistant Secretary of Defense for Research & Engineering (United States. Air Force Contract FA8721-05-C-0002)

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013., Cataloged from PDF version of thesis., Includes bibliographical references (pages [47]-53)., Following successful demonstrations of quantum algorithms and error correction with a handful of trapped ions in a macroscopic, machined Paul trap, there is a growing effort to move towards microfabricated traps with all the electrodes on a single chip. These traps, known as surface-electrode ion traps, are more amenable to being shrunk in size and replicated, or integrated with optical components and electronic devices. However, in the shift towards surface-electrode traps, and as traps are miniaturized in general, laser beams are brought closer to electrode surfaces, exacerbating laser-induced charging. Because of their charge, trapped ions are extremely sensitive to stray charges that accumulate on the trap surface. The DC potentials caused by stray charge displace the ion from the null of the RF trapping field, resulting in a fast, driven motion of the ion (known as micromotion) which hinders quantum operations by broadening transitions and causing decoherence. In a surface trap, micromotion detection is difficult as the laser beams used for measurement typically cannot crash into the trap, obscuring ion offsets out of the trap plane. Existing methods for micromotion detection permit ion positioning accurate to the ground state wavepacket size (of order 10 nm), but cannot identify ion offsets out of the trap plane with the same accuracy. Schemes for sensitive compensation often have restrictive requirements such as access to a narrow atomic transition. We introduce a new approach, which permits out-of-plane micromotion compensation to within 10s of nanometers with minimal overhead. Our technique synchronously detects ion excitation along the trap axes when it is driven by secular-frequency sidebands added to the RF electrodes; the excitation amplitude is proportional to the offset from the RF null. We make a detailed theoretical comparison with other techniques for micromotion compensation and demonstrate our technique experimentally., by Amira M. Eltony., S.M.