Ion-Trap-Based Quantum Computers: From Benchmarking to Outperforming Classical Digital Computers

Georgetown University, Washington DC

Investigators

Abstract

Our use of of quantum physics began around the turn of the 20th century, when scientists started exploring the ultrasmall world of atoms and electrons. While much of the theoretical basis for quantum mechanics was worked out in the 1920's, we still do not employ significant technologies that take into account the bizarre behaviors that are possible due to the quantum world (like teleportation or quantum interference). Recently, there has been significant advance in a new paradigm for computing, called quantum computing. With its operation based on the quantum-mechanical effects between its constituents, it can usher in a new realm of computation--where a small quantum computer can hold more memory than that of every conventional computer ever built (or to be built), or it can rapidly solve hard problems like finding the prime factors of large numbers and thereby breaking our current standards for encryption. While we don't yet have the "Microsoft quantum surface" devices available in stores, research labs have produced so-called quantum simulators, which emulate the behavior of coupled quantum systems and allow their properties to be read off at the end of the computation. This research project will work on finding ways to verify the correctness of these quantum computers when they surpass the abilities of conventional computers. This is done by finding special cases, where conventional computers can predict the results, and determining how to run the quantum computers for those special cases. In addition to the research work proposed, this project has a significant outreach component, where the group will be launching a Massive Open Online Course (MOOC) entitled "Quantum mechanics for everyone" on EdX in the fall of 2016, which will teach quantum mechanics principles with minimal math (no more complicated than taking square roots) and with a series of interactive computer demonstrations, tutorials, and illustrations. Three main themes will be pursued in this work: (1) Examining effects of the lattice vibrations on the performance of ion-trap-based quantum simulators by looking at both spin squeezing effects (where the Heisenberg uncertainty principal can be partially beaten) and on computation in the long-range interacting limit; (2) Determining techniques to speed up quantum computation from clock frequencies in the 10s of KHz to clock frequencies that can be pushed in the MHz range or further; and (3) Discovering whether macroscopic quantum tunneling effects, or fragile quantum states (like the so-called NOON states) can be formed and employed in these quantum simulators. The type of quantum simulator we work with is one that is built out of trapped ions that are driven by lasers that apply spin-dependent forces on the ions (where the spin degree of freedom is often a hyperfine state of the ion). The lasers push the ions according to their internal quantum states, while the coupling to the lattice vibrations drives a subsequent coupling between those internal states. By properly engineering these couplings, one creates a quantum computer/simulator. This theoretical work will pair closely with experimental work at NIST Boulder (Penning trap), Maryland (linear Paul trap), and UCLA (planar Paul trap).