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How to build a fault-tolerant logical qubit with quantum dots

Andrew Landahl, Sandia National Laboratories

(Session 1 : Thursday from 7:30-8:15)

Abstract. After a brief overview of Sandia's quantum information science effort, I will focus on our current "Grand Challenge" QIST program, a large part of which is aimed at designing a fault-tolerant logical qubit with quantum dots. Because this technology may not be familiar to everyone, I will spend some time reviewing it with especial focus on why silicon might be a good material for quantum-dot qubits. Many theoretical analyses of fault-tolerant quantum error correction omit engineering-level constraints such as the space needed to route control wires to the qubits. We have found that these kinds of considerations have a HUGE impact on the accuracy threshold, and in fact can even cause the accuracy threshold to disappear altogether. I will discuss how theoretical ideas such as quantum local check codes and dynamical decoupling can ameliorate some of these constraints in the quantum dot setting. We have developed several logical qubit architectures based on these ideas, and using high-performance computing we have generated optimal schedules for processing them. Our Monte-Carlo simulations point to the accuracy threshold disappearing entirely if dynamical decoupling is not used in conjunction with fault-tolerant quantum error correction, and when it is, the threshold lies between roughly 10^{-5} to 10^{-3} depending on which local check code is used. Based on arXiv:0904.0003. This work was supported through the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.