Naomi Nickerson

Abstract The architecture of a quantum computer has many aspects from the connectivity and arrangement of physical components, the interaction of classical and quantum information through to the design of logical gate instructions sets. Quantum error correction is central to any architecture for practical universal quantum computing to protect against the inevitable imperfections in quantum systems. This tutorial will introduce quantum error correction, what is needed for these theoretical concepts to be applied in real systems, and how this translates into principles for quantum architectural design.

Abstract We introduce fusion based quantum computing (FBQC) - a model of universal quantum computation in which entangling measurements, called fusions, are performed on the qubits of small constant sized entangled resource states. We introduce a stabilizer formalism for analyzing fault tolerance and computation in these schemes. This framework naturally captures the error structure that arises in certain physical systems, such as linear optics. FBQC can offer significant architectural simplifications, enabling hardware made up of many identical modules, and reducing classical processing requirements. We present two pedagogical examples of fault-tolerant schemes constructed in this framework and numerically evaluate their threshold under a general error model with measurement erasure and error, and a linear-optical error model with fusion failure and photon loss. In these schemes, fusion failures, as well as errors, are directly dealt with by the quantum error correction protocol. We find that tailoring the fault-tolerance framework to the physical system allows the scheme to have a higher threshold than schemes reported in literature. We present a ballistic scheme which can tolerate a 10.3% probability of suffering photon loss in each fusion.