We present a detailed description of an architecture for fault-tolerant
quantum computation, which is based on the cluster model of encoded qubits. In
this cluster-based architecture, concatenated computation is implemented in a
quite different way from the usual circuit-based architecture where physical
gates are recursively replaced by logical gates with error-correction gadgets.
Instead, some relevant cluster states, say fundamental clusters, are
recursively constructed through verification and postselection in advance for
the higher-level one-way computation, which namely provides error-precorrection
of gate operations. A suitable code such as the Steane seven-qubit code is
adopted for transversal operations. This concatenated construction of verified
fundamental clusters has a simple transversal structure of logical errors, and
achieves a high noise threshold ~ 3 % for computation by using appropriate
verification procedures. Since the postselection is localized within each
fundamental cluster with the help of deterministic bare controlled-Z gates
without verification, divergence of resources is restrained, which reconciles
postselection with scalability.Comment: 16 pages, 34 figure
