H. Bombín

Dept. Física Teórica I
Univ. Complutense, Madrid, España

Lecuture I: "Quantum Measurements and Gates by Code Deformation"

Abstract:
The usual scenario in fault tolerant quantum computation involves certain amount of qubits encoded in each code block, transversal operations between them and destructive measurements of ancillary code blocks. We introduce a new approach in which a single code layer is used for the entire computation, in particular a surface code. Qubits can be created, manipulated and non-destructively measured by code deformations that amount to `cut and paste' operations in the surface. All the interactions between qubits remain purely local in a two-dimensional setting. We propose a protocol to demonstrate the topological order of a spin-1/2 lattice model with four-body interactions. Unlike other proposals, it does not rely on the controlled movement of quasiparticles, thus eliminating the addressing and decoherence problems related to them. Rather, the protocol profits from the degeneracy of the ground state. It involves quasiparticle detection and strong Zeeman perturbations that are used to create holes and move them around in the system.

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