Fault-tolerant qubit from a constant number of components

Abstract

With gate error rates in multiple technologies now below the threshold required for fault-tolerant quantum computation, the major remaining obstacle to useful quantum computation is scaling, a challenge greatly amplified by the huge overhead imposed by quantum error correction itself. We propose a fault-tolerant quantum computing scheme that can nonetheless be assembled from a small number of experimental components, potentially dramatically reducing the engineering challenges associated with building a large-scale fault-tolerant quantum computer. Our scheme has a threshold of 0.39% for depolarising noise, assuming that memory errors are negligible. In the presence of memory errors, the logical error rate decays exponentially with $\sqrt{T/\tau }$, where $T$ is the memory coherence time and $\tau$ is the timescale for elementary gates. Our approach is based on a novel procedure for fault-tolerantly preparing three-dimensional cluster states using a single actively controlled qubit and a pair of delay lines. Although a circuit-level error may propagate to a high-weight error, the effect of this error on the prepared state is always equivalent to that of a constant-weight error. We describe how the requisite gates can be implemented using existing technologies in quantum photonic and phononic systems. With continued improvements in only a few components, we expect these systems to be promising candidates for demonstrating fault-tolerant quantum computation with a comparatively modest experimental effort.

27 pages, 13 figures; journal version

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• Realization of a Universal Quantum Gate Set for Itinerant Microwave Photons
• Deterministic generation of multidimensional photonic cluster states using time-delay feedback
• Performance analysis of quantum repeaters enabled by deterministically generated photonic graph states
• Universal Fault-Tolerant Quantum Computing with Stabiliser Codes
• Deterministic generation of qudit photonic graph states from quantum emitters
• 3-Fermion topological quantum computation
• Modular architectures to deterministically generate graph states
• Interleaving: Modular architectures for fault-tolerant photonic quantum computing
• Quantum Fourier transform on photonic qubits using cavity QED
• Generation of photonic tensor network states with Circuit QED
• Dark Exciton Giant Rabi Oscillations with no External Magnetic Field