Fault-Tolerant Code Switching Protocols for Near-Term Quantum Processors

Abstract

Topological color codes are widely acknowledged as promising candidates for fault-tolerant quantum computing. Neither a two-dimensional nor a three-dimensional topology, however, can provide a universal gate set $\{$H, T, CNOT$\}$, with the T-gate missing in the two-dimensional and the H-gate in the three-dimensional case. These complementary shortcomings of the isolated topologies may be overcome in a combined approach, by switching between a two- and a three-dimensional code while maintaining the logical state. In this work, we construct resource-optimized deterministic and non-deterministic code switching protocols for two- and three-dimensional distance-three color codes using fault-tolerant quantum circuits based on flag-qubits. Deterministic protocols allow for the fault-tolerant implementation of logical gates on an encoded quantum state, while non-deterministic protocols may be used for the fault-tolerant preparation of magic states. Taking the error rates of state-of-the-art trapped-ion quantum processors as a reference, we find a logical failure probability of $3\%$ for deterministic logical gates, which cannot be realized transversally in the respective code. By replacing the three-dimensional distance-three color code in the protocol for magic state preparation with the morphed code introduced in [1], we reduce the logical failure rates by two orders of magnitude, thus rendering it a viable method for magic state preparation on near-term quantum processors. Our results demonstrate that code switching enables the fault-tolerant and deterministic implementation of a universal gate set under realistic conditions, and thereby provide a practical avenue to advance universal, fault-tolerant quantum computing and enable quantum algorithms on first, error-corrected logical qubits.

27 pages, 22 figures

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Cited by in corpus (14)

• Automated Synthesis of Fault-Tolerant State Preparation Circuits for Quantum Error Correction Codes
• Experimental Demonstration of High-Fidelity Logical Magic States from Code Switching
• Code switching revisited: Low-overhead magic state preparation using color codes
• Lift-Connected Surface Codes
• Efficient fault-tolerant code switching via one-way transversal CNOT gates
• Quantum Circuit Discovery for Fault-Tolerant Logical State Preparation with Reinforcement Learning
• Efficient fault-tolerant implementations of non-Clifford gates with reconfigurable atom arrays
• Synchronization for Fault-Tolerant Quantum Computers
• Contextuality of Quantum Error-Correcting Codes
• Experimental measurement and a physical interpretation of quantum shadow enumerators
• Efficient simulation of logical magic state preparation protocols
• Measurement-free code-switching for low overhead quantum computation using permutation invariant codes
• Weakly Fault-Tolerant Computation in a Quantum Error-Detecting Code
• Universal quantum computation via scalable measurement-free error correction