Abstract
The ability to detect and deal with errors when manipulating quantum systems is a fundamental requirement for fault-tolerant quantum computing. Unlike classical bits that are subject to only digital bit-flip errors, quantum bits are susceptible to a much larger spectrum of errors, for which any complete quantum error-correcting code must account. Whilst classical bit-flip detection can be realized via a linear array of qubits, a general fault-tolerant quantum error-correcting code requires extending into a higher-dimensional lattice. Here we present a quantum error detection protocol on a two-by-two planar lattice of superconducting qubits. The protocol detects an arbitrary quantum error on an encoded two-qubit entangled state via quantum non-demolition parity measurements on another pair of error syndrome qubits. This result represents a building block towards larger lattices amenable to fault-tolerant quantum error correction architectures such as the surface code.
Highlights
The ability to detect and deal with errors when manipulating quantum systems is a fundamental requirement for fault-tolerant quantum computing
Quantum computers are susceptible to errors as quantum systems are highly sensitive to noise effects that can be exotic compared with the simple bit-flip errors of classical computation
Each code qubit in the surface code (SC) is coupled with two X-syndrome qubits and two Z-syndrome qubits, and, in turn, each syndrome qubit is coupled with four code qubits
Summary
The ability to detect and deal with errors when manipulating quantum systems is a fundamental requirement for fault-tolerant quantum computing. The protocol detects an arbitrary quantum error on an encoded two-qubit entangled state via quantum non-demolition parity measurements on another pair of error syndrome qubits. This result represents a building block towards larger lattices amenable to fault-tolerant quantum error correction architectures such as the surface code. The non-demolition nature of the protocol is verified by demonstrating the preservation of the entangled state constituting the codeword through high-fidelity syndrome measurements in the presence of an arbitrary applied error These error detection experiments constitute a key milestone for SC implementation, as our operations extend into the plane of the two-dimensional surface and we show the ability to concurrently perform bit- and phase-parity checks. Our results bolster the prospect of employing superconducting qubit lattices for large-scale fault-tolerant quantum computing
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