Achieving Fault-Tolerant Quantum Computing with High-Fidelity Logical Magic States

In a recent study published in Physical Review Letters, researchers from the University of Science and Technology of China, the Henan Key Laboratory of Quantum Information and Cryptography, and the Hefei National Laboratory have successfully demonstrated the preparation of a logical magic state with fidelity beyond the distillation threshold on a superconducting quantum processor. This breakthrough brings us closer to realizing fault-tolerant quantum computing, which is crucial for solving complex optimization problems and advancing various fields.

Quantum computers have the potential to outperform conventional computers in certain tasks due to their ability to process information using quantum states. However, they are also susceptible to noise, which can lead to computational errors. To overcome this challenge, researchers have been exploring fault-tolerant quantum computing approaches that can withstand noise and be scaled up more robustly. One common approach to achieve fault-tolerance is the preparation of magic states, which introduce non-Clifford gates.

The researchers’ protocol for preparing high-fidelity logical magic states involves injecting the state to be prepared into one of the qubits in the surface code and then propagating the state information to the entire surface code. This approach allows for the preparation of logical states with high fidelity, which is essential for implementing non-Clifford logical gates and achieving fault-tolerant quantum computing.

To test their protocol, the researchers applied it to Zuchongzhi 2.1, a 66-qubit quantum processor with a tunable coupling design. This processor’s design allows for manipulation of the interaction between any two adjacent qubits, ensuring that quantum gates maintain high fidelity despite a high degree of parallelism. This design is also conducive to expanding the scale of qubits on a single processor.

When the researchers implemented their protocol on the Zuchongzhi 2.1 processor, they achieved promising results. They non-destructively prepared three logical magic states with logical fidelities of 0.8771±0.0009, 0.9090±0.0009, and 0.8890±0.0010, respectively. These fidelities are higher than the state distillation protocol threshold, which is 0.859 for H-type magic states and 0.827 for T-type magic states.

This milestone achieved by the researchers brings us closer to realizing fault-tolerant computing based on the surface code. It demonstrates that low-fidelity magic states can be fed into the magic state distillation circuit, undergo multiple distillations, and ultimately be used to construct fault-tolerant non-Clifford logical gates.

In the future, the protocol developed by the researchers could be utilized by other research teams to realize high-fidelity raw logical magic states using a broader range of superconducting quantum processors. This could contribute to the development of robust fault-tolerance quantum computing, which would enable the creation of larger-scale quantum computers.

The researchers plan to continue exploring two main research directions in the field of quantum error correction. First, they aim to enhance the performance of a logical qubit (or error-corrected quantum memory) by reducing the physical manipulation error rate and increasing the number of encoded qubits. This would help suppress the logical error rate to practical levels. Second, they will conduct experimental research on error-corrected logical operations, such as lattice surgery, for application in future fault-tolerant quantum computing.