Logical Magic State Preparation with Fidelity beyond the Distillation Threshold on a Superconducting Quantum...

Area of Science:

• Quantum Computing
• Quantum Error Correction
• Solid-State Physics

Background:

• Fault-tolerant quantum computing relies on error correction codes like the surface code for noise resistance.
• Universality in quantum computation requires non-Clifford gates, often achieved through magic state preparation.

Purpose of the Study:

• To present a hardware-efficient and scalable protocol for arbitrary logical state preparation for the rotated surface code.
• To experimentally implement this protocol on a superconducting quantum processor.

Main Methods:

• Development of a novel protocol for logical state preparation.
• Experimental implementation on the Zuchongzhi 2.1 superconducting quantum processor.
• Characterization of logical fidelities for prepared magic states.

Main Results:

• Achieved an average logical fidelity of 0.8983±0.0002 for distance-three logical states.
• Prepared logical magic states |A^{π/4}⟩_{L}, |H⟩_{L}, and |T⟩_{L} with fidelities 0.8771±0.0009, 0.9090±0.0009, and 0.8890±0.0010, respectively.
• Fidelities exceed established thresholds for state distillation protocols.

Conclusions:

• The presented protocol offers a viable and efficient method for generating high-fidelity raw logical magic states.
• This is essential for implementing non-Clifford logical gates within the surface code framework.
• The work paves the way for practical, large-scale fault-tolerant quantum computers.