Quantum walks on a programmable two-dimensional 62-qubit superconducting processor (2102.02573v3)

Abstract: Quantum walks are the quantum mechanical analogue of classical random walks and an extremely powerful tool in quantum simulations, quantum search algorithms, and even for universal quantum computing. In our work, we have designed and fabricated an 8x8 two-dimensional square superconducting qubit array composed of 62 functional qubits. We used this device to demonstrate high fidelity single and two particle quantum walks. Furthermore, with the high programmability of the quantum processor, we implemented a Mach-Zehnder interferometer where the quantum walker coherently traverses in two paths before interfering and exiting. By tuning the disorders on the evolution paths, we observed interference fringes with single and double walkers. Our work is an essential milestone in the field, brings future larger scale quantum applications closer to realization on these noisy intermediate-scale quantum processors.

• The paper demonstrates high-fidelity continuous-time quantum walks using a robust 62-qubit superconducting processor.
• It implements a Mach-Zehnder interferometer on the qubit array to verify coherent quantum state manipulation and non-local interference.
• Walker interactions in the multi-particle setup align with theoretical models, highlighting potential for scalable quantum information processing.

Quantum Walks on a Programmable 62-Qubit Superconducting Processor

The paper presents a significant advancement in quantum computing technology through the development and utilization of an 8x8 two-dimensional superconducting qubit array composed of 62 functional qubits. It presents groundbreaking work in quantum information processing by demonstrating high-fidelity quantum walks, both single and two-particle, and implementing a Mach-Zehnder interferometer on the superconducting platform. This work not only enhances the understanding of quantum mechanics but also provides a stepping stone for scalable quantum applications.

Technical Overview

Quantum walks (QWs) are the quantum analog of classical random walks and hold great promise for applications in quantum simulations, quantum transport, and quantum computing. The authors successfully fabricate and utilize a robust architecture of superconducting qubits, realizing a programmable QW system. The qubit array is designed with considerable attention to wiring solutions, employing techniques such as pass-through holes to address scaling challenges, which augments its real-time configurability.

The effective Hamiltonian of the system is described using the Bose-Hubbard model. The experimental setup allows for coherent control of the qubits for time-independent evolution, facilitating continuous-time quantum walks (CTQWs). Measurement of the system over several iterations demonstrates high-fidelity evolution, confirming the processor's capability for accurate state manipulation.

Key Experimental Achievements

1. Continuous-Time Quantum Walks: Single and two-walker QWs were demonstrated, with observed high correlation and agreement with numerical simulations. The team's methodology in tuning qubit frequencies achieved promising results in terms of walker propagation speeds, aligning with theoretical expectations governed by the Lieb-Robinson bounds.
2. Mach-Zehnder Interferometer: The researchers implemented an interferometer within the qubit array, navigating prescribed paths by altered frequency settings on qubits to demonstrate the coherence of quantum walkers. The interference fringes observed in experiments underscored the robustness of non-local correlations generated, which are critical for quantum computation.
3. Multiple Walkers and Walker Interaction: Two-particle quantum walks exhibited interference patterns similar to the single-particle setup, yet with additional complexities that open doors to further exploration in multi-particle quantum systems.

Implications and Future Directions

The insights obtained through this paper are multi-fold. Practically, the demonstrated control over superconducting qubit systems strengthens the case for using them in developing scalable quantum computers. The possibilities of tackling more complex quantum many-body simulations, quantum search algorithms, and the realization of universal quantum computation are significantly enhanced by this achievement.

The theoretical implications include enriched understanding of multi-walker quantum dynamics and interference employment in quantum computation—a frontier that could redefine computational complexity classes.

Looking forward, further developments could include increasing qubit numbers, thereby expanding computational capabilities and addressing challenges such as error rates and coherence times. It is plausible that this work will catalyze technological developments in quantum gate speeds, error correction, and the precise encoding of quantum algorithms, all of which hold promise for a future where quantum computing unleashes its full potential.