Design Considerations for Near-term Quantum Processors

Sami Rosenblatt, Jared Hertzberg, José Chavez-Garcia +9 more

He-Liang Huang, Youwei Zhao, Chu Guo

Quantum computational advantage is a critical milestone for near-term quantum technologies and a crucial step toward building practical quantum computers. Recent successful demonstrations of quantum computational advantage owe much to specially designed random quantum circuit (RQC) protocols that enable hardware-friendly implementation and, more importantly, pose great challenges for classical simulation. Here, we report an automated protocol-design approach for determining the optimal RQC in the Zuchongzhi quantum computational advantage experiment. Without a carefully designed protocol, the classical simulation cost of the Zuchongzhi 56-qubit 20-cycle RQC experiment would not be considerably higher than Google’s 53-qubit 20-cycle experiment, even though more qubits are involved. For Google’s latest RQC experiment using 70 qubits and 24 cycles, we estimate that the classical simulation cost can be increased by at least one order of magnitude using the proposed approach. The proposed method can be applied to generic planar quantum processor architectures and addresses realistic imperfections such as processor defects, underpinning quantum computational advantage experiments in future generations of quantum processors.

Thi Ha Kyaw, Tim Menke, Sukin Sim +5 more

With the increasing size of quantum processors, submodules that constitute the processor hardware will become too large to accurately simulate on a classical computer. Therefore, one would soon have to fabricate and test each new design primitive and parameter choice in time-consuming coordination between design, fabrication, and experimental validation. Here we show how one can design and test the performance of next-generation quantum hardware---by using existing quantum computers. Focusing on superconducting transmon processors as a prominent hardware platform, we compute the static and dynamic properties of individual and coupled transmons. We show how the energy spectra of transmons can be obtained by variational hybrid quantum-classical algorithms that are well suited for near-term noisy quantum computers. In addition, single- and two-qubit gate simulations are demonstrated via Suzuki-Trotter decomposition. Our methods pave a promising way towards designing candidate quantum processors when the demands of calculating submodule properties exceed the capabilities of classical computing resources.

Jernej Rudi Finžgar, Christian B. Mendl, Technische Universität München

Alessandro Baroni

Alexander McCaskey, Eugene Dumitrescu, Dmitry Liakh +3 more

Heterogeneous high-performance computing (HPC) systems offer novel architectures accommodating specialized processors that accelerate specific workloads. Near-term quantum computing technologies are poised to benefit applications as wide-ranging as quantum chemistry, machine learning, and optimization. A novel approach to scale these applications with future heterogeneous HPC is to enhance conventional computing systems with quantum processor accelerators. We present the eXtreme-scale ACCelerator programming model (XACC) to enable near-term quantum acceleration within existing conventional HPC applications and workflows. We design and demonstrate the XACC programming model within the C++ language by following a coprocessor machine model akin to the design of OpenCL or CUDA for GPUs. However, we take into account the subtleties and complexities inherent to the interplay between conventional and quantum processing hardware. The XACC framework provides a high-level API that enables applications to offload computational work represented as quantum kernels for execution on an attached quantum accelerator. Our approach is agnostic to the quantum programming language and the quantum processor hardware, which enables quantum programs to be ported to multiple processors for benchmarking, verification and validation, and performance studies. This includes a set of virtual numerical simulators as well as actual quantum processing units. The XACC programming model and its reference implementation may serve as a foundation for future HPC-ready applications, data structures, and libraries using conventional-quantum hybrid computing.