OQTOPUS: Open Quantum Toolchain

• OQTOPUS is an open-source quantum platform that standardizes the full lifecycle from circuit design to quantum hardware execution.
• It utilizes a modular, microservice-based architecture featuring server-side transpilation, multiprogramming, and real-time error mitigation for efficient operations.
• Transparent software publication and community contributions drive collaborative innovation and accelerate standardization in quantum computing ecosystems.

OQTOPUS (Open Quantum Toolchain for OPerators and USers) is a full-stack, open-source quantum computing software platform designed to provide a transparent, standardized, and efficient software environment for both quantum system operators and end-users. It addresses the lack of accessible and disclosed operational software near quantum computers—an issue that, if unaddressed, slows ecosystem development and impedes progress toward standardized, supercomputer-scale quantum systems. With its openly published entire software stack, OQTOPUS enables community-driven quantum computing advancement by lowering technical barriers for research institutes, commercial providers, and developers (Kakuko et al., 31 Jul 2025).

1. System Architecture and Design

OQTOPUS is architected as a comprehensive operational software stack encompassing the full lifecycle of quantum computation—from remote job submission, through cloud-based orchestration, to execution on quantum hardware. The system is organized into a modular, microservice-based backend residing in proximity to the quantum hardware and a user-facing frontend accessible via cloud interfaces.

Component	Functionality	Location
OQTOPUS Frontend	Circuit composer, code editor, submissions	User environment
OQTOPUS Cloud	Job and user management (serverless/AWS)	Centralized cloud
OQTOPUS Engine	Job scheduling, transpilation, error mitigation	Backend (near hardware)
Tranqu Server	Transpiler microservice via gRPC	Backend
Device Gateway	OpenQASM3 parsing, virtual/physical qubit mapping	Backend
Quantum Processor Control	Direct quantum processor and pulse control	On-premises

Features such as the server-side transpiler, job multiprogramming, and error mitigation modules are implemented within the backend facility, enabling real-time interactions with the quantum hardware and the ability to react dynamically to evolving device conditions.

2. Key Features Implemented Near Hardware

A defining aspect of OQTOPUS is the implementation of mission-critical services as close as possible to the quantum device. This strategy enables:

• Server-Side Transpilation: User-generated quantum circuits are optimized and converted to device-compatible representations in the backend. The use of microservices, such as the Tranqu Server (interfaced by gRPC), allows for scalable integration of multiple transpiler technologies. This proximity to hardware ensures up-to-date awareness of device topology and gate fidelity during optimization.
• Multi-Programming: OQTOPUS supports aggregation of distinct user circuits into a composite circuit. This approach increases quantum processor throughput and utilization by executing multiple workloads in parallel—crucial for efficient use of large-scale and costly quantum chips.
• Server-Side Execution: Hybrid quantum-classical algorithms can be executed on the provider's server, reducing client-server latency and eliminating the need for repeated client-side circuit submission. This capability is especially relevant for algorithms (such as the Variational Quantum Eigensolver) demanding multiple quantum-classical feedback iterations.
• Error Mitigation: Automated mitigation routines use a Qiskit 1-qubit tensor product readout scheme. Calibration and mitigation strategies adjust according to real-time characterization of the hardware, allowing more reliable quantum expectation value estimation under operational noise and readout errors.

These features collectively shift operational complexity from the client onto robust, scalable infrastructure located at the quantum processor site, increasing efficiency and reliability.

3. Open-Source Scope and Community Model

OQTOPUS is identified as one of the largest open-source software projects in quantum computing, publishing its complete stack—including modules rarely disclosed by other providers—on public code repositories. This transparency:

• Facilitates participation by organizations wishing to develop or operate quantum computing services.
• Promotes rapid troubleshooting, extension, and peer review by the global research and developer community.
• Accelerates the pace of standardization by providing shared software components and detailed documentation for key functionalities (job scheduling, transpilation, error mitigation, cloud orchestration).

By lowering onboarding and operational barriers, OQTOPUS enables institutions to prototype, deploy, and maintain quantum computing systems without needing proprietary vendor software.

4. Job Types and Experimental Demonstrations

OQTOPUS supports a diverse set of quantum computational workloads, demonstrated on a superconducting quantum computer at Osaka University.

• Sampling Job: Users submit a quantum circuit (composed, for instance, of Hadamard and CNOT gates) through the OQTOPUS API. Following backend transpilation (OpenQASM 3), results are visualized as histograms of bitstring outcomes, confirming correct backend integration and circuit execution.
• Estimation Job: Users request the estimation of an observable, e.g., ⟨H⟩ for Hamiltonian $H = 1.5\,XX + 1.2\,YZ$. The backend decomposes $H$ into Pauli operators ($P_i$), collects measurement statistics, and displays the expectation value:

$\langle H \rangle = \sum_i c_i \langle P_i \rangle$

Error mitigation is applied in real time, and repeated sampling for uncertainty estimation does not require client-side job resubmission. The system produces intuitive outputs (e.g., ⟨H⟩ ≈ 0.0282), demonstrating correct expectation value processing.

These use cases confirm the connectivity of the entire stack—from GUI-level circuit composition, through cloud job management, to device-specific transpilation and execution—enabling reproducible results on real quantum hardware.

5. Impact on Standardization and Ecosystem Development

OQTOPUS addresses the need for standardization in quantum cloud computing by openly publishing all layers of its operational infrastructure. Its modular, microservice-based design allows for straightforward integration of alternative transpilers, schedulers, or calibration protocols. This transparency enables:

• Cross-institutional and industrial collaboration on shared code infrastructure.
• Accelerated convergence toward best practices in cloud quantum systems.
• A template for quantum system development that can be adopted or adapted for future platforms.

By removing traditional barriers of proprietary backend software, OQTOPUS plays a central role in fostering a broad, well-supported developer and operator community.

6. Future Directions

The ongoing development of OQTOPUS includes:

• Expansion of the supported transpiler set within Tranqu (the transpiler microservice).
• Automatic multiprogramming enhancements (such as batch aggregation of requested circuits from multiple users).
• Open-source publication of systems for quantum device control and real-time system monitoring to further support research and operational transparency.

These improvements aim to support calculations at the scale of supercomputing resources and to establish OQTOPUS as a reference implementation for future quantum computing system design and operation. The commitment to open-source, community-driven development is a central tenet and is expected to enable continued growth of a robust, collaborative quantum computing ecosystem (Kakuko et al., 31 Jul 2025).