Researchers ask industry for heterogeneous systems that blend quantum computing and classical computing

Questions and answers:

• What is the main goal of DARPA's HARQ program? To develop heterogeneous quantum computing architectures to overcome the scalability limitations of homogeneous single-qubit systems and enhance future quantum computing, sensing, and communications.
• What are the two technical focus areas of the HARQ program? MOSAIC, which focuses on quantum circuit compilers and software for heterogeneous systems; and QSB, which addresses interconnect technologies to link different qubit species.
• Why are heterogeneous architectures important in quantum computing? They combine different types of quantum and classical components to optimize performance, and offer greater scalability and efficiency than do homogeneous systems that rely on only one type of qubit.

ARLINGTON, Va. – U.S. military researchers are asking industry to develop heterogeneous quantum computing architectures for future applications of quantum computing, quantum sensors, and quantum communications.

Officials of the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., issued a program solicitation (DARPA-PS-25-31) for the Heterogeneous Architectures for Quantum (HARQ) program.

The principal objective of HARQ program is to establish a new heterogeneous quantum computing paradigm that eliminates the constraints of homogeneous single-qubit systems.

The scaling limitations of homogeneous quantum computing architectures are expected to limit the size and computational power of these complex systems. Using optimal qubits for computational functions could unlock scalability to applications in materials, chemistry simulation, and biological modeling. HARQ will test whether heterogeneous architectures are more scalable than homogeneous architectures.

Quantum interconnects

Researchers particularly are interested in quantum interconnects, quantum circuit compilers, distributed algorithms, resource estimation, quantum memory and repeaters, quantum frequency converters, microwave-to-optical transducers, and other elements at the interface of the quantum computing hardware and software stack.

Heterogeneous quantum computing architectures either combine different types of quantum components, or integrate quantum and classical computing to optimize overall performance and overcome the limitations of homogeneous quantum devices.

Heterogeneous quantum computing architectures can include quantum components optimized for different roles; integrating classical and quantum resources; layered and modular design; co-design and hardware-aware error correction; and systematic design frameworks and toolboxes.

While large-scale quantum computers offer revolutionary capability, attention today focuses on homogeneous architectures that are designed around one qubit species. Classical computing, on the other hand, relies on diverse specialized approaches for optimal performance in processing, memory, and communications.

Tell me more about why the military is interested in quantum computing ... 

• The military is interested in quantum computing for its potential game-changing capabilities in defense and national security applications in cryptography and cyber security; artificial intelligence (AI) and machine learning; quantum sensing and navigation; mission planning and resource allocation; sensor placement and routing autonomous uncrewed aircraft; chemical detection; modeling nuclear or other advanced weapon systems; target recognition; decision support systems; detecting stealth aircraft and submarines; and GPS-independent navigation.

The power of modern-day systems like supercomputers, smart phones, and radar comes from the ability to select the best components for every function, and to move data quickly and efficiently between them. Qubit computers excel at select processing, memory, and communications functions, yet no known qubit excels at all compute functions.

Military quantum computing refers to the use of quantum computing technology by defense and military organizations to revolutionize their computing capabilities and operations. Quantum computers process information using quantum bits (qubits) instead of classical bits, enabling them to perform complex calculations and handle vast amounts of data much faster and more efficiently than traditional computers.

The HARQ program seeks to eliminate the constraints of homogeneous, single-qubit computers, test whether they are more scalable than homogeneous architectures, and demonstrate component-level innovations.

HARQ has two technical areas: multi-qubit optimized software architecture through interconnected compilation (MOSAIC); and Quantum Shared Backbone (QSB).

Modeling, simulation, and software

MOSAIC will drive theory, modeling, simulation, and software development to develop heterogeneous quantum circuit compilers that optimize resource allocations among diverse qubit species. QSB focuses on interconnect technologies to communicate among different qubit species.

Companies interested should submit abstracts no later than 28 Aug. 2025 and proposals no later than 14 Oct. 2025 to the DARPA BAA Tool online at https://baa.darpa.mil. Companies must submit abstracts before submitting proposals. Those submitting promising proposals will be asked to give oral presentations to DARPA between 22 Oct. and 4 Nov. 2025. The project should begin on 1 Feb. 2026.

Email questions or concerns to DARPA no later than 1 Oct. 2025 at [email protected]. More information is online at https://sam.gov/opp/944007d554364a1aad811469028a7e73/view.