TAKEAWAY: The Patent Trial and Appeal Board recently decided that claims directed to solving certain equations using a hybrid quantum-classical computer system represented patent-eligible subject matter.
In Ex parte Yudong Cao, Appeal 2024-002159 (Feb. 13, 2025), the Patent Trial and Appeal Board (the “Board”) concluded that a method for solving a linear system of equations using a hybrid quantum-classical computer system amounted to a technological improvement, and therefore patent-eligible subject matter under 35 U.S.C. § 101.
The instant application (App. No. 16/591,239, “the ’239 Application”) relates to a hybrid quantum-classical (HQC) computer system that includes a classical computer and a quantum computer for solving a linear system of equations. The application discloses that during operation, the HQC computer system splits the linear system to be solved into subsystems that are small enough to be solved by the quantum computer, under the control of the classical computer. The classical computer synthesizes the outputs of the quantum computer to generate the complete solution to the linear system. During prosecution, the Examiner determined that the claims of the ’239 Application were directed to the abstract idea of mathematical relationships, and did not represent patent-eligible subject matter under 35 U.S.C. § 101. More specifically, under Step 2A, Prong 2 of the 2019 Revised Patent Subject Matter Eligibility Guidance, 84 Fed. Reg. 50 (Jan. 7, 2019), the Examiner determined that the additional element of “on a quantum computer, controlling a plurality of qubits, according to the set of circuit parameters… to prepare a quantum state…” in claim 1 was an attempt to limit the abstract idea to a particular field of use or technological environment, which did not integrate the abstract idea into a practical application or amount to significantly more than the abstract idea. The Applicant appealed the Examiner’s rejection of the application.
The Board reversed the rejection, concluding that the additional element represented “the focus of the invention,” and “integrate[d] the recited abstract idea into a practical application.” That is, the Board determined that “the additional element integrate[d] the abstract idea of mathematical relationships into a practical application of enabling noisy quantum computers, which have limited circuit depth, to practically solve linear systems—a technology improvement.” To support its decision, the Board referenced the specification of the ’239 Application, which describes that existing techniques for using quantum computers to solve linear systems cannot be implemented on current quantum computers (e.g., HQC computer systems), which are noisy and have low circuit depths.
This decision provides patent practitioners with an example of patent-eligible subject matter in the context of HQC computer systems. In view of the decision, patent practitioners may seek to clearly set forth the deficiency in the prior art that the claimed invention addresses and explicitly provide the technical improvement of the claimed invention to demonstrate the patent-eligible subject matter claimed.