Michael E. Byczek

*Attorney at Law*

The CPC (Cooperative Patent Classification) is a joint partnership between the USPTO (United States Patent and Trademark Office) and European Patent Office (EPO).

There are two primary components of the CPC. The "scheme" is a broad overview of each classification group. The "definitions" provide a detailed description.

For example, quantum computers have its own CPC classification under the Physics scheme (G).

G06 is titled "COMPUTING; CALCULATING OR COUNTING"

G06N is titled "COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS".

The definitions for G06N provide the most detailed way to classify a patent. Examination of the definitions for G06N show the following:

Quantum computing, i.e. information processing based on quantum-mechanical phenomena.

Computation performed by a combination of atomic or subatomic particles where the interactions are no longer described by macroscopic physics but by the theory of quantum mechanics.

Models of quantum computing, e.g. quantum circuits or universal quantum computers.

Models or logical architectures, as opposed to the hardware architectures covered by group G06N 10/40, of quantum computing, independent of whether or not a physical realisation is also disclosed. In particular, general logical/physical models of quantum computing, e.g. related to quantum circuit, are classified in group G06N 10/20.

The physical realisations of a specific model (see examples below) are classified in both G06N 10/20 and G06N 10/40.

A "quantum circuit" is a sequence of quantum logic gates, e.g. quantum gate array, quantum register or quantum random access memory. It should be noted that these are terms of art representing quantum models and should not be confused with physical circuit versions, e.g. electrical circuitry, in general. Quantum circuits are typically obtained via "quantum circuit synthesis", "quantum circuit decomposition" or "quantum compilers" (also not to be confused with "classical" compilers).

Typical examples of quantum gates: Clifford gates, controlled gates, e.g. cX, cY, cZ, CNOT, Hadamard gate, Pauli-X/Y/Z gates, SWAP gate, T gate, i.e. pi/8, Toffoli gate, i.e. CCNOT, Deutsch gate, Ising XX/YY/ZZ coupling gates, phase shift gates.

Other typical models of quantum computing: adiabatic quantum computation [AQC], topological quantum computing, quantum simulations, e.g. universal quantum simulator, quantum state machines, quantum cellular automata, quantum Turing machines [QTM]. Models wherein the units of quantum information are based on d-level quantum systems (qudits), e.g. using qutrits (d=3).

Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control.

Physical realisations or hardware architectures, as opposed to the logical architectures covered by group G06N 10/20 for quantum computing, independent of whether or not a model of quantum computing is also disclosed. Executing models of quantum computing on a specific physical realisation (see examples below) are classified in both G06N 10/20 and G06N 10/40.

Physical realisations typically fall in one of the following categories: superconducting quantum computers, e.g. based on charge qubits, flux qubits, phase qubits, Transmon, Xmon, trapped ion/atom quantum computers, e.g. based on Paul ion trap, optical lattices, spin-based quantum computers, e.g. based on quantum dots, NMR, NMRQC, nitrogen-vacancy centres, fullerenes, Kane or Loss- DiVincenzo quantum computers, based on quantum optics, e.g. linear optical quantum computers.

Examples of quantum components and qubit manipulations: qubit coupling, control or readout, storing quantum states, quantum processor, quantum bus, quantum memory, quantum network (for computations), quantum repeater (for computations).

Quantum algorithms, e.g. based on quantum optimisation, quantum Fourier or Hadamard transforms.

All quantum algorithms and not limited to, e.g. quantum optimisation (see examples below). In particular, quantum computing algorithms for specific problems, e.g. NP problem, are classified in group G06N 10/60. Algorithms based on quantum optimisation also includes so-called "hybrid quantum-classical algorithms". The physical realisations of a specific algorithm (see example below) are classified in both G06N 10/40 and G06N 10/60.

Quantum algorithms typically fall in one of the following categories:

- based on amplitude amplification, e.g. Grover's algorithm;

- based on Fourier or Hadamard transforms, e.g. Shor's algorithm, Simon's algorithm, Deutsch- Josza algorithm, quantum phase estimation algorithm [QPEA] or quantum eigenvalue estimation algorithm;

- quantum optimisation, e.g. quantum annealing, Ising machines, variational quantum eigen-solver [VQE], quantum alternating operator ansatz [QAOA], quantum approximate optimisation algorithm, including hybrid quantum-classical algorithms, e.g. quantum machine learning, machine learning based quantum algorithms;

- quantum walks.

Quantum error correction, detection or prevention, e.g. surface codes or magic state distillation

Arrangements to achieve fault-tolerant quantum computations. Typical solutions rely on the introduction of ancillary, i.e. additional or auxiliary qubits, such as stabiliser codes, but this place also covers ancilla-free solutions, i.e. no additional qubit necessary. Other examples: bit flip codes, sign flip codes, Shor code, topological codes, e.g. surface codes, planar codes, toric codes.

Arrangements for assessing the quality of quantum computers, whether characterised by a metrics or figure of merits, e.g. quantum fidelity, quantum volume, quantum purity, error rate, or by its calculation or measurement, e.g. randomized benchmarking [RB], cross-entropy benchmarking [CEB], random circuit sampling [RCS].

Quantum programming, e.g. interfaces, languages or software-development kits for creating or handling programs capable of running on quantum computers; Platforms for simulating or accessing quantum computers, e.g. cloud-based quantum computing

All arrangements for quantum programming, such as quantum instruction sets, quantum software development kits, or quantum programming languages. Typical examples: Quil, Qiskit, or QCL.

Platforms for simulating or accessing the quantum computers, such as cloud-based quantum computing. Typical examples: IBM Q Experience, Quantum Inspire, Azure Quantum, Amazon Braket, Rigetti Quantum Cloud Services, Quantum Playground.

The USPTO Patent Public Search Tool (https://ppubs.uspto.gov/pubwebapp/static/pages/landing.html) lets you search by CPC classification numbers.

The way to search for CPC G06N 10/00 is "G06N10/00.cpc.". Another way is "G06N 10/00". However, the 2nd format may not reveal all patents that have been classified according to that number.

The number of published patents for each classification is shown below. To conduct a patent search, the reviewer needs to examine every patent for these classifications. This is why it's important to narrow down how an invention works to avoid having to read hundreds or thousands of patents.

The following search results are listed in this format (i.e.): "G06N10/00.cpc" / "G06N 10/00".

G06N 10/00: 6,175 / 1,683

G06N 10/20: 769 / 97

G06N 10/40: 1,320 / 116

G06N 10/60: 627 / 60

G06N 10/70: 396 / 48

G06N 10/80: 355 / 39

Using quantum computers and the CPC as an example, there are 9,642 patents that have been classified according to quantum computers as defined by the CPC. It's possible that not all these patents are actually based on quantum computers. It's also not practical to read almost 10,000 patents to conduct a technical analysis that compares a new invention against those that have already been filed with the USPTO.

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