A Quantum Processing Unit (QPU), also known as a quantum processor or quantum computer, is a specialized coprocessor that processes information according to the laws of quantum mechanics. Analogous to a Graphical Processing Unit (GPU), it is designed to solve specific problems faster or with fewer resources than other types of processors.
A QPU is similar to a Central Processing Unit (CPU), but uses qubits which pass through quantum gates that encode a particular computation before being measured. Since qubits obey different rules than classical bits, the design of quantum algorithms is radically different from classical algorithms.
The range of tasks for which a QPU is well suited for in the long-term is finding elements in unstructured data, computing the electronic structure of molecules, factoring integers into prime numbers, solving specific systems of linear equations, estimating determinants, simulating classical nonlinear dynamics, etc.
There are several modalities for building a quantum processing unit. Some architectures use the energy levels of atoms or superconducting systems to encode quantum information, while others rely on the spatial degrees of freedom of photons. Each of these technologies has its own advantages and limitations.
Frequently asked questions
- What is the most powerful QPU?
There is a wide variety of QPU modalities, therefore it is hard to compare them. As a matter of fact, benchmarking a QPU is a wide research topic. A way to compare them could be counting their number of qubits, but it overlooks many things as error rates, connectivity, clock rate. Other proposals were made but none has been consensually accepted.
- How can I access a QPU?
Many QPU vendors make them available on cloud facilities. It is the case for Quandela and you may find Quandela QPUs on cloud.quandela.com.
- Are they being used in production by companies today?
There have been many proofs of quantum computing supremacy or quantum computing advantage but never for industry relevant cases. Therefore, there are no quantum computing algorithm in production today. Nonetheless, quantum advantage for other information processing tasks were demonstrated and put in production. As it is the case for the generation of certified quantum random numbers.