Why we need hybrid classical-quantum computing?
In the history of computation, new technological advancements have usually completely replaced the old ones. For instance, in the first half of the 20th century a slide rule was in the pocket of every engineer, but it became obsolete with the widespread adoption of electronic pocket calculators.
Our current computing devices are based on semiconductor technology. It is believed that quantum computers will be the next big advancement in computing technology.
So, are we soon going to leave our laptops on a desk to gather dust? Is the next transformation going to be as total as those before?
The computational landscape is currently evolving vigorously, with classical computers (i.e. normal computers) displaying immense power while quantum computers, though groundbreaking, are relatively small and influenced by noise. In the near term, the advantage of quantum computers may be limited to very specific computational tasks.
The strength of classical computers lies in their robustness and maturity, having been developed over several decades.
The quantum computers will need classical computers
Hybrid computing refers to a computational approach that combines elements from different technologies to improve the overall performance.
The rough idea in hybrid classical-quantum computation is that quantum capabilities are used in specific parts of computation and classical computing takes care of the rest. The objective is to optimize performance and achieve solutions that would be unattainable with either technology in isolation.
Hybrid classical-quantum computation is not just an intermediate phase.
Even if quantum computers will become bigger and more powerful, they will need classical computers. A quantum computer uses two-level quantum systems, called qubits, to store and process information.
Quantum systems are highly sensitive and susceptible to disturbances, requiring precise management to maintain coherence. A large-scale quantum computer will consists of thousands of qubits. Therefore, those qubits need a fair amount of control, calibration, and tuning. Classical computers excel in controlling and stabilizing these fragile quantum systems. They can handle the intricate control of quantum bits, enabling quantum computers to focus on quantum algorithms essential for computation.
In this sense, quantum computing will always be hybrid computing.
Maximizing the strengths of both technologies
Perhaps the most essential point related to hybrid computing is to recognize that quantum computers are not intended to replace conventional computers but rather augment them. Quantum computers are positioned to function as quantum processing units (QPUs) that enhance specific aspects of computation.
By integrating quantum processors into classical computer architectures, we can create a hybrid system that maximizes the strengths of both technologies.
Classical computers offer versatility, manageability, and efficiency in handling everyday tasks, while quantum processors will bring unparalleled potential for solving some complex problems exponentially faster.
It is not expected that quantum computing will outperform classical computing in all computational tasks. Rather, the set of problems with a quantum advantage can be quite limited, but it is likely to include some important problems related e.g. to optimization and material simulations.
Hybrid classical-quantum computing has the potential to revolutionize various industries, advance scientific discovery, and address challenges that were once deemed insurmountable.
Classical and quantum computing paradigms must lean on each other, and in the same way the respective research areas should have a supportive and mutually beneficial relationship. At the very least, classical and quantum computing research should be in a friendly competitive mode and boost each other to find solutions that benefit an end-user.
But they can also be in a much deeper symbiotic relationship.
Already the division of a computational task into suitable sub-tasks tailored for classical and quantum computers requires deep knowledge of the strengths and weakness of both technologies and expertise to compare them. Algorithms and software must take into account both classical and quantum parts, and be able to fluently merge them together.
To truly make the hybrid classical-quantum computation as the next influential step in computation, collaborative efforts are needed from computer scientists, software developers and quantum physicists.
The writer Teiko Heinosaari works as a professor in quantum computing at the Faculty of Information Technology.
