In this section we will focus on the history, state of the art, and future of universal gate quantum computing, as it is the model used for IBM QX and the focus of this book.
Quantum computing has made great strides in recent years but it is not a new idea. Quantum physics was developed in the 1920s and 1930s. In the early 1980s, physicist Richard Feynman encouraged computer scientists to develop new models of computation based on quantum physics, which showed the promise of performing computation in a different and more efficient manner. In the 1990s, the field of quantum computing progressed when the first algorithms were developed that could run more efficiently on quantum computers than on classic computers. In the 2000s, practical quantum computers began to be able to implement some of the theoretical algorithms from the 1990s for very small inputs.
Important historical developments in quantum computing include:
- Feynman's introduction of quantum computing (1981-1982)
- The demonstration that quantum computing can perform better than classic computing (1985)
- Shor's algorithm (1994)
- Quantum error correction (1995)
- Grover's algorithm (1996)
- The quantum threshold theorem (1999)
- Cross pollination from different quantum computing systems in recent years
At the time of writing this book, IBM offers a 5-qubit and 16-qubit computer available in the cloud via IBM QX and has a 50-qubit quantum computer available to research partners and a 100-qubit quantum computer under way. Rigetti Computing offers an 8-qubit device. While these computers currently demonstrate interesting principles of quantum computation and allow for prototyping and testing algorithms, they are not yet large enough in terms of qubit size and robust enough to exhibit quantum supremacy.
At the time of this book's writing, IBM estimates that exhibiting quantum supremacy for a specialized application should be possible with 50-100-qubits. This should happen in the near future. Demonstrating quantum supremacy for one specialized application is different to being able to realize the full potential of quantum computing. To have truly useful quantum computers across a variety of fields with universal gate quantum computers, the quantum computing hardware must advance to incorporate more qubits that work together robustly for a longer period of time. Many of these qubits will not be used in the core computation, but rather for error correction to deal with errors introduced by the environment during the course of computation.
The outlook for quantum computing going forward is a topic of debate, and some experts argue it's difficult to predict. Some ideas about where quantum computing is heading in the near future include:
- Hybrid quantum systems that are made of different quantum computing techniques
- Continued steady progress in hardware and big leaps in quantum algorithms
- Real world practical applications
In the far future, we may see these advances enabling large quantum computers, and encouraging their wide-scale use.
The big near term milestones will be a demonstration of quantum computational supremacy (performing a computation on a quantum processor that takes much longer to compute using conventional high-performance computing), a demonstration of quantum advantage (demonstrating that a quantum processor can perform a -useful- computation faster than conventional computing resources) and a demonstration of fault-tolerance with active error correction. I would expect each of these to occur within the next ten years, and probably within the next five. The demonstration of quantum computational supremacy is likely to be the first to occur, and is likely within the next two years. Within fifty years, I would certainly expect quantum computers to be much more similar to todays computer architectures in terms of having multiple components dedicated to different functions (processing, storage, communication) and in terms of being used as general purpose computing devices rather than single purpose co-processors.
– Dr. Joe Fitzsimons, Principal Investigator, Centre for Quantum Technologies; Founder, Horizon Quantum Computing