New disruptive technology is promising to take the power of computing to unprecedented heights. And for predicting the speed of the progress of “quantum computing” technology, Hartmut Neven, director of Quantum AI Labs of Google has given the proposal of a new rule for quantum computers that is similar to Moore’s Law which measured the progress of normal computers for more than 50 years. But the question is if “Neven’s Law” can be trusted as an actual representation of what is occurring in quantum computing and what will be the situation in the future.
Quantum computers use physical systems for storing data unlike the normal computers which store data as electrical signals having either of 0 or 1 state. This helps in encoding information in multiple states that allows exponentially faster calculations than the normal computers. It is still in infancy and a quantum computer has not been built yet which crosses the existing supercomputers. There is some skepticism about its progress however there is also excitement now how quick the progress is occurring. Thus it would be helpful to have an idea of what can be expected from quantum computers in future.
Moore’s law describes that the processing power of normal digital computers to double almost every two years creating exponential growth. It is named after Gordon Moore, Intel co-founder and it accurately describes the rate of increase in the transistor number which can be integrated into a silicon microchip. Moore’s law is not applicable to quantum computers as they are designed differently on basis of laws of quantum physics. This is where Neven’s law states that quantum computing power is experiencing doubly exponential growth relative to normal computing.
Doubly exponential growth increases in powers of powers of two: 2^2 (4), 2^4 (16), 2^8 (256), 2^16 (65,536) and so on. If this was applicable to normal computers in Moore’s law, then smartphones and computers would have been present by 1975. Neven hopes that this fast pace should lead to quantum advantage where the smaller quantum processors overtake the highly powerful supercomputers.
Neven said that researchers at Google can decrease the error rate in the prototypes of quantum computers, allowing them to build more complex and powerful machines with every iteration. This progress is exponential however a quantum processor is exponentially better than a normal processor of the same size. Reason being a quantum effect called entanglement allows various computational tasks to be performed at the same time creating exponential rates. Hence, quantum processors developing at an exponential rate and being exponentially faster than normal processors makes them develop at a doubly exponential rate than the classical processors.
Although this is exciting, the Neven’s rule is based on a small number of prototypes where progress has been measured in a small period of time. So several data points can be taken which fits other growth patterns. There is also the issue that as quantum processors become more powerful, the small technical problems get much larger. The minor electrical noise in quantum computers leading to errors could grow in frequency as the complexity of the processor grows. This could be solved by using error correction protocols, where many backup hardwares have to be added to the redundant processor. Hence the computer would have to be much more complex without gaining any extra power. This could impact Neven’s rule.
Moore’s law foresaw the progress of normal computing for a time period of 50 years without being a fundamental natural law. It allowed the microchip industry to adopt roadmaps for developing regular milestones, assess investment and evaluate revenues. If Neven’s rule becomes as prophetic as Moore’s law it will have ramifications more than the prediction of quantum computing performance. We do not know yet about the commercialisation of quantum computers, however, this can be quickly known if Neven’s law holds true.