In a paper published in Nature, Google has revealed its plans to demonstrate that quantum computers can perform a computational task beyond the capability of a classical computer, a claim known as quantum supremacy. Key in Google’s plan is building a 50-qubit processors to solve quantum sampling problems.
Google’s approach to demonstrating quantum supremacy is based on simulating coin tosses with quantum entanglement, the property of a quantum system where the quantum state of each particle cannot be described independently of the others. A classical computer cannot easily solve this problem because the representation of all possible states of 50 particles that can be in either of two states requires hundreds of terabytes. Qubits, on the contrary, can represent both states at the same time, i.e. a particle being present or not, making it possible to represent the whole 50-coin system using a single qubit for coin.
Google has already successfully simulated a 9-qubit quantum computer performing quantum sampling and it is now actively pursuing a 50-qubit quantum computer, the News Scientist reports. The main challenge there is demonstrating low error rates as the number of qubits increases, which is the main issue with quantum scalability. Google is aiming to build a quantum system capable of two-qubit fidelity of at least 99.7 per cent by the end of the year, explained Google engineer Alan Ho.
Google is not the only player in the quantum computing arena that is researching new ways to build scalable quantum computers. Yet, building a scalable quantum processor, while an important advancement in itself, might not provide the final proof of quantum supremacy. Indeed, what would also be required is proving that classical computers are not able to perform the same computation. This does not seem to be a trivial task, since many quantum systems may be simulated using current computers without representing their whole state.
