Updated: Oct 10, 2019
Last year, Google unveiled a 72 cubic chip called Bristlecone. Google publicly claimed that they thought it was likely they would have 'quantum supremacy' within the year. But what does quantum supremacy mean?
Quantum supremacy, in short is the line after which a quantum computer will be able to surpass the capabilities of the worlds fastest supercomputers. So what is holding us back from achieving quantum supremacy now?
Number of Qubits
Since quantum computers rely on qubits, which can be one four zero, or in a superposition, adding a few extra qubits can speed up the processing power exponentially. Adding a few extra bits to classical computer will makes virtually no difference, but having a quantum computer with 72 qubits in total is nothing to laugh at. We are making steady incremental advancements In the number of qubits that we can harness, and this is incredibly encouraging. But it's not just that simple. The more qubits that you add to machine, the more errors we encounter.
Keeping the qubits in just the right state depends on having an extremely controlled environment. Most methods of building quantum computers involve cooling superconducting circuits down to far colder than outer space. These machines are also extremely sensitive to even the slightest vibrations and other types of environmental interference. Any of these can cause qubits to 'decohere' - or become unstable - and this introduces errors into calculations So having 72 qubits, and having 72 'coherent' qubits is very different.
Some researchers have suggested that quantum supremacy is a difficult term to qualify, and that we should be talking instead about 'quantum advantage' or 'quantum ascendancy' instead. These terms put more emphasis on defining and achieving tasks that only quantum computers can do. John Preskill, A theoretical physicist at Caltech and the originator of the term 'quantum supremacy' has suggested that we are entering in the age of 'noisy quantum' rather that 'quantum supremacy', and that the age of quantum supremacy may still be decades away. Even so, what we are beginning to be able to do with our 'noisy' quantum computers is extremely promising in a number of specific fields, especially in those that can tolerate a little noise like computer vision, and the practical applications will only continue to grow in number.