John Martinis, one of Google’s quantum computing gurus, laid out Google’s “stretch goal”: to build and test a 49-qubit (“quantum bit”) quantum computer by the end of 2017. This computer will use qubits made of superconducting circuits. Each qubit is prepared in a precise quantum state based on a two-state system. The test will be a milestone in quantum computer technology. In a subsequent presentation, Sergio Boixo, Martinis’ colleague at Google, said that a quantum computer with approximately 50 qubits will be capable of certain tasks beyond anything the fastest classical computers can do.
Researchers say that quantum computers promise an exponential increase in speed for a subset of computational chores like prime number factorization or exact simulations of organic molecules. This is because of entanglement: If you prepare entangled qubits, you will be able to manipulate multiple states simultaneously.
New Scientist reports that Google is testing a 20 qubit quantum computer. Alan Ho, an engineer in Google’s quantum AI lab, revealed the company’s progress at a quantum computing conference in Munich, Germany. His team is currently working with a 20-qubit system that has a “two-qubit fidelity” of 99.5 per cent – a measure of how error-prone the processor is, with a higher rating equating to fewer errors.
For quantum supremacy (Quantum computers faster than current classical comuputers), Google will need to build a 49-qubit system with a two-qubit fidelity of at least 99.7 per cent. Ho is confident his team will deliver this system by the end of this year. Until now, the company’s best public effort was a 9-qubit computer built in 2015.
A 2014 prototype of a Google qubit (0.6 cm by 0.6 cm) known as a transmon, based on superconducting circuits. Google’s quantum computing test will use 49 updated versions of these qubits.
Ho says it will be 2027 before we have error-corrected quantum computers, so useful devices are still some way off. But if Google can be the first to demonstrate quantum supremacy, showing that qubits really can beat regular computers, it will be a major scientific breakthrough.