A New Scientist investigation reveals Google's grand plans for its quantum computer, as well as the first hints about what's really going on under its hood
THEY could be the most powerful computers in the world – so perhaps it's no surprise that the biggest internet company on the planet is testing one out.
Last year Google purchased a quantum computer from D-Wave Systems in British Columbia, Canada, currently the only firm claiming to sell chips powered by exotic physics. However, this claim is controversial; some say D-Wave has yet to fully demonstrate its chips' quantum capabilities. Now a New Scientist investigation reveals Google's future plans, as well as the results of its recent tests to address the quantumness controversy.
In theory, quantum computers offer a huge advantage over ordinary PCs. Regular computers code information in binary bits that are either on or off – 0 or 1. But a quantum "qubit" can be both at the same time. This could let quantum machines crunch through certain problems, like searching a database, at blistering speeds even compared to a supercomputer. Such zippy calculation is an attraction for companies like Google that deal with large volumes of data.
Google certainly isn't alone in its quantum aspirations: its D-Wave Two machine is housed at NASA's Ames Research Center in California and maintained by the Universities Space Research Association (USRA). New Scientist's freedom of information request to see the contract signed between the parties reveals they are pursuing a range of applications.
Aiming high
Their joint aims are easy to state, if difficult to achieve: "The goal is to develop quantum AI [artificial intelligence] algorithms, test them on real world problems and quantify the gains over classical computing machinery."
Then there are the parties' individual goals. Google wants "revolutionary new powerful quantum algorithms" for its core operations. These include ranking search results, personal assistants, ad placement and spam filtering.
Personal assistants may conjure images of a quantum-powered version of Siri, Apple's digital assistant, able to chat and joke with you. But there is no guarantee a quantum computer will be better at this than a regular computer. Google wants to be the first to find out either way.
NASA is after better algorithms for air traffic control, planning rover missions on other planets, analysing data and more. The agency has said it wants to use quantum computers to help in the search for exoplanets.
There are also plans to hook the D-Wave computer up to the NASA Ames supercomputer to develop hybrid quantum-classical AI algorithms.
At least, that's the long-term plan. However, an important stepping stone is to prove the D-Wave really can solve problems faster than ordinary PCs. Now Google researchers, working with others at NASA and D-Wave, say they've found the first evidence that it employs quantum effects to perform computation.
So far, labs around the world have been able to build machines with just a few qubits, which can only handle problems that wouldn't trouble a pocket calculator. But since 2007, when D-Wave Systems first revealed a 16-qubit chip it claimed could solve Sudoku problems by exploiting quantum mechanics, it has repeatedly ramped up the number of qubits in its computers. The D-Wave Two has around 500 qubits and the firm plans to release a 1152-qubit version next year.
So how is D-Wave seemingly able to out-qubit everyone else? The company uses a different approach to most others in the game, called quantum annealing. Rather than shunting qubits through the quantum analogue of the logic gates found in regular computers, it translates problems into a landscape of hills and valleys. D-Wave's qubits explore this landscape to settle on the lowest energy state, which corresponds to the solution. For this to work, the qubits must be cooled as close to absolute zero as possible – the chips are housed in a custom fridge the size of a small room.
However, critics said it wasn't clear the energy-landscape approach would provide an advantage, and had doubts that D-Wave's computers are properly quantum.
Champing at the qubit
One way to prove quantumness is showing that your qubits have a property called entanglement. This can't be measured directly while the D-Wave is operating, so it has to be inferred by other means. The firm has published a number of studies to try and demonstrate such properties, but the crucial question of whether they were actually involved in computation remained open.
Now a team led by Google's Hartmut Neven has revealed what they think is going on under the hood (arxiv.org/1411.4036). They found the computer performed better at lower temperatures – which suggests it was harnessing quantum effects during computation (see "Quantum chill").
Although hopeful, the results don't demonstrate the explosive quantum speed-up promised by theory. But the team stresses that the progress made so far is "a big step" towards proving a speed-up compared to a version of D-Wave that had no quantum properties.
"If the device had failed that test then we'd be sure that there is no chance for quantum speed-up in these types of problems," says Matthias Troyer of ETH Zurich in Switzerland, who has studied D-Wave computers in detail. "They've seen the machine uses quantum mechanics to solve a problem."
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