There is yet another contender for most powerful quantum computer ever. IonQ has announced a new machine with 32 quantum bits, or qubits, that the firm says is more practically powerful than any of its competitors.
Unlike ordinary bits, which can store only a 0 or 1, qubits can store a combination of these states, allowing quantum computers to process far more information. IonQ鈥檚 machine doesn鈥檛 have more qubits than any other computer, but the firm says its quantum volume 鈥� a metric coined by IBM that accounts for the number of qubits, their error rate and a few other key properties 鈥� far surpasses that of any other. The firm鈥檚 device has a quantum volume of over 4 million, compared with the previous record of just 64.
This quantum volume means IonQ鈥檚 computer is closer to being able to solve practical problems. 鈥淚 think it鈥檚 not flimflam, it鈥檚 not hype,鈥� says Peter Knight at Imperial College London. 鈥淭his will be regarded as a tremendous advance.鈥�
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IonQ has managed to create a device with such a high quantum volume by trying to make qubits that are as error-free as possible. Rather than using superconducting chips that are similar to ordinary computer circuits, as many other quantum computers do, IonQ uses single ions as qubits and manipulates them with lasers.
鈥淭he qubits themselves are perfect, although there are some errors that we add when we use them,鈥� says Chris Monroe, IonQ鈥檚 chief scientist. The error rate of the device is less than 1 per cent, he says, making it more accurate than most of the other quantum computers on the market. The qubits are also remarkably well-connected, which means it is easier to run more complex algorithms.
鈥淚t doesn鈥檛 have more qubits than anybody else, but they鈥檝e reduced their errors in such a way that they鈥檙e almost perfect, and that gives them this additional oomph, this additional power,鈥� says Knight. 鈥淲ith a modest number of qubits, they鈥檝e achieved a great deal more.鈥�
But whether IonQ鈥檚 device is actually better than its competitors鈥� isn鈥檛 necessarily clear, says John Preskill at the California Institute of Technology. 鈥淚鈥檇 say the most obvious competitor is Google鈥檚 Sycamore device,鈥� he says. In 2019, Google claimed that Sycamore used 53 qubits to solve a problem that couldn鈥檛 be solved or simulated in a reasonable amount of time by any classical computer, a milestone called quantum supremacy.
Monroe says that the IonQ device is 鈥渟ort of on the edge鈥� of achieving quantum supremacy. A classical supercomputer could still solve the problems that this quantum computer can, but it might take weeks to months to do so, he says. 鈥淏ut as long as the quantum computer is faster, it鈥檚 still useful.鈥�
鈥淚f you want to measure power of a quantum computer in terms of how difficult it is to simulate with a classical computer, it doesn鈥檛 smell right to claim that a quantum computer with 32 qubits is more powerful than a 53 qubit device,鈥� says Preskill. It is hard to directly compare the two devices because they are fundamentally different types of quantum computer, but the difficulty of simulating a quantum computer grows exponentially with an increase in the number of qubits, he says.
Monroe says that IonQ is already working on doubling the number of qubits, which will make this device a billion times harder to simulate with a classical computer. Since the company has focused on producing high-quality qubits, even increasing their number by a small amount should provide a significant boost to quantum volume.
