In 2019, Google announced that its 53-kilobit hardware had achieved quantum supremacy—performing a task that couldn’t be managed by a convention computer—but that claim was challenged by IBM. In the same year, IBM launched its 53-bit quantum computer. In 2020, IonQ unveiled a 32-qubit system that the company said was “the world’s most powerful quantum computer”. And just this week, IBM released its new 127-qubit quantum processor, which the press release describes as a “small miracle of design.” “The good news, from my point of view, is that it works,” says Jay Gambetta, IBM’s vice president of quantum computing.
Now QuEra claims to have made a device with far more qubits than any of these competitors.
The ultimate goal of quantum computing, of course, is not to play Tetris but to outperform classical computers in solving problems of practical importance. Enthusiasts believe that when these computers become powerful enough, perhaps within a decade or two, they could have transformative effects in fields such as medicine, finance, neuroscience, and artificial intelligence. Quantum machines would likely need thousands of qubits to manage such complex problems.
However, the number of bits is not the only important factor.
QuEra is also touting the improved programmability of its device, where each qubit is an ultra-cold single atom. These atoms are neatly arranged by a series of lasers (physicists call them optical tweezers). The qubit mode allows the device to be programmed and tuned according to the problem under investigation, and even to be reconfigured in real time during the computation process.
“Different problems will require placing atoms in different configurations,” says Alex Kisling, CEO of QuEra and co-inventor of the technology. “One of the unique things about our devices is that every time we turn them on, a few times a second, we can completely redefine the architecture and communication of qubits.”
The QuEra machine was built from a blueprint and techniques refined over several years, led by Michael Lukin and Marcus Greiner at Harvard University and Vladan Volitech and Dirk Englund at the Massachusetts Institute of Technology (all members of the QuEra founding team). In 2017, an earlier model of the device from the Harvard group used only 51 qubits; In 2020, they demonstrated a 256 qubit machine. Within two years, the QuEra team expects to reach 1,000 qubits, and then, without changing the platform too much, they hope to continue scaling the system beyond hundreds of thousands of qubits.
It’s QuEra’s unique platform – the physical way a system is assembled, the way information is encoded and processed – that should allow for such leaps in size.
Whereas Google and IBM’s quantum computing systems use superconducting qubits, and IonQ uses trapped ions, the QuEra platform uses arrays of neutral atoms that produce qubits with impressive (i.e., a high degree of “quantum”) coherence. The machine uses laser pulses to make atoms interact, stimulating them into an energy state – the “Rydberg state,” described by Swedish physicist Johannes Rydberg in 1888 – in which quantum reasoning can be done in a powerful and highly precise manner. Rydberg’s approach to quantum computing has been working for two decades, but technological advances – for example, with lasers and photonics – have been necessary to make it work reliably.
When computer scientist Umesh Vasirani, director of the Berkeley Center for Quantum Computing, first learned of Lukin’s research along those lines, he felt “irrationally prolific” — it seemed like a brilliant approach, though Vasirani wondered if his intuition was in touch with reality. “We have many well-developed pathways, such as superconductors and ion traps, that have been worked on for a long time,” he says. “Shouldn’t we think of different schemes?” He checked in with John Preskill, a physicist at Caltech and director of the Institute for Quantum Information and Matter, who assured Vasirani that his abundance was justified.
Preskill finds Rydberg platforms (not just QuEra systems) interesting because they produce highly entangled interactive qubits — “and that’s where quantum magic is,” he says. “I’m very excited about being able to discover unexpected things on a relatively short time scale.”
In addition to simulating and understanding quantum materials and dynamics, QuEra works on quantum algorithms to solve computational optimization problems that complete NP (i.e. very difficult). “These are really the first examples of a useful quantum feature that has scientific applications,” says Lukin.