A startup called Quantum Circuits is networking mini quantum devices together to create computers it will claims will be easier to scale up than rival machines.
Visit any startup or university lab where quantum computers are being built, and it’s like entering a time warp to the 1960s—the heyday of mainframe computing, when small armies of technicians ministered to machines that could fill entire rooms.
All manner of equipment, from super-accurate lasers to supercooled refrigerators, is needed to harness the exotic forces of quantum mechanics for the task of processing data. Cables connecting various bits of gear form multicolored spaghetti that spills over floors and runs across ceilings. Physicists and engineers swarm around banks of screens, constantly monitoring and tweaking the performance of the computers.
Mainframes ushered in the information revolution, and the hope is that quantum computers will prove game-changers too. Their immense processing power promises to outstrip that of even the most capable conventional supercomputers, potentially delivering advances in everything from drug discovery to materials science and artificial intelligence.
The big challenge facing the nascent industry is to create machines that can be scaled up both reliably and relatively cheaply. Generating and managing the quantum bits, or qubits, that carry information in the computers is hard. Even the tiniest vibrations or changes in temperature—phenomena known as “noise” in quantum jargon—can cause qubits to lose their fragile quantum state. And when that happens, errors creep into calculations.
The most common response has been to create quantum computers with as many qubits as possible on a single chip. If some qubits misfire, others holding copies of the information can be called upon as backups by algorithms developed to detect and minimize errors. The strategy, which has been championed by large companies such as IBM and Google, as well as by high-profile startups like Rigetti Computing, has spawned complex machines evocative of those room-sized mainframes.
The problem is, the error rates are extreme. Today’s largest chips have fewer than a hundred qubits, but thousands or even tens of thousands may be needed to produce the same result as a single error-free qubit. Each qubit needs its own control wiring, so the more that are added, the more complex a system becomes to manage. More gear will also be needed to monitor and manage rapidly expanding qubit counts. That could drive up the complexity and cost of the computers dramatically, limiting their appeal.
Robert Schoelkopf, a professor at Yale, thinks there’s a better way forward. Instead of trying to cram ever more qubits onto a single chip, Quantum Circuits, a startup he cofounded in 2017, is developing what amount to mini quantum machines. These can be networked together via specialized interfaces, a bit like very high-tech Lego bricks. Schoelkopf says this approach helps produce lower error rates, so fewer qubits—and therefore less supporting hardware—will be needed to create powerful quantum machines.
Skeptics point out that unlike rivals such as IBM, Quantum Circuits has yet to publicly unveil a working computer. But if it can deliver one that lives up to Schoelkopf’s claims, it could help bring quantum computing out of labs and into the commercial world much faster.
The drive to create longer-lasting qubits
The idea of bolting together smaller quantum building blocks to create bigger computers has been around for years, but it’s never quite caught on. “There’s not been a great, fault-tolerant machine that’s been built yet using the modular approach,” explains Jerry Chow, who manages the experimental quantum computing team at IBM Research. Still, adds Chow, if anyone can pull it off it will be Schoelkopf and his colleagues.
After training as an engineer and a physicist, including stints at NASA and Caltech, Schoelkopf joined Yale’s faculty in 1998 and began to work on quantum computing. He and his colleagues pioneered the use of superconducting circuits on a chip to create qubits. By pumping electrical current through specialized microchips held inside fridges that are colder than deep space, they are able to coax particles into the quantum states that are key to the computers’ immense power.
Unlike bits in ordinary computers, which are streams of electrical or optical pulses representing either a 1 or a 0, qubits are subatomic particles such as photons or electrons that can be in a kind of combination of both 1 and 0—a phenomenon known as “superposition.” Qubits can also become entangled with one another, which means that a change in the state of one can instantaneously change the state of others even when there’s no physical connection between them.