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In the wild and wooly world of quantum computing, everything must be taken with a grain of salt.

For example, Microsoft’s (MSFT) comment that it will have a production-ready quantum computer in five years’ time—a comment made to this blog in February—is met with a pleasant smile and something of a shrug by James Clarke, the director of quantum hardware for Intel (INTC). I had lunch with Clarke on Thursday in Manhattan.

Intel quantum-computing director James Clarke Tiernan Ray for Barron's

“If you look at the first transistors, they came out in about the late ’40s,” observes Clarke. “Then, in the late ’50s, came the first integrated circuits. It wasn’t until the late ’60s, or early ’70s, that you got the first microprocessors."

“It makes sense, then, that with something as complex as quantum, you’d be looking at another decade for it to reach maturity,” he says.

Clarke’s express purpose was not to shoot down Microsoft; he has great admiration, in particular, for Leo Kouwenhoven, a professor of applied physics at Delft University of Technology in the Netherlands. Kouwenhoven in fact formed the QuTech group at Delft that is partnering with Intel to make the chip giant’s quantum computing parts.

Frontiers of chemistry

Rather, Clarke, a chemist by training, is simply fascinated by the still-fundamental problems of materials physics and engineering that Intel is trying to crack.

Similar to the early days of solid-state devices, finding the right materials for quantum is a basic challenge right now, he explains.

For example, while silicon is well-understood for making ordinary integrated circuits, there are three different flavors of silicon present in ordinary chip manufacturing, referred to as silicon 28, 29, and 30. Silicon 28 is the most common, but most silicon that goes into wafers has some admixture of the three. Silicon 29 has “an extra nuclear spin,” says Clarke. That can create havoc for quantum mechanical systems. In particular, it shortens the very small window of time—“coherence,” as it’s called—in which a qubit, a quantum bit, can function, before the entire system has to be reset.

Intel partnered with a company that does what’s called “nuclear enrichment” to basically rid silicon materials of the pesky 29 version, to create a purer form.

All this has to be tested, which is a more complex process than for traditional transistors. “We’re pretty happy with the yield we are getting” for quantum chips fabricated using 12-inch silicon wavers, Clarke says, meaning how many good die of a quantum chip come out of the manufacturing process. But, at the ultracold temperatures at which quantum chips must be run—on the order of 20 millikelvin, equivalent to minus 460 degrees Fahrenheit—parts can turn out to be unusable even if they passed the basic defect inspection and test. These are the kinds of new complexities arising with quantum.

Qubits in high volume

Intel's "Tangle Lake" quantum chips. Intel Inc.

So far, Intel has produced only test chips, in two flavors. The first, called superconducting quantum chips, are code-named “Tangle Lake.” They consist of 7, 17, or 49 quantum bits. Over time, the hope is to expand each part to thousands of qubits in order to perform complex logic operations. These first parts are really only enough for a very basic logic gate. RF connectors made of gold dot one side of the chips, giving them a distinct look, which you see in the accompanying illustration.

The second version is what are known as “spin qubits.” They have the advantage of having a longer coherence time—a longer time to be manipulated before needing to be reset—on the order of as much as a millisecond, versus the 50 microseconds of Tangle Lake. That’s a big deal, suggests Clarke, given that after qubits decohere, the chip needs to be effectively rebooted before it can be used again.

Intel’s quantum chips, unlike Microsoft’s, do not use what are called “Majorana fermions,” a particle that has the property of being both matter and antimatter. And unlike Microsoft's approach, Intel is not exploiting topological aspects of particles, though Clarke says study of topology is ongoing in many respects at the quantum labs and throughout Intel.

Intel wafer of "spin qubit" chips. Intel Inc.

Instead, the silicon approach is one that Intel believes is well suited to using Intel’s chip-manufacturing facilities to ultimately produce parts in high volume. Among the samples Clarke brought to lunch was the spiffy 12-inch wafer of spin qubits. I had to admit, it looked like any other logic wafers I’d seen in past, which is to say, it looked viable.

A new architecture

Microsoft would argue in its defense that its Majorana fermions mean its chips need fewer qubits to do error-correcting, making them more efficient. To that, Clarke replies that many details of the design of chips are still being worked out, not just by itself but by the industry, and aspects of design and programming, rather than strict qubit counts, can have a big impact on error rates.

While the chip’s logic gates are made up of single electrons in a cavity, there is a lot more to how the part needs to be designed, aspects of which Intel is just now learning. “We have teams of engineers working on not just the chemistry and physics, but also the software, and even the instruction set architecture,” says Clarke.

The instruction set architecture, or ISA—the full set of programming commands one uses to program any kind of chip—will have to be refined for quantum parts as researchers learn what the optimal way is to program chips that can take advantage of quantum nonlinearities such as “entanglement.” Intel is developing a new ISA, called “QISA,” for quantum.

Such work may in fact bring new understanding of quantum phenomena, says Clarke. He offers as an example the prospect that “it could be there is some sort of principle that says you can’t entangle [qubits] more than a certain amount."

For more information on the Intel effort, check out the various materials posted in Intel's newsroom.

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