Honeywell says that it will release the world’s most powerful commercial quantum computer by mid-2020. The US-based manufacturer of scientific and commercial equipment says that the device is based on trapped ions, which is a different technology than that being pursued by most other commercial developers including Google and IBM. Honeywell researchers have published details of a smaller version of the machine that has a “quantum volume” of 16 and say that it should be straightforward to scale this up to 64.

The fundamental requirement for quantum computation is a set of quantum bits (qubits) that can interact to form quantum logic gates that process quantum information. In principle, quantum computers can perform certain computational task much faster than conventional computers. However, qubits tend to be very fragile so creating practical quantum computers is a significant scientific and technological challenge.

Some experts use the concept of “quantum volume” as a figure of merit for a quantum computer. Developed at IBM, it considers the number of qubits, the degree of connectivity between qubits and the qubits’ coherence times (how long they survive). So far, IBM has created a system with a quantum volume of 32, but Honeywell says it can do better.

Long tradition

While most commercial quantum computers use superconducting circuits as qubits, the first ever qubits were made from trapped ions in 1995 by David Wineland, Chris Monroe and colleagues at NIST in Colorado. “Back then, we were thinking, ‘Somebody smart in solid state physics is going to figure out how to scale this up, because to scale you have to have a solid-state system,’” recalls Monroe – who is now at the University of Maryland. Superconducting circuits have since become popular because they are solid-state systems that can be built using lessons learned from the semiconductor industry,

Recently, however, the superconducting platform has encountered problems. “Superconducting systems had so many advantages they went through in years what had taken decades of work in trapped ions and rapidly surpassed them,” says quantum computing expert Barry Sanders of the University of Calgary in Canada. “The question is whether the golden era is gone,” he adds.

While Monroe was an early proponent of solid-state quantum computers, he is now a sceptic. “We don’t know how to make perfect little solid-state qubits and replicate them to be absolutely identical,” he says. “I’m turning completely around on this: I don’t think any solid-state system will ever scale,” referring to the need to integrate relatively large numbers of qubits to create useful quantum computers.

External errors

In 2015, Monroe co-founded IonQ, which in 2019 produced the first commercial quantum computer made from trapped atomic ions. “With atomic qubits, each qubit is an atomic clock: it is by definition a perfectly replicable system. All the errors are from the outside world – laser beams, microwave fields, imperfect vacuums,” he says. While these errors can be difficult to deal with, he points out that the semiconductor industry overcame formidable challenges in order to produce modern computer chips.

Now, Honeywell has released details of a trapped-ion quantum computer that it intends to launch commercially this year. A subsidiary called Honeywell Quantum Solutions claims to have developed a new ion trap that allows the qubits to remain coherent for significantly longer than in competing systems. The researchers say their system uses ytterbium-171 ions as qubits and barium-138 ions for sympathetic cooling.

Honeywell says that unlike competing designs, its system simultaneously meets several important requirements for a commercially viable ion-based quantum computer. While the researchers were unavailable for comment, they claim in a preprint on arXiv that the near-term obstacles to the scalability of their design are not severe. The four-qubit device described in the preprint has quantum volume of 16 and but Honeywell this will be boosted to 64 in a new device released this year.

Sanders describes the preprint as “very honest”. “They’re saying ‘this group did this, this group did that, and that group did that, but we’ve integrated all these advances into one system,’ he says.

Monroe says: “It’s not going to be easy for trapped ions to scale, but we can predict with confidence that we’ll have better lasers, better integration with optical chips and ion traps themselves, better detectors, all these things, and I think having a big company like Honeywell involved is a big deal because they have a rich history of this type of engineering.”