News Highlights: Quantum computer race intensifies as alternative technology gains steam.

An ion trap from Honeywell’s quantum computer. Credit: Honeywell Quantum Solutions

A technology for building quantum computers that has long been discarded by large corporations is gaining momentum. As quantum computers have transformed from academic practice to big business over the past decade, the spotlight has been mainly on one approach: the tiny superconducting loops being embraced by technology giants such as IBM and Intel. Thanks to superconductors, Google was able to claim last year that it had achieved “quantum advantage” with a quantum machine that for the first time performed a certain calculation beyond the practical capabilities of the best classic computer. But a separate approach, using ions trapped in electric fields, is gaining momentum in the search for a commercial quantum computer.

Earlier this year, technology and manufacturing company Honeywell launched its first quantum computer with trapped ions as the basis for its quantum bits, or ‘qubits,’ which it has been quietly working on for over a decade. Honeywell, headquartered in Charlotte, North Carolina, is the first established company to take this route. In October, seven months after launch, the company unveiled an upgraded machine; it already has plans to scale this up.

And last month, IonQ, a University of Maryland spin-out company, announced a trapped ion machine that could prove competitive with IBM or Google, although the company has yet to publish details of its performance. Smaller spin-out companies – such as UK-based Universal Quantum and Alpine Quantum Technology in Innsbruck, Austria – also attracting investment for trapped ion projects.

Trapped-ion quantum computers are far from new: they formed the basis of the qubits in the first basic quantum circuit in 1995, long before anyone used superconducting loops. But efforts to put all the building blocks together to build viable commercial systems “are now bursting at the scene,” said Daniel Slichter, a quantum physicist at the National Institute of Standards and Technology (NIST) in Boulder, Colorado.

Honeywell’s Ion Trap in a Vacuum Chamber Credit: Honeywell Quantum Solutions

“I think people today say ‘superconductors’ and ‘trapped ions’ in the same breath, and they didn’t even say that five years ago,” said Chris Monroe, a physicist at the University of Maryland in College Park who worked on the study. experiment from 1995 and is a co-founder of IonQ. Quantum computing is still in its infancy, and while several companies are trying to argue that their quantum computer is the most advanced (see ‘Who is the best?’), It is too early to say what types of hardware, if any, will prevail will have. As companies embrace a range of technologies, the field is wider than ever.

Huge calculations

Classical computers store their information as 1s and 0s, but qubits exist in a delicate superposition of 1 and 0. The quantum entanglement phenomenon allows the states of qubits to become intertwined, and interference from their wave-like quantum states would cause a quantum computer to become entangled. should be able to perform some massive calculations exponentially faster than the best classic machines. This includes finding the factors of prime numbers.

Any system with two possible quantum mechanical states – such as the oscillations in a superconducting loop or energy levels of an ion – could form a qubit, but all hardware types have advantages and disadvantages, and each faces significant hurdles to form a full-fledged quantum computer. A machine capable of delivering on the original promise of quantum computing by cracking conventional encryption, for example, would require millions of individually controllable qubits. But size isn’t the only issue: the quality of the qubits and how well they fit together are just as important.

The frequency of errors in delicate qubits and their operations, caused by noise, tends to increase the more connected. To have millions of qubits compute together, each has to work with error rates low enough to detect and fix errors in a process known as error correction, although physicists also hope that smaller, noisier systems will be useful in the short term. .

Who is the best?

Laboratories have long struggled to build the quantum computer with the most qubits. But judging which machine is the most powerful is fraught, says Sabrina Maniscalco, a quantum physicist at the University of Helsinki. “There is not just one measure of performance,” she says.

In June, technology company Honeywell in Charlotte, North Carolina, claimed to have created the most powerful quantum computer in the world, measured by “quantum volume.” This metric takes into account the number of qubits, connectivity, noise, and error rates of a system, capturing the complexity of problems it can solve. The machine’s quantum volume was 64, twice that of IBM’s leading device at the time. As a comparison tool, quantum volume is better than judging by the number of qubits alone, but it’s still a rather crude measure, Maniscalco says.

Head-to-Head Comparisons – an alternative way to measure the relative capabilities of devices – are not always productive, because the performance of each computer depends on the task, says Margaret Martonosi, chief of the US National Science Foundation’s directorate of computer science in Alexandria, Virginia. Without knowing how critical features will scale, a prototype’s performance tells us little about the power of a full version, she adds.

When using a metric, companies should be careful about making big claims, says Doug Finke, a computer scientist in Orange County, California who runs the industry tracking website Quantum Computing Report. Honeywell’s claim that his machine was the most powerful was premature, as few developers use quantum volume, he says. And in October, the first time IonQ formally used the benchmark, the University of Maryland spin-out company said they expected their latest machine to have a 4 million quantum volume, which, if substantiated, would surpass Honeywell’s record. .

Another measure of power is a quantum computer’s ability to beat a classic machine on a problem – which is what Google did last year with a 54 quibit machine. For Finke, achieving this “quantum advantage” in a commercially valuable problem is “the real measure of the success of a quantum computer”.

Pros and cons

In recent years, rapid advances in superconducting cycles threatened to leave trapped ions in the dust. Google and IBM and others have developed machines with about 50 or more high-quality qubits. IBM is aiming for a 1,000 qubit machine by 2023. John Martinis, a quantum physicist at the University of California, Santa Barbara – and head of quantum hardware at Google until April – thinks Google will use the same basic architecture as to achieve quantum advantage to achieve error correction, the next big milestone.

Superconducting qubits have thus far benefited from being familiar to many companies, as their base components are compatible with classic chip technology. But trapped ion qubits, which store information in the energy levels of individual charged atoms in an electric field, have many inherent benefits, says Sabrina Maniscalco, a quantum physicist at the University of Helsinki. Their operations are much less prone to error, and the delicate quantum states of individual ions last longer than those in superconducting qubits, which, while small, are still made of a very large number of atoms. In addition, superconducting qubits tend to interact only with their closest neighbors, while trapped ions can interact with many others, making it easier to perform some complex calculations, she says.

But trapped ions have drawbacks: They interact more slowly than superconducting qubits, which will be important when it comes to justifying real-time errors coming out of the system, says Michele Reilly, founder of quantum software company Turing in New York. And there are limits to the number of ions that can fit and interact in a single trap. IonQ’s latest model features 32 trapped ions in a chain; if you pick 2 with lasers, they interact. To scale up to hundreds of qubits, the company is working on ways to connect multiple chains of qubits with photons. The company aims to double the number of qubits per year.

The control room for Honeywell’s quantum computer. Credit: Honeywell Quantum Solutions

Meanwhile, Honeywell plans to link each ion together by physically moving them around a giant chip2 – an idea first developed at NIST in the late 1990s. The latest system from the company’s Honeywell Quantum Solutions (HQS) division, dubbed H1, consists of just 10 qubits, but lead scientist Patty Lee says the company is already in its next iteration. Over the next 5 years, the team plans to connect about 20 qubits, allowing the machine to solve problems that would otherwise be impractical on classic machines, said Tony Uttley, president of HQS.

The challenge is to maintain the quality and precision of qubits while controlling tens or even hundreds at the same time – which neither Honeywell nor IonQ have shown they can do. While many of the necessary components are individually mastered, “what is needed is an integrative system-level approach that puts everything together, tests and solves the problems,” said Barbara Terhal, a theoretical physicist at the University of Delft. Technology in the Netherlands.

Not a clear winner

Trapped ion hardware isn’t alone in attracting significant investment. The success of superconducting qubits has opened the doors to several technologies, Slichter says, including silicon-based spin qubits, which store quantum information in the nuclear spin states of an atom embedded in a silicon crystal. In a coup for this technology, Martinis joined Silicon Quantum Computing in Sydney, Australia, on a six-month sabbatical in September – his first step away from superconducting systems in nearly two decades. Martinis doesn’t care which design wins in the end. “I want to help someone build the first quantum computer. I don’t have to be [or] whatever I work with, ”he says.

The race is also far from known, says Maniscalco, and there may never be a winner. “There may not be one winning platform, but we have a hybrid or different platforms that are useful for different tasks.”

Via: www.nature.com

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