There is a fierce race for the best quantum computers and superconducting qubits are in the lead

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In the last five years, progress on quantum computers has accelerated dramatically. The most stunning event to occur throughout our lifetimes occurred in October of 2019 when a group of Google researchers lead by John Martinis released in Nature a scholarly essay detailing how he had attained quantum supremacy.

The shockwave from this breakthrough was felt for months, but subsequent achievements have left little room for dispute that quantum computing is advancing at a rate that was once thought impossible. IBM, one of the businesses competing most aggressively in this area, has already built and tested its 433-qubit quantum processor, Osprey. He also claims that Condor, a quantum device with 1,121 qubits, would be available in 2023.

Quantum computers are now in the hands of governments and huge corporations, but firms like Intel, Google, Honeywell, and IonQ are also investing in the field. Many new companies have also made substantial inroads into this sector; some, like China's SpinQ and Australia's Quantum Brilliance, have very promising innovations at hand. Naturally, they are all working towards the same goal: creating the first quantum computer that can fix its own errors.

Multiple routes can get us to a quantum computer that can tolerate errors. In June of 2021, we spoke with Ignacio Cirac, a Spanish physicist who heads the Theoretical Division at the Max Planck Institute for Quantum Optics and is universally regarded as one of the founding fathers of quantum computing, who told us that creating error-free quantum computers is a very difficult task. Despite the challenges, he assured us that the arrival of these machines is inevitable. They're on their way, although slowly, he said.

According to Ignacio Cirac, quantum computers with the ability to correct their own mistakes will be required to solve most of the problems that scientists hope to address in the future, including optimisation problems, cryptography problems, and artificial intelligence problems. Many millions of qubits are possible. Given that IBM has the state-of-the-art quantum processor, which only contains a few hundred qubits, it is clear that there are numerous technical hurdles that need to be overcome.

More qubits might be made possible with the use of superconductors, although they are less error-resistant than ion trap qubits. What makes this road so intriguing is because there isn't just one way to take it. Companies doing research in the area of quantum computing are developing a wide variety of qubit technologies, all of which are at various stages of maturity. Superconducting qubits are being used by a wide range of firms, from IBM and Intel to Google and even smaller startups like Atlantic Quantum, IQM, Anyon Systems, Rigetti Computing, and Bleximo.

In reality, if we just consider the amount of businesses actively developing such quantum bit technology, we can infer that this is the technology that has the greatest backing and investment, and is therefore, in some sense, ahead of the competition. We can get more qubits with this approach than with ion trap qubits, another option to superconductors, but it's also more error-prone. These latest qubits are also distinguished by operating at a temperature of roughly 20 millikelvin, or nearly -273 degrees Celsius, to achieve the greatest possible isolation from the environment.

Now we know that ion traps are the most promising alternative to superconducting qubits. Ionised atoms, having a non-zero global electric charge, are used in this technology, which is being developed by a number of different businesses including IonQ and Honeywell. As a first step, this feature enables isolation and confinement inside an electromagnetic field.

IonQ employs lasers to manipulate the quantum state of its qubits, which it does by cooling the qubits to lower the degree of computational noise. Here, IonQ employs lasers to manipulate the quantum state of its qubits, which were previously cooled using ion traps to decrease computing noise. However, it does not rely on just one laser, but rather employs separate lasers for each ion, in addition to a global laser that affects the entire ensemble.

Even though Honeywell, like IonQ, makes use of ionised atoms and lasers, its method for establishing entanglement between two ions and acting on them with a laser is different. This article's cover shows what Honeywell ion trap qubits look like, and they don't resemble superconducting qubits in the slightest. It seems to reason that this is the case given how drastically different their technology is from our own.

When compared to superconducting qubits, ion-trapped qubits are more durable and can avoid quantum decoherence for longer periods of time. While ion-trap and superconducting qubits are currently the most advanced technologies, other technologies are also making significant strides forward. The one that employs implanted ions in macromolecules can both store data and do basic computations. Although there is still a great deal of work to be done, several Spanish research groups are focusing on molecular quantum computing.

It is now difficult to foretell which of these technologies will succeed in delivering the required quantity of qubits and reliability for fine-tuning an error-tolerant quantum computer. The use of neutral atoms as a qubit technology is also highly exciting. Several academic institutions are advocating for it, and it has considerable appeal due to its ability to amass a large number of qubits while still exhibiting high precision and a high error tolerance. In reality, this approach combines the benefits of superconductors and ion traps in some mysterious way, albeit more work has to be done in this area.

It is now difficult to foresee which of these technologies will succeed in delivering the required quantity of qubits and reliability for building an error-tolerant quantum computer. It's possible that one of the technologies we haven't covered here will be the one that eventually makes it to this point. Although there is still much to be solved, researchers are making great strides forward in the field of quantum computing, so we can be confident that significant progress will be made by the end of this decade.