At last, we are discovering what quantum computers will be useful for

Over the past decade, quantum IT has become an industry of $ 1 billion. Everyone seems to invest in technology giants, such as IBM and Google, the US military.

But Ignacio Cirac at the Max Planck Institute of Quantum Optics in Germany, a pioneer in technology, has a more sober assessment. “A quantum computer is something that does not exist at the moment,” he says. Indeed, the construction of the one that actually works – and is practical to use – is incredibly difficult.

Rather than the “bits” of conventional machines, these computers use quantum bits, or qubits, to code information. These can be made in several ways, from the tiny superconductive circuits to extremely cold atoms, but all are complex to build.

The advantage is that their quantum properties can be used to make certain types of calculations faster than standard computers.

These accelerations are attractive for a range of problems with which normal computers have trouble, from the simulation of exotic physics systems to the effective planning of passenger flights or grocery deliveries to supermarkets. Five years ago, it seemed that quantum computers would improve these challenges and many others.

Today, the situation is much more nuanced. Progress in the construction of ever larger quantum computers has certainly been amazing, several companies developing machines with more than 1000 qubits. But that has also revealed difficulties impossible to ignore.

A major problem is that, as these computers are growing, they tend to make more mistakes, and find ways to prevent or repair them has proven more difficult than expected. Last year, Google researchers made the most notable breach of this problem so far, but even so, the quantum computers useful in its own right are not yet there – as Cirac points out.

For this reason, the list of realistic applications for these machines can be shorter than we used to hoped. Weigh the cost of building a counterfeit economies than the imagination it could achieve and, for many use cases, this may not have economic meaning. “The biggest false idea is that a quantum computer can accelerate any problem,” says Cirac.

So what problems could still benefit from quantum calculation? Quantum computers could break the cryptography systems that we are currently using for secure communication, making technology interesting for governments and other institutions whose security could be in danger, explains Scott Aaronson at the University of Texas in Austin.

Another place where quantum computers should still be useful is the modeling of chemical materials and reactions. Indeed, quantum computers, themselves a system of quantum objects, are perfectly suited to simulate other quantum systems, such as electrons, atoms and molecules.

“These will be simplified models; They will not represent real materials. But if you design the system appropriately, they will have enough properties of real materials that you can learn about their physique, ”explains Daniel Gottesman at the University of Maryland.

Quantum chemistry simulations may seem more niche than planning flights, but some of the possible results – find a superconductor at room temperature, for example – would be transformers.

The extent to which all of this can really be achieved depends significantly on quantum algorithms, the instructions that indicate to quantum computers how to execute – and help to correct these annoying errors. This is a new difficult area which, according to Vedran Dunjko at the University of Leiden, in the Netherlands, which obliges researchers like him to face fundamental questions about what information and IT are.

“This offers incredible motivation to study the harshness of the problems and the power of computer devices,” explains Dunjko. “For me, that would be a sufficient reason to devote a significant fraction of my life to these questions.”