An ERC grant for Zaki Leghtas: one step closer to the quantum computer?

“Applying for an ERC Starting Grant involves a lot of introspection” explains Leghtas, a researcher within the joint project team Quantic (CNRS, ENS PSL, Inria, Mines ParisTech PSL, Sorbonne University), and a research professor at both the ENS and at Mines ParisTech. “First and foremost, you need to ask yourself: what is it that I want to work on for the next five years? You then have 30 pages to prove that you have a worthy project and that you're the right person to lead it.” In the end, Leghtas was successful: after applying for the grant in October 2018, his request was definitively granted in July 2019. The total amount awarded was €1.5m over five years. 

There are two components to the project behind the application. The first relates to the construction of a superconducting circuit capable of automatically correcting quantum errors. The objective here is to overcome one of the main obstacles standing in the way of development of the quantum computer, the supercomputer of the future. 

Innovation lies in creativity

Inside a computer, information is constantly contaminated by errors. In the quantum world, measuring such errors is extremely difficult, given that measurement impacts the parameters.

Google and IBM, both of whom are researching the subject, are seeking to operate a quantum computer even with these errors, until such time when it is possible to eliminate them. 

But the many hours spent by Zaki Leghtas during his Inria/Mines PhD speaking with Mazyar Mirrahimi, head of the project team Quantic, or, more recently, with Michel Devoret at Yale, saw the emergence of an innovative idea for automatically correcting quantum errors: encoding information not in qbits (the equivalent of the bits used in conventional computers) but instead in harmonic oscillators. For the layman, these can be thought of as being similar to pendulums, which disperse energy using friction. “For quantum physicists, generating friction in order to correct errors may seem counter-intuitive, given that friction normally creates errors.” admits Zaki Leghtas. “However, in the system we devised, this friction eliminates existing errors, without creating any new ones.”   

A wide range of applications

According to Leghtas, this totally unique idea will make it possible to produce efficient superconducting circuits capable of being used as building blocks for a quantum computer. And the possibilities don't stop there, either: the ability to correct errors would open the door to quantum metrology, i.e. the construction of measurement apparatus with previously inconceivable levels of precision, or even quantum communication, which would enable high-security exchanges. Another potential application is quantum simulation. “This would enable us to artificially construct a molecule on the quantum computer and then see how it evolves, simulating chemical reactions and materials. Multiple applications could stem from this”. 

The road ahead of them is a long one, however. Given that, as Zaki Leghtas explains, “the devil is always in the detail”, the theory still has to be refined, before being tested. Indeed, it is on these two points that two-thirds of the ERC Starting Grant will be spent. The funds will be used to take on a postdoctoral researcher and two students, to cover management costs, and to purchase highly specialist equipment, including a “superfridge”. What sets superconducting circuits apart is that they only operate at a temperature of 1 Kelvin (-272°C). Heat is simply not allowed, owing to the way in which it introduces thermal photons into the circuit, creating noise and additional errors. In short, the researchers will need to take a “chilled” approach to their work!

Back to basics

The remaining third of the budget, meanwhile, will be spent on the second component of the project, which is more basic. “This relates to a subject I find fascinating: the use of superconducting circuits to detect elementary particles, offering unrivalled levels of precision.” It is these particles, known as “Cooper pairs” (pairs of electrons), which transport current in a superconductor.

These have already been detected indirectly, but I want to build a superconducting circuit that will enable me to measure these pairs of electrons in another superconductor. This will take me closer to the fundamental quest of all physicists, which is to understand nature.

With five years ahead of him, it’s time for Zaki Leghtas to get to work.