# Rubicon for Physicist Jelmer Renema

Physicist Jelmer Renema will spend two years conducting research at Oxford University in Great Britain funded by a Rubicon grant from NWO.

### Building a computer with light particles

Renema has been awarded the grant for his project '*Falling off the complexity cliff: pushing boson sampling towards the non-computable regime'*. Renema intends to expand the capacity of the computer so that calculations can be made better and faster. ‘Using just a few light particles you can build a computer that can calculate molecules faster than any standard computer.'

#### Specific calculation

'My research is about building a non-universal quantum computer. This means a quantum computer that can only perform a specific calculation. The motivation behind this is that building a fully functioning quantum computer appears to be extremely difficult. It is a project the size of the Manhattan project, or building the first nuclear fusion reactor. So this crosses an entire generation.

For that reason, it’s interesting to see in the meantime if we could build a machine that can execute some calculation—which is difficult in 'classical' terms—more efficiently based on quantum technology. Up until now, our primitive quantum calculations have always been easily imitated by a classical computer. For example, if you want to factorize the number 15 in prime factors, it will take years on a quantum computer plus a lab full of people, while you could easily take a pen and a piece of paper and quickly find that 3 multiplied by 5 gives 15.

Our goal is to make a quantum calculation which is not that easily reproducible on a regular computer. That calculation doesn’t even have to be promising in terms of applications. It’s all about showing that a quantum calculation can in fact be faster than its classical counterpart.'

#### Boson Sampler

'There is a specific proposal for such a non-universal quantum computer; the Boson Sampler. A Boson Sampler is a network of certain glass fibers, that are placed in a glass plate. When two of those fibers meet, a photon *(light particle, edit.)* could jump over from one fiber to the other. Now if there is a photon in each of the fibers, they will influence each other’s path in a way that can only be described by quantum mechanics.

This leads to a level of complexity that rises above classical capabilities. But in the experiment this happens automatically: the machine calculates itself efficiently. My ultimate goal is to extend the existing Boson Sampler to a version that is large enough so that a classical computer won’t be able to keep up with its speed. Then, we have demonstrated that quantum calculators are indeed fundamentally different from classical computers.’

### Seventeen grants

Rubicon is an NWO finance instrument for scientists who have recently obtained their PhD, to gain experience at foreign top institutes, as stepping stone towards a scientific career.* *NWO received 106 applications, of which 17 were honoured (16%). The ratio of men to women submitting an application was 52/55, the number of men to women receiving a grant was in percentage terms 15/16% and in numbers 8/9.

Of the seventeen researchers to receive a grant, seven will be going to the US, seven to the UK and the three remaining to Switzerland, Sweden and Spain.