## Koen Groenland

## About me

I am the* ***quantum innovation office*** r *at the

*University of Amsterdam*and

*QuSoft*. My goal is to accelerate the development of valuable

*quantum technology*by Netherlands-based companies. As one of the main valorization activities, we build the

*Quantum.Amsterdam*innovation hub , for which I am

**community manager**.

I am also involved in scientific research on quantum computers. In my work, we find input signals (like electronic or laser pulses) that make a quantum computers perform a desired operation on quantum data. Examples are shuttiling information from one part of the computer to another, or executing the quantum-version of certain logical gates like AND and OR. **READ MORE >**

# News

## Available MSc student project: The Quantum Benchmarking tool

December 2022

Benchmarks are used to compare the speeds of computers. For quantum computers, no standardized benchmarks exist yet, but it's up to you to invent and implement one. There are several challenges: all quantum computers work differently, and perhaps one computer excells at a certain task, whereas another performs best on a completely different task. What is a representative test that allows us to compare widely varying pieces of hardware?

Discuss with various experts from science (QuSoft, CWI, UvA) and industry what benchmarks are representative

Develop code that automatically performs benchmarks on various cloud services (IBM, Rigetti, IonQ, ... )

Assess the results and present them in an attractive manner (website or scientific paper)

Set the first steps towards a lasting initiative that regularly assess the ever improving set of available hardware.

Requirements:

You are a Master's student in Math, Physics, CS, or a related field, who is available for at least 6 months

Strong background in mathematics, especially linear algebra (knowledge of Quantum Mechanics appreciated but not strictly required)

Proficient with Python

Proficient in English, good social skills to work in a group and to talk to a wide variety of scientists and business experts.

Are you interested? Then let's further discuss this with a cup of coffee! Contact me at k.l.groenland@uva.nl.

(This project is open until removed from this webpage).

## Quantum Quest 2021 has started!

November 2022

The Quantum Quest is a free online webclass for students in the last years of high school (~16-20 years old). During a 5-week program, we dive into the **mathematics behind quantum computing**, going through probabilistic bits, quantum bits, unitary operations, and elementary algorithms and protocols (like Teleportation and Grover's search). To make the material sufficiently accessible, **we omit complex numbers** and work only with reals (and surprisingly, quantum computers still work fine!).

The course is extremely challenging and aiming at the best-of-class students. This year, we opened up submissions to anyone in the world, and have a very international audience (note the peak in Africa, especially Ghana, thanks to our collaboration with AIMS):

Signups for 2021 have closed... but if you're interested in participating:

All the course materials are freely available - especially the Syllabus is a great introduction to learn quantum by yourself! (https://www.quantum-quest.nl/material.html)

We're not sure whether the next edition will be in 2022 or 2023... but either way, keep an eye out on www.quantum-quest.nl

## More in-depth testing of N-qubit gates

May 2021

Juan Diego Arias Espinoza performed an extensive numerical analysis that our proposed method to perform an important gate, the Toffoli gate, performs very well on Trapped Ion computers. However, some clever tricks were needed to get the fidelities up to competitive levels. The result was recently published in PRA in the paper "High-fidelity method for a single-step N -bit Toffoli gate in trapped ions".

## Efficient circuits for Trapped Ion quantum computers

January 2020

We find a striking connection between the physics of quantum computers that use trapped ions, and the emerging field of quantum signal processing. This allows us to perform difficult quantum gates in less steps, relying only on the most simple entangling operation a trapped ion computer can perform.

(Update July 2020) This result is now published as follows:

Koen Groenland, Freek Witteveen, Kareljan Schoutens, Rene Gerritsma, *Signal processing techniques for efficient compilation of controlled rotations in trapped ions, *New Journal of Physics, Volume 22 (2020)

## Difficult quantum gates can be performed in a single step

November 2019

Together with Stig Rasmussen and Nikolaj Zinner from Aarhus University, we find that the notoriously hard Toffoli quantum gate can be performed using a surprisingly simple protocol. We require an all-to-all Ising type interaction between the qubits, and a resonant field on a single special qubit. After throwing away the special qubit, a Toffoli occurred on the remaining qubits.

(Update Februari 2020) This result is now published as:

S. E. Rasmussen, KG, R. Gerritsma, K. Schoutens, N. T. Zinner, *Single-step implementation of high fidelity n-bit Toffoli gates, *Phys. Rev. A **101**, 022308 (2020)* (*without paywall: arXiv:1911.07548)

## Popular state transfer protocols now work in more cases

September 2019

Certain experimental protocols, named with acronyms STIRAP or CTAP, turn out to work on many more systems than was previously known. We find that they naturally generalize to bipartite graphs.

KG, Carla Groenalnd, Reinier Kramer, *Adiabatic transfer of amplitude using STIRAP-like protocols generalizes to many bipartite graphs, *Journal of Mathematical Physics **61**, 072201 (2020); * * arXiv:1904.09915

## Transferring a quantum state over a network of coupled spins

January 2019

With the advent of advanced quantum information processing, it is of increasing importance to transport quantum information over a physical medium (think of a wire, or a network of wires). We consider the case where the information is encoded in a spin degree of freedom (think of an electron whose "rotation axis" can point either up or down), and the medium is made up of spins that are all pinned in place.

**It turns out that the repulsive forces between the spins can be used to delocalize the information over the whole network, and then localize it again at some other place. **This was known for mediums that form a perfect line. I generalize this to more general configurations, finding that information can be sent over many networks that look like a bipartite graph.

My article is planned for publication in** SciPost Physics** (DOI: 10.21468/scipostphys.6.1.011)

## Many-body strategies for multi-qubit gates

April 2018

Quantum computers, just like their classical counterparts, may use a *universal *gate set consisting of local gates, in order to approximate *any* possible operation on it's qubits. Typically, one chooses a two-qubit gate such as the *CNOT* together with a set of single-qubit gates.

However, we asked ourselves the question: **If N qubits are coupled by some interaction of our choice, can we construct interesting gates that act on all qubits at the same time? **

For this to work, we look at the so-called Krawtchouk chain, which is special because all of it's eigenvalues are integer numbers. Because this system is well understood, we can apply condensed-matter many-body techniques, resulting in two surprising new contributions:

The

**eigengate**, which maps computational states into eigenstates of the coupling Hamiltonian.**Resonant driving,**which, together with knowledge of the simple spectrum, allows us to select precisely 2 our of 2^N (and no more!) to undergo a transition.

Our article was recently published in PRA (https://journals.aps.org/pra/abstract/10.1103/PhysRevA.97.042321). Find the version without paywall at ArXiv or my GDrive.