Some thoughts on the tower of Babel


by Johannes Borregaard 

I am not particularly schooled in religious scripture of any kind. Nonetheless, one story that I vaguely remember having come across during my school years is the story of the tower of Babel from the Old Testament. The setting of the story (as far as I remember) is that all mankind speak the same language. As a result, they are able to join forces trying to build a tower so high that it reaches the heavens. The deity however prevents this by giving them different languages, so they no longer understand each other and scatters them all over the world.

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A nightly physics adventure


” WA R N I N G : 5 FAU LT S F O U N D ! “

by Niels Bultink

It was around 1:00 AM on a cold winter night in 2019 when I stepped out of a bar in the historic center of Delft. Time to go home, after celebrating Suzanne van Dam’s successful PhD defense. Evenings like these remind me why science is such a great endeavour. People might be working long hours to reach only tiny steps. But there is a team of people around you that understands the struggle. And, when those tiny steps lead to a big one, or occasionally even a breakthrough, celebration comes with all sorts of weird traditions. In short, it was an evening with a warm QuTech family feeling. For me personally it was also a nice change of scenery. Over the months prior, I had been working intensely on the final experiment of this thesis. In particular this week, I was finetuning day-in day-out to hunt for data sets that were fit for publication. Although the efforts of many had been finally coming together for quite some time: from design, to fabrication, to the integration of the setup; it is this final stage of an experiment that can make or break years of struggle for the whole team.
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Kavli Warriors


by Christian Möhle

In recent days my daily walk to the coffee machine has become ever more painful as Guan would spot me and start to yell at me (with a big smile in his face): “Christian, write your blog post!”. So here I am, finally finding some time to write my first blog post ever. It won’t be about qubits or any other physics topic, but rather about our glorious football team, the Kavli Warriors. Continue reading Kavli Warriors

Poem: Betelgeuse & his little brother


by Barbara Terhal

Barbara Terhal, faculty member at QuTech, wrote a poem about the tiny virus that holds the world in a firm grip these days, which we have printed below. We also invite anyone who has converted their thoughts in these unusual circumstances into poetry, to add their poems in the comment section at the bottom of this page.

Betelgeuse & his little brother

What if,
Now that the stocks are down
And the virus is up
Betelgeuse bursts
Like a balloon
Spewing hot radiation
Into space

Would we think that the small
And the large are connected?
Shaking hands across space

We can’t even see
The little copy machine
Crawling over us!

How wrong such interpretation

And still, how much we don’t know:
Blind, deaf and dumb towards the
Living creepy nanometer

Who knows proto-life ladders
All the way down to a few molecules
Mixing this or that way
Like those belches of Betelgeuse
Who also wish to become
In their impatient energetic strivings
Stable reproducible forms

They just shoot for the steady eons
rather than the unambitious span
of some human centuries

Cover picture: the star Betelgeuse in December 2019. Picture made using the Very Large Telescope of the European Southern Observatory (ESO/M. Montargès et al.).


Barbara Terhal is currently Professor at the EEMCS Department at the TU Delft and research staff member at QuTech. As a theorist she has been trying to get people to build quantum computers since her PhD in 1999 with mixed results so far.

Quarantine puzzle


The days get sunnier, yet the working from home continues. Some labs over the world are closed. At QuTech we have the luck that the labs stayed open, although the people in it disappeared. Monitoring measurements remotely and struggling with simulations is, also at QuTech, the new standard. With, of course, the now very well-known background noise of the video calls; people who are still on mute while talking, interesting background sounds and the frequency with which you can, or can’t hear someone with a failing internet connection (fun fact: the QuTech communications team even made a bingo card for everyone, containing the most-heard sentences in quantum video calls). The most interesting things we had so far were someone trying to fix his finances and stocks during a group meeting (and wasn’t muted), someone’s child breaking into a group meeting and someone’s pet chicken overtaking a whole meeting with its noise.

Yet more and more, we’re getting used to it. And a new normal requires new ways of keeping in touch and having fun together (one of the things I like of the video calls is that you get a sneak peak of someone’s home). That’s why the QuTech blog team organised a pub quiz for QuTech last Friday. It was a great success! The teams were competitive and we had a lot of fun with distributing the bonus points for best outfit and best background image. Of course, we don’t want to withheld you, therefore we made a puzzle out of the bonus questions of the quiz for you to think about during this long weekend.

In this puzzle you see nine tiles. Each tile cryptically describes a word that has something to do with quantum computers. You can fill in your answers in the answer card below (which also tells you how many letters an answer should have). If you fill it out correctly, you can read another word in the yellow tiles. A small note, a word like T2 would be spelled T-two and thus would occupy 5 tiles. Enjoy and good luck! The answers will be added to this post next week.

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Fabricating a superconducting quantum processor in a cleanroom


by Christos Zachariadis

Nowadays, quantum computers promise to be a revolutionary technology. As a result, quantum computing has become one of the hottest areas of research in the last decade. A lot of effort has been made on all layers of this new computer stack; from the creation of quantum algorithms to the development of hardware for devices. Lately, the bottleneck of the latter one starts to become more troublesome. Fabricating a growing number of qubits is increasingly difficult and samples are hard to reproduce on a large scale. In this blogpost, we’ll discuss the origins and the difficulties of fabricating a superconducting quantum processor. Continue reading Fabricating a superconducting quantum processor in a cleanroom

Three ways to enjoy yourselves at the QuTech Uitje


by Arian Stolk

CAUTION: This post will NOT contain any physics (ignoring any possible corny physics jokes)! That is right, no discussions about entanglement, (qu)-bits and/or crazy science in the coming story. It is not that I do not like to talk about these things, on the contrary. Yet, I thought it would be an interesting idea to talk about a more none-science-y aspect of QuTech. And I would like to do it using a yearly recurring event: the QuTech Uitje.

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Cooling a Hot Photon Wind (part 1)


Combining low temperatures and high frequency signals is becoming ever more important in the development of quantum technologies. In QuTech for example transmon based devices use some signals in the 2-10 GHz range and spin qubits use even higher frequencies; over 20 GHz. It is desired that the noise in the working bandwidth should be as low, and as cold, as possible, but these devices can be also quite susceptible to unwanted photons at much higher frequencies, 50-100 GHz, leading to extra quasiparticle generation or photon assisted tunneling that can destroy the fragile quantum states. This post aims to be an easy to read tutorial and guide as we look at a model to reduce the distribution of thermal photons from a high temperature to a low one. In the particular case of a 1-dimensional coaxial cable carrying photons from room temperature towards a cold sample mounted in a dilution refrigerator. I’ll try to convey some intuition how this model behaves and what this means for cryogenic design.

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Have you ever been to Ytterby?


by Sara Marzban

In this post I’m going to briefly describe the solid state system, namely rare-earth crystalline material, that the Tittel lab at Qutech is using to do all sorts of cool quantum communication experiments, including building the hardware required for an elementary link of a quantum repeater.

In this era of online communications, the security of transmitted and received information is extremely important. Quantum communication is an absolutely secure method of communication between points A and B. However, building these secure quantum communication networks has proven to be difficult. In a quantum communication network, fragile quantum states are transmitted between a transmitter (point A) and a receiver (point B). During transmission, decoherence can be introduced into the system, either from losses in the transmission line, absorption in the system or from environmental contamination. Some of the losses occurring over the full length of the transmission line scale exponentially with distance and as a consequence, quantum communication is restricted to a range of about 200 km, beyond which quantum states can no longer be reliably measured [1, 2, 3].
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A word from an editor emeritus and new blog team members!


With QuTech expanding from a quantum transport research group to a large institute focusing on quantum computers, the number of people walking around in the hallways expands. It makes you almost forget that there are also people leaving. But as the seasons go by, PhD students at QuTech come and go. It gives QuTech its characteristic dynamic character. But it also brings sadness every time we have to wave someone goodbye. And this is exactly what this blogpost is about. Since editorial duties for this blog are performed on a volunteer basis by PhD students (in what little remains of their free time), this means that any editor’s tenure is inherently limited by his or her PhD track. Therefore, with some sadness, we have to say goodbye to Jonas, the founding father of the QuTech blog and involved from the very start. He finished his PhD and moved to Amsterdam. He was an amazing and creative member of the team and we would like to thank him for the time he has spent making this blog an inspirational place for quantum computing.

But of course he wouldn’t leave without equally capable replacement. And, since QuTech is growing, we also extended the editorial team. That is why we proudly announce the two newest team members, Tim and Matteo. Actually Tim and Matteo have been active on the blog for a while. So the time is definitely there for a more official introduction. Continue reading A word from an editor emeritus and new blog team members!