Quarantine puzzle

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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

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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

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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)

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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?

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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!

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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!

Quantum Computational Supremacy

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by Adriaan Rol

Last week Google and collaborators published a paper in which they claim to have achieved Quantum Supremacy, one of the major milestones in quantum computing. The idea of quantum supremacy is to use a programmable quantum device to perform a task that is out-of-reach for any classical computer. Google claims to have solved a problem in seconds that would take tens of thousands of years on a state of the art supercomputer. The quantum supremacy experiment has been a long-standing milestone in the field of quantum computation, and as such, skepticism has arised; soon after publication of the article a group in IBM research has challenged the results [1].

Rather than joining in on the controversy of whether or not Google has really achieved quantum supremacy , I want to focus on some more basic questions: what is quantum supremacy, how does one demonstrate quantum supremacy and why is this such an important milestone?
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Quantum internet: at the verge of an emerging technology

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by Bas Dirkse

The internet as we know it today has become an integral part of our lives. We use this piece of technology on a daily, hourly, almost continuous basis. We use it at work, to relax, to socialize, to fact check our friends during an argument and even to control the thermostat at our homes. We can definitely claim that, despite the internet bubble in the 90’s, the technology has far outperformed its expectations of the early 60’s and 70’s in the societal and financial benefits it provided. Will the same bright future be reserved for the quantum internet? Will it deliver the same amount of societal and financial benefits to the world as its classical sibling has done? Continue reading Quantum internet: at the verge of an emerging technology

Counting women in physics

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by Floor van Riggelen

Take a close look at this famous picture. These are the people who attended the fifth Solvay International Conference (1927), where the leading physicists of that time discuss the newly formulated quantum theory. What stands out to me is that this is quite a homogeneous group: 28 white (including Jewish), middle aged guys, plus Marie Curie. Of course, these were different times. Comparing this to QuTech in Delft, the place where I work, (an example of a physics research environment in general) there are some improvements when it comes to diversity. Currently 23% of the QuTech employees are non-European and 17% percent are female, according to a recent official review [1]. However, a quick count on the QuTech webpage will tell you that if you only look at scientists and technical staff [2], this percentage drops to about 10%. At QuTech there are still several scientists who are the only woman in their research group. Looking at it in this way, it seems that not much has changed in almost 100 years of quantum physics. Continue reading Counting women in physics

Diary of an international student at QuTech

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by David Maier


QuTech not only offers a wide range of interesting research, but also a diverse group of employees from numerous countries around the world. As a student from the far away country of Germany I was very curious if I would be able to fit in and overcome the cultural differences. Four months ago I came to Delft for my master’s project. In this little piece I would like to tell you from a humorous perspective about some of the challenges I faced as an international student coming to Delft and how you can overcome them too.

Disclaimer: this text contains irony.
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