How to make artificial atoms out of electrical circuits – Part II: Circuit quantum electrodynamics and the transmon

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by Christian Dickel

There are different kinds of scientific papers. Some are like James Joyce’s Ulysses – you really want to read them but you have never made it through. There are the English classics – they are timeless and awe-inspiring. Like Shakespeare, some papers have changed the english language and, for example, teleported the wrong ideas into the heads of numerous journalists. In my group, we have a Harry Potter paper that we read again and again and keep discovering new insights. This is Jens Koch et al.’s 2007 classic “Charge insensitive qubit design derived from the Cooper pair box”, which introduced the transmon qubit.

Continue reading How to make artificial atoms out of electrical circuits – Part II: Circuit quantum electrodynamics and the transmon

A day in the life of a Master student

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Author: Sophie Hermans

Hi! My name is Sophie Hermans and I am a Master student in the group of Ronald Hanson. I have started my MSc project about five months ago in the “cavity team”. Today I will take you along and show you what I do on a regular day.

There is no better way than to start the day with a freshly brewed, warm and strong cup of coffee.


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Who simulates a quantum simulation?

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by Christian Dickel

Elon Musk puts the odds of us living in a “base reality” at one in a billions. His more likely alternative: we live in a simulation running on a computer. After the Matrix movie and in the age of computer games, this might not be an absurd idea to many people anymore. I will not focus on the merits of the simulation hypothesis here. However, as a quantum scientist, I am convinced that if we were living in a simulation it would have to  be a quantum one. Here, I want to explain why that is and I’d like to share some of my recent experience with quantum simulations – maybe the most interesting-looking application for future quantum computers at this point. In the process of the quantum simulation we also simulated the simulation – a concept that is kind of hinted at in Musk’s phrase “base reality”. From the base reality there could be a whole ladder of simulations within simulations all the way down – except for the problem of diminishing computer power. To answer the question in the title, in our research group my colleagues Marios and Nathan recently simulated a quantum simulation before running it on a small scale quantum processor.
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The APS March meeting

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By Jonas Helsen, Christian Dickel, Adriaan Rol, James Kroll and Suzanne Van Dam

The March Meeting of the American Physical Society, held every year in March (hence the name) is probably the largest meeting of physicists in the world. Held in a different city in the US every year it is a five day long whirlwind of talks, discussions, meetings, catching up with old friends and making new ones from all over the world. Since a sizeable subsection of the March meeting deals with quantum information processing (as of this year we are officially a Division!) a large group of Qutech scientists made the trek to New Orleans, both to speak about our latest developments and to learn about science going on all around the world. For this occasion we asked a few people to jot down their impressions of this weeklong carnival of physics and have bundled them in this blogpost. We will also add some pictures which hopefully convey the general scale and feel of the March meeting.

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Why turning a ket into a cat may or may not be a good idea

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By Adriaan Rol

When I’m at a party people often ask me what I do.

There is a lot of things I can talk about: why is a quantum computer interesting or useful , or:  what do I actually do during my day. But quite often people end up asking a confused question about this curious story of an undead cat. In this blog post I will try to shed some light on this case as well as delve into the question of why we use these kind of stories.

Dead? Or alive? Or both?

When trying to understand a new theory we physicists love our thought experiments.  We take some mathematical model of the world, change some parameters to see how it behaves and try to extract some rules of thumb or intuition from it. Continue reading Why turning a ket into a cat may or may not be a good idea

Progression of technology for quantum control or: jumping and drifting of NV centres

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Technological sophistication is a cornerstone of our society. Apart from a few outstanding examples, technology has always advanced towards a new echelon, which in turn enabled further advance. Whether one investigates the height of the tallest skyscrapers, or the timeline from the first transistor to today’s computers, the principle remains the same: inventions are being made with increasingly faster strides. Of course this trend should hold true for our favourite qubit! Along these lines I will delve into a technological aspect of my favourite qubit: the nitrogen-vacancy (NV) centre in diamond.

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Nanoscale Superstition

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by Michiel de Moor

In our cleanroom, we use nanofabrication techniques to combine materials in a precise and controlled way in order to study the wonders of quantum physics. For a nice introduction on the topic, I recommend reading Madelaine Liddy’s blog post. This post is not about nanofabrication specifics, but more about the people involved in the process.

Doing nanofabrication takes up a significant amount of time. Often it’s very difficult to understand what the important parameters are, and outcomes can seem random. As scientists, we should be rational and analyze the problem, then test possible solutions until we understand what is happening. But as people, we are susceptible to the same kind of magical thinking that makes people believe lightning strikes are a sign of Zeus’ displeasure.

As with cooking food, every research group will have their own fabrication recipes (which are, of course, the very best in the world). Continue reading Nanoscale Superstition

Climbing the Ivory Tower

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by Julia Cramer

After some years of doing science in the dark basement of a physics building, one may wonder: ‘who am I?’ Searching for answers at Google Images, there turns out to be a distinct difference between the stereotypes ‘scientist’ and ‘physicist’. Surprisingly, a ‘scientist’ always wears a lab-coat plus safety glasses. The ‘scientist’ works in a clean lab environment, handling chemicals and a microscope. According to Google, the ‘scientist’ is happy and young, can be male or female, black or white.

How large is the contrast to Google’s ‘physicist’: an old, somewhat otherworldly, serious man wearing thick glasses. The man standing in front of a whiteboard is writing down equations and drawing spheres on a blackboard. It is interesting to notice that Google barely makes a distinction between ‘physicist’ and ‘professor’. Leaving behind the fact that both a ‘scientist’ and a ‘professor’ can be an academic in any kind of field, I wonder why the ‘physicist’ never conducts any experiments.

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Quantum Teleportation Explained

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by Jérémy Ribeiro

Have you ever dreamt about teleportation? You wonder if it is possible, or if we can use it to travel faster than light, or at least to communicate instantaneously. Then you are at the good place. Here I will explain what quantum teleportation is. Behind this very attractive name that reminds us of science fiction, a communication protocol is hidden which uses the mysterious quantum mechanics.

Why do I talk about quantum teleportation ?

I wanted to write about this protocol because we hear a lot about it and a lot of information and explanations can be found about it. But sometimes those are partially wrong, or are a complete nonsense. For example we can read that quantum teleportation is an instantaneous transfer of information at a distance which respects special relativity… Well this is a contradiction.

These misconceptions of the protocol are not surprising since it relies on one of the most ununderstandable and less well understood phenomenon of quantum mechanics: the famous entanglement.

That’s why I will try to clarify what this notorious quantum teleportation actually is. For that I will have to introduce a little bit of quantum mechanics. Therefore there will be some mathematical expressions, but I’ll guide you through it to make you understand what is going on. It shouldn’t be too difficult since you should have already seen all the mathematical concepts in high school (vectors), and I think it is worth it and permits to really understand what quantum teleportation is.

So what is that quantum teleportation ?

The first thing to understand is that we only teleport a quantum state (we will call it \Phi), and not a particle nor any other kind of matter. Only information is transmitted from one place to another. So somehow we will scan the physical system in the first place (which will destroy the state), send the information (by phone, internet or any other way of communication) to an other place and there reconstruct the state. But to do that there are some obstacles. The main obstacle the “scanning phase” is not trivial since we cannot (by the law of quantum mechanics) get all the
information on a state by measuring it, as I will explain later, but only partial information. To overcome that we will need to use a correlated state which will somehow compensate the lack of information.

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