## 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.

## Media Misconceptions: Quantum versus Classical Computers

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by Christian Dickel

It is an honor to write the first blog post here and being conscious of that certainly influenced what I was going to write about. They say write what you know, but this is a blog so I’m going to write what I think. The blog will hopefully be a place for opinions and discussions. So I’ll begin with a question:

Do physics institutes need blogs? Certainly it is a neat additional way to communicate with other scientists, especially to share more provocative thoughts and give people a chance to discuss in the comments. But science is kind of a gated community and a blog is a nice way to open it more. For communication with the rest of society, journalists often come in whenever some piece of science has an air of general interest. But especially in a field receiving a lot of interest and a lot of funding from the public, we should try to explain what we do directly to anybody who is interested enough to end up on our website. A blog is a chance for us to share and discuss our perspective on the story of quantum computing as it is being written.

## Quantum computers and the media

There are news article on quantum computing almost weekly somewhere on the internet and one can use them to follow the story of the quantum computer. But the news has a certain inertia and a need to fit complicated arguments into a single sentence or paragraph. Some of the one-liners are productive simplifications, but they can also be misleading. Exploring all the misconceptions about quantum computing requires more than one blog article. I considered going through the list found here and fact-checking it, but this blog article would not have been very serious then. I thought it better for the first blog article to be a link from the past to today and focus on a single aspect that annoys me in the way the quantum computer story is told: I will try to give a more nuanced view on the relationship between the classical and quantum computer. Maybe later there will be more blog articles on other common misconceptions about quantum computers.

## Welcome to the QuTech blog!

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by Stephanie Wehner and Leo Kouwenhoven

Writing a blog post about quantum information and taking a picture of a rapidly approaching wave are almost equally ephemeral – a fleeting impression of an exciting development that has long moved onwards once the ink is dry. In the past two years, QuTech has grown to over 140 people working towards a quantum computer and quantum internet – or if you put the two together, a quantum cloud. We have celebrated scientific successes such as the first loophole free Bell test, and seen significant developments when Intel decided to enter the quantum domain, joining Microsoft as an industrial partner of QuTech.

More interesting, however, is undoubtedly the road ahead. Evidently, it is an intriguing prospect that already relatively few qubit quantum computing devices may solve useful problems faster than any classical machine. For us in the field, however, they would also invariably transform the landscape of quantum technology research we are accustomed to – both for theoretical and experimental research. An availability of few qubit devices promises the novel opportunity to develop new applications and algorithms by a heuristic approach often taken in classical computing – simply because we all have a classical computer on our desk to try them out. From an experimental perspective, we may see a divergence of experiments that aim to probe physics but work with only a handful of qubits, and the more engineering oriented aspect of designing larger scale computing technology. All the while, quantum information has made a sweeping entrance into many other areas of physics – offering the perspective of information as a powerful new way to decipher nature.

To advance quantum technologies, the European commission has recently established a 1bn euro flagship. Whether intentionally or not, the video provided for the flagship highlights the situation our field may find itself in. Feeling the rapidly approaching wave the question will be whether we do – as the surfer – fully commit to these possibilities by taking the chance to pop up on the surfboard. Or, whether we will keep hanging onto the well accustomed board and thus invariably wipe out. Success in quantum technologies does indeed require all the commitment we can muster, since realizing a quantum computer is incredibly challenging. Only time will tell whether we will be able to overcome all obstacles, but as with all great endeavours the only path lies forward.

Initiated by our excellent blog editorial team, we hope this blog may allow you to take part in some of these exciting developments. Written by all members of QuTech, it will feature a diverse set of posts ranging from ongoing research, people at QuTech, to – hopefully – easier explanations of what all this quantum stuff is actually about.

Sometimes, the blog may also give you a glimpse into what these scientists – like the theorist and experimentalist pictured here – are up to all day.

See you soon at the QuTech Blog. Enjoy!

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Welcome to ‘Bits Of Quantum’, the official blog by QuTech! QuTech is an academic research institution that houses many scientists who spend a large part of their time doing mathematics, experiments, and a lot of quantum mechanics. We would like to share bits of our quantum research with you, and give you a taste of what life in a large research institute is like. To that end we,  PhD students from different parts of QuTech, started the blog you are looking at right now. As the editorial team we are very excited about channeling all the stories that can be told by and about QuTech and quantum technologies. Thank you for reading this blog and we hope you enjoy reading the many posts to come!

Regards,

The editorial team,
Anne-Marije, Guan, Tim, Matteo and Adriaan

Adriaan Rol – Hi, I am Adriaan, an experimentalist in Leo DiCarlo’s group where we are working on a quantum computer based on superconducting transmon qubits.
I really enjoy trying to find the (abstract) essence of things while at the same time being able to experimentally test if my ideas actually work.
Whenever I’m not in the lab you’ll probably find me on the water or enjoying an overpriced coffee at my favourite coffee place.

Guanzhong Wang My name is Guanzhong Wang (feel free to call me Guan when you meet me in or out of the lab) and I’m a PhD student in the group of Leo Kouwenhoven. I work on one of the more unusual approaches to building a quantum computer here in QuTech – using what’s called a topological qubit. I hope through our posts I’ll be able to convince you this is a truly challenging yet worthwhile endeavor that embodies both mathematical and engineering beauty. Happy reading!

Anne-Marije ZwerverHi! My name is Anne-Marije and I’m a PhD candidate in the Vandersypen lab, where we are able to catch and control single electrons for the purpose of quantum computation. I am absolutely fascinated by quantum mechanics and it is a great adventure to work with bits of quantum daily and stretch up the boundaries of what we know and can do nowadays. Also, I love speed skating, philosophy and hanging out with friends. Enjoy the blog!

Tim Coopmans I am Tim, a PhD student in the group of David Elkouss and Stephanie Wehner. I work on the quantum internet as a theorist, in particular on bridging the gap between theoretical proposals for its design and the hardware that is currently built in the lab. I am a big fan of jazz music and far-fetched puns – not necessarily in that order.

Matteo Pompili – Hi, I am Matteo, a PhD student in Ronald Hanson’s group. I am trying to build a quantum internet — a network made with quantum entanglement — using defects in Diamond. I like dogs and lasers. But mostly dogs (but also lasers).

## We would like to thank our editors emeriti.

Jonas Helsen (July 2016 – June 2019) – Hey! My name is Jonas and I am one of the theorists at QuTech. I only started my PhD a year ago so I still have lots to learn but I’m really excited about being here! I’m also passionate about teaching people about the magical world of quantum computing which is why I co-started Bits Of Quantum with my lovely co-editors! Happy reading!

James Kroll (July 2016 – May 2019)-  I am James, an experimental physicist hailing from Scotland. I work in the topological quantum computing roadmap of Leo Kouwenhoven, as it requires an exciting mix of condensed matter physics theory, experimental cryogenics, electrical engineering and computer programming – all things that I somehow enjoy. If I’m not in the lab, you will most likely find me cycling somewhere or reading. Or eating. That’s a pretty important part of my life.

Suzanne van Dam (July 2016 – February 2019) – My name is Suzanne, and I am doing a PhD in the lab of Ronald Hanson, since two years now. One of my favourite things is to see the quantum world in the lab on a daily basis. My hope is that from this blog it will become clear why I am so excited about this!

All correspondence can be sent to blog@qutech.nl.