It is a cold Monday afternoon when we have our appointment with Wolfgang Tittel, professor in physics and specialized in photon entanglement, quantum teleportation, and quantum memory. As we expect from a busy professor, he is still in another meeting when we arrive, so we decide to wait two meters outside his door. When we go and check if he’s almost done with this other meeting, his office suddenly appears deserted. In a vivid demonstration of his expertise, he seems to have teleported away from his office…
Luckily, he reappears quickly and lets us into his spacious office. One wall is completely covered by a large whiteboard, covered in scribbled equations and diagrams. Clear signs of occupation by a physics professor. Professor Tittel himself welcomes us with a smile, clearly relishing the opportunity to talk about his work. What follows is an interview with professor Tittel, shortened and lightly edited for clarity.
What type of research do you do?
My research lies in the framework of the quantum internet. More precisely, it is about quantum key distribution (QKD) and the creation of quantum key distribution systems over very long links. This requires quantum repeaters. To create the quantum internet, we send photons down an optical fiber, but, just as in standard telecommunication, these photons get lost at some point. In standard telecommunication, you can use amplifiers to boost the signal level, but for quantum internet this doesn’t work because of the no-cloning theorem. Instead, we can use a so-called quantum repeater.
At the heart of Quantum Mechanics lies quantum superposition. This strange phenomenon is often described as the capacity of a quantum system to be in multiple incompatible states at the same time. The most famous example of this is Schrödinger’s cat, which would be both dead and alive at the same time. But how can this be? How can we humanly make sense of that apparent contradiction? Well… I think we cannot! More precisely, I think there is a problem of language in here. Exactly what a quantum scientist means by being “in superposition”, I think, is quite far from what the layman has in mind.
A simple analogy
To start explaining what a quantum scientist has in mind when he/she says that a state is in superposition I will use a simple analogy: Shapes.
What? How is that related to the topic?
You’ll see! How would you describe or draw a shape that is both a disk and a rectangle?
That does not make any sense! Maybe something like this:
Yeah you see, it does not make sense to you, and you struggle to draw anything because I said something that does not make sense. This is exactly what happens when someone says that Schrödinger’s cat is both dead and alive! It is not clear what he/she means, and stated like that it is non-sense. When a quantum scientist says that a physical system is in superposition of two states (dead and alive), he/she means that it is in a state that is neither the first (dead) nor the second (alive) but it is in another state that possesses some of the characteristics of both (dead and alive).
Hmm…This is quite hard to visualize for me. Don’t you have an example?
Yes! For the example of the shape it could look like this:
Oh I see!
This is a relatively good analogy. This shape is neither a rectangle nor a disk, however it has some of the properties of both. Moreover I like this analogy because in quantum mechanics you cannot “see” the quantum state the physical system is in. In other words, if someone gives you a system in a certain unknown state, you cannot learn the state. If you try to measure it, you will only see a “projection” of it… Continue reading Dead or Alive: Can you be both?
When did we have our first quantum bit? To answer, one needs to agree on the definition. When does a two-level system become a qubit? In my view, only when coherent quantum dynamics is demonstrated. In the summer of 2002, Rabi oscillations of a superconducting flux qubit were observed in our laboratory. They were published in Science ; the primary authors were Irinel Chiorescu (postdoc, now professor at Florida State University) and Yasunobu Nakamura (on sabbatical from NEC Japan, now professor at University of Tokyo). As we all know, much has happened in the years after. Here I want to describe what happened before. How did we come to this point? I concentrate on my personal story and on superconducting circuits. In our Quantum Transport group we had the parallel research line on semiconductor quantum dots by Leo Kouwenhoven and his people that led to our first spin qubit in 2006.
In the fall of 2015 QuTech and Intel Corporation joined forces in an active collaboration working on the realisation of a quantum computer. The collaboration comprises comprises Edoardo Charbon’s control electronics, Koen Bertels’ architecture work, Leo DiCarlo’s superconducting qubits and Lieven Vandersypen’s silicon spin qubits. After having worked on the Delft side of the spin qubit part of that collaboration for almost two years, I spent three months this summer in Hillsboro, Oregon to be on the other side of the phone in our weekly Skype meetings. In this blogpost, I will share some of my experiences with you.
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.
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.
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. Continue reading Who simulates a quantum simulation?
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.
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 actuallydo 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.
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.