Bob, say something if you quant hear me!

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Perhaps you have become convinced that sharing quantum entanglement with a distant party is a useful resource. By itself, it might not allow you to communicate the weather to your grandmother, but, if pure enough, and assisted by some classical communications, it does allow you to win funny card games or, (perhaps) more importantly, to transmit quantum information via teleportation. The question is, how do we manage to share quantum entanglement with a distant party in the first place? Here, I want to discuss what are some of the challenges for establishing long-distance entanglement and a very idealized solution.

Let us consider that two distant parties, that we call (surprise) Alice and Bob, are connected via a quantum channel. A quantum channel is just a channel that allows us to transmit quantum information. The typical example of a quantum channel for connecting distant parties is a cable of optical fibre. Hence, let us assume that Alice and Bob are connected via some long optical fibre cable. Since I am a theorist, we also imagine that Alice and Bob have noise-free quantum memories available to them and, even more, they can transfer qubits from their memories to the input of the channel and store incoming qubits into the memory without any error or decoherence.

Alice prepares an entangled state locally between two qubits in her memory.

Continue reading Bob, say something if you quant hear me!

Hiding Schrodingers cat: a qubit of quantum error correction

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by Tom O’Brien

If you’re reading a blog named ‘bits of quantum’, I guess I can assume you know a little bit about quantum computing and have a rough idea of what a qubit is. And, if you’ve read some of the previous articles on this blog, you may have gotten some idea of how difficult it is to make one. Being a quantum mechanic is real tough work, man!

Probably the largest challenge in quantum computing right now is minimizing the rate at which errors accumulate as you perform a computation on your quantum chip. In classical computers (your PC, or mobile phone), this is pretty much a solved problem. The probability of an error in any given operation is usually less than 1 in 1,000,000,000,000,000. This means in the process of me writing this blog post and it popping up on your screen probably less than one error has occurred. They’re not perfect, but after 50+ years of research and refinement, computers are pretty damn good these days.

Continue reading Hiding Schrodingers cat: a qubit of quantum error correction

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

Around the World in 40 Days (Part One)

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By James Kroll

Research in academic is a tough, gruelling but ultimately rewarding job (otherwise we wouldn’t work so hard at it!). Usually if you ask a scientist about what it is like to work in research, you will be subjected to a coffee fuelled rant about tiresome data analysis, demanding students and endless paper preparation. Unless you catch us in an unusually good mood we won’t take the time to talk about the many things about our job that we genuinely enjoy.

Continue reading Around the World in 40 Days (Part One)

Research mentality at the Applied Physics sports day

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by Suzanne van Dam

Last Thursday was the yearly Applied Physics sports day. As is tradition, QuTech participated in big numbers. We competed with three teams, and it was clear already from the start that the goal of the day was not just to participate, it was also to win!

The QuTech team.
Figure 1: The QuTech team.

The winners mentality of the QuTech teams made me wonder: why were we more competitive than the average student team? Is there an analogy between sports and research that underpins this?

Continue reading Research mentality at the Applied Physics sports day

The remarkable effectiveness of math

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by Jonas Helsen

So this post will be a bit more, let’s say, philosophical. I’d like to share some of my thoughts on a particular subject which has always struck me when I was studying physics and also now while I’m doing it in what might be called a professional fashion. That subject is mathematics. More precisely it is mathematics as applied to physics. Now I won’t pretend to be anything close to a real mathematician, but when you need a math-person and there are no mathematicians around you can probably do worse than a theoretical physicist. In physics, and also in computer science, we use math; a lot of it. In fact I would say that, and I think most physicists would agree with me, that mathematics is the language the universe is written in. Or at least the only language capable of describing it in an efficient manner. People often marvel at the ability of mathematics to capture physical phenomena in an extremely accurate and efficient manner, often waxing philosophically about the inherent simplicity of the universe. Here I’d like to give some of my, fragmented and incomplete, thoughts on the matter. While I certainly think that the fact that nature is describable at all is a fact worth pondering over long and hard I think the prevalence of math in physics and its remarkable effectiveness is at least partly due to decidedly more down to earth cultural forces present throughout the history of mathematics.

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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