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.
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.
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.
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.
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.
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 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?
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.
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?