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.
In a series of blog posts, I want to introduce the bread and butter of the DiCarlo group within QuTech: Studying quantum effects in superconducting electrical circuits. In the title, I suggest that we are building artificial atoms, but that depends on the definition of “atomness”. I hope to give the reader some insight to judge for him or herself whether our work comes short of this or goes beyond it. Also, I want to convey some of the amazement I feel working on a subject that brings together electrical engineering, superconductivity, and quantum mechanics in its purest form.
This blog post is rather long, but I have marked non-essential sections with a *.
One of the things that is often repeated about quantum computing is the idea that a quantum computer is somehow more powerful than regular computers because, when considering a problem it can “try all possible solutions at once”. Let’s get this out of the way first and say that this is not exactly the case. While we would very much love a computer that tries all solutions at once (this would be extremely useful) quantum computers sadly aren’t quite this powerful. Of course, as with all good clichés it does contain a grain of truth. In this blog post I will try to explain in a (sort of) simple way what makes quantum computers more powerful than classical computers.
You have probably heard that entanglement is a very strong correlation way beyond anything we can conceive classically. However, as we’ve seen from Jeremy’s post , these strong correlations by itself do not allow us to send any information to the other part. So what can we use entanglement for?… To play games!
There are many things that might pop in to your mind when I propose that you may be able to do quantum mechanics in the comfort of your own home. A ‘quantum kitchenette’ is probably not one of them.
This may have been a bit facetious, but it is true that many of the things you find in your kitchen such as a fridge, a microwave and beer bottles are perfectly analogous to the tools that are used in labs around the world to perform cutting edge experiments in quantum mechanics – in particular with applications in quantum computing.
These tools are technically challenging to fully understand, very expensive and equally impressive in their capabilities. As an experimental physicist, one of the most enjoyable parts of the job is using this equipment, understanding fully how it works so we can use and repair it if need be, but also the small idiosyncrasies that each specific piece of equipment acquires over time.
On a personal level, you really do develop an intimate relationship with your equipment, such that in some cases you are the only one who can use it reliably. A shorter way to summarise the connection might be: “Boys and their toys”, or whatever phrase would convey the same meaning in a more egalitarian manner.
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.
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.
Entanglement may seem mysterious. It permits us to have correlations between two separate systems that are arbitrarily far from each other. Moreover these correlations are stronger than any (non causal) classical correlation we can think of. In some ways it looks like the two quantum systems can communicate between each other. This is why some people think that it might be possible to use it to devise an instantaneous communication system. I will try here to give you an intuition as to why this is not possible. But before we see why using only entanglement does not permit you to communicate, we have to understand what we really mean by ‘communicate’.
The general purpose programmable computer has been an enabling technology that has exceeded the original expectations in countless ways. From the humble beginnings of the original transistor, we now have devices that contain several billion transistors all working perfectly in unison in the smartphones we keep in our pocket. Our great hopes for the quantum computer are partially based on the belief that this could happen once again with the quantum computing paradigm.
The main challenge for realizing the quantum computer is certainly finding a suitable ‘quantum hardware’, that’s why it is still mainly a physics effort. However, it will also require a significant amount of computer programming and design. This makes our field interdisciplinary and soon computer scientists and engineers will likely play important roles in the further development of the quantum computer.