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.
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.
After some years of doing science in the dark basement of a physics building, one may wonder: ‘who am I?’ Searching for answers at Google Images, there turns out to be a distinct difference between the stereotypes ‘scientist’ and ‘physicist’. Surprisingly, a ‘scientist’ always wears a lab-coat plus safety glasses. The ‘scientist’ works in a clean lab environment, handling chemicals and a microscope. According to Google, the ‘scientist’ is happy and young, can be male or female, black or white.
How large is the contrast to Google’s ‘physicist’: an old, somewhat otherworldly, serious man wearing thick glasses. The man standing in front of a whiteboard is writing down equations and drawing spheres on a blackboard. It is interesting to notice that Google barely makes a distinction between ‘physicist’ and ‘professor’. Leaving behind the fact that both a ‘scientist’ and a ‘professor’ can be an academic in any kind of field, I wonder why the ‘physicist’ never conducts any experiments.
Sweet Grandmother’s Spatula! After pulling out your fresh cookies from the oven and taking your first taste you notice that in creating your cookie dough, you accidentally mixed up the sugar and salt. Now your dreams of enjoying that oh so sweet sugar cookie have been dashed away and you are left with a confectionary calamity. However, all is not lost…. your seemingly imperfect dough with salty defects can be fixed to result in the masterpiece of baked goods. Thus I present to you, the challenge of baking the chocolate chip and sea salt cookie. When balanced correctly, these two flavours can enhance each other to create complex layers of pure deliciousness.
Now you may be asking yourself, what does this have to do with quantum mechanics? Picture your salty cookie, full of defects within its dough, seemingly useless. However, if you add the right amount of chocolate chips in places as accurately as possible, you will achieve the right balance of flavour and achieve the perfect chocolate chip and sea salt cookie, a true baking delicacy. Likewise, in experiment, we begin with a crystal that contains lattice defects with quantum properties. In the general scheme of things, the goal is to add other materials within or near the substrate in as precise a location and concentration as possible so that we may enhance, control and measure these defects.
When people talk about physics, and in particular the human side of it, the ‘doing’ physics, they will usually point out that there exist two main forms of physicists. There are experimentalists, who spend their days gathering data in labs or tinkering with huge particle accelerators. These physicists, although rarely actually wearing white lab coats – at least in my experience – seem to be the closest to the pop culture stereotype of a scientist: wedding a strong analytical spirit to a practical, do-it-yourself mindset and a work ethic that often borders on obsession. They form the majority of physics practitioners and often speak with mild disdain about the ‘other’ type of physicist: the theorist. Theorists differ from experimentalist in that they mostly do, well, theory. Their days are usually not spent tinkering with equipment or analysing data but rather studying literature and diving into the complicated mathematics needed to describe modern physics. They often eschew the practical in favour of a generalist, axiomatic mindset; using as few assumptions as possible to describe the largest possible piece of the physical puzzle.
Throughout history these two strands of physics were usually not distinct professions but merely reflected the interests of a singular physicist. Even Newton, the prototype of a theoretical physicist, regularly performed experiments using prisms and even built one of the earliest reflecting telescopes. In my understanding of the history of physics these two strands of physicist started splitting into true professions in the late 19th century and early 20th century in response to the ever growing complexity of physics. Over time they grew further apart until the present day where among many theorists it is considered a point of pride to have never performed any experiments at all. Entire careers can be wholly devoted to the understanding of ‘physical theories’ that are decades away from being subjected to experimental verification. On the other hand, as the scale and complexity of experiments has grown, many experimentalists find themselves spending most of their time not doing physics but the cutting edge engineering work necessary to perform modern experiments to begin with. This has lead both groups to develop language and practices which differ immensely and can lead to almost Babylonic misunderstandings in the occasions where theorists and experimentalists do meet.
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.