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.
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?
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.
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’.
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.
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.
Welcome to ‘Bits Of Quantum’, the official blog by QuTech! QuTech is an academic research institution that houses many scientists who spend a large part of their time doing mathematics, experiments, and a lot of quantum mechanics. We would like to share bits of our quantum research with you, and give you a taste of what life in a large research institute is like. To that end we, four PhD students from different parts of QuTech, started the blog you are looking at right now. As the editorial team we are very excited about channeling all the stories that can be told by and about QuTech and quantum technologies. Thank you for reading this blog and we hope you enjoy reading the many posts to come!
The editorial team, Jonas, James, Adriaan and Suzanne
Jonas Helsen – Hey! My name is Jonas and I am one of the theorists at QuTech. I only started my PhD a year ago so I still have lots to learn but I’m really excited about being here! I’m also passionate about teaching people about the magical world of quantum computing which is why I co-started Bits Of Quantum with my lovely co-editors! Happy reading!
James Kroll – I am James, an experimental physicist hailing from Scotland. I work in the topological quantum computing roadmap of Leo Kouwenhoven, as it requires an exciting mix of condensed matter physics theory, experimental cryogenics, electrical engineering and computer programming – all things that I somehow enjoy. If I’m not in the lab, you will most likely find me cycling somewhere or reading. Or eating. That’s a pretty important part of my life.
Adriaan Rol – Hi, I am Adriaan, an experimentalist in Leo DiCarlo’s group where we are working on a quantum computer based on superconducting transmon qubits.
I really enjoy trying to find the (abstract) essence of things while at the same time being able to experimentally test if my ideas actually work.
Whenever I’m not in the lab you’ll probably find me on the water or enjoying an overpriced coffee at my favourite coffee place.
Suzanne van Dam – My name is Suzanne, and I am doing a PhD in the lab of Ronald Hanson, since two years now. One of my favourite things is to see the quantum world in the lab on a daily basis. My hope is that from this blog it will become clear why I am so excited about this!