Dan Browne

Dan Browne

Dan Browne is a Professor of Physics at University College London. His research specialism is the theory of quantum computers.

Activity

  • That is a great question, Melvin. There is a bit of an art to identifying problems suitable for quantum computers to provide a speed up. This usually involves identifying a bottleneck in known classical algorithms - i.e. what part of conventional algorithms is slow and scaling poorly - and knowing a quantum algorithm which has a speed up for solving that kind...

  • Welcome to the course, Chris!

  • This is a great summary. We have been able to demonstrate these kinds of effects with atoms and molecules, but as you point out, it would be impossible for a human skier. Decoherence is too strong for large objects like humans for persistent quantum effects like this to be seen. Nevertheless, we know of no fundamental reason (yet) why it could never happen...

  • Hi Gemma. This is a very good question. Quantum computers will have the most impact on society once they are able to be used to perform calculations impossible on today's (classical) supercomputers. When this will happen is hard to predict, but I talk about a possible timeline in Video 2.16 next week.

  • Welcome to the course Karthick! I hope you find it helpful. There are many post-graduate opportunities in quantum computing at the moment and I hope the course helps you get a clearer vision of the field and the state of the art.

  • Welcome to the course Ale!

  • Thanks Martin! You might not be able to upload the picture, but you could post a link. It is fun to see how artists have interpreted quantum phenomena.

  • Thanks for this Patrycja. I've not watched this new Black Mirror series yet. I'm curious to see how the quantum computer is presented there!

  • To your third question, the leading algorithm for factoring large numbers on a classical computer is called the general number field sieve, whereas the leading quantum algorithm is called Shor's algorithm. The two algorithms work in completely different ways, relying on different mathematical aspects of the factoring problem.

    You can find articles on both...

  • To your second question, the answer is "yes and no". On the one hand, a perfect quantum computer can be perfectly simulated by a classical computer (although this will take memory and run time which grows exponentially in the number of qubits, so the computation may be too slow to be feasible), and on the other, a quantum computer can perform classical...

  • Hi Angus. These are some good questions. To start with your first one, this depends what you mean by useful. After a qubit has been measured, its state will have changed (we sometimes say the state has "collapsed"), the superposition destroyed and the information it contained will have been read out. So you could say that this qubit is no longer playing an...

  • Yes it is striking how many "traditional" companies in engineering and finance are starting to take quantum computing seriously.

  • This is a good summary Saul. The potential power of quantum computers is something which sometimes gets overhyped and exaggerated, and in particular you sometimes read that quantum computers might speed up all current computations, which we do not believe to be true, but you have avoided this with your careful wording. One very pedantic comment - on your last...

  • Quantum gravity is perhaps the least understood area of physics. It is very much a work in progress. Interstellar incorporated a lot of known physics (such as time dilation in gravitational fields) in the plot to an impressive degree.

  • It is indeed possible to access real quantum computers at IBM over the internet. Anyone can register to do it, and I will lead a live workshop (which I recommend you sign up to) in September where we will lead participants through doing their own experiments on IBM's devices.

  • The principle of superposition (sometimes described as allowing simultaneous states of 0 and 1) is absolutely key in the difference between quantum and classical computing and something which will be an important focus of the course. Quantum computers do indeed hold the potential for cracking public key encryption, due to Shor's algorithm for factoring...

  • Hi Saul. Welcome. We are glad to have you on the course. Computer science will give you a solid background for learning about quantum computing. I'm aware that many computer science departments are starting to offer quantum computing courses to their undergraduates (though usually in the 3rd or 4th year). Is Sheffield offering that?

  • Welcome to the course Martin! With a Chemistry and Computing background you are well-placed to learn quantum computing. What are you most looking forward to in the course?

  • I don't understand Shazam well enough to know if a quantum computer could speed it up, but this is a great suggestion. Classical artificial intelligence is making such rapid progress these days, that it is unclear whether AI really needs the help of a quantum computer. However, the idea of combining ideas from AI and Quantum is very exciting and is a very...

  • This is a great response. Microsoft are taking a very different path to most other companies, and it will be exciting to see if they can succeed in this approach.

  • Are you referring to this story: https://thenextweb.com/news/research-milestone-solve-quantum-computing-scalability ?
    This is quite an exciting development indeed. There are some big challenges in realising large scale quantum computing with photons, and a significant one is that implementing quantum logic gates which generate entanglement between photons is...

  • You are right. That's the wrong way round! Thanks for spotting this. I will edit it.

  • Welcome to the course Sarah. Quantum computing has inspired quite a bit of art and music. You might be interested in this music which was composed (generated?) using a quantum computer https://www.soundclick.com/artist/default.cfm?bandID=1491038. Also check out Baba Brinkman's rap on quantum computing, written with the help of the quantum engineers at Google...

  • @SarahH Thanks for your comment and link. That is an excellent video for understanding binary. It is important to feel comfortable with how bits are used and how they represent numbers and information before moving on to qubits.

  • Welcome to the course, Anna. Your computer science degree will help you! In many ways, quantum computing is very similar to classical computing, and an understanding of the basics of classical computing is essential to appreciating the differences (and therefore potential advantages) of quantum computing. Many researchers in quantum computing have a computer...

  • All very good points.

  • These are some good points. It is interesting to see a call for regulation in this video from two leaders of startup companies. It is usually assumed that startup companies want to be freewheeling and unencumbered by regulation, but the video shows that this is far from the case.

  • @EdwardShelley Thanks. This is an entertaining and informative video.

  • Thanks very much for you kind words Peter. Entanglement is indeed one of the most fascinating and surprising aspects of quantum mechanics. It was first proposed in the 1930s by Schrödinger, and the rise of quantum computing in the mid-1990s spurred on a lot of theoretical research. Nowadays entanglement is well understood in many ways, but still continues to...

  • This is a very good point. Indeed several people have predicted that quantum computing power might achieve a similar Moore's law scaling. These include the former CEO of D-wave 'Geordie Rose who posited "Rose's law" that there would be exponential scaling in quantum annealing processors, and the head of Google's quantum team Hartmut Neven proposed "Neven's...

  • That's right. Both genetic algorithms and quantum annealers are optimisation algorithms, so there are indeed similarities between them. A key difference is that the quantum annealer is using quantum mechanical effects to "search" for the optimal solution, rather than trying many variants and picking the best.

  • There are several ideas for using quantum mechanical effects for non-destructive imaging. It is a very promising area. In the UK research efforts are being led by the Quantum Imaging Hub https://www.quantic.ac.uk/aboutus/.

  • We certainly see quantum computing having a cultural impact. A lot more quantum ideas are appearing in scientific fiction these days, and increasingly, I feel, in art.

  • Thanks @LakhbirBawa Quantum computers have huge potential in these areas and it will be interesting to see how software engineers are able to take advantage of them.

  • Thanks @PeterDarvas There is a subtle relationship between quantum computers and big data. On the one hand, quantum states can represent a lot of data at once, but both reading in and reading out this data can be slow and difficult. The most promising applications of quantum computers seem to be where the problem posed can be described by a relatively small...

  • That's an interesting comment @AbdelrahimShaaban It is a very interesting question whether banks and funds will be able to gain a trading advantage by using quantum computers. There is huge potential here, and some far-sighted banks are already putting together in-house quantum computing teams to push this forward.

  • That's a great suggestion @EdwardShelley . We do expect quantum computing to have a significant impact on encryption. To build a quantum computer large enough, and low-error enough to crack the public key encryption we currently use is still a very significant challenge, but it is believable that it could be here within a decade. Now is certainly the right...

  • Thanks for your comment @RaunakMisra. Can you please clarify what you are asking? Is it about the heads and tails experiment in the live workshop?

  • Many of the textbooks out there are at a graduate student level, but I've heard good things about Quantum Computing for Everyone by Chris Bernhardt. I've actually just ordered a copy of this book myself to check it out.

  • Hi @JosephineMagnani, we have some suggestions for further resources in the next section 1.21. Another book that I have heard good things about (but haven't had chance to read myself yet) is "Quantum Computing for Everyone" by Chris Bernhardt.

  • Thanks @LakhbirBawa, that is a good overview of the potential promise of quantum computing. We do not yet know for certain that weather modelling and financial modelling will be accelerated on quantum computing, but there is certainly a lot of interest, particularly in the latter, and major banks, such as JP Morgan and Goldman Sachs now have in-house teams...

  • Thank you! I myself have collaborated with an artist to develop art based upon quantum technologies. In the end, an installation, based on the way data is stored using quantum cryptography, was used as a window covering on a new office building in central London! You can see it in the photos here:...