Quantum brains

I’m going to talk about quantum brains. But before I do, I have to take a bit of a philosophical detour. So bear with me and we’ll get onto the meaty quantum bits (qubits?) soon.

Disclaimer 1: This is a very general introduction article – it is probably not suitable for QIP scientists who may attempt to dispose of me (probably with giant lasers) for lack of scientific rigor…. *ducks to avoid flying qubits*

We need to think about what we are trying to build. Say we want to build a brain (in silicon, for arguments sake). Well, for a start that’s not really enough information to get on with the task. What we actually want is a mind in a box. We want it to think, and do human-like things. So we run into a problem here because the mind is a pretty vague and fuzzy concept. So for the purpose of this argument, I’m going to use Penrose’s definition of 4 viewpoints of how the mind might be connected to the physical brain, which is given in his book Shadows of the Mind, but I will summarise here for those who are not familiar with the definitions:

There are basically 4 different ways you can interpret the way the mind is related to the actual signals buzzing around and the physics going on in that wet, squishy 3lb lump that sits in your skull. Here they are:

(A) – The ‘mind’ just comes about through electro-chemical signals in the brain. You could fully reproduce a ‘mind’ in any substrate using standard computer providing you could encode and simulate these signals accurately enough. It would think and be conscious and self-aware in exactly the same way as a human being.

(B) – The workings of the brain can be simulated in exactly the same way as in (A) but it would never be conscious or have self-awareness, it would just be a bunch of signals that ‘seemed’ to be behaving like a human from the outside. It would effectively be a zombie, there would be no ‘mind’ arising from it at all.

(C) – There’s no way you can simulate a mind with a standard computer because there’s some science going on that creates the ‘mind’ that we don’t yet know about (but we might discover it in the future).

(D) – There’s no way you can ever simulate a mind because our minds exist outside the realm of physical science. Period. Even that science which we are yet to discover. (This is a somewhat mystical / spiritual / religious argument).

Interestingly Penrose goes for C – mainly because he believes that there are quantum processes occurring in the brain, and the quantum mechanics going on in there cannot be simulated using a conventional computer. So it’s not that we don’t understand the science yet, but we can’t build computers that are able to take that science into account (i.e. model the quantum mechanics correctly). Or can we… don’t we have, like quantum computers now?

Now back to the quantum braaains…

What do I think is the most exciting prospect for quantum computers? Forget factoring, what about building quantum brains? Note: I’m using the phrase ‘brain’ here in a rather unscientific sense to mean a large collection of interconnected agents – essentially a large neural network.

I am a supporter of (A) – which is a variant of the Strong AI hypothesis. That is, a human-level intelligence could be fully simulated on an alternate substrate using a standard, ‘classical’ computer and actually BE conscious and self-aware. However, with this point of view, one might wonder what a similar level of integration would be capable of if it could use some aspects of quantum mechanics as an integral part of its operation.

My viewpoint conveniently makes my argument for the further development of QCs pretty watertight. If quantum computers ARE required to simulate the human brain, (which I do not believe to be the case), then we should probably develop them anyway. If they are NOT required, but are believed (at least by some) to be fundamentally more efficient for certain computational tasks, then wouldn’t it be a cool experiment to make a brain which could harness that extra computational power? I mean… it would be a fundamentally different type of intelligence. Doesn’t that sound cool? Doesn’t that just make you smile and make the hairs on the back of your neck stand on end? Or maybe that’s just me…

Attentive readers may note that I have subtley disregarded option D here. That’s because D stands for Deepak Chopra, who is much better at explaining how QM ties in with that viewpoint than I am.

Quantum Neural Networks have already been explored theoretically. (See here, here, here for just a taste). I think very small QNNs could be realised experimentally at present. If they can be shown to work in principle, they can be scaled up and investigated further.

Adiabatic Quantum Systems based on the Ising model are perfect for this task. Their structure and behaviour resembles a spin-glass, which is mathematically equivalent to certain types of neural network. A spin glass can store patterns in ‘stable’ configurations of spins, just as the brain stores memories as patterns in configurations of the synaptic strengths between neurons (a simplistic model but it’s kinda the main point).

Of course there’s always the problem of decoherence – and it most likely will be a problem in large scale quantum systems. There’s probably some puddles of coherence around the place, maybe they overlap, maybe they don’t. No-one really knows. Could those puddles of local coherence provide any extra computational power? How connected (or perhaps disconnected) would they have to be? Can we design scalable solid state systems with larger puddles?

Again, that sounds to me like something we should investigate.

In conclusion

We should be able to simulate anything that the brain is doing (even if we need quantum computers). If the brain IS using large scale coherence in its operation, it shows us that it IS possible to build large scale coherent quantum systems (if nature can do it then so can we). This would be useful for all sorts of things, like simulating protein folding. In fact this would arguable be the best outcome. I kinda hope Roger Penrose is right…

However, I don’t believe he is right, as I currently believe the level of large-scale quantum coherent phenomena in the brain is very close to ZERO. But that means we can only IMPROVE the level by which quantum mechanics could be leveraged in brain-like systems, by building huge and densely connected NNs using quantum devices such as superconducting qubits. We can explore completely new territory in the building of intelligent systems…

Thus we have a win-win situation :)

In other words, QCs are cool and we should build them.
And we need more money *ahem*

Note: I argue this and a bunch of other stuff in my QC & AI lecture. Here is the link to my post about that

Disclaimer 2: This topic has also probably been debated to death and back on various places around the internet but it’s always good to exhume it once more for a guest appearance. In fact if I wasn’t feeling so lazy (and cold, the heating in here appears to be broken at the moment) I might have bothered to dig up some references. It’s also a useful place to send people to if they want to know my point of view on this.

EDIT: To perfectly illustrate both my points that a.) there’s loads of stuff on the internet + I’m lazy and b.) software systems are surprisingly intelligent already (WordPress helpfully pointed out the link for me) here’s some stuff that Geordie wrote about this a while ago:

Can an artificial general intelligence arise from a purely classical software system?

Media coverage, skew, and general not-in-the-Christmas-spirit ranting

Bah, humbug.

A little earlier I nonchalantly and lazily microblogged using the oh-so-professional channel of my Facebook status about something that slightly irritated me whilst watching the news. Here was what I wrote:

One attempted act of terrorism: Almost 24/7 news coverage. Thousands of scientific breakthroughs every day: Not even a few minutes of airtime. No wonder the general public feel isolated from science, in fear of technological advancement and generally depressed at the state of the world…

Anyway, seeing as the comment sparked quite an interesting conversation, I thought I’d relay these thoughts on this, my slightly more traditional soap-box haunt.

Obviously my comment pertained to the recent attempt to bring down a plane travelling from Amsterdam to Detroit. How much about this could there possibly be to report? Hours worth of television time, apparently.

It just depresses me that the news programs, day after day, cover crime, terrorism, war and political unrest as their main stories, then attempt to lighten this doom-riddled cake of hopelessness with a cherry in the form of a ridiculous human factor story about some family’s cat being rescued from a tree (or something equally banal). Earlier today I watched a story about freak weather in the UK – the seemingly important aspect of this being a woman who gave birth in an ambulance because it was stuck in the snow on a sliproad on the A14. Oh, and then there’s 10 minutes of football news!! If I were sat at a desk I would somewhat non-figuratively be slamming my head against it at this point. Luckily for me I’m on a sofa.

I’m not just going to have a long rant here about what I think the news SHOULD be covering, I think that much is pretty obvious from my list of interests ~superconducting flux qubits, yey!~ <-excuse the voices in my head.
Moreover, I'm wondering: What can we actually DO about it?

During my time in a University setting, I think I've only once been invited to a seminar by a person from the Press (in this case it was Radio 4). I think that the press just do not engage enough with scientists. There is so much cool research just waiting to be explored and popularised. There is also a large body of enthusiastic, young PhD students who would be willing to talk about what they are doing, which would not only help popularise their respective subjects, but also break that 'mad professor / scientist' stereotype which seems to still be hanging around a couple hundred years after it was actually representative.

However, until the 'media approaching scientists' kind of thing reaches a critical mass, it will be up to the scientists to shout louder and more ingeniously to make people take note. It will be up to them to chase down the media opportunities.

And I believe that there is a somewhat insidious problem here – primarily that it's not considered a worthwhile activity amongst science/engineering peers to communicate and popularise your research. Carl Sagan et al. are very much the exception rather than the rule. Popularisation is certainly not taught alongside science, or encouraged, even though there are lots of external grants available for this kind of thing. We rely on the rebellious defector amongst academics to propagate the enthusiasm. Instead, we should be supporting those who wish to act as spokespeople for their research.

A lot of media types are also looking for the ‘scare story’ angle. They will try every trick on the book to hype the negative angle of your research, especially of you are working in disruptive or controversial technology areas. I think that academics should be trained to answer media questions a bit like politicians: Get across the positive impact at all costs (short of actually, you know, lying..). And for goodness sake don’t mention Skynet. Or nano greygoo*ahem* tech. It’s ‘submicron’ or ‘molecular’ engineering, guys!

Ultimately, the goverment hands out the money to the funding councils, and therefore if we as scientists aren’t in the forefront of their minds (I mean look, we’re competing with the NHS, the education system, the war in Afghanistan, etc….), if they don’t see our science and go “Wow, you know – that’s not only the future of our country, but it’s actually pretty interesting too”, then funding for our research will indeed be cut.

So go out there and tell people that your research, be it Physics or whatever, is awesome. In any way you can. Ignore anyone who tells you that it isn’t worthwhile. And if you do it right – if you do it *really* right – then those people might just mention it to their friends the next time they have tea and cake ;)


Note: On this topic with a slightly more transhumanist slant, inspired by the conversation, Stuart has also written a blogpost.

Merry Christmas by the way people.

A flurry of interesting preprints…

My pick of interesting recent ArXiv papers…
So much to read, so little time!

Robust Entanglement in Anti-ferromagnetic Heisenberg Chains by Single-spin Optimal Control

Quantum System Identification: Hamiltonian Estimation using Spectral and Bayesian Analysis

Hierarchical Genetic Algorithm Approach to Determine Pulse Sequences in NMR

Efficient creation of multipartite entanglement in flux qubits

Spin Systems and Computational Complexity

Algorithmic Technique for Decomposing Unitary Operations in NMR Quantum Computation

Qudos on the Qudits!

Martinis group at UCSB have demonstrated operations on a quantum bit with 5 levels (qudit with d=5) instead of the usual 2 (qubit):

“Emulation of a Quantum Spin with a Superconducting Phase Qudit”
Matthew Neeley,1 Markus Ansmann,1 Radoslaw C. Bialczak,1 Max Hofheinz,1 Erik Lucero,1 Aaron D. O’Connell,1 Daniel Sank,1 Haohua Wang,1 James Wenner,1 Andrew N. Cleland,1 Michael R. Geller,2 John M. Martinis1,

They use a standard type of phase qubit experiment in which the quantum states are defiined by a ladder of energy levels in a single potential well, rather than the more common flux qubit where the energy levels arise from the degeneracy between two adjacent wells. The qubits/qudits are controlled by applying very careful timed and shaped pulses of microwaves to excite the quantum states between levels and to allow the levels to interact with one another. The energy between each level is very slightly different due to the anharmonicity of the Josephson junction’s energy landscape, so each level transition has a unique ‘frequency signature’. (This scheme wouldn’t work if the quantum states were in a harmonic oscillator, as all the levels would be equally spaced.)

The group demonstrate a shift in the Ramsey fringes which equates to the expected Berry phase produced by the rotation of the quantum state around the Bloch Sphere. They also demonstrate robust Rabi oscillations and the swapping of quantum information between states. The relaxation times of the states are all in the 100’s of ns, but are smaller for the higher states.

I can’t really stress how exciting this result is for experimental quantum computation with superconducting circuits – it opens up new possibilities for implementation of algorithms and quantum simulation. The group focus on the potential of the technique for emulating quantum spin systems.

I wonder what algorithms have been developed that require multi-dimensional Hilbert spaces for their implementation? I know that higher dimensional quantum bits can help make quantum cryptography more secure. I find a sudden renewed interest in learning about qudits…

I’m also slightly smug in my opinion that this once again puts Josephson SC qubits marginally ahead in the awesomeness stakes. (Those ion trap guys were really giving us a run for our money). Qutrit systems (3 levels) have been realised in NMR and Ion trap QC but I believe that experiments like this really open up the door for more complex QIP realizations.

It’s not cake but it’s close!

Here are some pictures of our Liquid Nitrogen Ice cream endeavours… mmm. Disclaimer: Don’t try this at home unless you have had training in handling cryogenic liquids :)

physics and cake

Ingredients: Cream, milk or that strange stuff we don’t have over here, sugar, crushed fruit, and liquid nitrogen. Recipe: Stir the sugar into the cream until it dissolves, then beat it with a whisk until it is light and fluffy. Then add the fruit, mix it in, and then add the LN2, stirring continously until it has hardened. It takes about 5 minutes, as opposed to waiting for it to cool in the freezer for hours. You can use chocolate chips too but for some reason the fruit one seemed to come out better.

physics and cake

Because you have to keep stirring it, it tends to come out in fluffy bits rather than scoopable ice cream, but you can still pack it into a bowl or cone the same way :)

physics and cake

Rather tasty too. You have to be careful when you eat it, sometimes you get a REALLY cold bit in the middle and a rather bad Ice Cream Headache
To keep it from melting on a hot summer’s day, just add more LN2 topping:

physics and cake

Supercool talks

So we’ve had a week of University Admissions open days and activities days here in Physics land. Here are a couple of pictures where I’m giving a talk entitled ‘Supercool Computers’ to AS level students (16-18).


We typically show some demonstrations with Liquid Nitrogen, verify that gases do not follow the ideal gas law using balloons, show electrical resistance at low temperatures, explore Lenz’s law at different temperatures using magnets and copper tubes and show some of the lovely properties of (High-Tc) superconductors such as the Meissner effect by levitating magnets.


The talk also introduced some fairly advanced concepts such as some fundamental aspects of Quantum Mechanics and practical Quantum Computing. In fact we have a HTC SQUID set up in the talk demonstrating the wave properties of electrons, analogous to the Young’s double slit experiment. The idea is to whet the appetite of potential students and make them realise that Physics isn’t all astronomy and the LHC, and that device physics/QC can also be a damn sexy thing to study :)

It’s all rather fun. I had this great toy to play with called a ‘visualizer’ which is basically a camera hooked up to the projector. Great for showing demos. I even zoomed in on some SQUID chips to show the audience the results of the microfabrication process.

Eventually I’m hoping to get a video of the talk up online when I’ve harrassed someone into filming the event and done it enough times to get all the demos working smoothly. We had issues with a dodgy multimeter this time. Lesson of the day: Never work with children or electronics.

Circuit diagrams of real neural systems


How to Map Neural Circuits With an Electron Microscope


“This giant, and potentially revolutionary, task requires custom software, electron microscopes and an incredibly sharp knife. If everything goes right, the team may be the first to create a circuit diagram that explains how mammals see.”

Photo Credit: Marc Lab / Moran Eye Institute

This is just too cool for words.

I’m reading permutation city by Greg Egan at the moment – which paints a picture of a world where the human nervous system has been sufficiently ‘mapped’ to such an extent that simulations of the brain can be run resulting in artificial (or actual – you decide) intelligence. Strong AI for the win! *ahem*

How far away is this technology? If we can map neural pathways by taking slices, scanning them with an SEM/TEM, and and automatically reconstructing the 3D original using clever software.. then all you need to do is bring it to life digitally using a wetware-friendly circuit simulator – I’m not sure such a thing exists… If not, lets develop one and call it MeatSPICE :)

Seriously, I have a colleague who does work on electrical models of the nervous system. You can essentially model neurons and axons as electrochemical transmission lines with inductance, capacitance and resistance. It’s a good way for physicists, biologists and biochemists to collaborate.

I also have a slight penchant for this kind of thing seeing as I love using the SEM as an imaging tool. In addition, I recall spending a couple of weeks once doing some work experience at the histopathology department of my local hospital; watching how you actually make those waxy slices and observing them under an optical microscope. (Although we were looking for cancer cells in that particular case and musing over how you could automate such a task).

I’d love to put a load of these ideas together into something tangible to research (as an aside to my already busy schedule!), but it’s a wide, diverse assembly of proto-thoughts (of which I have far too many), requiring quite a large collaboration from different fields.

On a slightly different note, WIRED has now been released as a magazine version in the UK. Which means all my pocket money is belong to them :(