7 ms·

Google Project Lets You Program a Simulated Quantum Computer

139 points by amaks 12y ago

Oculus 12y ago
Google also released a video[1] describing their joint investment in a D-Wave "quantum computer" (given the debates I've left it in quotes) with NASA. It talks about some cool potential applications and attempts to break down the very basics. What I'm wondering is if the investments into quantum computing by Google is merely them sinking left over R&D cash or if they believe that powerful quantum computers can be achieved relatively soon? 1 - https://www.youtube.com/watch?v=CMdHDHEuOUE https://www.youtube.com/watch?v=CMdHDHEuOUE
dangirsh 12y ago
For those that might prefer a more functional/strongly typed approach, see Quipper (embedded in Haskell): http://www.mathstat.dal.ca/~selinger/quipper/ http://www.mathstat.dal.ca/~selinger/quipper/ Unfortunately, the examples in the documentation aren't as well known as Shor's or Grover's algorithm. For Shor's, I think this is due to the difficulty of encoding the modular exponentiation within the framework.
tobyjsullivan 12y ago
Simulator doesn't seem to work for me with Chrome. JS Console reports WebGL issues...
- theon144 12y ago
  While it does work perfectly for me in Firefox, against which it warned me. Ha.
Xcelerate 12y ago
This is great! I think quantum computers are inevitable at some point as soon as we figure out how to effectively isolate them from their environment (to prevent decoherence). In this case, the theory is way ahead of the practice, and it would seem wise to go ahead and begin offering CS courses now in quantum programming and quantum algorithms so by the time these computers are built, we're all ready to hit the ground running. Websites like this one Google has made are a good start. Quantum computing will revolution a lot of fields. In my field (molecular dynamics and quantum chemistry), there's an issue known as the fermion sign problem, which essentially puts a hard limit on what we can accomplish through classical simulation. It basically says that the most accurate methods of performing quantum simulation scale with 2^(3N) number of particles. There is no classical computer that can handle this for any molecular system of interest, and there will never be one either. However, a quantum computer can solve this problem in non-exponential time (can't remember the exact complexity off-hand). What does this mean? Quantum simulation will lead to huge advances in materials science. Maybe we could even find a room-temperature superconductor with this kind of approach.
- deleted 12y ago
  [deleted]
- ballstothewalls 12y ago
  How can you say that no classical computer will ever be able to handle a simulation that big? Where is the bottleneck?
  - Xcelerate 12y ago
    Let's say you want to simulate three carbon atoms with near perfect accuracy (not considering constituent quarks, radiative effects, or relativistic effects). We'll remove the BO approximation though. So that's 2^(3 atoms * 3 coordinates * 3*12 particles) = 2^324. That's more than the number of particles in the universe. A classical computer that can handle that is simply not gonna happen. And that's just three atoms.
    - ScottBurson 12y ago
      Are you sure it shouldn't be 2^(3 + 3 + 3*12) = 2^42 ? That would still be a pretty big number, but not yet astronomical.
    - ballstothewalls 12y ago
      I understand that is massive, but aren't computers today doing things that seemed utterly impossible forty years ago?
  - Dn_Ab 12y ago
    Simulating classical systems results in slow downs that are only polynomially with respect to system size while quantum systems slow exponentially. Consider that a quantum system of n qubits would require a classical system able to cope with 2^n bits. But you might be right since there is a (remote) possibility that classical systems can efficiently simulate quantum systems. However, it is generally believed that quantum computers are more powerful than classical but not strong enough to solve NP-complete problems.
  - 12y ago
habosa 12y ago
This is a naive question, but how can we simulate a quantum computer on a classical computer? Isn't the whole point of developing quantum computers that they enable computations that are totally outside the capabilities of a classical computer? I'm sure I'm missing something simple here.
- thret 12y ago
  “Anyone who considers arithmetical methods of producing random qubits is, of course, in a state of sin” John von Neumann
- Xcelerate 12y ago
  Every computation that can be performed on a quantum computer can be performed on a classical computer, albeit sometimes with exponential slow-down.
  - ntoshev 12y ago
    Right, so the value of the simulation is somewhat questionable. Exponential slowdown is enough to kill all intuition about what works and what doesn't. You only get some correctness gurantee and that would be for very small problems / test cases.
    - kremlin 12y ago
      I see the value: you get to debug real, working algorithms based on a quantum computer so that once they're available, you already know many of the fundamentals and pitfalls of programming it. I was thinking myself about the problem of 'slowdown' of this type of approach -- I think it would be interesting if the simulated quantum computer could also give you performance metrics that say, 'If this were run on a real quantum computer, it could have been done in 100 cycles as opposed to 2000.' So you could make an algorithm in normal computing, and one on a simulated quantum computer, and compare the running time of the normal computation with the projected running time of the simulated quantum algorithm (obviously the actual running time of the simulation would be incomparable to the projected running time). I think that would be quite useful.
grdvnl 12y ago
If any Pythonista's out there want to do some simulation, [Sympy](https://github.com/sympy/sympy https://github.com/sympy/sympy) offers some simple quantum gates to work on.
- krastanov 12y ago
  Qutip is much better adapted at that (also in python). https://github.com/qutip/qutip/ https://github.com/qutip/qutip/
ibrad 12y ago
This is the new 60s . We will start by creating quantum punch cards. But eventually it will get better and easier.
- mantrax5 12y ago
  It's not the new 60s, because we already have existing computers to back us up in terms of automation, simulation and so on of whatever is to come. Case in point, the article. It'll be the "60s" maybe for a few months, at the most. Development is accelerating, and it'll never slow down.
- jesuslop 12y ago
  We are waiting for the would-be Shockley, Brattain and Bardeens.
hellbreakslose 12y ago
Thats actually really cool, its about time for our generation to get more familiar with the future!
S4M 12y ago
Apology for the naive question, am I supposed to be able to see the difference between a quantum computer and a standard computer from the simulator? I ran some basic examples, and while it seems a neat scripting language to play with the computer, I couldn't see anything unusual. My vague knowledge about quantum computers is that they don't deal with binary bits (that can be only 0 or 1), but their "bits" (qubits?) can be anything from 0 to 1, which should accelerate massively some calculations.
- j2kun 12y ago
  > but their "bits" (qubits?) can be anything from 0 to 1 This is not the interesting part, because there are models of computation that allow for this, but are believed to be equivalent to classical computation. What makes quantum computing different is that 1. the basic data are unit vectors in a 2^n dimensional vector space (when you have n qubits) and 2. you don't have direct access to the qubits during a computation, and "reading" a qubit destroys all the information in any related qubits! So imagine a classical computer program where reading a variable destroyed the content of your other variables! That's closer to the quantum model. So it's more of a semantic difference than a syntactic one.
higherpurpose 12y ago
DJB will probably be quite excited about this.
fulafel 12y ago
Anyone know details about the WebGL GPU acceleration? I assume "GPU-accelerated quantum computer" means the computations are also GPU-accelerated.
drkevorkian 12y ago
This is a cool demo, but I'm afraid this is the wrong pedagogical approach to understanding quantum computing. The representation of the quantum state as a bar chart is difficult to interpret and provides little intuition. The fact is, visualizing vectors in high-dimensional spaces is hard, much less vectors in high-dimensional complex spaces. Bra-ket notation is pretty much the best thing we have right now. But more generally, "Quantum programming" will almost certainly look nothing like this. This is like programming a classical computer by describing a boolean circuit. It's an extremely useful model for researchers working with actual hardware, but there's a reason we currently program with lambda calculi, not NAND gates. Understanding how to capture the possibilities of quantum circuits in a higher-level language is an open problem. Many interesting attempts have been made at solving it, but none convincingly in my opinion.
kvb 12y ago
MSR's LIQUi|> [1] looks like an interesting approach to this problem (although I'm not sure there's a publicly available way to use it). [1] http://research.microsoft.com/apps/video/default.aspx?id=194277 http://research.microsoft.com/apps/video/default.aspx?id=194...
jameshart 12y ago
Damian Conway's Perl Quantum::Superpositions module (http://search.cpan.org/~lembark/Quantum-Superpositions/lib/Quantum/Superpositions.pm http://search.cpan.org/~lembark/Quantum-Superpositions/lib/Q...) dates back to 2000 and lets you play around with datatypes that act like they are in multiple superposed states at once; Damian's presentation of the module was an entertaining journey into language hacking as well as quantum physics - well worth looking up on youtube.
- jerf 12y ago
  Bear in mind that the resulting module is not real "Quantum Computing", but an implementation of the conventional misunderstanding of quantum computing. Damian Conway understands real QC just fine (at least well enough to know this). It's a choice he made to implement this library for fun, as is his wont [1]. However, be aware that playing with that module will do nothing whatsoever to prepare you for real quantum computing. [1]: http://www.csse.monash.edu.au/~damian/papers/HTML/Perligata.html http://www.csse.monash.edu.au/~damian/papers/HTML/Perligata....
porsupah 12y ago
Perhaps also germane to the discussion is the University of Bristol's "Quantum in the Cloud" project, which similarly offers access to a simulator - but, once you've refined your project, you can then submit it to a real quantum computer: http://www.bristol.ac.uk/physics/research/quantum/qcloud http://www.bristol.ac.uk/physics/research/quantum/qcloud
peterderivaz 12y ago
I enjoyed this blog post and Javascript implementation of an interactive Quantum circuit inspector. http://strilanc.com/quantum/2014/03/07/Building-your-own-Quantum-Fourier-Transform.html http://strilanc.com/quantum/2014/03/07/Building-your-own-Qua... It is a lower level than the Google project and only suitable for 3 qbits circuits, but I found it very useful for building up an intuition about the basic logic gates.

139 points by amaks 12y ago

Google also released a video[1] describing their joint investment in a D-Wave "quantum computer" (given the debates I've left it in quotes) with NASA. It talks about some cool potential applications and attempts to break down the very basics. What I'm wondering is if the investments into quantum computing by Google is merely them sinking left over R&D cash or if they believe that powerful quantum computers can be achieved relatively soon? 1 - https://www.youtube.com/watch?v=CMdHDHEuOUE https://www.youtube.com/watch?v=CMdHDHEuOUE

dangirsh 12y ago

For those that might prefer a more functional/strongly typed approach, see Quipper (embedded in Haskell): http://www.mathstat.dal.ca/~selinger/quipper/ http://www.mathstat.dal.ca/~selinger/quipper/ Unfortunately, the examples in the documentation aren't as well known as Shor's or Grover's algorithm. For Shor's, I think this is due to the difficulty of encoding the modular exponentiation within the framework.

tobyjsullivan 12y ago

Simulator doesn't seem to work for me with Chrome. JS Console reports WebGL issues...

theon144 12y ago
While it does work perfectly for me in Firefox, against which it warned me. Ha.

Xcelerate 12y ago

This is great! I think quantum computers are inevitable at some point as soon as we figure out how to effectively isolate them from their environment (to prevent decoherence). In this case, the theory is way ahead of the practice, and it would seem wise to go ahead and begin offering CS courses now in quantum programming and quantum algorithms so by the time these computers are built, we're all ready to hit the ground running. Websites like this one Google has made are a good start. Quantum computing will revolution a lot of fields. In my field (molecular dynamics and quantum chemistry), there's an issue known as the fermion sign problem, which essentially puts a hard limit on what we can accomplish through classical simulation. It basically says that the most accurate methods of performing quantum simulation scale with 2^(3N) number of particles. There is no classical computer that can handle this for any molecular system of interest, and there will never be one either. However, a quantum computer can solve this problem in non-exponential time (can't remember the exact complexity off-hand). What does this mean? Quantum simulation will lead to huge advances in materials science. Maybe we could even find a room-temperature superconductor with this kind of approach.

deleted 12y ago
[deleted]
ballstothewalls 12y ago
How can you say that no classical computer will ever be able to handle a simulation that big? Where is the bottleneck?
- Xcelerate 12y ago
  Let's say you want to simulate three carbon atoms with near perfect accuracy (not considering constituent quarks, radiative effects, or relativistic effects). We'll remove the BO approximation though. So that's 2^(3 atoms * 3 coordinates * 3*12 particles) = 2^324. That's more than the number of particles in the universe. A classical computer that can handle that is simply not gonna happen. And that's just three atoms.
  - ScottBurson 12y ago
    Are you sure it shouldn't be 2^(3 + 3 + 3*12) = 2^42 ? That would still be a pretty big number, but not yet astronomical.
  - ballstothewalls 12y ago
    I understand that is massive, but aren't computers today doing things that seemed utterly impossible forty years ago?
- Dn_Ab 12y ago
  Simulating classical systems results in slow downs that are only polynomially with respect to system size while quantum systems slow exponentially. Consider that a quantum system of n qubits would require a classical system able to cope with 2^n bits. But you might be right since there is a (remote) possibility that classical systems can efficiently simulate quantum systems. However, it is generally believed that quantum computers are more powerful than classical but not strong enough to solve NP-complete problems.
- 12y ago

habosa 12y ago

This is a naive question, but how can we simulate a quantum computer on a classical computer? Isn't the whole point of developing quantum computers that they enable computations that are totally outside the capabilities of a classical computer? I'm sure I'm missing something simple here.

thret 12y ago
“Anyone who considers arithmetical methods of producing random qubits is, of course, in a state of sin” John von Neumann
Xcelerate 12y ago
Every computation that can be performed on a quantum computer can be performed on a classical computer, albeit sometimes with exponential slow-down.
- ntoshev 12y ago
  Right, so the value of the simulation is somewhat questionable. Exponential slowdown is enough to kill all intuition about what works and what doesn't. You only get some correctness gurantee and that would be for very small problems / test cases.
  - kremlin 12y ago
    I see the value: you get to debug real, working algorithms based on a quantum computer so that once they're available, you already know many of the fundamentals and pitfalls of programming it. I was thinking myself about the problem of 'slowdown' of this type of approach -- I think it would be interesting if the simulated quantum computer could also give you performance metrics that say, 'If this were run on a real quantum computer, it could have been done in 100 cycles as opposed to 2000.' So you could make an algorithm in normal computing, and one on a simulated quantum computer, and compare the running time of the normal computation with the projected running time of the simulated quantum algorithm (obviously the actual running time of the simulation would be incomparable to the projected running time). I think that would be quite useful.

grdvnl 12y ago

If any Pythonista's out there want to do some simulation, [Sympy](https://github.com/sympy/sympy https://github.com/sympy/sympy) offers some simple quantum gates to work on.

krastanov 12y ago
Qutip is much better adapted at that (also in python). https://github.com/qutip/qutip/ https://github.com/qutip/qutip/

ibrad 12y ago

This is the new 60s . We will start by creating quantum punch cards. But eventually it will get better and easier.

mantrax5 12y ago
It's not the new 60s, because we already have existing computers to back us up in terms of automation, simulation and so on of whatever is to come. Case in point, the article. It'll be the "60s" maybe for a few months, at the most. Development is accelerating, and it'll never slow down.
jesuslop 12y ago
We are waiting for the would-be Shockley, Brattain and Bardeens.

hellbreakslose 12y ago

Thats actually really cool, its about time for our generation to get more familiar with the future!

S4M 12y ago

Apology for the naive question, am I supposed to be able to see the difference between a quantum computer and a standard computer from the simulator? I ran some basic examples, and while it seems a neat scripting language to play with the computer, I couldn't see anything unusual. My vague knowledge about quantum computers is that they don't deal with binary bits (that can be only 0 or 1), but their "bits" (qubits?) can be anything from 0 to 1, which should accelerate massively some calculations.

j2kun 12y ago
> but their "bits" (qubits?) can be anything from 0 to 1 This is not the interesting part, because there are models of computation that allow for this, but are believed to be equivalent to classical computation. What makes quantum computing different is that 1. the basic data are unit vectors in a 2^n dimensional vector space (when you have n qubits) and 2. you don't have direct access to the qubits during a computation, and "reading" a qubit destroys all the information in any related qubits! So imagine a classical computer program where reading a variable destroyed the content of your other variables! That's closer to the quantum model. So it's more of a semantic difference than a syntactic one.

higherpurpose 12y ago

DJB will probably be quite excited about this.

fulafel 12y ago

Anyone know details about the WebGL GPU acceleration? I assume "GPU-accelerated quantum computer" means the computations are also GPU-accelerated.

drkevorkian 12y ago

This is a cool demo, but I'm afraid this is the wrong pedagogical approach to understanding quantum computing. The representation of the quantum state as a bar chart is difficult to interpret and provides little intuition. The fact is, visualizing vectors in high-dimensional spaces is hard, much less vectors in high-dimensional complex spaces. Bra-ket notation is pretty much the best thing we have right now. But more generally, "Quantum programming" will almost certainly look nothing like this. This is like programming a classical computer by describing a boolean circuit. It's an extremely useful model for researchers working with actual hardware, but there's a reason we currently program with lambda calculi, not NAND gates. Understanding how to capture the possibilities of quantum circuits in a higher-level language is an open problem. Many interesting attempts have been made at solving it, but none convincingly in my opinion.

kvb 12y ago

MSR's LIQUi|> [1] looks like an interesting approach to this problem (although I'm not sure there's a publicly available way to use it). [1] http://research.microsoft.com/apps/video/default.aspx?id=194277 http://research.microsoft.com/apps/video/default.aspx?id=194...

jameshart 12y ago

Damian Conway's Perl Quantum::Superpositions module (http://search.cpan.org/~lembark/Quantum-Superpositions/lib/Quantum/Superpositions.pm http://search.cpan.org/~lembark/Quantum-Superpositions/lib/Q...) dates back to 2000 and lets you play around with datatypes that act like they are in multiple superposed states at once; Damian's presentation of the module was an entertaining journey into language hacking as well as quantum physics - well worth looking up on youtube.

jerf 12y ago
Bear in mind that the resulting module is not real "Quantum Computing", but an implementation of the conventional misunderstanding of quantum computing. Damian Conway understands real QC just fine (at least well enough to know this). It's a choice he made to implement this library for fun, as is his wont [1]. However, be aware that playing with that module will do nothing whatsoever to prepare you for real quantum computing. [1]: http://www.csse.monash.edu.au/~damian/papers/HTML/Perligata.html http://www.csse.monash.edu.au/~damian/papers/HTML/Perligata....

porsupah 12y ago

Perhaps also germane to the discussion is the University of Bristol's "Quantum in the Cloud" project, which similarly offers access to a simulator - but, once you've refined your project, you can then submit it to a real quantum computer: http://www.bristol.ac.uk/physics/research/quantum/qcloud http://www.bristol.ac.uk/physics/research/quantum/qcloud

peterderivaz 12y ago

I enjoyed this blog post and Javascript implementation of an interactive Quantum circuit inspector. http://strilanc.com/quantum/2014/03/07/Building-your-own-Quantum-Fourier-Transform.html http://strilanc.com/quantum/2014/03/07/Building-your-own-Qua... It is a lower level than the Google project and only suitable for 3 qbits circuits, but I found it very useful for building up an intuition about the basic logic gates.