Time Travel Computer S. Aaronson and J. Watrous. Closed Timelike Curves Make Quantum and Classical Computing Equivalent, Proceedings of the Royal Society A 465:631-647, 2009. arXiv:0808.2669.
What weve learned from quantum computers so far: 15 = 3 × 5 (with high probability)
Linear-Optical Quantum Computing www.scottaaronson.com/papers/optics.pdf My student Alex Arkhipov and I recently proposed an experiment, which involves generating n identical photons, passing them through a network of beamsplitters, then measuring where they end up Our proposal almost certainly wouldnt yield a universal quantum computerand indeed, it seems a lot easier to implement Nevertheless, we give complexity-theoretic evidence that our experiment would solve some sampling problem thats classically intractable Groups in Brisbane, Australia and Imperial College London are currently working to implement our experiment
Summary 1.From a theoretical standpoint, modern computers are all the same slop: polynomial- time Turing machines 2.We can imagine computers that vastly exceed those (by using closed timelike curves, etc.) 3.But going even a tiny bit beyond polynomial-time Turing machines (say, with linear-optical quantum computers) is a great experimental challenge