The mathematical foundations built on motivation from experiments being in place, we now look at the properties of qubits that distinguish them from classical bits, and also which make their manipulation and behavior somewhat counter-intuitive.
In this contribution, I suggest that it is sometimes a step forward to reverse our intuition on “what is fundamental”, a move that is somewhat reminiscent of the idea of noncommutative geometry. I argue that some foundational conceptual problems in physics and related fields motivate us to attempt such a reversal of perspective, and to take seriously the idea that an information-theoretic notion of observer (“mind”) could in some sense be more fundamental than our intuitive idea of a physical world (“matter”). I sketch what such an approach could look like, and why it would complement but not contradict the view that the material world is the cause of our experience.
Most modern physical theories are formulated in terms of differential equations. As a result, if we know exactly the current state of the world, then this state uniquely determines all the future events - including our own future behavior. This determination seems to contradict the intuitive notion of a free will, according to which we are free to make decisions - decisions which cannot be determined based on the past locations and velocities of the elementary particles. In quantum physics, the situation is somewhat better in the sense that we cannot determine the exact behavior, but we can still determine the quantum state, and thus, we can determine the probabilities of different behaviors - which is still inconsistent with our intuition. This inconsistency does not mean, of course, that we can practically predict our future behavior; however, in view of many physicists and philosophers, even the theoretical inconsistency is somewhat troubling. Some of these researchers feel that it is desirable to modify physical equations in such a way that such a counter-intuitive determination would no longer be possible. In this paper, we analyze the foundations for such possible theories, and show that on the level of simple mechanics, the formalization of a free will requires triple interactions - while traditional physics is based on pairwise interactions between the particles.
Bosonic bunching is a term used to describe the well-known tendency of bosons to bunch together, and which differentiates their behavior from that of fermions or classical particles. However, in some situations, perfectly indistinguishable bosons may counter-intuitively bunch less than classical, distinguishable particles. Here, we report two such counter-intuitive multiphoton bunching effects observed with three photons in a three-mode balanced photonic Fourier interferometer. In this setting, we show that indistinguishable photons actually minimize the probability of bunching. We also show that any non-trivial value of the three-photon collective photonic phase leads to a decreased probability of all photons ending up in the same mode, even as we increase pairwise indistinguishability. Our experiments feature engineering of partial indistinguishability scenarios using both the time and the polarization photonic degrees of freedom, and a polarization-transparent 8-mode tunable interferometer with a quantum-dot source of single photons. Besides the foundational understanding, the observation of these counter-intuitive phenomena open news perspective in devising more efficient ways of routing photons for advantage in metrology and quantum computation.