Some context:
I've been involved with the QEYSSat project, working on studies and prototypes, for the last 6 years. It's wonderful to see it selected as one of the two projects to receive funding, thereby allowing it to become an actual mission. Very exciting times!
It's well known that quantum entangled systems can exhibit correlations that go beyond those that could be seen if Nature worked in intuitive “classical” ways. However, as Richard Feynman noted, classical theory can support exhibiting such correlations if we invoke negative probabilities to describe their properties. What he did not do was specify how these negative probabilities ought to be chosen, and without any justification, an infinite number of different combinations could be chosen that will satisfy the relevant equations.
The concept of negative probabilities seems nonsensical because they cannot actually be observed—indeed, they cannot be observed even within the framework of quantum theory due to the effects of measurement back-action. Here, we show how they can instead be inferred through the use of weak measurements, where a meter is only weakly coupled to the property of interest, thereby avoiding the back-action problem. Each individual weak measurement has a high uncertainty, but by measuring many instances of a larger ensemble, an average can be found that implies a specific set of anomalous (i.e. beyond 0–1) probabilities. With an experimental demonstration, we thus give an empirically justified method for choosing the anomalous probabilities that allow the classical model [...]
Quantum mechanics implies properties of Nature that clash with our intuitive notions of how the universe ought to work. Testing these properties (to see if quantum mechanics is, indeed, true) involves generating entangled quantum states of two or more particles and measuring them under a number of strict conditions. While work is progressing to meet all of these conditions when using only two particles, no one has yet met even one of these conditions for more than two particles, which is considerably more difficult experimentally. Here, we conduct an experiment where we meet two of the most challenging conditions—namely measurement locality and freedom of choice—while generating triplet entangled photon states. We demonstrate that quantum mechanics wins out over intuition, measuring a violation of Mermin's inequality outside the classical bound by nine standard deviations.
Also check out the News and Views article in the same issue, written [...]
We perform a thorough theoretical analysis of the expected key rate, success of Bell test, and teleportation distance of experiments performed between the ground and a satellite in low Earth orbit. Our findings demonstrate that successful, regularly repeatable demonstrations are feasible with current technologies and relatively small telescopes.
An ensemble cast detail the new physics that could be explored by taking quantum optics experiments into space. My first publication as part of Prof. Thomas Jennewein's group, I contributed details about near-term tests and our present work at the Institute for Quantum Computing, and helped out with logistics and proofing.
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