Three laser beams intertwine into a triangle. Each is linked to the other two: this is the structure of the new scheme that physicists call "fully connected three-mode squeezed vacuum." This is not just three independent light sources: inside a special crystal, triples of entangled photons are born, and the connection between them resembles a complete graph of three points, where all possible lines are drawn.
The main surprise: pairwise control of these beams is impossible. If you take any two of the three, the quantum influence of one on the other (the so-called "steering") is zero. This is like three people holding hands in a circle: individually, no one leads anyone, but together they can move in harmony. However, you can direct one beam to control the remaining two simultaneously: this is collective steering, and it is stronger the brighter the light.
The physicists also tested how robust this connection is to losses. Light passes through fogged glass: at 50% losses, collective steering of one beam over two disappears when the glass transmits only 58% of the light. In contrast, the reverse steering, two beams over one, holds up to 50.2% transparency. The quantum entanglement itself between particles does not vanish as long as any light passes through the glass. Finally, the authors added another trick: if you "subtract" one photon not from a single beam but from a mixture of two beams, a special quantum ripple (negativity of the Wigner function) appears in the remaining light, even with losses up to 33%.
In the chain scheme, where beams are connected sequentially (like train cars), only one of the three Armstrong tests shows quantum correlation. The triangular scheme, however, lights up all three: it's like the difference between a garland where bulbs are connected in a chain and a triangle where each bulb is connected to the other two.