Experimental Genuine Quantum Nonlocality in the Triangle Network
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anton vrba
May 14, 2026, 10:25:45 AMMay 14
to Bell Inequalities and quantum foundations
This makes interesting reading. Elegant Joint Measurements (EJM) and triangle networks are new to me, and I am trying to understand where exactly entanglement, or lets call it nonlocal quantum correlations originate from, (1) the pulse laser, (2) the SPDC or (3) the measurement stations.
Quote: "Here, we experimentally study the elegant distribution generated in the triangle
network, a striking example of network nonlocality which is
genuine to networks, that is cannot be interpreted as coming
from standard Bell nonlocality. We provide strong evidences
that our experimentally observed distribution can not be explained with a LHV triangle network local model.
"
Austin Fearnley
May 15, 2026, 7:57:07 AMMay 15
to Bell inequalities and quantum foundations
EPR Source seems to be the entanglement source (see page 6 of arxiv paper). This EPR Source is shown as the top half of Figure 8 and includes the BBOs.
The BBO crystal is a frequency doubler and is birefringement and I think is the source of entanglement.
(This is all new to me and I had to search for this information.)
I am more interested in entanglement than in Bell's Theorem (which I completely accept) so I am not overly impressed by the triangle network adding anything new of importance to non-locality. But it is interesting to know of the new experimental work.
It is a long time since I looked at quantum logical gates (spurred on by Richard a year or two ago) where the Hadamard gate plus CNOT creates entanglement. I had already assumed that a complicated quantum circuit would create triangles and other structures of entanglement loops. The problem as I see it is to delay decoherence or loss of entanglement. Maybe by somehow boosting entanglement. There are techniques shown online for boosting but I do not understand them.
Figure 8 seems very neat and orderly in a way which should lead to allowing entanglement to endure. I mean the routes from the measurement devices at the bottom of the figure back to the BBO crystals at the top of the figure are clear. In my retrocausal model (and probably all other models?) it is important not to break or block routes back (in time) to the BBOs or entanglement sources. Else one gets decoherence.
The BBO crystal is a frequency doubler and is birefringement and I think is the source of entanglement.
(This is all new to me and I had to search for this information.)
I am more interested in entanglement than in Bell's Theorem (which I completely accept) so I am not overly impressed by the triangle network adding anything new of importance to non-locality. But it is interesting to know of the new experimental work.
It is a long time since I looked at quantum logical gates (spurred on by Richard a year or two ago) where the Hadamard gate plus CNOT creates entanglement. I had already assumed that a complicated quantum circuit would create triangles and other structures of entanglement loops. The problem as I see it is to delay decoherence or loss of entanglement. Maybe by somehow boosting entanglement. There are techniques shown online for boosting but I do not understand them.
Figure 8 seems very neat and orderly in a way which should lead to allowing entanglement to endure. I mean the routes from the measurement devices at the bottom of the figure back to the BBO crystals at the top of the figure are clear. In my retrocausal model (and probably all other models?) it is important not to break or block routes back (in time) to the BBOs or entanglement sources. Else one gets decoherence.
Austin Fearnley
May 17, 2026, 6:37:08 AMMay 17
to Bell inequalities and quantum foundations
Very sorry, my error in my previous post, it is Figure 9 (not 8).
I have looked up BBO devices again using Google search AI:
"A high-energy "pump" photon (typically a ultraviolet laser at 405nm) passes through the crystal.
The BBO crystal splits this single photon into two lower-energy photons (typically near-infrared at 810nm).
Due to the fundamental laws of conservation of energy and momentum, the properties of these two exiting photons are intrinsically tied together. "
and ...
"Second Harmonic Generation (SHG): Beyond splitting light, BBO crystals can be run in reverse to double the frequency of classical lasers, creating the specialized UV pump beams required elsewhere in the optical loop"
The paper mentions that they use doubling (first) and then (presumably) splitting afterwards.
The BBO crystal splits this single photon into two lower-energy photons (typically near-infrared at 810nm).
Due to the fundamental laws of conservation of energy and momentum, the properties of these two exiting photons are intrinsically tied together. "
and ...
"Second Harmonic Generation (SHG): Beyond splitting light, BBO crystals can be run in reverse to double the frequency of classical lasers, creating the specialized UV pump beams required elsewhere in the optical loop"
The paper mentions that they use doubling (first) and then (presumably) splitting afterwards.
Also I wondered if multiplexing was possible for qubits and, yes, google AI says that quantum computing is using multiplexing.
The paper mentions that they use doubling first and then (presumably) splitting afterwards [which google says corresponds to 'time multiplexing']. The paper mentions pulses and their time widths therefore I assume that qubits are being multplexed in sequence, and not by grouping them together simultaneously [which would be 'frequency multiplexing'].
The paper mentions that they use doubling first and then (presumably) splitting afterwards [which google says corresponds to 'time multiplexing']. The paper mentions pulses and their time widths therefore I assume that qubits are being multplexed in sequence, and not by grouping them together simultaneously [which would be 'frequency multiplexing'].
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