In a hard experiment, 168 hours of data collection was required to capture 57 photon events, researchers at the University of Tampere confirmed that even if a single light particle was divided into pairs, angular momentum protection (same is true of the fundamental laws of physics).
The achievements have verified the most basic principles of quantum theory, and at the same time opened up the pathways of advanced quantum technology.
The team used a very delicate process in which a single photon carrying orbital angular momentum is converted into a photon pair, and then carefully tracks whether the preservation law is held. Just like finding a needle in a haystack, only one billion input photons successfully transformed one, making each detection precious.
Testing the physics of quantum limits
Protecting the processes that are permitted or prohibited by law. When billiards collide, their sports will be transferred according to momentum protection. Light can also carry angular momentum through its spatial structure, i.e. the idea of a bottle opener-shaped beam twisted in space.
Previous experiments used powerful laser beams containing trillions of photons to verify angular momentum protection. But quantum mechanics requires protection laws to apply to individual particles, not just large collections. So far, no one has tested this fundamental principle at the single photon level.
The researchers created a cascaded system in which a photon pump conversion process is performed. They imprint a specific amount of orbital angular momentum onto a single photon and then watch them split into pairs by spontaneous parameter downconversion of the spontaneous parameter crystal.
Needle field detection
The experimental challenge is huge. Key technical barriers include:
- Only one billionth of the input photons successfully converted to a pair
- Low detection rates per hour as low as 1.3 predicted photon pairs
- Statistical significance measurement session lasts up to 168 hours
- Suppress background noise to near zero
- Extremely stable optical alignment for several days
The team used nanowire detectors and space light regulators with 80% efficiency to shape and analyze the distorted wavefronts of photons. Each detection requires precise timing correlation to distinguish real events from random background noise.
“Our experiments show that even if the process is driven by a single photon, the elements are indeed preserved,” explains Dr. Lea Kopf, the lead author of the study. “This confirms the most fundamental level of key conservation methods, ultimately based on the symmetry of the process.”
Quantum Mathematical Action
The protection rules follow simple arithmetic: when a photon with zero angular momentum splitting, the two generated photons must have equal opposite values. Therefore, if a photon gets +1 unit, its partner must have -1 unit to ensure that the total remains at zero.
The researchers tested it with photons carrying up to two orbital angular momentum. In each case, pairing was subject to protection laws, with 76% of the tests showing perfect compliance, and the rest attributed to experimental flaws rather than violations.
It is worth noting that when they compared the results of single-photons with traditional laser pump experiments, the correlation reached 99.5%. This close-perfect match proves that quantum and classical physics operate on different scales with the same protection principles.
Entangled signature
In addition to protection verification, the team also observed preliminary evidence of photon-neck quantum entanglement. When particles are entangled, measuring a particle immediately affects its companion regardless of distance – Einstein’s “far-range weird action”.
Orbital angular momentum entanglement can enable quantum computers to process information on higher dimensions than current polarization-based systems. These “Qudits” replace simple 0-1 bits and can represent multiple values at the same time, greatly expanding computing power.
Professor Robert Fickler, who leads the research group, highlights the broader implication: “This work is not only fundamentally important, but also brings us closer to the generation of new quantum states where photons are entangled in various possible ways, namely space, time and polarization.”
Now, researchers plan to improve conversion efficiency and develop better detection protocols to make these quantum needles easier to find. Their ultimate goal involves creating three photon entangled states that can enable more complex quantum communication networks and computing architectures.
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