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Scientists Just Split a Single Photon. Here’s What They Found
Scitech Daily ^ | August 19, 2025 | Tampere University

Posted on 08/19/2025 10:49:42 AM PDT by Red Badger

By splitting a single photon, scientists confirmed that angular momentum is always conserved — a billion-to-one experiment that reinforces the foundations of quantum physics. Credit: SciTechDaily.com

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Physicists have, for the first time, shown that even a single photon obeys one of nature’s strictest rules: conservation of angular momentum.

Achieved only once in a billion attempts, this needle-in-a-haystack success not only proves a cornerstone law of physics at the smallest scale but also opens a pathway to advanced quantum technologies, from entangled states to secure communication.

Quantum-Level Confirmation of Angular Momentum Conservation

Researchers at Tampere University, working with colleagues in Germany and India, have demonstrated for the first time that angular momentum remains conserved when a single photon splits into two. This result confirms a core principle of physics at the quantum scale and marks a milestone that could help in creating advanced quantum states for use in computing, communication, and sensing technologies.

Conservation laws are central to science because they determine which processes are possible and which are not. A familiar example is seen in billiards, where the momentum of one ball transfers to another during a collision. A similar principle applies to objects that spin, which carry angular momentum. Light, too, can possess angular momentum, specifically orbital angular momentum (OAM), which relates to the spatial shape of a light beam.

At the quantum level, this means that individual photons carry specific amounts of OAM that must be preserved when they interact with matter. In a study recently published in Physical Review Letters, the Tampere-led team investigated whether this conservation rule still applies when a lone photon is divided into a pair. Their work pushed the limits of conservation testing to the smallest possible scale.

Single Photon Splitting Into Two - Schematic of a single photon with zero angular momentum (green) splitting into two photons (red) with either zero or opposite angular momenta (sketched through the spatially varying color), which adds up to zero confirming the fundamental angular momentum conservation law. Credit: Robert Fickler / Tampere University

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One Minus One Equals Zero

According to the rule, if a photon without OAM splits into two, the angular momentum values of the resulting photons must cancel each other out. For instance, if one photon emerges carrying one unit of OAM, the second must carry negative one. Put simply, the equation 1 + (-1) = 0 must always hold. While similar rules have been tested many times in laser-based optics experiments, this had never before been confirmed for a single photon.

“Our experiments show that the OAM is indeed conserved even when a single photon drives the process. This confirms a key conservation law at the most fundamental level, which is ultimately based on the symmetry of the process,” explains Dr. Lea Kopf, who is the lead author of the study.

Finding the Photonic Needle in the Laboratory Haystack

The team’s experiments rely on delicate measurements as the required nonlinear optical processes are very inefficient. Only every billionth photon is converted to a photon pair, such that measuring the conservation of OAM for single photons resembles the proverbial search for the needle in the haystack.

An extremely stable optical setup, low background noise, a detections scheme with the highest possible efficiency, and a lot of experimental endurance enabled the researchers to record enough successful conversions such that they could confirm the fundamental conservation law.

First Signs of Quantum Entanglement

In addition to confirming OAM conservation, the team observed first indications of quantum entanglement in the generated photon pairs, which suggests that the technique can be extended to create more complex photonic quantum states.

“This work is not only of fundamental importance, but it also takes us a significant step closer to generating novel quantum states, where the photons are entangled in all possible ways, i.e., in space, time, and polarization,” adds Prof. Robert Fickler, who leads the Experimental Quantum Optics group where the experiment was performed.

Future Directions in Quantum Photonics

Looking forward, the researchers plan to improve the overall efficiency of their scheme and develop better strategies for measuring the generated quantum state such that in the future these photonic needles can be found easier in the laboratory haystack. Moreover, the researchers aim at leveraging the generated multi-photon quantum states for novel fundamental quantum tests and quantum photonics applications such as quantum communication and network schemes.

Reference:

“Conservation of Angular Momentum on a Single-Photon Level”

by L. Kopf, R. Barros, S. Prabhakar, E. Giese and R. Fickler, 20 May 2025, Physical Review Letters.

DOI: 10.1103/PhysRevLett.134.203601


TOPICS: Astronomy; History; Science; Weird Stuff
KEYWORDS: angular; astronomy; entanglement; momentum; photon; physics; quantum; quantummechanics; science; split; stringtheory

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1 posted on 08/19/2025 10:49:42 AM PDT by Red Badger
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To: MtnClimber; SunkenCiv; rktman; mowowie; SuperLuminal; Cottonbay; telescope115; laplata; ...

A Quantum of Ping!.................


2 posted on 08/19/2025 10:50:23 AM PDT by Red Badger (Homeless veterans camp in the streets while illegals are put up in 5 Star hotels....................)
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To: Red Badger
entangled states

Well, we've got a lot of them...

3 posted on 08/19/2025 10:52:01 AM PDT by Jim W N (MAGA by restoring the Gospel of the Grace of Christ (Jude 3) and our Free Constitutional Republic!)
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To: Jim W N

I don’t know why they haven’t used this ‘entangling’ for a super secure communications system yet..................


4 posted on 08/19/2025 10:53:03 AM PDT by Red Badger (Homeless veterans camp in the streets while illegals are put up in 5 Star hotels....................)
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To: Jim W N

George Washington warned us about this.


5 posted on 08/19/2025 10:53:07 AM PDT by ClearCase_guy (The list of things I no longer care about is long. And it's getting longer.)
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To: Red Badger

Is that how they make pho?


6 posted on 08/19/2025 10:53:42 AM PDT by nickcarraway
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To: Red Badger

(1) Who says “they” haven’t? 😎

(2) Fundamental discoveries can be very difficult to develop into practical applications.


7 posted on 08/19/2025 10:54:51 AM PDT by NorthMountain (... the right of the people to keep and bear arms shall not be infringed)
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To: Red Badger
A single photon? Ha!


8 posted on 08/19/2025 10:56:29 AM PDT by Magnum44 (...against all enemies, foreign and domestic... )
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To: Red Badger

“You kids put that thing back together right now!” Dang kids.


9 posted on 08/19/2025 10:57:55 AM PDT by Billthedrill
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To: Red Badger

As always, another great post. thanks.

I’m far from being a scientist/physicist, but this seems very important.


10 posted on 08/19/2025 10:58:19 AM PDT by laplata (They want each crisis to take the greatest toll possible.)
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To: Red Badger

How manty times can a photon be split into two photons?
Is it photons all the way down?


11 posted on 08/19/2025 10:59:19 AM PDT by Rightwing Conspiratr1
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To: Rightwing Conspiratr1

It’s like a Russian Nesting Doll...............


12 posted on 08/19/2025 11:01:59 AM PDT by Red Badger (Homeless veterans camp in the streets while illegals are put up in 5 Star hotels....................)
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To: Red Badger

They found a Bozon and a Moron each of whom promptly registered as Democrats.


13 posted on 08/19/2025 11:03:14 AM PDT by TTFlyer (Lenin: that by the infliction of terror, a well-organized minority can conquer a nation.)
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To: nickcarraway

Just add water..................


14 posted on 08/19/2025 11:04:00 AM PDT by Red Badger (Homeless veterans camp in the streets while illegals are put up in 5 Star hotels....................)
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To: nickcarraway

“Is that how they make pho?”

They make a TON of ‘em.


15 posted on 08/19/2025 11:05:00 AM PDT by Migraine
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To: Rightwing Conspiratr1
“Even the fleas have fleas!”

I was expecting revelation of yet another sub-subatomic particle.

16 posted on 08/19/2025 11:06:43 AM PDT by sjmjax
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To: Magnum44

“A single photon? Ha!”

So you’re waving it off?


17 posted on 08/19/2025 11:06:56 AM PDT by Migraine
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To: Migraine

Get back to me when it’s a torpedo.


18 posted on 08/19/2025 11:09:39 AM PDT by blackdog ((Z28.310) "Diggin the scene with a gangster lean" (Mayfield, Curtis) )
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To: Red Badger

-I don’t know why they haven’t used this ‘entangling’ for a super secure communications system yet..................-

I don’t think that would work as you can’t transmit information via entangled particles.


19 posted on 08/19/2025 11:09:58 AM PDT by bosco24
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To: TTFlyer
They found a Bozon and a Moron each of whom promptly registered as Democrats.

Bozon and Moron then Spiton and Peedon the US Constitution, per the Democrats' instructions.

20 posted on 08/19/2025 11:10:01 AM PDT by Migraine
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