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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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To: Red Badger

It’s turtles all the way down.


21 posted on 08/19/2025 11:13:45 AM PDT by nickcarraway
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To: bosco24

That’s what they want us to think...................


22 posted on 08/19/2025 11:16:09 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

According to the book Atomic Adventures by James Mahaffey, that project has been underway for several years now. The application is more focused on instant communications from very long distances across the universe.


23 posted on 08/19/2025 11:16:39 AM PDT by cbvanb
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To: cbvanb

What Star Trek calls “Sub-Space Communications”..............


24 posted on 08/19/2025 11:17:50 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: Rightwing Conspiratr1

-How many times can a photon be split into photons?

The energy of the daughter photosn is half the starting photon so even there’s no fundamental cap on the number of splitting events the practical energy of the split is a factor in making the split or knowing you have split the later generations of daughter photons.


25 posted on 08/19/2025 11:20:42 AM PDT by bosco24
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To: blackdog

Get back to me when it’s a torpedo.

><

I’d be quite happy with my personal phaser.


26 posted on 08/19/2025 11:27:45 AM PDT by The_Media_never_lie
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To: nickcarraway
Is that how they make pho?

They use it to make a pho ton

27 posted on 08/19/2025 11:28:17 AM PDT by ShadowAce (Linux - The Ultimate Windows Service Pack )
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To: Red Badger

Found? The answer to why when someone says “knock knock” we automatically reply “who is there”


28 posted on 08/19/2025 11:28:53 AM PDT by llevrok (Keep buggering on!)
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To: Red Badger

Why are WE having to do this work?! Where’s that lazy AI?!


29 posted on 08/19/2025 11:35:41 AM PDT by Az Joe (Live free or die)
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To: nickcarraway

This sounds phake to me.

Speaking of sound, can they split sound waves? If a tree falls in the woods and there are two microphones, do the waves split and conserve angular momentum? How about Christina Agular momentum?


30 posted on 08/19/2025 11:41:52 AM PDT by Larry Lucido
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To: Red Badger

That a photon has angular momentum at all is one of the strangest things the mind can contemplate.


31 posted on 08/19/2025 12:01:04 PM PDT by Steely Tom ([Voter Fraud] == [Civil War])
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To: cbvanb

“The application is more focused on instant communications from very long distances across the universe.”

Information cannot exceed the speed of light in a vacuum.


32 posted on 08/19/2025 12:09:22 PM PDT by TexasGator (The 750 hp Florida Gnat)
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To: Red Badger

Now what?


33 posted on 08/19/2025 12:18:00 PM PDT by Vaduz
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To: The_Media_never_lie

Me too. They would really solve the problem of body disposal.


34 posted on 08/19/2025 12:19:23 PM PDT by xp38
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To: Vaduz

You split a photon you get two photons................


35 posted on 08/19/2025 12:19:33 PM 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
"I don’t know why they haven’t used this ‘entangling’ for a super secure communications system yet.................."

They have, it's just not built into existing devices yet (routers, firewalls, etc.). Right now it requires external servers for key exchange. Look up "QKD" (Quantum Key Distribution) for more info.

36 posted on 08/19/2025 12:29:00 PM PDT by NaturalScience
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To: Red Badger

Just glad they did this to a single photon rather than to a married photon.


37 posted on 08/19/2025 12:34:11 PM PDT by Verginius Rufus
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To: Red Badger
IANA physicist, obviously.

How do you split a photon? What "blade" do you use?

When you split a photon, what do you get? Smaller photons? How many? Why two, not three, or a thousand?

Can you reassemble the pieces, I.E. build photons out of smaller photons? Do you need glue?

Photons are units of light. When you split a photon, do you get more light, or less? In what spectrum? Visible, IR, UV, what?

38 posted on 08/19/2025 12:34:54 PM PDT by ZOOKER
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To: Red Badger

Just great one more thing to drag around.


39 posted on 08/19/2025 12:36:08 PM PDT by Vaduz
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To: Red Badger

If’n a photon splits it becomes a banana split.


40 posted on 08/19/2025 1:18:45 PM PDT by bunkerhill7 (Don't shoot until you see the whites of their lies)
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