Quantum Teleportation Finally Succeeds with "Separate Light" — Achievements of the German Team Advance Quantum Repeater Development

2025年11月20日 00:37

Quantum Teleportation Succeeds with "Separate Light Sources" —— A Step Closer to the Quantum Internet

On November 18, 2025, a research team from the University of Stuttgart in Germany and others announced that they had achieved quantum teleportation between photons emitted from two semiconductor quantum dots located at separate locations. The paper is published in Nature Communications, marking a significant milestone towards realizing quantum repeaters, which are considered the "heart" of the quantum internet.Phys.org

Below, we will explain what this achievement means, using simple diagrams and potential reactions on social media.

What's so amazing about this? In a nutshell…

Previously:Quantum teleportation was possible if the light came from the same place and the same device
This time:Quantum teleportation was achieved between light emitted from two quantum dots located at separate places
- Successfully "transferring the 'state' of this light exactly to that light" = Quantum Teleportation
- Moreover,it was done by frequency conversion to the telecom wavelength band, which is convenient for communication infrastructure

This capability significantly increases the possibility of building "quantum repeaters that connect distant nodes" based on semiconductors.Phys.org

The everyday internet is actually quite vulnerable

The original article straightforwardly points out the current internet's vulnerabilities.Phys.org

Hacking can lead to bank accounts and IDs being stolen
AI is making phishing attacks increasingly sophisticated
Even encryption methods themselves might be broken by future quantum computers

Against this backdrop, there is growing anticipation forquantum cryptography and quantum communication.

By utilizing quantum properties,

"Eavesdropping always leaves traces"
"Perfect copying is prohibited (quantum 'no-cloning theorem')"

These characteristics enable highly eavesdrop-resistant communication.

The Wall of Quantum Internet and Quantum Repeaters

To create a practical quantum internet,it is almost essential to be able to use the current optical fiber infrastructure as is.Phys.org

Conventional Internet:
- Optical signals gradually weaken, so they are connected by "volume-up" with optical amplifiers approximately every 50 km
Quantum Internet:
- Quantum states cannot be copied, so they cannot be "amplified" in the same way

This is where the **quantum repeater** comes in.

It's not just an "amplifier," but
a device that "teleports quantum information to another photon at an intermediate node, relaying it like a baton"

This achievement can be considered a breakthrough in the most challenging part of realizing this quantum repeater,

the "baton passing" part.Phys.org

A Simple Diagram of the Experiment

1. Two quantum dots are located at separate places

Quantum Dot:
- A structure like an "artificial atom" in a semiconductor of nanometer size
- Because it has a fixed energy,it can become a light source that emits "characteristically uniform" photons when conditions are rightPhys.org+1

In this experiment,

QD1: Single photon source (emits only one photon)
QD2: Source that emitsentangled photon pairs

were used respectively.

Nature

2. Encode "information to be teleported" onto the first photon

Quantum information is encoded as polarization (horizontal/vertical or their superposition) on the photon emitted from QD1
This is the "photon carrying the information to be teleported."Nature

3. The second and third are "entangled pairs"

From QD2,two photons are emitted consecutively:
- The "XX photon" (photon 2) emitted first
- The "X photon" (photon 3) emitted later
These two are in a quantum entangled state,
- where measuring one strongly constrains the state of the other.Nature

4. Overcoming the major issue of "different frequencies" with frequency conversion

In reality, the light emitted from separate quantum dots

has slightly different colors (frequencies)
or their temporal profiles don't match

, so they cannot be said to be "exactly the same light."However, in quantum teleportation,
it is crucial that the interfering photons are almost completely indistinguishable.Phys.org

Therefore, the research team prepared

two quantum frequency convertersthat can change the frequency while maintaining polarization,
and converted the light from QD1 and QD2 to the telecom wavelength band, matching the colors perfectly

.

This feat was accomplished.Phys.org

5. Instantly transferring "information only" with Bell measurement

The photon to be teleported (photon 1 from QD1)
and one of the entangled pair (photon 2 from QD2)

are passed through a special measurement device called a **Bell state measurement**.Nature

Depending on the result obtained from this measurement,

the remaining photon 3 on the QD2 side (the other of the entangled pair)
assumes the state that "photon 1 originally had"

This is "quantum teleportation." Not the material itself, butonly the state is "moved" in a non-copyable form.Nature

Experimental Conditions and Achievements: Still 10m, But a Big Step