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Quantum cryptography
Impractical teleportation
(Fig.1) Quantum teleportation needs ordinary classical methods to send real information, irrelevant to quantum mechanics.
Contrary to an incredible amount of overhyped fake news, quantum teleportation or entanglement are useless pseudo-science sending No information or doing No work faster than light, like fictional Star Trek.
This last paragraph says -- useless teleportation
"it also presents significant challenges. The field is still in its infancy, and much work remains to be done" ← still useless, just repeating the same old phrases,
This-Callenges and Limitations (2026) say -- Impractical quantum internet
" One key hurdle is distance: photon loss in optical fiber limits direct transmission to about 100 kilometers."
"Quantum teleportation rates over real-world fiber are still quite low, typically in the range of hertz to kilohertz... it's far too slow to support distributed quantum cloud computing."
The fact that quantum teleportation, quantum computers, quantum communication (= irrelevant to quantum teleportation ) are still useless despite extremely longtime researches shows all these fishy quantum mechanical technologies are hopeless, deadend forever, contrary to overhyped fake news.
Contrary to the overhyped media, quantum teleportation is just a classical phenomenon irrelevant to (magical) quantum mechanics,
In quantum teleportation, traditional classical communication channels (= ordinary phones, email slower than light ) are necessary to send information (= quantum teleportation just sends information via ordinary classical methods slower than light, this-2nd-last-paragraph, this quantum teleportation ).
This is why sending information instantaneously or faster-than-light by (overhyped) quantum teleportation or entanglement is impossible forever.
This-lower-Is Quantum teleportation faster than the speed of light ? says
"Overall, quantum teleportation does Not travel faster than the speed of light but instead relies on the instantaneous transfer of information through entanglement.... Despite quantum entanglement appearing to interact instantaneously, no matter the distance, it is impossible to send data using quantum entanglement"
This 1st-paragraph says -- Teleportation = classical
"Because the transmission depends on classical communication (= ordinary phones, email slower than light ), it cannot be used for faster-than-light transport or communication of classical bits."
This p.3-last~p.4 says -- Teleportation needs classical channel
"Quantum teleportation does Not transmit any faster-than-light causal influence, because you also need the classical channel - limited to light speed
at best - to complete the process."
This-2nd-last-paragraph says -- Classical communication needed
" As quantum teleportation still requires we send a piece of classical information, we are effectively limited in how fast we can send a state."
This-2nd-paragraph says -- Teleportation slower than light
"However, the teleportation requires both quantum ( useless, illusory ) entanglement and classical communication, meaning it doesn't exceed the speed of light."
Overhyped quantum teleportation and quantum internet are useless forever.
Quantum teleportation is just the measurement of (classical) light polarization (= called Bell state measurement ) + sending information via ordinary classical communication channel ( this p.2-Figure 1a, this p.5-figure, this-introduction ). ← No quantum speed-up nor utility
This-2nd-last paragraph (= 2. ) says -- Teleportation = classical
"System A applies Bell State Measurement and sends the result of the measurement (2 classical bits) to System B through classical channel." ← quantum teleportation needs to send information by ordinary classical communication.
This-Step 4: Bell measurement-last-paragraph says
"This is why quantum communication is Not faster than the speed of light... because we need the classical information, which is limited by the physical channel and the speed of light even in the best case."
This recent site (2025) ↓
1.2.3. say -- Teleportation = measure light + classical communication
"1. Quantum entanglement – A pre-shared quantum connection between two parties (often referred to as Alice and Bob)." ← Prepare two lights with correlated (= entangled ) polarizations from EPR source
"2. Bell-state measurement – A special type of quantum measurement (= of two polarized lights ) performed by the sender."
"3. Classical communication – Two bits of classical information (= of polarization of light ) sent from Alice to Bob to complete the teleportation."
This-Why it's not faster than light says
"The reason quantum teleportation doesn't break the speed-of-light limit lies in quantum randomness. When Alice performs her Bell-state measurement, she cannot control the result. This randomness means you can't use teleportation to send pre-defined messages. The two classical bits sent to Bob are essential to reconstruct the state, and these bits must travel through a normal communication channel, at or below the speed of light"
As shown in the upper figure, in quantum teleportation, two (classical) polarized lights ① and ② are sent to Alice detectors.
And the third light ③ whose polarization is orthogonal to light ② is sent to Bob detector.
When Alice detectors measure these two lights ① and ② to have polarizations orthogonal to each other (= ex, light ① is vertically-polarized, light ② is horizontally-polarized ) using classical beam splitters and photodetectors (= called Bell state measurement or BSM ), it means the polarization of the light ③ (= orthogonal to light ② ) is the same as the polarization of light ① ( this 3rd-paragraph )
↑ This information of polarizations of lights ① and ② must be sent from Alice to Bob through ordinary classical communication channels ( this 3rd-paragraph ).
Based on this classically-sent information, Bob decides whether he changes the polarization of light ③ or not, which is quantum teleportation protocol ( this p.3(or p.2)-upper ).
↑ No faster-than-light spooky quantum entanglement nor teleportation happens.
Chinese satellite's alleged teleportation or entanglement is also an useless and meaningless technology.
Quantum communication, network internet, teleportation try to use very weak light or fragile photons as quantum information which is too easily lost to sent over practical long distance (= via classical method Not faster than light ), so impractical forever.
↑ This fragile quantum information or photons are too easily lost, so cannot be used for practical internet or communication that needs all information (= photons ) to be sent to destination with zero photon loss, which is impossible ( this-Callenges and limitations ).
This recent site (2025) ↓
5th-paragraph says -- Distance limitation
"current quantum communication is severely distance-constrained.... QKD implementations are currently limited to tens of kilometers"
6th-paragraph says -- Severe quantum information loss
"signal loss is inevitable over distance - but with quantum, we can't just slap in repeaters and amplifiers like we do with traditional networking"
8th-paragraph says -- Impractical quantum network
"quantum networking in its current form is Not going to magically replace our traditional networks anytime soon. The notion of a global quantum internet is still firmly in the theoretical realm"
2nd-last-paragraph says -- Unrealistic quantum internet
"The quantum networking reality remains firmly grounded in experimental metro deployments - exciting, but still a far cry from a quantum internet."
(Fig.2) ↓ Quantum teleportation (= Bell state measurement of light after passing beam splitter ) uses classical light interference.
In fact, Bell state measurement (= BSM ) of the (useless) quantum teleportation or entanglement uses just classical lights' interference at the beam splitter, and No quantum mechanics is involved.
In the beam splitter (= BS ), the transmitted light's phase is unchanged, and only one reflected light (= exiting the upper side in Fig.2 ) is supposed to experience the phase π shift (= becoming the opposite destructive light phase, this p.32, this p.2-(4), Fig.1, this p.3-left-4th-paragraph ).
So when two lights with the same polarizations (= horizontal-horizontal H-H lights or vertical-vertical VV lights ) arrive at this beam splitter from the upper and lower directions, these two lights with the same polarizations interfere with each other constructively (= same phase side ) in one side and destructively (= opposite phase side due to one reflected light's phase flip ) in the other side, and resultantly, these two same-polarized lights (= denoted as φ± ) always exit from the same side of the beam splitter.
↑ This case is called Hong-Ou-Mandel effect, and it is just classical light interference after phase shift at the beam splitter ( this p.2 ) + detecting classical weak light whose intensity surpassing the detection threshold of photodetector as (fictitious) photon, No quantum mechanics is involved.
On the other hand, when two lights with different polarizations (= H-V or V-H ) enter this beam splitter, these two lights with different polarizations never interfere with each other, hence, these two lights with different polarizations can exit from different sides of the beam splitter (= ψ- ) avoiding destructive interference or exit from only one side of the beam splitter (= ψ+ ).
It means when two photodetectors at the opposite exits of the beam splitter can detect two lights at the same time (= ψ- ), these detected lights must have different polarizations (= Bell state measurement distinguishing different light polarizations ).
If only one photodetector at either side of beam splitter can detect light (= or fictitious photon ), we can think of multiple cases where this detected light may consist of only one same polarization or two different polarizations, which can Not be distinguished ( this p.11, this p.3-right ).
Even in the latest experiment, this Bell state measurement can only distinguish these different patterns of light polarization state (= H-V or H-H or V-V .. ) with impractically-low 57.9 % success rate ( this 8th-paragraph ).
And as shown here, Bell state measurement (= BSM ) that allegedly causes quantum teleportation is just classical phenomenon of classical polarized light interference at the beam splitter, and (fantasy) quantum mechanics is irrelevant.
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