(Fig.1) ↓ Just using classical polarized light. No quantum mechanics
Contrary to an incredible amount of overhyped fake news, quantum teleportation is useless, sending No information or doing No work.
This last paragraph says
"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,
The fact that quantum teleportation, quantum computers, quantum communication are still useless despite extremely longtime researches shows all these fishy quantum mechanical technologies are hopeless, deadend forever.
In quantum teleportation, traditional classical communication channels are necessary to send information (= sending information via ordinary classical methods slower than light is necessary ).
This is why sending information instantaneously or faster-than-light by (overhyped) quantum teleportation or entanglement is impossible forever.
This 1st-paragraph says
"Because the transmission depends on classical communication, it cannot be used for faster-than-light transport or communication of classical bits."
Quantum teleportation is just the measurement of (classical) light polarization (= called Bell state measurement ) + sending information via ordinary classical communication channel ( this-lower, this p.2-Figure 1a, this p.5-figure ). ← No quantum speed-up nor utility
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 quantun 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.
(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 impracticaly-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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