The following is a development sensible after this paper –
It explains the construction of a quantum repeater, somewhat
like a classical amplifier. Input is two streams of electrons. Output is two
streams also. As a block box implemented cleverly in the paper, the states on
electrons are switched. That dos not foul one thing you can’t do in quantum
world, but trivial in classical – copy the state. One consequence of the black
box is that the input sequence of electrons emerges dead with no correlation to
what they were! However the live copy stream may be at much higher intensity!
So this repeater works like an amplifier! While quantum
beams have been tested in space between Chinese satellites 1200 km apart,
things are bad in glass fibers. Note that emergent electrons have full state,
including entanglement information. So a fiber based method can entangle two
electrons that never met!
But what does entanglement mean? Identically correlated
states! In particular, if you write information at one end, and read at the
partner, it is the same despite no sending! Clearly, such information can NEVER
be insecure! Entanglements may be for short while, but the cable delivers a lot
of partners!
BTW,. Image search for article above yielded fascinating
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