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Re: Optical repeaters
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At 08:04 AM 2/20/96 -0800, [email protected] wrote:
>At 07:35 PM 2/19/96 -0800, Timothy C. May wrote:
>>By analogy, it is not clear to me that a simple regeneration mechanism,
>>with no local observer or recording apparatus, will collapse the wave
>>function. Seems to me an experiment may have already been done along these
>>lines: separate fibers producing an interference pattern and then these
>>inline amps added...if the interference pattern remains, as I would expect,
>>then the amps/regenerators did not constitute a "measurement" in QM terms.
>
>An amplification mechanism will usually couple the signal to the vacuum,
>and introduce vacuum noise. Another way of thinking of vacuum noise
>is that amplification mixes the state of the signal, with the (unknown)
>phase of the universe at infinity.
I would think that the action of a optical fiber amplifier is, in a sense,
"negative loss," or the inverse of the kind of loss normally found in a
fiber cable. Thus, if quantum crypto can be done through a long fiber at
all, the fiber amplifier shouldn't negatively affect it. However, if
polarization is important (and I know that "polarization maintaining" fibers
are available) then I assume that the amplifier would probably also have to be
designed to ensure that polarization would also be maintained through the
EDFA (Erbium-Doped Fiber Amplifier.)
Jim Bell
[email protected]
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