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The presence of a 1550nm 400Gb/s signal is really just a distraction here and doesn’t add to the experiment in a meaningful way. I don’t think anyone is surpri

The presence of a 1550nm 400Gb/s signal is really just a distraction here and doesn’t add to the experiment in a meaningful way. I don’t think anyone is surprised that you can separate channels by wavelength, even if those channels are quantum. So this really comes down to observing teleportation given the high loss of the fiber at 1310nm at 30km. From that point of view the experiment is pretty solid but I’m not sure it’s worthy of a press release.

magicalhippo 2y ago
The lasers generating the signal are not perfect and generate a Gaussian-like profile of wavelengths, albeit narrow. In this experiment[1] they sent single photons alongside the classical data: Alice’s qubit is then encoded onto the horizontal (H) and vertical (V ) components of the heralded photon’s polarization |ψ〉A = α|H〉 + β|V 〉using polarization waveplates. This photon is then multiplexed using an O-band/C-band WDM to co-propagate with the 400-Gbps C-band classical signal over 15.2 km of spooled optical fiber (SMF-28(R) ULL) to Charlie. To prevent the detection of C-band photons due to insufficient filter isolation, we cascade two cascaded O-band/C-band WDMs before the FBGs and a 1290-nm DWDM to achieve >190 dB rejection of C-band light. WDM = wavelength division multiplexer, FBG = fiber Bragg grating[2]. If it was just a distraction, why did they bother adding 190+ dB of filter rejection? [1]: https://opg.optica.org/optica/fulltext.cfm?uri=optica-11-12-1700&id=565936 https://opg.optica.org/optica/fulltext.cfm?uri=optica-11-12-... [2]: https://en.wikipedia.org/wiki/Fiber_Bragg_grating https://en.wikipedia.org/wiki/Fiber_Bragg_grating
- mmmBacon 2y ago
  The lasers are not Gaussian but Lorenztian. This is a detail that’s not terribly important. The lasers generate frequencies in C-band at ~194THz. The O-band photon source is ~229THz. Classically these fields do not interact. For passive beam splitting, there is also no quantum interference. The photo detectors are broadly sensitive to both frequency bands. So if the C-band light hits the photodiode you won’t be able to count photons. The filters are there to reduce the background “noise” of the C-band light hitting the photodiode that’s being used for photon counting. The use of filters for this purpose is very common and really not that interesting.

magicalhippo 2y ago

The lasers generating the signal are not perfect and generate a Gaussian-like profile of wavelengths, albeit narrow. In this experiment[1] they sent single photons alongside the classical data: Alice’s qubit is then encoded onto the horizontal (H) and vertical (V ) components of the heralded photon’s polarization |ψ〉A = α|H〉 + β|V 〉using polarization waveplates. This photon is then multiplexed using an O-band/C-band WDM to co-propagate with the 400-Gbps C-band classical signal over 15.2 km of spooled optical fiber (SMF-28(R) ULL) to Charlie. To prevent the detection of C-band photons due to insufficient filter isolation, we cascade two cascaded O-band/C-band WDMs before the FBGs and a 1290-nm DWDM to achieve >190 dB rejection of C-band light. WDM = wavelength division multiplexer, FBG = fiber Bragg grating[2]. If it was just a distraction, why did they bother adding 190+ dB of filter rejection? [1]: https://opg.optica.org/optica/fulltext.cfm?uri=optica-11-12-1700&id=565936 https://opg.optica.org/optica/fulltext.cfm?uri=optica-11-12-... [2]: https://en.wikipedia.org/wiki/Fiber_Bragg_grating https://en.wikipedia.org/wiki/Fiber_Bragg_grating

mmmBacon 2y ago
The lasers are not Gaussian but Lorenztian. This is a detail that’s not terribly important. The lasers generate frequencies in C-band at ~194THz. The O-band photon source is ~229THz. Classically these fields do not interact. For passive beam splitting, there is also no quantum interference. The photo detectors are broadly sensitive to both frequency bands. So if the C-band light hits the photodiode you won’t be able to count photons. The filters are there to reduce the background “noise” of the C-band light hitting the photodiode that’s being used for photon counting. The use of filters for this purpose is very common and really not that interesting.