Quantum Dispersion Compensator

Dispersive Channel

Fiber length 150 km

Dispersion Compensator

Compensator strength 100%

100% = exactly matched to this fiber's dispersion. Below or above 100% under/over-compensates.

Readouts

Width at source

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Width at receiver

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Timing / entanglement fidelity

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Residual net dispersion

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How it works

A time-bin-encoded photon leaves the source as a sharp Gaussian wavepacket in time. As it propagates through the fiber, chromatic dispersion means its different frequency components travel at slightly different group velocities, so the packet smears out — the longer the fiber, the more the smear. Because the photon's quantum information (or its entanglement with a partner photon) is carried in precise arrival-time correlations, this smearing directly degrades fidelity.

width(z) = sqrt(w0² + accum(z)²)
accum(z) = D·L·z − comp(z)   [comp(z) = 0 unless compensator on]
fidelity = w0 / width(L)

Fiber length — longer channels accumulate more chromatic dispersion, so the packet arrives more smeared and fidelity drops.
Compensator — a device engineered with the opposite dispersion sign, inserted partway down the channel, that cancels accumulated smearing.
Compensator strength — how well the compensator's dispersion magnitude matches the fiber's. At 100% it exactly cancels the channel's dispersion and the packet arrives as sharp as it left. Under (<100%) or over (>100%) compensation leaves residual net dispersion and only partially restores fidelity.

Real-world relevance: dispersion-compensating fiber (DCF) or chirped fiber Bragg gratings are standard components in quantum key distribution and quantum-repeater links, restoring the timing precision that entangled-photon and time-bin qubit protocols depend on.

Photon wavepacket Compensator zone Source / receiver

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