Atomic photons retain programmable spatial states through 20 metres of fibre
A laboratory experiment prepared high-dimensional quantum states using single photons and a calibrated optical fibre. Long photon coherence helped preserve interference while wavefront shaping controlled the outgoing spatial patterns. The peer-reviewed work demonstrates a building block for quantum information transport over 20 metres, with photon counts and environmental drift still constraining performance.
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A photon carries several spatial possibilities
A photon travelling through an optical fibre can follow different spatial modes, or patterns of light. Controlling their amplitudes and relative phases allows information to be encoded in more than two quantum states. The peer-reviewed experiment combined single photons generated using warm rubidium atoms with a calibrated multimode fibre. It prepared output patterns associated with mathematical transformations, including the quantum Fourier transform.[1]
Calibration compensates for spatial mixing
Multimode fibre scrambles spatial patterns as light propagates. The team measured that response and adjusted the incoming wavefront through digital optical phase conjugation. A companion photon's detection heralded the photon used in the experiment. Its long coherence helped keep contributions travelling through different modes able to interfere. Tests used fibres of 2 and 20 metres and included encodings extending to seven dimensions.[1]
More dimensions strain photon counts
With more output modes, each receives fewer detected photons. Losses, residual mixing and calibration errors consequently become more important. The longer fibre was also more sensitive to environmental drift. Input preparation and the target mapping shared a modulator; the result characterizes programmed state synthesis within a calibrated subspace. The experiment did not determine a working distance beyond 20 metres or demonstrate an operational communication network.[1]
