Photon-based quantum cryptography, communication, and computation schemes have increased the need for light sources that produce indistinguishable coherent pulses at a high rate. Ideally a single-photon source, such as the weak laser diode, would produce completely characterized single photons on demand. However, it is important to realize that any mode mismatch between these photons degrades the interference visibility and, subsequently, the performance of the corresponding applications. In other words, all of the currently available sources are significantly far from ideal, and the most important question is how close a real “single-photon source” approaches this ideal.
As reported in this Optics Express article, L. C. Comandar and co-authors drastically improve the mode overlap between independently seeded, gain-switched laser diodes operating at gigahertz repetition rates by implementing a pulsed light seeding technique. Injecting pulsed light reduces the emission-time jitter and enables frequency chirp synchronization while maintaining random optical phases of the emitted laser pulses. The hope is that this light source is close to an ideal solution for generation of high rate, indistinguishable coherent pulses for quantum information applications.
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