3 - Detection
Harnessing potential advances offered by quantum correlations across multiple time-frequency modes of light requires a new generation of quantum detectors capable of detecting this multiplicity of modes. Here we focus on development of detection techniques to address the increased dimensionality of the optical time-frequency modes. The work is closely tied with progress in the sources, manipulation, theory and applications WPs to ensure that detector bandwidth and resolution are well matched to application requirements.
Time-multiplexed detectors (TMDs)
Measuring photon numbers is an important task to, for example, characterise quantum states. However, most modern photon-sensitive detectors can only distinguish between “no photon” or “one or more photons”; these are also called "binary detectors" or "click detectors". It is, however, possible to create an effective photon-number resolving detector from many parallel, or multiplexed, click detectors. Multiplexing can be realised by using beamsplitters to distribute photons over many separate detectors, as seen in picture (A). This method is effective as long as the number of detectors is large compared to the number of photons of the measured light, since the probability of two photons hitting the same detector is small. We can dramatically reduce the number of physical detectors needed, and therefore the system size and cost, by applying the same idea in the time domain. Using this technique, we measure the number of photons in an optical pulse by distributing them over many time bins using beam splitters and optical delay lines, as seen in picture (B). This method is very resource efficient, requiring only two photon detectors. As part of the QCUMbER research programme, these detectors have been built, characterized, and used to infer properties of quantum states.
If you have questions, please feel free to contact Johannes Tiedau from the University of Paderborn.