Exploring new physics usually requires a new, better way of measuring a particular quantity. Optical measurements are ultimately limited by quantum mechanical effects, such as the uncertainty principle, shot noise or decoherence. However, quantum mechanics also offers new prospects for metrology. Our focus is on applying quantum mechanical tools and techniques to improve the performance of measurement devices and systems.
How do we do this? Some of our recent experiments have looked at novel approaches that bridge fundamental and applies physics. For example:
Absolute measurement of spectral radiance through quantum cloning
On the very small (quantum) scale, information cannot be copied exactly. On the other hand, at larger (classical) scales, information can be copied perfectly. The size of a system can then be determined by measuring the fidelity with which it can be copied. Our system consists of photons, our method determines their number to sufficient accuracy as to provide a primary standard of spectral radiance.
Intrinsically stable light source, and 6-digit power-meter
When an experiment is extremely stable, it is possible to average measurements for a very long time, achieving extreme precision. We use the spontaneous emission of a fully inverted erbium-doped fibre (EDF) as a light source. To take advantage of the stability of this source, we developed a power-meter with a 6-digit stability. Combining these two components, we are able to perform experiments of extremely high precision, as well as calibrate and evaluate the stability, precision and accuracy of the rest of our laboratory equipment.
Absolute calibration of single-photon detectors
The efficiency of single photon detectors is crucial for experiments such as device-independent tests of non-locality, or cryptography. It is also important to compare the performance of devices developed by different groups and companies. Single photon detectors are hard to calibrate, not only because they work at extremely low light levels, but also because of their nonlinear nature. Effects such as after-pulsing and dead-time must carefully be taken into account to achieve consistent results.
Measurement of low intensity light beams (1-10000 photons)
Classical light detectors work well at intensities of 10000 photons or more. Single photon detectors work well for just a single photon. However, there is a gap between these light levels that are typically inaccessible. We are particularly interested in this range, as it is where the “quantum to classical” transition occurs. We pursue different ways to achieve measurements in this region, based on detectors multiplexed in space and time, on avalanche photodiodes in the linear regime, or on CMOS and CCD technology.
Characterisation of CCD and CMOS image sensors
Image sensors are omnipresent in modern technology: photo and video cameras, mobile phones, computers as well as many of our scientific experiments include such devices. Technology has evolved so much, that today these devices work at very low light intensities and are mostly limited by quantum effects. We use our knowledge in the field of low intensity optics and quantum mechanics to characterise this type of detectors and apply them to new types of experiment.
Contact: Hugo Zbinden