Physicists know that light is made of packets called photons, but they have longed to actually see light's discrete nature. Now they can, in an ingenious experiment at the Ecole Normale Supérieure in Paris that captures a few photons in a tiny chamber and counts them like marbles. Along with painstaking engineering, the experiment required a supersensitive scheme for detecting photons: individual atoms, crossing the chamber one by one in an excited state that is sensitive to the presence of the photons.
We report on building a pulsed source of cold Tm atoms and loading of the narrow-line magneto-optical trap (MOT) from the cold atomic beam. We achieve the loading rate of the first-stage MOT in the primary chamber up to 108 atoms/s and obtain a cold atomic beam with the mean longitudinal velocity ∼10 m/s and an angular spread of 18 mrad in a pulsed mode. In this regime, we can form a cold atomic beam with up to 5 × 106 atoms at a 5 Hz repetition rate. We also introduce a novel method to enhance the capture velocity of the narrow-line MOT by incorporating an additional axial cooling beam and achieve loading efficiency η = 10% of the second-stage MOT in the science chamber. Our approach could be extended to other atomic species with similar properties, such as Sr, Yb, Dy, and Er, serving as a convenient alternative for the traditional 2D-MOT schemes. Providing rapid loading of the MOT in the science chamber, it would reduce preparation time of the atomic ensemble leading to a shorter dead time in spectroscopy experiments and a higher repetition rate.
Ars Technica: Orbital angular momentum is one of the quantum properties of photons and has a theoretically infinite number of possible values. This makes it a subject of interest for researchers trying to increase the amount of data a single photon can represent. A team led by Xinlun Cai of the University of Bristol in the UK may have taken the first real steps toward that goal. The researchers shined IR laser light through ring-shaped silicon chambers scored with grooves, which diffracted the light, causing helical interference patterns. The patterns were dependent on the photons' original polarization and the diameter and grooving of the ring chambers. The team also created additional patterns by combining light that passed through different rings. Data transfer is only one possible use for orbital angular momentum manipulation, but researchers must overcome the loss of pattern coherence due to interactions with molecules in air or fiber-optic cables before it is useful in quantum devices.