Detection of a spinning object using light's orbital angular momentum

The linear Doppler shift is widely used to infer the velocity of approaching objects, but this shift does not detect rotation. By analyzing the orbital angular momentum of the light scattered from a spinning object, we observed a frequency shift proportional to product of the rotation frequency of the object and the orbital angular momentum of the light. This rotational frequency shift was still present when the angular momentum vector was parallel to the observation direction. The multiplicative enhancement of the frequency shift may have applications for the remote detection of rotating bodies in both terrestrial and astronomical settings

Precise quantum tomography of photon pairs with entangled orbital angular momentum

We report a high fidelity tomographic reconstruction of the quantum state of photon pairs generated by parametric down-conversion with orbital angular momentum (OAM) entanglement. Our tomography method allows us to estimate an upper and lower bound for the entanglement between the down-converted photons. We investigate the two-dimensional state subspace defined by the OAM states ± and superpositions thereof, with =1, 2, ..., 30. We find that the reconstructed density matrix, even for OAMs up to around =20, is close to that of a maximally entangled Bell state with a fidelity in the range between F=0.979 and F=0.814. This demonstrates that, although the single count-rate diminishes with increasing , entanglement persists in a large dimensional state space

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Bounds and optimisation of orbital angular momentum bandwidths within parametric down-conversion systems

The measurement of high-dimensional entangled states of orbital angular momentum prepared by spontaneous parametric down-conversion can be considered in two separate stages: a generation stage and a detection stage. Given a certain number of generated modes, the number of measured modes is determined by the measurement apparatus. We derive a simple relationship between the generation and detection parameters and the number of measured entangled modes.Comment: 6 pages, 4 figure

Triticum timopheevii s.l. (‘new glume wheat’) finds in regions of southern and eastern Europe across space and time

Triticum timopheevii sensu lato (‘new glume wheat’, NGW) was first recognised as a distinct prehistoric cereal crop through work on archaeobotanical finds from Neolithic and Bronze Age sites in northern Greece. This was later followed by its identification in archaeobotanical assemblages from other parts of Europe. This paper provides an overview of the currently known archaeobotanical finds of Timopheev’s wheat in southeastern and eastern Europe and observes their temporal span and spatial distribution. To date, there are 89 prehistoric sites with these finds, located in different parts of the study region and dated from the Neolithic to the very late Iron Age. Their latest recorded presence in the region is in the last centuries BCE. For assemblages from the site as a whole containing at least 30 grain and/or chaff remains of Timopheev’s wheat, we take a brief look at the overall relative proportions of Triticum monococcum (einkorn), T. dicoccum (emmer) and T. timopheevii s.l. (Timopheev’s wheat), the three most common glume wheats in our study region in prehistory. We highlight several sites where the overall proportions of Timopheev’s wheat might be taken to suggest it was a minor component of a mixed crop (maslin), or an unmonitored inclusion in einkorn or emmer fields. At the same sites, however, there are also discrete contexts where this wheat is strongly predominant, pointing to its cultivation as a pure crop. We therefore emphasise the need to evaluate the relative representation of Timopheev’s wheat at the level of individual samples or contexts before making inferences on its cultivation status. We also encourage re-examination of prehistoric and historic cereal assemblages for its remains

The angular momentum of light inside a dielectric

We consider whether or not a short pulse of light carrying angular momentum will exert a torque when propagating through a transparent disc. The approach is based on the 'Einstein-box' argument which we apply to discuss linear optical momentum in a medium. Two competing theories due to Minkowski and Abraham, at least superficially, suggest that the disc will not or will rotate. Our analysis suggests that the disc will rotate and that an experiment using optical tweezers should be able to detect the rotation

Optical Angular Momentum

Spin angular momentum of photons, and the associated polarisation of light, has been known of for many years. However, it is only over the last decade or so that physically realisable laboratory light beams have been used to study the orbital angular momentum of light. In many respects orbital and spin angular momentum behave in a similar manner, but they differ significantly in others. In particular, orbital angular momentum offers exciting new possibilities with respect to the optical manipulation of matter, and to the study of the entanglement of photons. 'Optical Angular Momentum' brings together 44 landmark papers, reproduced over eight chapters, offering the first comprehensive overview of the subject as it has developed. In each chapter the editors have written a concise introduction putting the selected papers into context and outlining the key articles associated with this aspect of the subject. The volume chronicles the first decade of this important subject and gives a definitive statement of the current status of all aspects of optical angular momentum

Two-photon entanglement of orbital angular momentum states

We investigate the orbital angular momentum correlation of a photon pair created in a spontaneous parametric down-conversion process. We show how the conservation of the orbital angular momentum in this process results from phase matching in the nonlinear crystal

Entanglement of orbital angular momentum for the signal and idler beams in parametric down-conversion

We calculate the anticipated correlation between measurements of the orbital angular momentum of the signal and idler beams for parametric down-conversion. These calculations apply to the experiments where the orbital angular momentum state is measured by the use of computer-generated holograms. Displacement of these holograms with respect to the beam axis allows the measurement of superpositions of Laguerre-Gaussian modes. The correlations between such superposition modes of the signal and idler beams show their entanglement and could be used for Bell-type tests of nonlocality