Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session Y1: Orbital Angular Momentum of Light and MatterInvited
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Sponsoring Units: DCMP DAMOP Chair: Charles Clark, NIST Room: Ballroom I |
Friday, March 18, 2016 11:15AM - 11:51AM |
Y1.00001: Ghost imaging with entangled photons and orbital angular momentum Invited Speaker: Miles Padgett We utilise the position and orbital angular momentum (OAM) correlations between the signal and idler photons generated in the down-conversion process to obtain ghost images of a phase object. By using an OAM phase filter, which is non-local with respect to the object, the ghost images exhibit isotropic edge-enhancement. The strong spatial correlations between the signal and idler photons generated by spontaneous parametric downconversion have been widely utilised in many different imaging systems. The use of a scanning single element detector to recover the spatial information in the signal and idler beams fundamentally limits the detection efficiency of the imaging system to a maximum of 1/N where N is the number of pixels in the image. Our approach overcomes this limitation by replacing the scanning detector by an intensified CCD camera, therefore detecting all photons irrespective of their position within the image. Using a camera in this way, coupled with the OAM edge-enhancement and image reconstruction techniques allows us to obtain images of phase objects with an average of fewer than one photon per image pixel. [Preview Abstract] |
Friday, March 18, 2016 11:51AM - 12:27PM |
Y1.00002: Twisting Neutron Waves Invited Speaker: Dmitry Pushin Most waves encountered in nature can be given a ``twist'', so that their phase winds around an axis parallel to the direction of wave propagation. Such waves are said to possess orbital angular momentum (OAM). For quantum particles such as photons, atoms, and electrons, this corresponds to the particle wavefunction having angular momentum of $L\hbar$ along its propagation axis. Controlled generation and detection of OAM states of photons began in the 1990s, sparking considerable interest in applications of OAM in light and matter waves\footnote{``Orbital angular momentum: origins, behavior and applications,'' A. \textit{M. Yao} and \textit{M. J. Padgett}, Adv. Opt. Photonics \textbf{3}, 161 (2011)}. OAM states of photons have found diverse applications such as broadband data multiplexing, massive quantum entanglement, optical trapping, microscopy, quantum state determination and teleportation, and interferometry. OAM states of electron beams have been used to rotate nanoparticles, determine the chirality of crystals and for magnetic microscopy. Here I discuss the first demonstration of OAM control of neutrons\footnote{``Controlling neutron orbital angular momentum,'' \textit{C. W. Clark, et al.}, Nature \textbf{525}, 504 (2015)}. Using neutron interferometry with a spatially incoherent input beam, we show the addition and conservation of quantum angular momenta, entanglement between quantum path and OAM degrees of freedom. Neutron–based quantum information science heretofore limited to spin, path, and energy degrees of freedom, now has access to another quantized variable, and OAM modalities of light, x-ray, and electron beams are extended to a massive, penetrating neutral particle. The methods of neutron phase imprinting demonstrated here expand the toolbox available for development of phase-sensitive techniques of neutron imaging. [Preview Abstract] |
Friday, March 18, 2016 12:27PM - 1:03PM |
Y1.00003: Twisted photon entanglement through turbulent air across Vienna Invited Speaker: Mario Krenn For photons with spatial structures, the influence of turbulent atmosphere is an active field of studies. Even though there is a lot of effort in the analytical or numerical analysis and lab-scale experiments, it is surprising that there are no long-distance outdoor experiments targeting that question. Thus in 2014, we performed the first experiment in a real-world scenario, where we transmitted classical information encoded in OAM-modes at a distance of 3 kilometers across the city of Vienna [1]. Here we will present the results of our follow-up experiment, which brings our investigation to the quantum level [2]. Specifically, we will present how we were able to verify quantum entanglement of photons that were transmitted over the same turbulent link of 3 kilometers across Vienna. In the experiment, we started with polarization-entangled two-photon states. The first photon is transformed into an OAM-state, and sent to a telescope at the roof of our institute 3040 meters away. There we use special slit-masks to measure superposition-bases of OAM. The photons after the mask are detected with single-photon detectors, and recoded as time-stamps. Its sisterphoton is measured at the sender. By comparing the time-stamps and the mask positions, we can measure visibilities in two mutual unbiased bases, which are sufficient to apply an entanglement witness. We show that our results cannot be produced by separable states, thus verify entanglement of OAM in a long-distance real-world scenario.\newline \newline [1] Krenn, M., Fickler, R., Fink, M., Handsteiner, J., Malik, M., Scheidl, T., Ursin, R., & Zeilinger, A., Communication with spatially modulated light through turbulent air across Vienna. NJP, 16(11), 113028 (2014).\new line \new line [2] Krenn, M., Handsteiner, J., Fink, M., Fickler, R., & Zeilinger, A, Twisted photon entanglement through turbulent air across Vienna. PNAS, 112(46), 14197-14201 (2015). [Preview Abstract] |
Friday, March 18, 2016 1:03PM - 1:39PM |
Y1.00004: Creating High-Harmonic Beams with Controlled Orbital Angular Momentum Invited Speaker: Robert W. Boyd A beam of light with an angle-dependent phase $\Phi = \ell \phi$, where $\phi$ is the azimuthal coordinate, about the beam axis carries an orbital angular momentum (OAM) of $\ell \hbar$ per photon. Such beams have been exploited to provide superresolution in visible-light microscopy. The ability to create extreme ultraviolet or soft-x-ray beams with controllable OAM would be a critical step towards extending superresolution methods to extremely small feature size. Here we show that OAM is conserved during the process of high-harmonic generation (HHG). Experimentally, we use a fundamental beam with $\ell = 1$ and interferometrically determine that the {\it q}-th harmonic has an OAM quantum number $\ell$ equal to its harmonic order {\it q}. We also show theoretically how to couple an arbitrary low value of the OAM quantum number $\ell$ to any harmonic order {\it q} in a controlled manner. Our results open a route to microscopy on the molecular, or even submolecular, scale. \\ Reference: G. Gariepy, J. Leach, K.T. Kim, T. J. Hammond, E. Frumker, R.W. Boyd, and P. B. Corkum, Phys. Rev. Lett. 113, 153901 (2014). [Preview Abstract] |
Friday, March 18, 2016 1:39PM - 2:15PM |
Y1.00005: Unveiling orbital angular momentum and acceleration of light beams and electron beams Invited Speaker: Ady Arie Special beams, such as the vortex beams that carry orbital angular momentum (OAM) and the Airy beam that preserves its shape while propagating along parabolic trajectory, have drawn significant attention recently both in light optics and in electron optics experiments. In order to utilize these beams, simple methods are needed that enable to easily quantify their defining properties, namely the OAM for the vortex beams and the nodal trajectory acceleration coefficient for the Airy beam. Here we demonstrate a straightforward method to determine these quantities by astigmatic Fourier transform of the beam. For electron beams in a transmission electron microscope, this transformation is easily realized using the condenser and objective stigmators, whereas for light beam this can be achieved using a cylindrical lens. In the case of Laguerre-Gauss vortex beams, it is already well known that applying the astigmatic Fourier transformation converts them to Hermite-Gauss beams. The topological charge (and hence the OAM) can be determined by simply counting the number of dark stripes of the Hermite-Gauss beam. We generated a series of electron vortex beams and managed to determine the topological charge up to a value of 10. The same concept of astigmatic transformation was then used to unveil the acceleration of an electron Airy beam. The shape of astigmatic-transformed depends only on the astigmatic measure and on the acceleration coefficient. This method was experimentally verified by generating electron Airy beams with different known acceleration parameters, enabling direct comparison to the deduced values from the astigmatic transformation measurements. The method can be extended to other types of waves. Specifically, we have recently used it to determine the acceleration of an optical Airy beams and the topological charge of so-called Airy-vortex light beam, i.e. an Airy light beam with an embedded vortex. [Preview Abstract] |
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