Controlling neutron orbital angular momentum

Abstract

The quantized orbital angular momentum (OAM) of photons offers an additional degree of freedom and topological protection from noise. Photonic OAM states have therefore been exploited in various applications ranging from studies of quantum entanglement and quantum information science to imaging. The OAM states of electron beams have been shown to be similarly useful, for example in rotating nanoparticles and determining the chirality of crystals. However, although neutrons--as massive, penetrating and neutral particles--are important in materials characterization, quantum information and studies of the foundations of quantum mechanics, OAM control of neutrons has yet to be achieved. Here, we demonstrate OAM control of neutrons using macroscopic spiral phase plates that apply a 'twist' to an input neutron beam. The twisted neutron beams are analysed with neutron interferometry. Our techniques, applied to spatially incoherent beams, demonstrate both the addition of quantum angular momenta along the direction of propagation, effected by multiple spiral phase plates, and the conservation of topological charge with respect to uniform phase fluctuations. Neutron-based studies of quantum information science, the foundations of quantum mechanics, and scattering and imaging of magnetic, superconducting and chiral materials have until now been limited to three degrees of freedom: spin, path and energy. The optimization of OAM control, leading to well defined values of OAM, would provide an additional quantized degree of freedom for such studies.

Scattering of wave packets with phases

“…The so-called vortex (or twisted) particles with orbital angular momentum (OAM) relative to a propagation axis and the Airy beams represent the simplest examples of such non-plane-wave states. They were shown to be solutions of the wave equations [7][8][9][10][11][12][13][14], and the corresponding beams of photons, electrons, and neutrons were generated in recent years [15][16][17][18][19][20]. Vortex electrons with the kinetic energy of 200 − 300 keV can be focused to a spot of anÅngström size [21], their OAM can be as high as = 200 [22], their magnetic moment increases proportionally to [13], and this brings about new effects in the electromagnetic radiation [23,24].…”

Mechanical effects on atoms interacting with highly twisted Laguerre-Gaussian light

“…Another related new development has been the production of twisted matter (de-Broglie) waves. Such matter waves have been realized for electrons and neutrons and proposed for atoms [11][12][13][14][15][16][17][18][19][20]. It has been shown that the diffraction of an atom wave packet from a light mask with a forklike intensity profile results in the generation of atom vortex Bessel and LG beams endowed with the property of quantized orbital angular momentum [19].…”

Quantum scattering beyond the plane-wave approximation

“…Such a twisted photon, |ω, k z , κ, ℓ, λ⟩, is a (paraxial) monochromatic state with the OAM ℓ, a helicity λ, a longitudinal momentum k z , and an absolute value of the transverse momentum κ. During the last several years, 200-300-keV electrons and cold neutrons carrying the OAM were also generated [9,10,11,12], along with the so-called Airy photons and electrons [13,14] and their different generalizations. Possible applications of these states to the hadronic physics have been discussed in Refs.…”