Spin - Orbital Angular Momentum Entanglement with Neutrons

It has been long known that Orbital Angular Momentum (OAM) of bound massive particles and free photons is quantized. However, in recent years stable OAM has also been observed in free massive particles, namely electrons. Even more recently it was demonstrated that OAM states can be prepared in free thermal neutrons using a spiral phase plate. This type of OAM is characterized as extrinsic OAM, which refers to the fact that each neutron in the beam has the same OAM with respect to the optical axis of the beam, but has a different intrinsic OAM, that is to say OAM with respect to their respective momentum vector. Thus new methods for generating OAM in neutrons were developed theoretically. It is predicted that a magnetic quadrupole can be used to create neutron OAM, entangled to the neutron spin (spin-orbit states). In addition to this existing theoretically method, we propose to apply static homogeneous electric field to generate OAM. Field polarization along the direction of particle propagation induces longitudinal spin orbit states, while a transversely polarized electric field generates transverse spin orbit states. Transversal OAM, induced by static electric fields, has not yet been observed in massive free particles. To sum up, the aim of the project is to prepare and identify longitudinal and transversal entangled spin orbit states with neutrons.

It has been long known that Orbital Angular Momentum (OAM) of bound massive particles and free photons is quantized. However, in recent years stable OAM has also been observed in free massive particles, namely electrons. Even more recently it was demonstrated that OAM states can be prepared in free thermal neutrons using a spiral phase plate. This type of OAM is characterized as extrinsic OAM, which refers to the fact that each neutron in the beam has the same OAM with respect to the optical axis of the beam, but has a different intrinsic OAM, that is to say OAM with respect to their respective momentum vector. Thus, new methods for generating OAM in neutrons were developed theoretically. It is predicted that a magnetic quadrupole can be used to create neutron OAM, entangled to the neutron spin (spin-orbit states). In addition to this existing theoretically method, we propose to apply static homogeneous electric field to generate OAM. Field polarization along the direction of particle propagation induces longitudinal spin orbit states, while a transversely polarized electric field generates transverse spin orbit states. Transversal OAM, induced by static electric fields, has not yet been observed in massive free particles. Within the framework of this projected we able to demonstrate OAM generation via Schwinger scattering in perfect Quartz, utilizing the internal electric fields of the asymmetric crystal. Furthermore, we generalize magnetic methods which employ coherent averaging and apply this to neutron interferometry. Two aluminium prisms are inserted into a nested loop interferometer to generate a phase vortex lattice with significant extrinsic OAM. Moreover, we could show the applicability of our mode entangled interferometer at Atominstitut Tu Wien to generaate OAM via a procedure called coherent averaging; a new spin echo interferometry tool, which uses incomplete recombination of the two path states to generate composite wavefunctions with special structure. In particular we show that this method produces neutron wavefunctions that exist in a superposition of two quantum mechanical OAM modes, l = 1. Finally, a coupling between Earth's rotation and orbital angular momentum (OAM), known as the Sagnac effect, is observed in entangled neutrons produced using a spin-echo interferometer. After correction for instrument systematics the measured coupling is within 5% of theory, with an uncertainty of 7.2%. This demonstrates the feasibility of using the Sagnac effect to definitively measure neutron OAM and paves the way towards a future observation of the quantum Sagnac effect.