Abstract The orbital angular momentum state (OAM) of the photon can be theoretically evaluated from minus infinity to infinity, and the different orbital angular momentum states are orthogonal to each other. Therefore, in recent years, it has attracted wide attention from the academic circle and the industry. The purpose of this paper is to study the characteristics of single photon orbital angular momentum transfer based on information processing technology and to provide Suggestions for its technical optimization. Based on the characteristics of the angular momentum state of photon orbit, this paper studies its application and related problems in information processing and transmission. In this paper, quantum multiuser communication technology is studied, and a multiuser communication scheme based on photon orbital angular momentum state is proposed. The scheme takes advantage of the orthogonality of different orbital angular momentum states of the photon and assumes that the sender and receiver share a pair of entangled orbital angular momentum states. On this basis, the spatial light modulator is used to modulate it to the entangled photon of the sender, so that the sending photon carries all the user’s information at the same time. Finally, the receiver accurately extracts the information of each sender by measuring the coincidence count and according to the specific receiving rules. Numerical simulation and experimental results show that the coincidence rate of different coding schemes is between 0 and 0.66, which proves the feasibility of the scheme.
We investigate two-photon entangled states using two important degrees of freedom of the electromagnetic field, namely orbital angular momentum (OAM) and spin angular momentum. For photons propagating in the same direction we apply the idea of entanglement duality and develop schemes to do entanglement sorting based on either OAM or polarization. In each case the entanglement is tested using appropriate witnesses. We finally present generalizations of these ideas to three- and four-photon entangled states.
We show that the use of path-entangled states of photons, having nonzero orbital angular momentum (OAM), increases the resolution and sensitivity of angular-displacement measurements performed using an interferometer. In the ideal case of maximally path-entangled states, the resolution of angular-displacement measurements increases by a factor of
Nl, while the uncertainty in the measurement of angular displacements scales as
1/Nl, where
N is the number of entangled photons, half of which carry, on average, an OAM of $+l\ensuremath{\hbar}$ per photon and the other half carry an OAM of $\ensuremath{-}l\ensuremath{\hbar}$ per photon. We analyze measurement schemes for two- and four-photon entangled states produced by parametric down-conversion and, by employing a 4$\ifmmode\times\else\texttimes\fi{}$4 matrix formalism to study the propagation of entangled OAM modes, obtain explicit expressions for the resolution and sensitivity in these schemes. These results constitute an improvement over what could be obtained with
N nonentangled photons carrying an orbital angular momentum of $|l|\ensuremath{\hbar}$ per photon.