Infinitesimal propagation equation for decoherence of an OAM entangled biphoton in atmospheric turbulence

Controlling the biphoton orbital angular momentum eigenmodes using asymmetric pump vortex beam

We report on controlling the bi-photon orbital angular momentum (OAM) eigenmodes in the spontaneous parametric down conversion process by simply adjusting the asymmetry of the pump vortex beam. Adjusting the optic axis of the spiral phase plate (SPP) of phase winding corresponding to OAM mode, l, with respect to the beam propagation axis, we have transformed a Gaussian beam into an asymmetric vortex beam with OAM modes, l, l-1, l-2, 0 with different weightages. Pumping the nonlinear crystal with such asymmetric vortices and controlling their asymmetry we have tailored the spiral spectrum of th…

高纯度的OAM纠缠光子从SPDC中产生，具有减少的空谱相关性

High Purity OAM Entangled Photons from SPDC with Reduced Spatial Spectral Correlations

通过优化SPDC源配置，实现高纯度OAM纠缠光子生成，减少空间光谱相关性以提升高维量子通信性能

Decoherence of orbital angular momentum entanglement in a turbulent atmosphere

The evolution of an entangled photon state propagating through a turbulent atmosphere is formulated in terms of a set of coupled first order differential equations, by using an infinitesimal propagation approach. The orbital angular momentum (OAM) basis is used to described the density matrix of the state. Although the analysis is done in the paraxial limit for a monochromatic optical field, the formalism is comprehensive in the sense that it does not require any assumptions about the strength of the turbulence and it can incorporate any spectral model for the turbulence. As a comparative exam…

Biphoton states in correlated turbulence

The effect of turbulence on a pair of photons propagating together through the same medium is analyzed. The behavior is compared to the case where these photons propagate separately through different turbulent media. The analysis is done with a multiple phase screen approach, by deriving and solving an infinitesimal propagation equation. We apply these results to the case where the initial photons are entangled in their spatial degrees of freedom with the aid of spontaneous parametric down-conversion. It is found that for this input state, the decay of entanglement in correlated media under th…

Physical meaning of the deviation scale under arbitrary turbulence strengths of optical orbital angular momentum

The recently so-called deviation scale [C. M. Mabena et al., Phys. Rev. A 99, 013828 (2019)] bridges the connection between the result of the infinitesimal propagation equation (IPE) prediction and that of the single phase screen (SPS) approximation. Thanks to the multiple phase screen (MPS) approach, in this paper we elaborate the physical meaning of the deviation scale: the spatial accumulation of slight intensity modulation of incident orbital angular momentum (OAM) carrying beam splits the original vortex into multiple individual vortices with a topological charge (TC) of +1 and re-generat…