Protecting orbital-angular-momentum photons from decoherence in a turbulent atmosphere

Abstract

One of the most important properties of orbital angular momentum (OAM) of photons is that the Hilbert space required to describe a general quantum state is infinite dimensional. In principle, this could allow for encoding arbitrarily large amounts of quantum information per photon, but in practice, this potential is limited by decoherence and errors. To determine whether photons with OAM are suitable for quantum communication, we numerically simulated their passage through a turbulent atmosphere and the resulting errors. We also proposed an encoding scheme to protect the photons from these errors, and characterized its effectiveness by the channel fidelity.

Universal entanglement decay of photonic-orbital-angular-momentum qubit states in atmospheric turbulence

“…It is useful to recall the properties of the linear map A that represents the action of an ensemble-averaged phase screen on a single photon density operator [25], A relates the input and the output density matrices of a single photon in the OAM basis, cr(0) and a, respectively, through the equation (2) and includes the propagation distance implicitly, through its dependence on the Fried parameter [see Eqs. (4) and (5) below].…”

“…The first successful quantum key dis tribution protocol with OAM photons was demonstrated [12] over a distance of only 210 m-much shorter than over 100-km-long free space links which were attained for quantum information transmission with polarized photons [13,14], In recent years, experimental [15][16][17][18][19] and theoretical [20][21][22][23][24][25] efforts have been dedicated to clarifying and to partially mitigating [18,19,25] the impact of turbulence on single and entangled OAM photons. Despite some progress, there are still fundamental open issues concerning the behavior of OAM photons in turbulence, one of them being the description of the OAM photons' entanglement evolution.…”

Biphoton states in correlated turbulence

“…The decay of entanglement in biphoton states that are entangled in there spatial degrees of freedom has been studied theoretically [7][8][9][10][11][12][13], numerically [14], as well as experimentally [15][16][17][18]. There has also been a number of demonstrations of the use of OAM modes for the implementation of classical free-space communication links [19,20] in addition to the free-space entanglement-based quantum key distribution, using OAM qubits [21,22].…”

“…Hence, if we were to compute the ensemble average of Eq. (11), all the terms that contain N (a, z) would be removed, leaving only the freespace propagation terms without the effect of the turbulent medium.…”

Universal Decay of Quantumness for Photonic Qubits Carrying Orbital Angular Momentum Through Atmospheric Turbulence

“…Photons' wave front will be distorted due to refractive index fluctuations of the turbulent atmosphere, which may lead to random phase aberrations on a propagating optical beam [7]. A large amount of efforts, both theoretical [8][9][10][11][12] and experimental [13][14][15][16], have been devoted to exploring the impacts of atmospheric turbulence on the propagation of photons carrying OAM and protecting OAM photons from decoherence in turbulent atmosphere.…”