Creation of single-photon entangled states around rotating black holes

TL;DR

This paper explores how photons emitted near rotating black holes can form highly entangled quantum states, potentially enabling quantum information processing using astrophysical sources.

Contribution

It introduces a novel model of bipartite quantum systems based on photon polarization and orbital angular momentum near black holes, linking astrophysics with quantum information.

Findings

Photons near rotating black holes can be maximally entangled in polarization and orbital angular momentum.

The entanglement can reach all four Bell states in extreme black hole conditions.

Quantum information encoding in astrophysical photons is feasible with current technology.

Abstract

Recently, numerical simulations showed that X-ray photons emitted by accretion disks acquire rotation of polarization angle and orbital angular momentum due to strong gravitational field in the vicinity of the rotating black holes. Based on these two degrees of freedom we construct a bipartite two-level quantum system of the accretion disk's photons. To characterize the quantum states of this composite system we consider linear entropy for the reduced density matrix of polarization with the intention to exploit its direct relation with the photons degree of polarization. Accordingly, the minimum degree of polarization of X-ray radiation located in the transition region of the accretion disk indicates a high value of the linear entropy for the photons emitted on this region, inferring a high degree of entanglement in the composite system. We emphasize that for an extreme rotating black hole in the thermal state, the photons with energies at the thermal peak are maximally entangled in polarization and orbital angular momentum, leading to the creation of all four Bell states. Detection and measurement of quantum information encoded in photons emitted in the accretion disk around rotating black holes may be performed by actual quantum information technology.