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Quantum 2.0 Conference and Exhibition

Two-Pumps-Based Entanglement Generation Source Enabling Entanglement-Assisted Communication over Beyond Strong Atmospheric Turbulence Channels

Ivan B. Djordjević, Vijay Nafria

Published Jan 1, 2024• 0 citations
Publisher

Abstract

Two S-/L-band pumps, satisfying PPLN-waveguide quasi-phase-matching-condition, are used to generate bright entangled-photons providing needed flexibility in wavelength-selection over entire C-band. By performing phase-conjugation on idler photons, we demonstrate entanglement-assisted communication at 1Gb/s over 1.5km FSO link operated in beyond strong turbulence regime.

DOI
10.1364/quantum.2024.qth3a.37

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Optics Express•Oct 30, 2023•26 citations
Two S-/L-band pumps, satisfying PPLN-waveguide quasi-phase-matching-condition, are used to generate bright entangled-photons providing needed flexibility in wavelength-selection over entire C-band. By performing phase-conjugation on idler photons, we demonstrate entanglement-assisted communication at 1Gb/s over 1.5km FSO link operated in beyond strong turbulence regime.
A high-speed entanglement assisted communication that operates at 10 Gb/s is proposed, which performs a highly efficient, PPLN-waveguide-based, entanglement generation by making the simultaneous use of S- and L-band pumps. The two-pump-based entanglement generation source satisfies the quasi-phase-matching-condition over the entire C-band. To improve the system reliability, our system performs the phase-conjugation on idler photons in contrast to conventional ways of performing the phase-conjugation on signal photons. To study the performance of the proposed entanglement-assisted system we have developed the 1.5 km long outdoor free-space optical (FSO) link at the University of Arizona campus. Experimental results indicate that the proposed entanglement-assisted system significantly outperforms the classical counterpart at 10 Gb/s, operated in strong turbulence regime. We also demonstrate that the traditional entanglement-assisted system performing the optical phase conjugation on signal photons at the receiver side is not operational at all in strong turbulence regime given that it is extremely difficult to perform the phase-conjugation on weak signal photons when the number of received photons is low. To improve the system performance the adaptive optics is performed on signal photons.
Optical communications over terrestrial free-space optical (FSO) channels are affected by various effects including diffraction, absorption, scattering, and turbulence effects. In several recent papers we have shown that entanglement assisted (EA) communication systems significantly outperform corresponding classical counterparts in strong turbulence regime. In traditional EA communications the phase-conjugation, required before the homodyne detection takes place, is performed on signal photons. However, given that many photons get lost due to diffraction, scattering, absorption, and turbulence effects, it is extremely difficult to perform the phase-conjugation on received signal photons when average number of received photons is smaller than 1. To solve this problem, we recently have proposed to perform phase-conjugation on bright idler photons instead. To operate the EA communication system over turbulent FSO links it is required to generate many bright entangled photons so that signal photons can survive beyond strong turbulence regime. To solve this problem, we have proposed to properly design periodically poled lithium niobate waveguides so that we can use telecom available lasers operated in S-, C-, and L-bands as the pump lasers instead of high-cost 780 nm pump lasers. In this invited paper, we will review our recent activities in EA communion studies over terrestrial FSO links and present recent experimental results demonstrating that EA communication systems performing the phase-conjugation on idler photons significantly outperforms both classical counterpart and the EA communications with phase-conjugated receiver in strong turbulence regime.
We propose a degenerate entanglement-assisted (EA) free-space optical (FSO) communication system employing spatial light modulator (SLM)-based beam steering and a novel dual-pump configuration. The system utilizes a type-0 periodically poled lithium niobate (PPLN) waveguide to generate signal and idler photon pairs at 1570 nm, using two independent low-cost C- and L-band pump lasers. To enable homodyne detection, unmodulated idler photons are transmitted alongside modulated signal photons thus avoiding the need for phase conjugation and quantum memories. We demonstrate 1 Gb/s degenerate entanglement assisted transmission over a 1.5 km terrestrial FSO link at the University of Arizona campus, operating in the L-band. Experimental results show that the proposed degenerate EA system significantly outperforms its classical counterpart, particularly under strong atmospheric turbulence conditions.
We propose a low-complexity degenerate entanglement-assisted free-space optical (FSO) communication system employing a two-pumps approach, a type-0 periodically poled lithium niobate (PPLN) waveguide, a multistage WDM demultiplexer, and a properly biased Mach-Zehnder modulator on transmitter side and, for binary phase-shift keying (BPSK) signaling, a single PIN photodetector or avalanche photodetector (APD) on a receiver side. Two-pumps-based approach utilizes two independent pump lasers operating at telecom wavelengths. The portion of degenerate entangled photons is used as the unmodulated carrier and the rest to transmit the modulated PSK/quadrature amplitude modulation (QAM) signal. The unmodulated portion of entangled photons is selected by properly choosing the bias voltage and phase representing the transmitted bits. In BPSK signaling, the unmodulated carrier photons are used on receiver side to reconstruct the transmitted symbol by beating them with modulated signal photons on either PIN photodetector or APD. We also describe how to implement the M-ary PSK and QAM transmitters for the degenerate entanglement assisted communications. Further, we propose a low-complexity PSK/QAM demodulator compatible with the proposed degenerate entanglement assisted communication concept. To demonstrate the quantum advantage, we conducted 1 Gb/s degenerate entanglement assisted BPSK experiments over a 1.5 km terrestrial FSO link we have developed previously at the University of Arizona, between ECE Dept. and Optical Sciences Meinel buildings. We demonstrate that in the strong atmospheric turbulence regime the proposed low-complexity degenerate entanglement assisted communication system performs significantly better compared to corresponding classical laser and thermal source-based communications counterparts.