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Nonlinear Optics

High-Flux Entanglement Sources using Periodically-Poled Nonlinear Crystals

Marius A. Albotǎ, Friedrich König, Christopher E. Kuklewicz, Elliott J. Mason, Gaétan Messin, Jeffrey H. Shapiro, Franco N. C. Wong

Published Jan 1, 2002• 0 citations
Publisher

Abstract

Entangled photons are essential in many quantum information applications such as quantum communications, implementation of quantum computation algorithms, and cryptographic key distributions. Typically UV-pumped optical parametric downconversion in a thin angle-phase-matched beta barium borate (BBO) crystal produces spatially-separated, entangled photon pairs that are emitted in a cone.

DOI
10.1364/nlo.2002.fc8

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Entangled photons are essential in many quantum information applications such as quantum communications, implementation of quantum computation algorithms, and cryptographic key distributions. Typically UV-pumped optical parametric downconversion in a thin angle-phase-matched beta barium borate (BBO) crystal produces spatially-separated, entangled photon pairs that are emitted in a cone.
Summary form only given. Up to this point, photon-entanglement sources suffered from the compromise of being either compact or efficient, but not both at the same time [1-6]. Our new concept of creating entanglement [7] combines most of the advantages of the various existing schemes. The setup offers high coupling efficiencies due to its collinear design and is still as compact and simplistic as a BBO source [1], requiring only one crystal with uniform poling periodicity, pumped from only one direction.Periodic poling of a nonlinear crystal allows for a positive energy transfer from the pump (p) field to signal (s) and idler (i). The required poling periodicity to support a given process kp - ks - kt requires an alternation of the effective nonlinear coefficient deff in integer multiples of a certain grating length, the poling periodicity A = 2πμ/Δk, where m is an odd integer and Δk = kp - ks - kt is the momentum-difference vector. Note that Δk can be both positive and negative. Our source relies on the fact that one periodically poled crystal with grating period A, pumped with a given laser frequency, can provide phase-matching for two downconversion processes simultaneously: one with a positive momentum-difference vector Δk and one whose Δk is of same magnitude but opposite sign. Careful design of the experimental setup allows for generation of two orthogonally polarised pairs which are interchangeable in wavelength. This results in a polarisation- and frequency-entangled state.
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As some of the most promising quantum applications such as high resolution quantum optical coherence tomography (QOCT) [1] with dispersion cancellation as well as quantum key distribution require frequency entanglement. Therefore, frequency entanglement light sources are an essential importance for implement of many quantum optical applications. So Far, the most prominent method used for the entangled photon pair generation is spontaneous parametric down-conversion (SPDC) in nonlinear crystals. Recently, with adopting chirp quasi-phase matching (QPM) PPSLT (periodically poled stoichiometric lithium tantalate) has been used as source of entangled photons with large bandwidth [2]. However, improving the overall system efficiency is still remain challenging.
Entangled photon pairs generated via spontaneous parametric down-conversion (SPDC) in beta-barium borate (BBO) crystals are fundamental to the realization of anchor-free quantum metrology and spaceborne radiometric standards. High-precision calibration strictly necessitates rigorous spectral and spatial matching of these entangled photons. However, the spatial distribution of entangled photons exhibits a profound dependence on the phase-matching angle. Due to the combined effects of crystal fabrication tolerances, environmental perturbations, and the extremely low intensity of entangled signals (∼pW level), conventional mono-dimensional angle tuning struggles to balance the conflicting requirements of spectral bandwidth and spatial distribution matching. To address this bottleneck, a synergistic tuning strategy integrating angle, temperature, and stress is proposed in this work. A multi-channel, high-precision temperature control system based on series-connected thermoelectric coolers (TECs) was developed, achieving a control precision superior to 0.01 ℃ at a setpoint of 50 ℃. By combining theoretical derivations with thermo-structural coupled simulations, the tuning regularities of temperature (30–70 ℃) and stress on the photon output angle were quantitatively characterized. Experimental measurements on the multi-channel BBO crystal configuration (comprising eight crystals) achieved a maximum tuning range (Δ θ OA ) of 2.941° and identified a non-destructive stress threshold of 312.5 N. This work elucidates the intrinsic mechanisms of temperature and stress in BBO phase-matching, providing critical engineering methodologies and theoretical underpinnings for enhancing quantum calibration accuracy while offering a paradigm for the multi-dimensional tuning of nonlinear optical crystals.