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Conference on Infrared, Millimeter, Terahertz Waves and Applications (IMT)

Quantum entanglement source model pumped by low-power laser diode

Tianxuan Feng, Zhiying Song, Tong Wu, Xun Lu, Lijing Li

Published Apr 12, 2023• 1 citation
Publisher

Abstract

Nowadays, with the continuous development of optical quantum sensor technology, the importance of the quantum entanglement source is increasing day by day. As an indispensable part of optical quantum systems, the quantum entanglement source has a wide prospect of application in quantum communication, quantum imaging, quantum computing, life science and so on. However, the current power consumption and preparation cost of quantum entanglement sources are relatively huge, which impedes further integration and expansion. In view of these problems, we establish a quantum entanglement source model pumped by a low-power laser diode based on spontaneous parametric down-conversion (SPDC) theory and phase matching technology, to effectively analyze the influence of components and characteristics of each module of quantum entanglement source on its performance. Furthermore, we prepare a quantum entanglement source with a 10mW laser diode and a typical type-II barium metaborate (BBO) crystal to conduct experiment whose result is 2053 counts per second in average which is in desirable agreement with the model. To some extent, the low-power and low-cost goal of quantum entanglement source has been achieved, which has made a significant contribution to the practical application of quantum entanglement lighting, and is conducive to the popularization of optical quantum systems in the future.

DOI
10.1117/12.2662233

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Nowadays, with the continuous development of optical quantum sensor technology, the importance of the quantum entanglement source is increasing day by day. As an indispensable part of optical quantum systems, the quantum entanglement source has a wide prospect of application in quantum communication, quantum imaging, quantum computing, life science and so on. However, the current power consumption and preparation cost of quantum entanglement sources are relatively huge, which impedes further integration and expansion. In view of these problems, we establish a quantum entanglement source model pumped by a low-power laser diode based on spontaneous parametric down-conversion (SPDC) theory and phase matching technology, to effectively analyze the influence of components and characteristics of each module of quantum entanglement source on its performance. Furthermore, we prepare a quantum entanglement source with a 10mW laser diode and a typical type-II barium metaborate (BBO) crystal to conduct experiment whose result is 2053 counts per second in average which is in desirable agreement with the model. To some extent, the low-power and low-cost goal of quantum entanglement source has been achieved, which has made a significant contribution to the practical application of quantum entanglement lighting, and is conducive to the popularization of optical quantum systems in the future.
With the continuous development of optical quantum sensor technology, the importance of quantum entanglement sources is growing. As an essential component of optical quantum systems, entanglement sources have broad applications in quantum communication, imaging, computing, and other fields. However, the high-power consumption and preparation costs associated with these sources hinder their integration and expansion. To address these issues, we conducted experiments using a 40mW laser diode and a typical type-II barium metaborate (BBO) crystal to prepare a low-power and low-cost quantum entanglement source. Our results show an average count of over 15,000 entangled photons per second and over 7,500 entangled photon pairs per second, which are in good agreement with theoretical analysis. We have made significant progress towards achieving the goal of low-power and low-cost entanglement sources, which will facilitate the practical application of quantum entanglement lighting and promote the wider adoption of optical quantum systems in the future.
The quantum entangled photon-pair source, as an essential component of optical quantum systems, holds great potential for applications such as quantum teleportation, quantum computing, and quantum imaging. The current workhorse technique for preparing photon pairs involves performing spontaneous parametric down conversion (SPDC) in bulk nonlinear crystals. However, the current power consumption and cost of preparing entangled photon-pair sources are relatively high, posing challenges to their integration and scalability. In this paper, we propose a low-power system model for the quantum entangled photon-pair source based on SPDC theory and phase matching technology. This model allows us to analyze the performance of each module and the influence of component characteristics on the overall system. In our experimental setup, we utilize a 5 mW laser diode and a typical type-II barium metaborate (BBO) crystal to prepare an entangled photon-pair source. The experimental results are in excellent agreement with the model, indicating a significant step towards achieving the goal of low-power and low-cost entangled photon-pair sources. This achievement not only contributes to the practical application of quantum entanglement lighting, but also paves the way for the widespread adoption of optical quantum systems in the future.
Spontaneous parametric down-conversion (SPDC) is a reliable platform for entanglement generation. Routinely, a coherent laser beam is an essential prerequisite for pumping the nonlinear crystal. Here we break this barrier to generate polarization entangled photon pairs by using a commercial light-emitting diode (LED) source to serve as the pump beam. This effect is counterintuitive, as the LED source is of extremely low spatial coherence, which is transferred during the down-conversion process to the biphoton wavefunction. However, the type-II phase-matching condition naturally filters the specific frequency and wavelength of LED light exclusively to participate in SPDC such that localized polarization Bell states can be generated, regardless of the global incoherence over the full transverse plane. In our experiment, we characterize the degree of LED light-induced polarization entanglement in the standard framework of the violation of Bell inequality. We have achieved the Bell value S=2.33±0.097S=2.33\pm 0.097S=2.33±0.097, obviously surpassing the classical bound S=2S=2S=2 and thus witnessing the quantum entanglement. Our work can be extended to prepare polarization entanglement by using other natural light sources, such as sunlight and bio-light, which holds promise for electricity-free quantum communications in outer space.
Quantum computation and quantum communication require sources of entangled photons, especially from low-cost diode lasers. This study considered a polarization entangled photons pulse source produced via a spontaneous parametric down-conversion process in the type-I phase-matching of two nonlinear crystals, incorporating a continuous wave laser diode operating in pulse mode as a pump. The generated photons were measured based on visibility as a function of the pump frequency and collection apertures. A polarization correlation between photon pairs of approximately 93% and a Bell parameter S value of 2.56 ± 0.05 were obtained using the source described here.
Spontaneous parametric down-conversion (SPDC) is a reliable platform for entanglement generation. Routinely, a coherent laser beam is an essential prerequisite for pumping the nonlinear crystal. Here we break this barrier to generate polarization-entangled photon pairs by using a commercial light-emitting diode (LED) source to serve as the pump beam. This effect is counterintuitive, as the LED source is of extremely low spatial coherence, which is transferred during the down-conversion process to the biphoton wave function. However, the type-II phase matching condition naturally filters the specific frequency and wavelength of LED light exclusively to participate in SPDC such that localized polarization Bell states can be generated, regardless of the global incoherence over the full transverse plane. In our experiment, we characterize the degree of LED light-induced polarization entanglement in the standard framework of the violation of Bell's inequality. We achieve the Bell value $S=2.33\ifmmode\pm\else\textpm\fi{}0.097$, obviously surpassing the classical bound S=2S=2S=2 and thus witnessing the quantum entanglement. Our work can be extended to prepare polarization entanglement by using other natural light sources, such as sunlight and biolight, which holds promise for electricity-free quantum communications in outer space.
Spontaneous parametric down-conversion (SPDC) can produce entangled photons from a nonlinear medium driven by a pump beam, and has thus been a key resource in photonic quantum technologies. Historically, the low efficiency of SPDC prompted the use of lasers, which are high-intensity light sources, as pump sources. However, the practical implementation of laser-driven systems faces an imminent energy bottleneck. Lasers typically have suboptimal energy efficiencies due to lasing thresholds and the technical demands of thermal management. As a result, laser-pumped entangled photon sources suffer from significant power overhead, rendering quantum devices less sustainable. Over the past few decades, light-emitting diodes (LEDs) have emerged as inexpensive and energy-efficient alternatives for high-intensity light sources. Since 2010, studies have shown that LEDs can drive SPDC and generate photon pairs. These results suggests the potential to replace lasers with ubiquitous and natural light sources to build environmentally friendly quantum devices. However, replacing lasers with other light sources entails a lack of coherence in all degrees of freedom (DoFs) of the pump beam, including spatial, temporal-spectral, and polarization, which may influence the resulting entanglement generated from SPDC. While earlier studies established that pump coherence in a specific DoF sets an upper bound for entanglement in that same DoF, the cross-influence between different DoFs has not been fully investigated. In this thesis, we study the influence of the pump's spatiotemporal coherence on the polarization entanglement generated from SPDC. First, we experimentally demonstrate that polarization-entangled two-photon states can be generated from SPDC pumped by spatiotemporally incoherent light emitted from an LED. Although the resulting entanglement appears lower than that of laser-pumped SPDC, we theoretically show that spatiotemporal incoherence does not fundamentally constrain polarization entanglement; rather, the reduction arises from a coupling between spatiotemporal and polarization DoFs introduced by the experimental setup. We determined experimentally that this cross-influence acts as a deterministic mapping from the spatial components of the pump to the two-photon polarization state. Because this mapping depends on technical aspects of the setup, we envisioned that it could be either (i) engineered to structure entanglement in higher dimensions, or (ii) compensated to reduce spatial distinguishability. Building on the latter, we show that by placing the nonlinear medium in a phase-compensated interferometric setup, SPDC pumped by spatially incoherent light can produce high polarization entanglement that violates local realism, even without postselecting the SPDC field for a single spatial mode. Finally, as a proof-of-principle demonstration of a truly environmentally friendly quantum light source, we demonstrate the generation of polarization-entangled two-photon states from SPDC pumped by a natural source - sunlight.