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Generation and detection of entangled photon pairs

Beáta Plaskurová

Published Jan 1, 2025• 0 citations
OpenAlex

Abstract

In recent years, the use of entangled photons in quantum spectroscopy has gained attention, offering new possibilities for studying materials. In this work, we present an entangled photon source developed for future applications in ultrafast quantum spec- troscopy, particularly in biological research. Entangled photons at visible wavelengths are generated using pulsed type-I spontaneous parametric down-conversion (SPDC) in a Beta-Barium Borate (BBO) crystal, pumped by a 1030 nm laser after third and fourth harmonic generation. Photon detection was performed with an intensified sCMOS cam- era, enabling observation and study of spatial and, after integration of a custom-built spectrograph, spatio-energetic correlations between photon pairs. We optimized detec- tion, imaging, and data processing methods. We believe that our results, combined with the improvements we propose, form a solid foundation for integrating entangled photon pairs into time-resolved optical spectroscopy.

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In recent years, the use of entangled photons in quantum spectroscopy has gained attention, offering new possibilities for studying materials. In this work, we present an entangled photon source developed for future applications in ultrafast quantum spec- troscopy, particularly in biological research. Entangled photons at visible wavelengths are generated using pulsed type-I spontaneous parametric down-conversion (SPDC) in a Beta-Barium Borate (BBO) crystal, pumped by a 1030 nm laser after third and fourth harmonic generation. Photon detection was performed with an intensified sCMOS cam- era, enabling observation and study of spatial and, after integration of a custom-built spectrograph, spatio-energetic correlations between photon pairs. We optimized detec- tion, imaging, and data processing methods. We believe that our results, combined with the improvements we propose, form a solid foundation for integrating entangled photon pairs into time-resolved optical spectroscopy.
In recent years, the process of absorbing two photons using a non-classical light sources has been studied thoroughly. In particular, it has been experimentally demonstrated that the absorption cross section of two entangled photons is much greater than the absorption cross section of two uncorrelated photons. In this dissertation a source of entangled photons produced through spontaneous parametric down conversion or SPDC was constructed and characterized. It was found that for a pump laser of 411.32 nm and a BBO crystal of 1 mm the produced photons followed the same optical path as the laser, it was also found that the joint spectrum is symmetric at the degenerate wavelength of 822 ± 0.5 nm. This work conclude by showing a first approximation to execute a measurement of the Hong-Ou-Mandel effect. The objective of the measurements of joint spectrum and the Hong-Ou-Mandel effect are to understand the correlation properties of the photon source, with this information a virtual state spectroscopy technique can be implemented on the experiment constructed
The purpose of this project is to set up a system for creating entangled photon pairs for use in various quantum mechanical experiments, including the testing of Bell’s inequalities which demonstrates the fundamentally indeterministic nature of quantum mechanics. The photons are created by pumping a beta barium borate crystal with 405 nm laser light then, due to a process called type 1 spontaneous parametric down conversion, a single pump photon can be converted into two 810 nm photons in an entangled state. In the same lab, a similar set up has already been achieved using a 474 nm pump laser, but by using a shorter wave length, a higher detection rate can be achieved. Two collimators are set up to collect the down converted photons and send them to two photon counting modules. The collimators need to be positioned precisely to detect any down converted photons because they emerge from the crystal in a narrow beam that is at an angle with respect to the pump beam and only a miniscule fraction of pump photons are down converted. The angle at which the down converted photons emerge is a function of how the crystal is prepared and the polarization orientation of the pump beam. It was calculated using a program by National Institute of Standards and Technology.
The frequency correlation (or decorrelation) of photon pairs is of great importance in long-range quantum communications and photonic quantum computing. We experimentally characterize a spontaneous parametric down conversion (SPDC) source, based on a β-Barium Borate (BBO) crystal cut for type-II phase matching at 1550 nm which has the capability to emit photons with positive or no spectral correlations. Our system, depicted in Fig. 1a), employs a carefully designed detection method exploiting two InGaAs detectors.
For the last two decades, the focus of scientific research in the field of information transmission and processing has been in such sections of quantum optics as quantum computing and quantum cryptography. These areas of optics rely on the discovery of a special type of radiation - beams with pairs of bound or entangled photons. The experimental work in Russia, devoted to the entangled photons is undeservedly little. Therefore, the proposed work is important from a methodical point of view. Moreover, the experiment is performed on domestic equipment, much cheaper than most foreign analogues. The described system can be used as a prototype for setting up educational demonstration and laboratory works. Therefore, the proposed work will be of interest to researchers and universities involved in quantum optics. As a result of the work done, the attempt to create a source of entangled photons based on a barium beta-borate crystal can be considered successful. It should be added that in a second type of crystal pairs of entangled photons arise not only with respect to directions (and frequencies), but also with respect to two orthogonal polarizations. A similar source makes it possible to set up experiments similar to the Einstein-Podolsky-Rosen thought experience in Bohm’s interpretation. Therefore, it is also suitable for testing the Bell inequality. The article considers the practical importance of the phenomenon of generation of entangled photons for the purposes of quantum cryptography, the phenomenon of spontaneous parametric scattering and the creation of a source of entangled pairs of photons based on it, the experimental system and the results of the experiment on generation of correlated photon pairs, tangled with respect to directions and frequencies, the result of the experiment on observing the correlation in the detection times of pairs of entangled photons.
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.