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Spontaneous Parametric Down Conversion of Photons Through β-Barium Borate

Luke Horowitz

Published Jan 1, 2016• 0 citations
OpenAlex

Abstract

An apparatus for detecting pairs of entangled 405nm photons that have undergone Spontaneous Parametric Down Conversion through β-Barium Borate is described. By using avalanche photo-diodes to detect the low-intensity converted beam and a coincidence module to register coincident photons, it is possible to create an apparatus than can be used to perform quantum information experiments under a budget appropriate for an undergraduate physics lab.

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Issues of radio electronics•Oct 20, 2018•0 citations
An apparatus for detecting pairs of entangled 405nm photons that have undergone Spontaneous Parametric Down Conversion through β-Barium Borate is described. By using avalanche photo-diodes to detect the low-intensity converted beam and a coincidence module to register coincident photons, it is possible to create an apparatus than can be used to perform quantum information experiments under a budget appropriate for an undergraduate physics lab.
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.
Spontaneous parametric downconversion At the heart of all quantum optics experiments is called as Spontaneous parametric downconversion. This is a downconversion process when the output frequency is smaller than the input frequency. The whole process is Spontaneous. Experimentally we have to downconvert the photons and convert them into pairs of a photon. We use the Beta-barium borate(BBO) crystals to downconvert the coming violet-blue laser. We find the maximum number of counts on detectors and their coincidence. When the BBO crystals is well aligned, we find no difference in detecting vertically or horizontally polarized photons because they are orthogonal to each other. Proof of existence of photons We want to investigate the properties and verification of quantization of light. Experimently we want to establish the existence of single photon which shows the grainy-ness of individual photon quantum mechanically and shows wave like behaviour classically. We get the coincidences counts on detectors with addition of detector B’ by using PBS in the path of signal beam. Experimentally we prove the Quantum as well as classical nature of light by the measurement of second-order degree coherence in light g2(0). For classically the g2(0)≥1 and quantum mechanically g2(0)=0.When we add the delay time interval of 1ns after reflected and transmitted photons from PBS signal beam. The delay generator did not create a significant difference in the coincidence counts detection in the value of g2(τ ). Single photon interference and quantum eraser we want to observe the interference by making the single photons pass through the interferometer, and we will see the interference of the single photons. If the light passes through the interferometer, the visibility of the interference pattern to which extent these fringes are observed is dependent on the extent to which the ’which-way’ or ’which-path’ information is available to the experimenter. If the observer knows the information about the ’which-way’ of the light path, then we cannot observe the inference pattern. Because we only can make an interference pattern if we erase the which-way information of the light path. If you erase the information about the’ which-way,’ we can observe a very high interference pattern. We can erase the information about the light path’s ’which-way’ or ’which-path’ by using a polarizer and orienting at 45o. In this way, we can observe a very high pattern. If we introduce the angle of the polarizer at 0o or 90o, we see very low interference.
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.
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.