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Lab. 1: Entanglement and Violation of the Bell's Inequality

Mayukh Lahiri

Published Jan 1, 2010• 0 citations
OpenAlex

Abstract

Aim of this classroom-experiment is to test violation of the Bell’s inequality by using polarization-entangled photons. These photons are produced by spontaneous parametric-down conversion in a pair of Type-I BBO crystals.

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A Test of Bell's Inequality for the Undergraduate Laboratory

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The thesis documents the work done over the year to initiate an undergraduate Advanced Laboratory experiment which tests Bell's inequality.It provides reference theory for the experiment, including explanations of Bell inequalities, basics of nonlinear optics, type-I downconversion and entanglement, and polarization states of the entangled photons.A main result is the equipment and design proposal for the experiment, which will cost a total 19600, led in price by the 9000 of a four photodetector array and followed by the 5000 of a 405nm pump laser.Entangled photons are produced by pumping BBO in a two-crystal geometry.Although most of the light is transmitted, some undergoes type-I parametric downconversion.Degenerate pairs are in a tunable entangled state and can be used to show non-classical behaviour.Specifically, a violation of the CHSH Bell inequality can be observed.Usable coincidence rates of several thousand per second are expected.Experimental and data analysis methods are described as the basis of future laboratory documentation.Explanations of equipment alignment and adjustment and data collection are included, as well as derivations of relevant analyses of the experimental data.Lastly the coincidence circuit built for the experiment is reviewed.The circuit costs less than 40 to construct and demonstrates a coincidence window of between 18ns and 36ns.

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Experimentell undersökning av Bells olikhet för att utvärdera möjligheten att skapa en fysiklaboration

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This report investigates wether it is feasible for undergraduate students to conduct an experiment that violates Bell’s inequality using polarization of entangled photons created in BBO-crystals, within a time frame of up to three days. For this, we conducted the experiment ourselves by drawing inspiration from other setups. This study covers the historical buildup and theory from the EPR-Paradox to the experiments that refuted Bell’s inequality.We also lay out the fundamentals of spontaneous parametric down-conversion. In addition, this study gives detailed instructions on how to set up the experiment. Our results show that with a significance level of p = 2 ・ 10−5 that Bell’s inequality (S < 2) was violated by measuring an S-value of 2,1577 ± 0,0379. From our method analysis we conclude that it is unlikely that undergraduate physics students can conduct the entire experiment within three days. However, we suggest two alternative laborations based on partially assembled setups. Either the students could optimize the quantum state of the incoming photons or they could align the laser and optical components. Another possibility is to give a demonstration or conduct a signal processing (coincidence) laboration using a fully assembled setup.

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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.

•Jan 1, 2015•0 citations

Quantum mysteries tested: An experiment implementing Hardy’s test of local realism

Joseph Carlson, Matt Olmstead, M. Beck

We have performed a test of local realism using entangled photons produced by spontaneous parametric downconversion. This experimental test is based on an idea originally proposed by Hardy for a test of local realism without inequalities, although our experiment actually measures an inequality (as any experiment must). We find a more-than-70 standard deviation violation of the predictions of local realism. The experimental effort required for this test is essentially the same as that required for a test of a Bell inequality. However, this test is based on concepts that are easier to understand and more compelling than those behind the original Bell inequality.

American Journal of Physics•Feb 14, 2006•36 citations
The thesis documents the work done over the year to initiate an undergraduate Advanced Laboratory experiment which tests Bell's inequality.It provides reference theory for the experiment, including explanations of Bell inequalities, basics of nonlinear optics, type-I downconversion and entanglement, and polarization states of the entangled photons.A main result is the equipment and design proposal for the experiment, which will cost a total 19600, led in price by the 9000 of a four photodetector array and followed by the 5000 of a 405nm pump laser.Entangled photons are produced by pumping BBO in a two-crystal geometry.Although most of the light is transmitted, some undergoes type-I parametric downconversion.Degenerate pairs are in a tunable entangled state and can be used to show non-classical behaviour.Specifically, a violation of the CHSH Bell inequality can be observed.Usable coincidence rates of several thousand per second are expected.Experimental and data analysis methods are described as the basis of future laboratory documentation.Explanations of equipment alignment and adjustment and data collection are included, as well as derivations of relevant analyses of the experimental data.Lastly the coincidence circuit built for the experiment is reviewed.The circuit costs less than 40 to construct and demonstrates a coincidence window of between 18ns and 36ns.
This report investigates wether it is feasible for undergraduate students to conduct an experiment that violates Bell’s inequality using polarization of entangled photons created in BBO-crystals, within a time frame of up to three days. For this, we conducted the experiment ourselves by drawing inspiration from other setups. This study covers the historical buildup and theory from the EPR-Paradox to the experiments that refuted Bell’s inequality.We also lay out the fundamentals of spontaneous parametric down-conversion. In addition, this study gives detailed instructions on how to set up the experiment. Our results show that with a significance level of p = 2 ・ 10−5 that Bell’s inequality (S < 2) was violated by measuring an S-value of 2,1577 ± 0,0379. From our method analysis we conclude that it is unlikely that undergraduate physics students can conduct the entire experiment within three days. However, we suggest two alternative laborations based on partially assembled setups. Either the students could optimize the quantum state of the incoming photons or they could align the laser and optical components. Another possibility is to give a demonstration or conduct a signal processing (coincidence) laboration using a fully assembled setup.
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.
We have performed a test of local realism using entangled photons produced by spontaneous parametric downconversion. This experimental test is based on an idea originally proposed by Hardy for a test of local realism without inequalities, although our experiment actually measures an inequality (as any experiment must). We find a more-than-70 standard deviation violation of the predictions of local realism. The experimental effort required for this test is essentially the same as that required for a test of a Bell inequality. However, this test is based on concepts that are easier to understand and more compelling than those behind the original Bell inequality.