Measuring properties of entangled photons using the Hong-Ou-Mandel effect

April 5, 2021   /  

Student Name: Mili Barai
Major(s): Physics
Advisors: Dr. Cody Leary, Dr. John Lindner

We model Joint Spectral Intensities of two entangled photons created by spontaneous parametric down conversion using three crystals, beta-Barium Borate, Calcium Carbonate and Lithium Iodate. For an entangled photon pair, by changing the property of one photon, one can also change the property of the other photon in the pair. We can model Joint Spectral Intensities by considering the effect of crystal length and the angle at which the crystal is oriented with respect to the pump laser polarization. We learn that on increasing length of the crystal, peaks of Joint Spectral Intensities get narrower. On increasing the angle of tilt of the crystal, the singular probability peak divides into two peaks and moves out of the visible range. We then model the Hong-Ou-Mandel effect to measure properties of the two photons by modelling the photons passing through a beam splitter after going through two separate paths, with one path having a time delay and getting detected by the detectors at the beam splitter outputs. We model the rate of coincidence, or number of times both photons are detected at different ports simultaneously for different lengths of crystals. We find that on increasing the length of the crystal, the width of the Hong-Ou-Mandel dip increases as well. This project is important because it helps us learn about the properties of entangled photons, which have numerous applications such as quantum computing, quantum cryptography, and secure communications.

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Mili will be online to field comments on April 16: 10am-noon EDT (Asia: late evening, PST 6am-8am, Africa/Europe: late afternoon).

28 thoughts on “Measuring properties of entangled photons using the Hong-Ou-Mandel effect”

    1. Thank you, Dr. Lindner! It turns out that all crystals give the same pattern of output – i.e., on increasing the tilt angle from 0 to 90 degrees, we can get different wavelengths of colors in the visible range. Although, the tilt angle range is slightly different for different crystals.

  1. Congratulations on completing IS! Admittedly, I don’t understand most of what your project is about 🙂 Wishing you all the best!

    1. Thank you, Maya! I am going to pursue a master’s in medical physics at Creighton University.

  2. Congrats, Mili! Thanks for helping me through Physics this year. Couldn’t have done it without you!

  3. Mili, very nice work this year! I wonder how that double-peaked wavefunction type would manifest itself in the coincidence plot… A question for next year perhaps!

    1. Thank you for advising me this year! The double-peaked Joint Spectral Intensity plot could probably be approximated using two gaussian functions to get coincidence plots.

  4. Hi Mili,
    Very cool work! Do you have any suggestions for future work for this project?

    1. Thank you, Heather! Yes, my project focused on modeling the two processes, and it can be confirmed in lab in the future. Secondly, we were only able to get coincidence plots for a specific angle, due to complex math and time constraints, but it could also be done for larger angle ranges in the future.

  5. Great work! Congratulations Mili! I am curious as to how this would be used in secure communications, can you elaborate on that part?

    1. Thank you, Brandon! Entangled photons are able to share information, although they might be in different space physically, and so they can be used for secure communications. One can measure a photon’s property and can instantly know information about the other photon’s property as well!

  6. Congratulations Mili! This is so interesting, and I wanted to ask– how exactly does this work tie into secure communications?

  7. Congratulations Mili!! I’m thankful for the memories we have built together and I wish you best of luck in your life after Wooster!!!

  8. God job Mili, so in real words what was this about cause it was way too advanced for me.

  9. Mili’s brain is simply too powerful for Wooster…fantastic work! You are truly a brilliant researcher!

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