Sunday, October 16, 2011

Probing the Universe with HBT Interferometry

I recently came across the following paper on how HBT interferometry changed as a result of photons interacting with each other before they reached the detectors. What's HBT ? It's a strange phenomena in physics that eventually led to what is currently known as Quantum Optics. Wikipedia offers some definition

The Hanbury Brown and Twiss (HBT) effect is any of a variety of correlation and anti-correlation effects in the intensities received by two detectors from a beam of particles. HBT effects can generally be attributed to the dual wave-particle nature of the beam, and the results of a given experiment depend on whether the beam is composed of fermions or bosons. Devices which use the effect are commonly called intensity interferometers and were originally used in astronomy, although they are also heavily used in the field of quantum optics.

HBT was initially used by Hanbury Brown and Twiss in radio astronomy and then in the visible range to figure out the diameter of certain stars like Betelgeuse.

Since then HBT gave some impetus to quantum otpics and so on. The paper I was intially refering to is  Hanbury Brown and Twiss interferometry with interacting photons which was featured on this very interesting blog (

From Experimental observation of a speckle pattern propagating in a nonlinear medium. In the interaction free case, the width of a typical speckle is inversely proportional to the width of the source, W. In the presence of interactions, one needs to take into account the strength of the intensity fluctuations as well. Image credit: Adi Natan

What the paper showed was that if photons had somehow traveled through a nonlinear medium, the HBT interferometry figure would eventually be different at the detector. the authors point to a potential case where this happens: space. Beltegeuse is about 400 light years away from here, so we are talking about large distances and therefore some potential for the photons of Beltegeuse to have interacted with some medium before being detected on earth.

I was wondering the following, by performing HBT interferometry and evaluating the difference between what is to be expected from pure vaccuum and actual results, can we evaluate the medium between us and the 10^11 stars in the universe ? Also proponents of HBT interferometry suggest that it is immune [4] to the seeing effect, but in light of this study is that really the case ? If it is not immune to the seeing effect, then some of results could show signs of the atmosphere of exoplanets ?

Food for thoughts.

[1] Hanbury Brown and Twiss interferometry with interacting photonsY. Bromberg, Y. Lahini, E. Small  & Y. Silberberg
[2] On the Shape of the Photon: Quantum Coherent Control with Single PhotonsY. Silberberg
[3] Hanbury Brown – Twiss Effect / Intensity Interferometry
[4] Astronomical Applications of Quantum Optics

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