Science Cafe (April): Entanglements

4 min read

I would be lying if I said I wasn’t intimidated by this month’s topic for Science Café. Quantum physics, after all, can be quite complex even for established scientists – much less the average person. Surprisingly however, the talks were easy to follow as the speakers did their best to stay relevant with moderator Jenny Hogan from the Centre of Quantum Technology (CQT).

Specifically, the night’s topic centered around Entanglement in quantum physics. Here’s a creative crash course on what it is:

PRASANNA SELLATHURAI – Director for Missed Call

Winner of the Quantum Shorts Contest Series, Prasanna managed to join the session through zoom call to answer some of our audience’s questions.

Prasanna is a filmmaker who was in awe of physics since high school, now with a degree in the subject. Missed Call is an artistic take on entangled particles, paralleling entangled particles to the film’s protagonist and his father.

When asked about his interest and current profession, Prasanna notes, “You need creativity to do physics as well (…) it comes hand in hand.”

You can watch Missed Call here.

ZAW LIN HTOO & POOJA JAYACHANDRAN – PhD Students, CQT, NUS

Lin and Pooja introduce to the audience polarization of light and Bell’s Theorem. How are they related?

Polarization is the direction of light wiggling back and forth. Let’s say it’s moving up and down; if it meets a ‘blocker’ with an open vertical slit, the light can still pass through. If it meets one with an open horizontal slit, none can. At an angle of 45degrees however, some photons can pass through and do so randomly. Quantum is thus random and there is no way to predict when a photon will pass through with certainty. The best we can do is predict how likely it would pass through – say, at 50%.

At 45degrees, 50% of photons likely to pass through

Pooja then explains entanglement with a special box and polarizers that sends out entangled particles to 2 people (let’s call them Alice and Bob) who are lightyears apart in distance. After many rounds of sending photons, we establish that the outcomes, while random, are correlated. If Alice sees a photon, we instantly know (despite the distance and without communication) that Bob does not see a photon.

Einstein and two other scientists, Podolski and Rosen (let’s call them EPR) would conclude that this theory is incomplete as it is impossible (since we can’t communicate faster than light, right?) and that the particles must have been created in such a way – with ‘pre-agreements’ to always follow this pattern.

That’s where John Bell comes in. After going through a whole lot of equations and giving certain outcomes +1/-1 values, if we follow EPR’s theory that everything is pre-agreed on, the sum of average should be less than or equals to 2.

Somehow with Bell’s equations and calculations, he gets… 2.83?? This changes how the world works! *Mind blown*

CHRISTIAN KURTSIEFER – Experimental Physicist, Professor & Principal Investigator, CQT, NUS

Professor Kurtsiefer brings in a table-top experiment that proves entanglement. His presentation introduces the application of entangled space and elaborates more on the table-top project. Participants who successfully proved entanglement walked away with a neat certificate.