## Acting as a quantum: what can I do that a single photon can't?

Participants will first play a learning game using the online platform Kahoot! Afterward, they will go through the setup – pass through the symbolic doors and get reflected from the symbolic mirrors. They will play two main scenes: how a non-quantum object would pass the interferometer, and how a quantum object would pass it. In the second scene about the quantum object participants will act as a probability amplitude of the quantum object in groups of four people using a simple tool made from transparent paper. They will observe what happens and discuss it with each other. We will brainstorm altogether how one could potentially use this quantum phenomenon causing that photons (as well atoms in fact) always exit the interferometer from the same side, which is called quantum interference. The key quantum concept discussed here is a quantum superposition.

This game reproduces at human scale a Mach-Zehnder-Interferometer – a setup used in a real physical experiment about the single-photon interference described in this article https://iopscience.iop.org/article/10.1209/0295-5075/1/4/004 . The symbolic setup is rather simple to build: you need two symbolic doors (at 45-degree angle relative to the pathways) that one can enter that will represent two beamsplitters, and two symbolic walls representing the mirrors. The first door will give two options: go through straight or go through with a 90-degree turn, thus two possible paths will appear. Using the walls these paths will be directed such that they will cross while entering the second door from two different directions. Participants will first choose freely whether to cross straight or to turn 90 degrees at each door and we will count how many will end up on each of the two exits of the interferometer. This will represent the non-quantum case as if the rules of quantum physics do not apply. To show what happens when a quantum object goes through the same setup four participants will have to use a special tool I made representing a probability amplitude of a quantum object and discover how paradoxically the photon always exits from the same side of the interferometer. The tool consists of four transparent papers with the same drawing of a photon attached to the transparent reference sheet. The drawing should be rotated clockwise every time the person turns on the interferometer. The group of 4 people always split equally as each door, half going straight and half making a turn. At the exit, the drawings should be superposed and it will result in a black picture in one exit (no photon) and a drawing of a photon in the other exit (yes photon), if there was no disturbance on the way 😉

This hands-on activity was proposed four times to the general public at a mini-maker fair in Trieste in 2018. 10-15 people took part in each game.

Please don’t hesitate to contact Oxana Mishina for more details.