Learn about quantum errors through this fiction story, where the two main characters Drita and Ori, end up in the zoo during the last day of their quantum computing internship at the Institute of Quantum and Almost-Like-Magic Sciences.
-Welcome! I’m Qadmus. I will accompany both of you to the room of the last task of your internship. This is the hardest task of all, but should you succeed, you will be offered researcher positions in the prestigious “Institute of Quantum and Almost-Like-Magic Sciences”, or IQALMS. What are your names?
-Thank you, Qadmus. We are Drita and Ori.
-Nice. Two names in the quantum world that don’t start with a “Q”. I envy you.
The two interns had come to accomplish their last task in the labs of IQALMS. They had successfully finished all their previous internship tasks, but they had heard the last one was usually quite tricky. They would have to finish it in time and report the results to a committee led by a certain Dr. Errolz. Drita had a question:
-Qadmus, are the quantum computers running fine now? I heard there were some noise issues a few weeks ago.
-Well, we had to send a package to Ohio using quantum optimization algorithms. The algorithm worked fine, but the quantum computer gave us the wrong direction to send the package, due to some phase error. The robot carried the package to the correct location, but it had followed the opposite direction. It took the package to a rolling lift bridge, and instead of entering it from the right and leaving the package on the bridge, it entered the bridge from the left. The bridge was lifting at that moment, and the robot accidentally glued the package under the bridge. When the bridge went down again, our agents in Ohio assumed the package had fallen in the water, since the GPS showed it was there, but they couldn’t see it anywhere. They sent a diving team underwater for days. Only after some days did they realize the package was just underneath the bridge, glued.
Ok guys, here I leave you. In this room you will read the instructions for your last task. Good luck!
Drita and Ori entered the instructions room. They were written in an LED-like screen, where each digit was made of bright segments, each segment being controlled by one qubit.
The message on the screen said: “Measure the 4Lions. Make sure not to destroy them and send the results before midnight. Gather as much data as you can. Use smart quantum formalism.”
The two young interns were appalled. Ori asked:
-Measure 4 lions? Don’t destroy them? Who would want to destroy lions?
-Weird! Probably they want us to measure the size of these 4 lions or report their biological features. But where are we going to find 4 lions, Ori?
-Hmm… let me think. Well, there is the zoo nearby. Funny enough, there are exactly 4 lions there, two females, and two males. My brother was there last week. But I’m sure the zoo is closed at this hour. Should we sneak in, and approach the lions’ cages at night??
-Unbelievable! Although, we had been warned about the last task. Nobody said this was going to be easy.
They took their flashlights and backpacks and entered the zoo from a gap in the fence used by children to sneak in and collect pine seeds. Fortunately, they didn’t have to break into the building. They could see one of the lions’ cages from a high, barred window. Drita climbed the pine tree nearby and used the flashlight to look inside the lions’ cage. She could see a male and a female lion. She took some pictures quickly, so they could approximate the animals’ size.
-Ori, we are done with this cage, but we’d have to break in to reach the second cage, where the 2 other lions are. I am not comfortable with this idea.
-No problem, Drita. We don’t have to do that. There are 2 males, and 2 females. If this cage has 1 male and 1 female, the other cage must contain the same combination.
-Good point, Ori. I have an idea, we can express these results as a Psi+ Bell state, where a female lion corresponds to the |0> state, and a male lion to the |1> state. One cage is represented by |01> with probability one half, and the other one by |10>. We associate the lions’ size to each state.
Ori and Drita agreed, they approximated each lion’s size and represented their results via Bell formulism. They sent the results to the committee before midnight.
The next day, 8.30 am, IQALMS committee room:
The interns gladly presented their measurements at the zoo, the logic behind the Bell state, and were waiting for feedback from the committee. However, the members were not reacting. They seemed confused and completely frozen. One of them broke the silence:
-What’s happening here? Why are we talking about lions?
Silence, again. Dr. Errolz paused for a few moments, looked at a picture on his laptop and then started laughing.
-Oh wow, there’s been a big misunderstanding, a big mistake! There were some errors with the instructions screen yesterday, which today have been fixed with our error mitigation algorithms.
They all looked at the picture Dr. Errolz had just received that morning.
-Yesterday the screen was showing “Measure the 4Lions…”, today it is showing something else: “Measure the 47ions”, referring to one of the trapped-ion quantum computers of the institution.
Then, he started writing on the board. Each digit was represented by a small Bloch sphere. Each segment of the “7” was controlled by a qubit. First, a miscalibrated gate had introduced some extra phase to the diagonal leg of “7”, making it orthogonal to the horizontal upper segment, and converting 7 into: ͞|. Then, the horizontal segment ͞ was displayed as | due to a readout error, and the vertical leg was replaced by ͟ , thus forming an “L”. So, the 47ions had become 4Lions after several errors: 7, ͞|, |͟ .
They all started laughing, thankful that nobody was hurt. And of course, Drita and Ori earned their positions at IQALMS, thanks to their creativity and courage.
Furthermore, they learned an important lesson on errors and noise.