Escape at the Quantum Zoo

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The quantum zoo was getting a new exhibit. As with all major tasks at the zoo, the responsibility of welcoming the inhabitant fell to Bob Atom. Bob, chief keeper of the quantum zoo, had overseen the establishment of the zoo from the very beginning. He had been there when the physicist, Dr. Alice Bell, known for her maverick mission of bringing quantum physics to the uninformed masses, first came up with the idea of starting a zoo to introduce quantum physics to the public. “Everyone should understand quantum physics. Let’s set up a zoo of quantum animals”, she had announced with theatrical flair to her bemused students, who obviously did not understand quantum physics. Bob had been one of them. At the time, he had thought nothing more of it, being a graduating student too preoccupied with finding a job. However, Dr. Bell was not one to be discouraged. A few months later, Bob came across an advertisement on the Gridcloud. We are hiring a passionate keeper for the first quantum zoo in the multiverse, it had read. Applicants should possess a degree in quantum physics. Salary and lodging will be provided. It was the third line which caught Bob’s eye. Not wanting to be forcefully evicted by the artificially intelligent robotic landlord if he did not pay his rent soon, Bob decided to apply. There are only two possibilities: yes or no. He would either be selected or become homeless.

That was how Bob found himself caring for the denizens of the quantum zoo. Over the years, the zoo had acquired a small menagerie. There was the Schrödinger's Cat, a mysterious feline which lived in a box. Bob had no idea what it looked like or even whether it was alive or dead, since the act of observation instantaneously rendered it either alive or dead. As long as no one peeked by lifting the lid, it could be both alive and dead at the same time. Unfortunately, visitors to the zoo saw only a closed box. It was an interesting thought experiment but hardly an exciting exhibition. The elephant which was enticed with bananas to walk into the mini black hole made for a much more exciting lunchtime demonstration. Although visitors were horrified to witness the obliteration of Horatio the elephant at the event horizon, he always emerged unscathed at the other end to repeat the demonstration the next day. What the visitors did not realise was their observations and Horatio’s reality were different. As far as Horatio was concerned, he had been rewarded with his favourite treat at the end of the performance. The trio of Quantum Pigeons fitting into two pigeonholes such that no two of them end up in the same hole was the trick which violated logic. Like the Schrödinger's Cat, when the pigeons were unobserved, they could be in two places simultaneously, thanks to quantum superposition. This always puzzled Bob, whose understanding of quantum physics never extended beyond Dr. Bell’s lectures. Still, he scattered extra seed for them, in case a squabble broke out when two pigeons went for the same seed.

In preparation for the new arrival, Bob had installed several mirrors in the enclosure to prevent it from escaping. The photonic Cheshire Cat with its signature grin arrived one Monday morning. The plan was to show that the Cat could be separated from its grin in an interferometer, a device capable of diffracting photons. Before the demonstration, Bob had gone to fetch the Cat. As usual, he had to coax it out of invisibility. “Here kitty kitty”, he cooed. However, no Cat appeared this time. An inspection revealed the reason - a cracked mirror which had allowed the Cat to escape. With only two hours until show time, Bob had to find it soon. Bob, usually unperturbed by the antics of the quantum animals, experienced a moment of mild panic when he remembered that Dr. Bell would be teleporting to the zoo to view the exhibit that day. Searching the Gridcloud, he wished he knew more about finding (invisible) photonic cats. He could picture Dr. Bell admonishing him.

“Did you know that I had to go down a rabbit hole to acquire the Cheshire Cat? What do you mean it’s missing?”

“It escaped and I can’t locate it. How do I find an animal which may be invisible, except for its grin?”

That’s it! The grin of the Cat gives it its spin. It was Quantum Mechanics 101 - detect the spin angular momentum and find the Cat. Armed with a polarization detector, Bob scanned the periphery of the enclosure. The detector picked up a signal in the direction of the black hole. The signal became stronger as Bob approached the black hole. Then there it was, wet, shivering and mewing woefully beside a puddle. The Cat had wandered out of its enclosure, unable to resist the pull of the black hole. However, cats, including Cheshire Cats, have a knack for getting into trouble. The Cat had fallen into a puddle and was drenched from head to paw. It was such a harrowing experience that it was too frightened to become invisible. After a quick dry off, during which the Cat became annoyed and scratched Bob several times, the feline was rushed to the amphitheatre, just as visitors were streaming in. The audience burst into applause when they saw the grin appearing in the right arm of the interferometer while the Cat was in the left arm. The Cat, however, was not amused and glared at everyone. Nursing a bleeding finger, Bob spotted Dr. Bell smiling in the crowd and heaved a sigh of relief. The show was a success!

After he had fed the Cat and scratched it behind the ears, Bob replaced the cracked mirror to prevent another escape. It may have just been another day at the quantum zoo but that was too close a shave!

About the Author: 
Daphne Ng is a research fellow who enjoys writing about Science as much as researching about it. When she is not at the bench, she can be found at her laptop, working on a scientific story.