What everybody ought to know about Quantum Zeno Effect

  • By Yagnamurthi Pooja

Introduction

Have you ever wondered why things slow down especially when you observe? let say, you are observing milk that is kept to be boiled but you eventually feel the process of boiling is slower when you observe and faster when you don’t. Right!!

You might ask what that has to do with the quantum Zeno effect?

Find it yourself as this article helps you to get a clear idea about everything that you need to know about the Quantum Zeno Effect.

what is the Quantum Zeno effect?

If you have a quantum-mechanical system moving from state 1 to state 2, the probability of being in state 2 increases over time. you can prevent the state change by making repeated measurements. Every time you measure it to be in state 1 the transition is reset. Quantum Zeno Effect is also known as the Turing paradox.

why is it called the “Zeno” effect?

This effect is named after Zeno, a Greek philosopher who was born around 490BC.

Zeno is well known for his paradoxes and theories which inspired and challenged many mathematicians and scientists.

Zenos Achilles paradox:

It is the paradox that Achilles can never catch the turtle because he has to travel half the distance between him and the turtle, then another half and so on, and could never reach the turtle.

To highlight the idea that the system can never reach state 2, it is named after Zeno.

But the Quantum Zeno effect is not a paradox it is a real phenomenon that has been observed in experiments.

A quantum pot will never boil

If you can observe the effect has “quantum” in it. This emphasizes that it only happens in quantum measurements. This brings me to The adage “A watched pot will never boil” but we all know a watched pot will certainly be boiled at one or the other point in time.

But what if say “A quantum pot will never boil”.

if you consider the pot is a quantum pot and if you start observing it continuously by measuring the boiling point for every second or spending the whole time measuring, then the probability of not boiling will be 100% and the probability boiling will be 0%.

The main point is that the more you measure a quantum system it gets disturbed and stops evolving and stays at the initial stage.

George Sudarshan and B Misra on QZE

George Sudarshan and B. Misra from the University of Texas published an article “The Zeno’s paradox in quantum theory” in 1997.

To conclude the article they said that” In the limit of infinitely frequent measurements, a quantum system would remain in its initial state. Applied to the case of an unstable particle whose trajectory is observed in a bubble chamber or film emulsion, this result seemed to imply that such a particle would not decay, in contradiction to experiment”.

They also provided a mathematical definition and notion of the “Quantum Zeno paradox”.

The Experimental evidence

In 1990 Wayne Itano has done an evidence experiment on the Zeno effect at the US National Institute Of Standards(NIST) and technology in Colorado, using beryllium ions.

  • In this experiment, a few thousand beryllium ions are exposed to microwave to slowly transmit them from level 1 to level 2.
  • To study the evolution the measurements were taken by a UV ray with a frequency that allows an ion in state 1 to absorb the photon and re-emitted it on a carefully positioned camera.while, the state 2ions will not absorb any photon.
  • It will take 256 milliseconds to convert all beryllium ions from state 1 to state2.
  • During this time period, the state of the ions can be described by a wave function with 2 parts with the probability of being state2 increases with time
  • At the beginning of the experiment scientist trapped some ions in state 1 and exposed them to microwave then after 256 milliseconds, they turned on the pulse razer and non of the ions produced any light which means ions are converted to stage2 as expected.
  • But to test the Zeno effect the scientist repeated the experiment by introducing two laser pulses and one at the middle and the other at the end of the experiment but, in this case, the team observed that only 50% of ions are transmitted to stage 2.
  • This happened because at 128 milliseconds the ions are measured at that time many of the ions are at state 1 and this destroyed the evolution

These ions came back to stage 1 so they have to start over all again the probability of ions moving from stage 1 to stage 2 will decrease further with more measurements. So, this experiment supported the Zeno effect.

What is the anti-Zeno effect?

The anti-Zeno effect says that measuring a quantum object slowly can accelerate the evolution of the object which is completely opposite to the Zeno effect.

Schrodinger’s cat

Schrodinger’s Cat is a thought experiment of Austrian-Irish physicist Erwin Schrödinger.

In this thought experiment, Schrodinger imagines putting a cat in a box with a radioactive material that has a 50% chance of killing the cat in the next hour.

He questioned himself what will be the cat’s position when he went to observe the cat at the end of an hour. Probably it could be dead or alive, but according to quantum physics at the instance, before the box is opened the cat will be an equal part of dead and alive at the same time which is absurd and that is Schrodinger’s point.

How to Zeno effects work on Schrodinger’s cat

  • if we apply the Zeno effect on Schrodinger’s cat which means observing the cat multiple time the probability of the cat’s death will be decreased.
  • But, if we apply the anti-Zeno effect which is observing the less frequently the chances of a cat dying will be increased.

References

https://www.researchgate.net/publication/225157854_The_Quantum_Zeno_Effect_–_Watched_Pots_in_the_Quantum_World

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50483

https://www.nature.com/articles/s41598-017-01844-8

https://thinkbirth.blogspot.com/2008/11/watched-pot-effect.html

https://eportfolios.macaulay.cuny.edu/sciencefordessert/2012/08/28/the-quantum-zeno-effect/

https://phys.org/news/2017-06-quantum-zeno-effect-impacts-schroedinger.html

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