Autumn (or Spring for our readers in the Southern hemisphere) is a time of change, and things are changing as well for Bits of Quantum. Editorial duties on this blog are performed on a volunteer basis by PhD students (in what little remains of their free time), and this means that any editor’s tenure is inherently limited by his or hers PhD track. This is why, with some sadness, we announce the departure of James and Suzanne, who have handed in their editorial powers to finish up their doctoral track. They were great members of the team and we would like to thank them for the time they have spent making this blog an amazing place for quantum computing.
Luckily change also brings renewal and we are very happy to announce that Bits Of Quantum has two new editors: Guan and Anne-Marije. They have been unofficially part of the team for a while now and we figured it was high time to formalize their editor-ship. Continue reading Farewell, Editors Emeriti; Welcome, New Editors
by Jérémy Ribeiro
At the heart of Quantum Mechanics lies quantum superposition. This strange phenomenon is often described as the capacity of a quantum system to be in multiple incompatible states at the same time. The most famous example of this is Schrödinger’s cat, which would be both dead and alive at the same time. But how can this be? How can we humanly make sense of that apparent contradiction? Well… I think we cannot! More precisely, I think there is a problem of language in here. Exactly what a quantum scientist means by being “in superposition”, I think, is quite far from what the layman has in mind.
A simple analogy
To start explaining what a quantum scientist has in mind when he/she says that a state is in superposition I will use a simple analogy: Shapes.
What? How is that related to the topic?
You’ll see! How would you describe or draw a shape that is both a disk and a rectangle?
That does not make any sense! Maybe something like this:
Yeah you see, it does not make sense to you, and you struggle to draw anything because I said something that does not make sense. This is exactly what happens when someone says that Schrödinger’s cat is both dead and alive! It is not clear what he/she means, and stated like that it is non-sense. When a quantum scientist says that a physical system is in superposition of two states (dead and alive), he/she means that it is in a state that is neither the first (dead) nor the second (alive) but it is in another state that possesses some of the characteristics of both (dead and alive).
Hmm…This is quite hard to visualize for me. Don’t you have an example?
Yes! For the example of the shape it could look like this:
Oh I see!
This is a relatively good analogy. This shape is neither a rectangle nor a disk, however it has some of the properties of both. Moreover I like this analogy because in quantum mechanics you cannot “see” the quantum state the physical system is in. In other words, if someone gives you a system in a certain unknown state, you cannot learn the state. If you try to measure it, you will only see a “projection” of it… Continue reading Dead or Alive: Can you be both?