I What Is the Difference Between Loss and Cost Functions in Quantum Computing?

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SaschaSIGI
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Hello,
Im currently hearing a module about quantum computing and Im wondering what is the difference of a loss and cost function for variational quantum algortihms? Both functions also can be presented into a loss/cost landscape? Are they the same ?

Already a big thank you for all the upcoming answers!
 
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Hello, and :welcome: !

No answers in three weeks, so there must be something missing in this post.
Perhaps you can provide some context, examples, references ? Be more specific ?

Would be good to read the guidelines even though this isn't homework.

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BvU said:
No answers in three weeks, so there must be something missing in this post.
Perhaps you can provide some context, examples, references ? Be more specific ?
I don't think so, the problem is rather that https://en.wikipedia.org/wiki/Loss_function and other sources write
a loss function or cost function (sometimes also called an error function)
And even so there is the feeling that they really are used for the same thing but in slightly different contexts, it is hard to pin this down.
 
I always treat loss/cost/objective function as synonyms until a reference uses both and gives a definition of both that clarifies the distinction.
 
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. Towards the end of the first lecture for the Qiskit Global Summer School 2025, Foundations of Quantum Mechanics, Olivia Lanes (Global Lead, Content and Education IBM) stated... Source: https://www.physicsforums.com/insights/quantum-entanglement-is-a-kinematic-fact-not-a-dynamical-effect/ by @RUTA
If we release an electron around a positively charged sphere, the initial state of electron is a linear combination of Hydrogen-like states. According to quantum mechanics, evolution of time would not change this initial state because the potential is time independent. However, classically we expect the electron to collide with the sphere. So, it seems that the quantum and classics predict different behaviours!
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