Hi!
A friend of mine has been acepted to do a project programmed in Julia in Quantumz about tensor contraction algorithms.
They asked him what is his expected salary, and he asked me but I don’t know what to tell him.
Do you have any idea of what is a good initial salary for a temporary project if he is an undergraduate in physics?
I always tell people to pick a salary they would be happy with. The absolute levels are not as important as you being able to forget about it and get on with the more interesting aspect of work. 
The reason for me saying so is that if you ask 10 people the same question you’re going to get 10 different salaries recommended…
I would try to look up if there’s any posted salaries for internships in a similar field in a similar area. If it’s a company the salary should probably be higher than at a university.
I was paid something like 4.5k and 5.5k CAD in Montreal Canada for two summer research projects as an undergrad (3-4 months long) at a university, like 8-9 years ago. So I guess it should be a lot higher than that.
I must admit in general I would follow this advice, but the pay that my friend would be asking is a real underpayment for the work that he is going to pull off and the expertise needed to do the full project. Still thanks. 
I’ll look into this. This seems like great advice that I hadn’t though of. Thanks! 
The minimum that your friend would want is three times your rent. This should be more than enough to cover living expenses and food.
How much a premium over that minimum depends how this experience is characterized. Is this meant as more of a research experience for your friend? If so, they should ask what they need with a small margin.
To get one’s foot in the door, one might tolerate some underpayment as long as it covers expenses. Does your friend have a lot of experience doing this kind of research? Is your friend competing against other candidates who have degrees and experience?
Sometimes asking for too much can also price one out of the market of candidates. For an undergraduate, the real value may be in the experience rather than the monetary compensation.
As others have said, ask for what is needed and then some that your friend would be happy with. Without a degree sometimes getting the experience is more valuable for later. Think in the long term.