General background:
Quantum computing (theory) is at the intersection of math, physics and computer science. (Experiment also can involve electrical engineering.) Eventually you will want to learn aspects of all of these fields, but when starting you can use any for an entry into the field. Within each field, the subjects you will want to know are:
Physics:
First learn quantum mechanics. At more advanced levels, various
aspects of quantum information overlap with AMO, condensed matter and
high energy.
More
Math:
First linear algebra and probability. Later my preferences would be to
learn some group and representation theory, random matrix theory and
functional analysis, but eventually most fields of math have some
overlap with quantum information, and other researchers may emphasize
different areas of math.
Computer Science:
Most theory topics are relevant although are less crucial at first:
i.e. algorithms, cryptography, information theory, error-correcting
codes, optimization, complexity, machine learning. If you haven't had
any CS theory exposure, undergrad algorithms is a good place to start
because it will show you CS-theory ways of thinking, including ideas
like asymptotic analysis.
More:
General quantum computing texts:
Here is a very partial list of resources for learning more about quantum computing and quantum information.
If you want to get a flavor of what research is currently hot, then
one place to look is at the program of the last few QIP workshops. A
less curated list of interesting papers can be found at scirate.com ,
where looking at the most scited papers in the last year should bring
up some interesting work.
Specialized sources:
Some more specialized books/lecture notes are here. These are more modern and in-depth than the general resources above.
NOTE:
The above information is based on this MIT page.
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