`The "problem of quantization"`: 

>Find a vector space $Obs$ (as large as possible) of real-valued functions $f(p, q)$ on $R^{2n}$, containing the coordinate functions $p_j$ and $q_j$ $(j = 1, . . . , n)$,
and a mapping $Q : f → Q_f$ from $Obs$ into self-adjoint operators on $L^2(R^n)$ such that (q1)–(q5)* are satisfied.

>(*Please refer to the paper for the conditions (q1) - (q5).)

Ref: Quantization Methods: A Guide for Physicists and Analysts, pp. 2-3, [[math-ph/0405065](http://arxiv.org/abs/math-ph/0405065v1)]

`To researchers in this area`:

What is the current state-of-the-art in this area?