The invention relates to a device (100; 100') for detecting a single
microwave photon, comprising: a multi-state
quantum system comprising N qudits, N being greater than or equal to 1, the
system being capable of making, in response to reception of an incident
microwave photon, a number X greater than or equal to 2 of energy transitions between energy levels distributed between the N qudits, these energy transitions corresponding to respective frequencies f1,..., fx, a set of resonators (R1, R2,...) defining X+l electromagnetic
modes of respective frequencies fM,1 to fM,x+1, a parametric pumping
system for applying X pump tones of respective frequencies fp, i, respecting fM,i + fP,i = fi + fM,i+1 with each integer i
ranging from 1 to X, so as to convert, in frequency, by parametric pumping, the excitation contained in an
electromagnetic mode i into an excitation of the
electromagnetic mode i+1 and a transition i of the qudit in question, a system for reading the energy levels of the one or more qudits of the
quantum system delivering a datum providing information on whether an incident
microwave photon has been received or not.