Quantum state reconstruction for rigid rotors

We describe a quantum state reconstruction scheme for dipolar rigid rotors based on determination of the expectation value of the molecular orientation. A key feature is the use of half-cycle pulses to excite the rotor prior to the orientation measurement. The set of expectation values obtained by varying the intensity and polarization of the laser and the time interval between excitation and measurement can be inverted directly to yield the rotor density operator. When the density operator corresponds to the admixture of relatively few rotor states, our procedure successfully reconstructs both pure and mixed states.