Complete Quantum Coherent Control of Ultracold Molecular Collisions

We show that quantum interference-based coherent control is a highly efficient tool for tuning ultracold molecular collision dynamics that is free from the limitations of commonly used methods that rely on external electromagnetic fields. By varying the relative populations and phases of initial coherent superpositions of degenerate molecular states, we demonstrate complete coherent control over integral scattering cross sections in the ultracold $s$-wave regime of both the initial and final collision channels. The proposed control methodology is applied to ultracold ${\mathrm{O}}_2+{\mathrm{O}}_2$ collisions, showing extensive control over $s$-wave spin-exchange cross sections and product branching ratios over many orders of magnitude.

Figure 1

Minimum (lower traces) and maximum (upper traces) ICSs from the initial superpositions $|{\psi }_E⟩$ (black), $|{\psi }_2^S⟩$ (red), and $|{\psi }_3^S⟩$ (blue) to the final collisional channel (a) $|0,0⟩$ and (b) $|-1,+1⟩$.

Figure 2

Coherent control of the ICSs ${\sigma }_{s\to a^{\prime }{b}^{\prime }}$ for ultracold ${\mathrm{O}}_2+{\mathrm{O}}_2$ collisions starting from the initial superposition $|{\psi }_2^S⟩$ as a function of the superposition parameters $\eta$ and $\beta$ at a collision energy of $1\mu \mathrm{K}$. The final states are $|-1,+1⟩$ (a) and $|0,0⟩$ (b). Panel (c) shows the branching ratio ${\sigma }_{s\to -1+1}/{\sigma }_{s\to 00}$. While the values shown are limited to eight to aid visibility, the maximal value of the branching ratio is $1.2\times {10}^9$.

Figure 3

Minimum (lower traces) and maximum (upper traces) of the branching ratio ${\sigma }_{s\to -1+1}/{\sigma }_{s\to 00}$ for the initial superpositions $|{\psi }_E⟩$ (black), $|{\psi }_2^S⟩$ (red), and $|{\psi }_3^S⟩$ (blue). The branching ratios in the absence of control are also shown as middle traces for the initial states $|-1,+1⟩$ (triangles) and $|0,0⟩$ (squares).