We propose a method of measuring the van der Waals interaction in an ensemble of cold Rydberg atoms via electromagnetically induced transparency (EIT). By using the method of mean-field approximation, we examine the influence of the van der Waals interaction on the EIT spectrum. It is interesting to find that the van der Waals interaction strength is proportional to frequency shift of the transmission spectrum. This can be used to probe the van der Waals interaction strength. In addition, we discuss the evolution of the van der Waals interaction by adopting the model of the cubic lattice. It is found that the total atoms blockade appears in dense gases under the condition of the strong coupling. Also, we discuss the boundary condition of the total blockade and explain the evolution of the van der Waals interaction.
We report on the five-body repulsive and attractive van der Waals interactions between the strongly dipole-dipole coupled Rydberg states. Compared to four-body van der Waals interactions, five-body van der Waals interactions show more energy levels and more potential wells caused by avoided crossings. This research bridges the few-body physics and many-body physics. Other disciplines, such as chemistry, biology, and medical fields, will also benefit from better understanding van der Waals interactions.