Entangling phonons, which are the quantized particles of sound, is a challenging task due to the inherent nature of sound propagation and the difficulty of controlling individual phonons. While entangling photons or atoms is well-established and extensively studied, entangling phonons is a relatively new and emerging field of research.
Phonons are collective excitations in a solid material that arise due to the quantization of vibrational modes. They are typically created and detected through their interaction with other particles or material structures. Entanglement, on the other hand, involves the correlation of quantum states between particles, resulting in a nonclassical connection that is stronger than any classical correlation.
In recent years, there have been several theoretical proposals and experimental advancements towards entangling phonons. One approach involves using superconducting circuits or mechanical resonators coupled to phononic waveguides, where phonons can be generated, manipulated, and measured. By carefully engineering these systems, it becomes possible to generate entangled states between phonons.
For example, researchers have demonstrated the entanglement of microwave photons with phonons in superconducting circuits coupled to acoustic resonators. In another experiment, entanglement between two mechanical resonators, acting as phononic modes, was achieved through their mutual interaction with a third resonator.
While these developments are promising, entangling multiple phonons with a high degree of control and stability remains a significant experimental challenge. The fragile and dissipative nature of phonons makes their preservation and manipulation difficult. Nevertheless, ongoing research aims to overcome these obstacles and further explore the possibilities of entangling phonons, as it could have potential applications in quantum information processing, quantum communication, and sensing.