Advances in quantum technology have instigated extensive research on hybrid quantum systems. These systems provide multitasking capabilities because they combine various physical components with complementary functionalities. Interfacing mechanical elements like mechanical oscillators and other quantum systems could serve as critical components for improving the functionality of existing hybrid quantum systems. Among these quantum systems, hybrid spin-mechanical systems take the outstanding properties of both solid-state spins and nanomechanical oscillators and have been widely studied for application in quantum technology.
The study of hybrid spin-mechanical systems has also facilitated in-depth exploration of quantum nature, allowing observation of mechanical quantum effects, especially phonon blockade (PB). PB is associated with strong quantum mechanical nonlinearity. PB effects have been extensively studied in the past decade, paving the way for implementing quantum control at single phonon level. The possibility of inducing PB in different mechanical resonator-based systems has been recently demonstrated. However, moving into the stronger nonlinear region of the resonators remain challenging to achieve. Thus, to improve the performance of PB, it is important to develop an efficient approach that is not affected by strong coupling. Moreover, this approach should be able to yield a large mean photon number.
On this account, researchers from Harbin Institute of Technology: Dr Yan Wang, Dr Jin-Lei Wu, Dr. Jin-Xuan Han, Professor Yong Yuan Jiang and Professor Jie Song in collaboration with Professor Yan Xia from Fuzhou University designed a feasible experimental strategy for enhancing PB performance in a weakly coupled hybrid spin mechanical system. The aim was to achieve a strong PB with a large phonon mean number in the weak coupling regime. Their research work is currently published in the journal, Physical Review Applied.
In their approach, the proposed new system consisted of a well-designed hybrid device, where magnetically induced two-phonon interactions were implemented between an embedded nitrogen-vacancy center and a mechanical cantilever resonator. This was then combined with mechanical parametric amplification to facilitate exponential coupling enhancement better than those of existing schemes. The performance of the resulting hybrid system with the two-phonon nonlinearity as well as its practical applicability, was examined.
The researchers showed a strong PB and a large mean phonon number in the hybrid system in the weak-driving regime. The stronger PB was attributed to the effects of the mechanical parametric amplification, which ensured that the quantum effect of the PB was as strong as possible. The geometric arrangement of the nanomagnets in the hybrid system allowed quadratic interactions between the resonator and the nitrogen-vacancy spin. They also demonstrated the flexibility in tuning the PB by simply modifying the strength of the amplification, allowing parameter regions with ultrastrong PB and a high probability of detecting single phonons. Furthermore, it provided a powerful and feasible tool for exploring phonon statistics and their possible practical applications in various fields like quantum devices.
In summary, the authors successfully demonstrated the realization of strong PB and large mean photon number simultaneous in a weakly coupled hybrid system. Together with the flexible tunability of the system, the PB performance was significantly improved, achieving ultrastrong PB characterized by small second-order correlation functions. Most importantly, the proposed approach showed the possibility of achieving improved PB performance in a realistic experimental setup with accessible parameters. In a statement to Advances in Engineering, Professor Jie Song said their study findings provide an alternative and effective route for implementing a high-efficiency single-phonon source with potential application in quantum phononics and quantum devices.
Wang, Y., Wu, J., Han, J., Xia, Y., Jiang, Y., & Song, J. (2022). Enhanced Phonon Blockade in a Weakly Coupled Hybrid System via Mechanical Parametric Amplification. Physical Review Applied, 17(2), 024009-19.