Periodic Reporting for period 1 - UltraTopo (Ultra-coherent topological phononic waveguides—towards classical and quantum interconnect)
Reporting period: 2023-04-01 to 2025-03-31
Micro- and nanomechanical systems with exceptionally low dissipation rate have gained extensive interests because of their excellent performance in precise metrology, such as force/mass microscopy, time keeping, and quantum transduction1. In the last ten years, large progress has been made in understanding the dissipation mechanisms of mechanical systems, and new dissipation engineering techniques of soft clamping and strain engineering have been discovered. The latter have led to amazing achievements such as mechanical resonators with quality factors up to 10 billion at cryogenic temperature and up to 3.6 billion at room temperature. In addition to mechanical resonators, mechanical (phononic) waveguides are another fundamental building block. Similar to electrical wires and optical waveguides, they allow information transfer via phononic waves and then form a phononic circuit. Phononic waveguides have been established as good interconnect channels among different physical systems due to their direct and strong coupling to electrical, optical, and even spin systems, and also been proved practical for quantum signal transport. However, the state-of-art dissipation engineering techniques still have not been investigated in phononic waveguiding systems, and their large loss remains their major limitation preventing them from wide applications in physics and engineering.
Topological insulator is a new phase of matter that is electrically insulating inside the bulk but conductive on the surface. In the last five years, the concept of topology has been extended to the realm of phononics, which has overturned some of the traditional views on wave propagation and manipulation. Most importantly, it can be adapted to realize topologically protected backscattering-immune phonon transport, which remains a grand challenge for conventional schemes while building large systems. However, the existing topological phononic systems also show limitations due to their large dissipation. Luckily, the crystal structure of topological phononic devices makes them extremely suitable to employ the state-of-art dissipation engineering techniques for realizing extremely low loss. Such a combination has not been experimentally realized to date.
This project will merge the fields of dissipation engineering and topological phononics to construct a mechanical waveguiding channel with unprecedentedly low dissipation. The major objective is to reduce the loss of phononic waveguides by orders of magnitude such that elastic waves propagate over several meters, and then demonstrate applications of them for classical and quantum signal exchange between separate physical (electrical, optical, or mechanical) systems.
Topological insulator is a new phase of matter that is electrically insulating inside the bulk but conductive on the surface. In the last five years, the concept of topology has been extended to the realm of phononics, which has overturned some of the traditional views on wave propagation and manipulation. Most importantly, it can be adapted to realize topologically protected backscattering-immune phonon transport, which remains a grand challenge for conventional schemes while building large systems. However, the existing topological phononic systems also show limitations due to their large dissipation. Luckily, the crystal structure of topological phononic devices makes them extremely suitable to employ the state-of-art dissipation engineering techniques for realizing extremely low loss. Such a combination has not been experimentally realized to date.
This project will merge the fields of dissipation engineering and topological phononics to construct a mechanical waveguiding channel with unprecedentedly low dissipation. The major objective is to reduce the loss of phononic waveguides by orders of magnitude such that elastic waves propagate over several meters, and then demonstrate applications of them for classical and quantum signal exchange between separate physical (electrical, optical, or mechanical) systems.
This project has two main sub-objectives.
I have fully achieved the first goal to apply the state-of-the-art dissipation engineering techniques to a topological phononic system and experimentally demonstrate ultra-coherent topologically protected phonon transport.
Specifically, this part is divided into several tasks. First, design and simulation based on SiN membranes with thickness of 20 or 50 nm were conducted by combining the theory of topology and dissipation engineering, anticipating a low loss. Second, the devices were fabricated by collaborators, with different devices and thickness. Then, an optical interferometer integrated with an vacuum system was built, with piezoelectric actuator or micropin drive to actuate the mechanical motion. After build-up of the system, statistical characterization of the device losses has been conducted. After several experimental iterations, topological phononic waveguides with loss down to 3 dB/km have been realized in this project, which is even two orders of magnitude lower than which is expected in the proposal.
The second goal is to employ the ultra-coherent phononic waveguide to connect two microwave superconducting loop-gap resonators via electromechanical coupling or connect two optical systems via optomechanical coupling.For electromechanical coupling between microwave photons and phonons, a flip chip has been made with a resonator chip and a membrane chip. A piezoelectric actuator is used to control the gap between the two chips. A tuneable coupling is realized by turning the piezoelectric actuator with the best coupling realized to be around 1 Hz. For optomechanical coupling between infrared photons and phonons, a high quality optical Fabry-Perot cavity is made with mechanical membrane in the middle, which optical linewidth to be around 300 kHz. A laser to cavity lock with extremely low power is important for reducing the optical thermal effect. A stable Pound–Drever–Hall (PDH) lock with lock power down to 1 nW is realized. A mechanical vibration isolation system inside the dilution refrigerator is also designed, with which optomechanical cooling experiment is conducted and the optical thermal effect is calibrated at millikelvin temperature. To this end, the second goal the project is partly completed.
Besides, the excellent performance of topological waveguides realized in this project offers a valuable and rare opportunity to quantify the backscattering in topological bosonic systems, which has been long pursued in the whole topological society. Therefore, an extra task of calibrating the backscattering across a sharp corner is conducted. The results show 0.01% phononic energy is scattered back at each 120-degree sharp corner. Related theories are also made.
Outcome.
The experimental results lead to three publications. The most exciting one is recently accepted by Nature, which can also been seen in preprint arXiv 2408.08717. One is published in Opt. Express 31, 41773–41782 (2023), also can been at preprint https://arxiv.org/abs/2308.00767(opens in new window). Another one is still under preparation.
I have fully achieved the first goal to apply the state-of-the-art dissipation engineering techniques to a topological phononic system and experimentally demonstrate ultra-coherent topologically protected phonon transport.
Specifically, this part is divided into several tasks. First, design and simulation based on SiN membranes with thickness of 20 or 50 nm were conducted by combining the theory of topology and dissipation engineering, anticipating a low loss. Second, the devices were fabricated by collaborators, with different devices and thickness. Then, an optical interferometer integrated with an vacuum system was built, with piezoelectric actuator or micropin drive to actuate the mechanical motion. After build-up of the system, statistical characterization of the device losses has been conducted. After several experimental iterations, topological phononic waveguides with loss down to 3 dB/km have been realized in this project, which is even two orders of magnitude lower than which is expected in the proposal.
The second goal is to employ the ultra-coherent phononic waveguide to connect two microwave superconducting loop-gap resonators via electromechanical coupling or connect two optical systems via optomechanical coupling.For electromechanical coupling between microwave photons and phonons, a flip chip has been made with a resonator chip and a membrane chip. A piezoelectric actuator is used to control the gap between the two chips. A tuneable coupling is realized by turning the piezoelectric actuator with the best coupling realized to be around 1 Hz. For optomechanical coupling between infrared photons and phonons, a high quality optical Fabry-Perot cavity is made with mechanical membrane in the middle, which optical linewidth to be around 300 kHz. A laser to cavity lock with extremely low power is important for reducing the optical thermal effect. A stable Pound–Drever–Hall (PDH) lock with lock power down to 1 nW is realized. A mechanical vibration isolation system inside the dilution refrigerator is also designed, with which optomechanical cooling experiment is conducted and the optical thermal effect is calibrated at millikelvin temperature. To this end, the second goal the project is partly completed.
Besides, the excellent performance of topological waveguides realized in this project offers a valuable and rare opportunity to quantify the backscattering in topological bosonic systems, which has been long pursued in the whole topological society. Therefore, an extra task of calibrating the backscattering across a sharp corner is conducted. The results show 0.01% phononic energy is scattered back at each 120-degree sharp corner. Related theories are also made.
Outcome.
The experimental results lead to three publications. The most exciting one is recently accepted by Nature, which can also been seen in preprint arXiv 2408.08717. One is published in Opt. Express 31, 41773–41782 (2023), also can been at preprint https://arxiv.org/abs/2308.00767(opens in new window). Another one is still under preparation.
In the objectives, the researcher aimed to develop a phononic waveguide with loss down to 300 dB/km. In the project, we realized a loss down to 3 dB/km, which is two orders of magnitude better than the proposed performance. This performance is also four orders of magnitude better than any chip-scale phononic waveguides at room temperature. If the device is cooled down to millikelvin temperature, the propagation loss with be smaller than superconducting materials at chip-scale.
In the project, a low backscattering probability of 0.01% across a 120-degree sharp corner is realized, which is 500 smaller than any reported performance before.
In the project, a narrow linewidth (300 kHz) optical cavity is locked with only 1 nW optical power, even inside the dilution refrigerator.
In the project, a low backscattering probability of 0.01% across a 120-degree sharp corner is realized, which is 500 smaller than any reported performance before.
In the project, a narrow linewidth (300 kHz) optical cavity is locked with only 1 nW optical power, even inside the dilution refrigerator.