Abstract
We demonstrate excitation of phononic frequency combs in a Bulk Acoustic Wave system at a temperature of $20$mK using a single tone low power signal source. The observed ultra low power threshold is due to a combination of very high quality factor of $4.2\times 10^8$ and relatively strong nonlinear effects. The observed repetition rate of the comb varies from 0.7 to 2Hz and spans over tens of Hertz. The demonstrated system is fully excited via piezoelectricity and does not require mode spectra engineering and external optical or microwave signals. It is shown that the comb profile significantly depends on geometry of excitation and detection electrodes. Observed strong Duffing nonlinearity below the generation threshold suggests that the system is a phononic analogue to Kerr frequency combs excited in monolithic optical microresonators. The ultra-low power regime opens a way of integrating this phononic system with quantum hybrid systems such as impurity defects and superconducting qubits.
Highlights
Photonic frequency comb generators are an important tool used for many scientific applications allowing one to couple distant parts of the frequency spectrum [1]
The result is achieved at very low acoustic loss and strong nonlinearities
The comb generation is supported by the antiresonance phenomenon due to electrodes that is demonstrated by numerical simulation
Summary
Photonic frequency comb generators are an important tool used for many scientific applications allowing one to couple distant parts of the frequency spectrum [1]. Despite the fact that phononic systems play an important role in metrology and spectroscopy, demonstration of phononic or acoustic wave combs has been sporadic [13] Their complexity, requirements to design a certain mode structure, very high threshold powers [14], and requirement for extra laser sources [15] make these systems inapplicable for many low-energy applications. In these applications bulk acoustic wave (BAW) devices found very extensive use, e.g., frequency metrology [16], quantum hybrid systems [17,18,19], and fundamental physics tests [20,21,22,23].
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