Efficient Conversion of Optical to Mechanical States Close to the Single-Quantum Level

This study presents a high-efficiency interface between optical photons and mechanical excitations using a quasi-two-dimensional optomechanical crystal (OMC). By operating at Millikelvin temperatures, the researchers overcome the thermal noise limitations that have historically restricted optomechanically induced transparency (OMIT) protocols to classical, high-photon-number regimes. The system achieves a record-level photon-phonon conversion efficiency of 76% and a tunable bandwidth exceeding 4.5 MHz, enabling the coherent mapping of few-photon optical pulses onto long-lived GHz mechanical modes.

The team utilized a silicon-on-insulator OMC device designed with a snowflake-patterned phoxonic bandgap to confine both optical and mechanical modes. The experiment employs a red-detuned control pulse to create an OMIT transparency window, allowing for the coherent exchange of excitations between the optical and mechanical modes. To characterize the interface, the researchers used weak coherent optical pulses and verified the coherent nature of the converted phononic state through Hanbury Brown-Twiss (HBT) measurements. They also performed extensive calibrations of the added thermal noise and conversion efficiency as a function of pulse duration and bandwidth matching.

This work establishes optomechanical crystals as a viable, efficient platform for quantum information processing. By enabling the conversion of optical quantum states into mechanical excitations, this interface serves as a critical building block for quantum memories and hybrid quantum networks. The ability to operate at the few-photon level with high efficiency and large bandwidth makes this platform compatible with existing telecom-wavelength quantum emitters, providing a clear pathway toward deterministic single-phonon state preparation and fundamental tests of quantum mechanics.