Abstract
The demonstration of a quantum link between microwave and optical frequencies would be an important step toward the realization of a quantum network of superconducting processors. A major impediment to quantum electro-optic transduction in all platforms explored to date is noise added by thermal occupation of modes involved in the transduction process, and it has proved difficult to realize low thermal occupancy concurrently with other desirable features like high duty cycle and high efficiency. In this work, we present an efficient and continuously operating electro-optomechanical transducer whose mechanical mode has been optically sideband cooled to its quantum ground state. The transducer achieves a maximum efficiency of 47% and minimum input-referred added noise of 3.2 photons in upconversion. Moreover, the thermal occupancy of the transducer’s microwave mode is minimally affected by continuous laser illumination with power more than 2 orders of magnitude greater than that required for optomechanical ground-state cooling.
3 More- Received 24 December 2021
- Revised 12 April 2022
- Accepted 19 April 2022
DOI:https://doi.org/10.1103/PhysRevX.12.021062
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Faithful transduction of quantum states from microwave to optical frequencies would enable remote networking of superconducting quantum computers and secure communication guaranteed by the laws of physics. A principal challenge for all experimental efforts toward quantum transduction is the disruption of superconductivity by the laser light required to bridge the 5 orders of magnitude between microwave and optical photon energies. Here, we operate a transducer that couples a superconducting microwave circuit to an optical cavity via a low-frequency vibrational mode of a macroscopic drumhead resonator. Leveraging the tolerance of this design to high laser power and the exceptionally good isolation of the drumhead from its environment, we laser cool the vibrational mode to its quantum ground state, an important milestone toward realizing a practical quantum link.
In past experiments that have explored alternative transducer designs, laser heating of the superconductor has necessitated pulsed operation, which reduces the duty cycle significantly. In contrast, our transducer can operate continuously, and the laser does not appreciably heat the superconducting circuit. When any part of the transducer—whether the superconducting circuit or the drumhead’s vibrational mode—is not in its quantum ground state, it will add noise that would corrupt a quantum signal. We analyze the transducer’s added noise in different operating regimes and find that our transducer comes close to the threshold for quantum performance, despite excess noise induced by the strong microwave drive that couples the vibrations of the drumhead to the superconducting circuit.
With these results, we pave the way for continuous microwave-to-optical transduction of quantum states and entanglement distribution between superconducting quantum computers.