Improvements on microwave-to-optics conversion device for quantum information networks

Quantum information networks have the potential to greatly outperform conventional technology for certain communication and cryptography tasks. Superconducting circuits have been leveraged to build quantum processors, while optical fields can link two or more such processors for information exchange over large distances.

A nontrivial technical challenge in building such a setup lies in converting the circuit’s microwave signal into an optical signal for transmission. Previous attempts had added too much noise to preserve the crucial quantum information. A team of physicists from JILA at the University of Colorado Boulder has demonstrated an improved electro-optomechanical device that brings the field a step closer to successful microwave-to-optics conversion. They present their findings in Review of Scientific Instruments.

The authors created a more robust, modular system that places the inductor-capacitor (LC), mechanical and optical resonators inside a re-entrant 3D microwave cavity — a small aluminum box that supports a standing-wave microwave field. The LC resonator coupled wirelessly to loop antennas made from coaxial cables, which connect to the microwave input and output.

First author Tim Menke, currently a Ph.D. student at Harvard University, says one key advantage of this modular setup is that it decouples the optical assembly from the microwave part of the setup, instead of retaining a physical connection, which can become unstable as the system is cooled.

The researchers measured the microwave response and found that the cavity does not prevent or interfere with the electromechanical phenomena required for microwave-to-optics conversion. The results show flexibility in coupling between microwave transmission line and chip of an order of magnitude, according to Menke. Also, the cavity allows for adjustment of the microwave coupling to the converter chip with small loss.

Source: “Reconfigurable re-entrant cavity for wireless coupling to an electro-optomechanical device,” by T. Menke, P. S. Burns, A. P. Higginbotham, N. S. Kampel, R. W. Peterson, K. Cicak, R. W. Simmonds, C. A. Regal, and K. W. Lehnert, Review of Scientific Instruments (2017). The article can be accessed at https://doi.org/10.1063/1.5000973 .