Silicon opto-electro-mechanics for bridging the gap between photonics and microwaves

Introduction

Conversion between electrical and optical signals enabled the use of near-infrared (near-IR) photons for high data rate transmission through optical fibre networks. Likewise, coherent conversion between microwave and optical photons stands as a promising solution to transfer quantum states between remote quantum processors, thus enabling the development of large-scale quantum networks.

Challenges in Conversion

However, the vast frequency difference between microwave (GHz) and near-IR (200 THz) optical photons hampers direct coherent conversion. This limitation could be circumvented by phonon-mediated transduction, which is a coherent two-step process, comprising electromechanical and optomechanical conversions.

Potential of On-Chip Conversion

On-chip microwave-optical conversion mediated by GHz phonons has the potential to be extremely efficient due to:

• The large optomechanical response of common materials
• The similar wavelength of GHz phonons and near-IR photons

Yet, it is an open challenge to achieve efficient electromechanical and optomechanical conversion simultaneously in a single integrated circuit.

Current State of Technology

State-of-the-art demonstrations show that:

1. Surface acoustic waves (SAWs) allow efficient electromechanical conversion.
2. Cavity optomechanics utilize tightly confined optical and mechanical modes to yield strong optomechanical coupling.

However, combining these two approaches is still considered challenging, if not impossible.

SPRING Project Objectives

The SPRING project will overcome these limitations by developing a fundamentally new optomechanical coupling approach to bridge SAW electromechanics and cavity optomechanics.

Innovative Approach

The original idea is to use subwavelength nanostructuration of silicon cavities to couple tightly confined optical modes and SAWs.

Expected Outcomes

The SPRING strategy will be used to demonstrate coherent microwave-optical conversion of single photons and quantum state transfer between superconducting qubits, monolithically integrated in a silicon chip. This will open a new path for applications in communications, sensing, and computing.