Cavity QED

In our experiments, we investigate interfaces between single trapped ions and single photons in the framework of cavity quantum electrodynamics (QED). Cavity QED describes the interaction between quantized matter (e.g., ions) and single quanta of light (photons) with boundary conditions on the light mode provided by an optical resonator. By integrating an ion trap with the cavity, it is possible to investigate what happens when you leave an ion in the company of a single photon.

A light–matter interface

Our project addresses the following questions:

  • How can we build a quantum network for quantum information processing?
  • What is the interplay between coherent ion–photon interactions and dissipation introduced by the environment?
  • How can we use ions in a cavity to simulate other quantum systems?

Experimental apparatus

Big Cavity Experiment

Our current setup consists of a linear Paul trap for trapping 40Ca+-ions inside an optical cavity. Using a cavity-mediated Raman process, we can access a regime in which the rate of coherent atom–cavity coupling is similar to the rates of decoherent processes in the system, namely cavity and atomic decay. By translating the cavity with respect to the ions and changing the ion–ion separation, we can control the individual coupling of ions to the cavity mode. The ions’ electronic state is detected using fluorescence measurements with a photomultiplier tube or a camera, while cavity photons are detected on avalanche photodiodes.

Fiber-cavity apparatus

Fibercavity Experiment Close Up

Fibercavity Experiment Overview

We are currently developing a second experimental apparatus, the fiber-cavity setup, consisting of a miniaturized cavity-QED interface. It features a linear trap designed to integrate a fiber-based Fabry-Pérot cavity with minimum disturbance of the ion. The fibers forming the cavities are machined by CO2-laser ablation at the ENS-Paris in collaboration with J. Reichel.  They are then coated with a low-loss dielectric multilayer stack for high reflectivity at 854 nm in order to couple to the P3/2-D5/2 transition of 40Ca+. With a 500-600 μm long cavity of finesse 90,000, we expect to reach cavity parameters (g,κ,γ)=2π × (20,3,11.5) MHz, where g represents the atom-cavity coupling rate, κ is the decay rate of the cavity field, and γ is the spontaneous emission rate of the ion.  These parameters would allow us to access the regime of strong coupling between a single ion and an optical cavity, where coherent processes are dominant. 

Project members

Maria Galli, Viktor Messerer, Roberts Berkis, Svenja Müller, Tracy Northup

Former members: Klemens Schüppert, Paul Pritom, Markus Teller, Dario Fioretto, Konstantin Friebe, Florian Kranzl, Moonjoo Lee, Pierre Jobez, Florian Ong, Yunfei Pu, Yueyang Zou

Our original apparatus was built up in Rainer Blatt's group, where it was at the heart of several quantum experiments.  Former Blatt group members who worked on this project include: Bernardo Casabone, Birgit Brandstätter, Andreas Stute, Andrew McClung, Diana Habicher, Helena G. Barros, Piet Schmidt, Carlos Russo, François Dubin, Eoin Philips, Thomas Monz, Christian Maurer, Christoph Becher


Funding for this project is provided by


FWF logo

the Austrian Science Fund (FWF) through the Special Research Programme (SFB) BeyondC: Quantum Information Systems Beyond Classical Capabilities

BeyondC logo

Quantum Flagship logo

the European Commission's Horizon 2020 research and innovation program, via the Quantum Internet Alliance project, under grant agreement No. 820445

QIA logo

ARL logo

the Army Research Laboratory's Center for Distributed Quantum Information, via the project SciNet: Scalable Ion-Trap Quantum Network, Cooperative Agreement No. W911NF15-2-0060

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