New Perspectives on Quantum Information Processing with Single Ions in Nano-sized Particles

Quantum information processing is a field of study that relies on the interaction of qubits, which are the fundamental units of quantum information. Scientists are continuously searching for the most efficient and accurate qubit platform to perform computational tasks. Additionally, there is a growing need to connect quantum processing systems with quantum networks, necessitating the generation of entanglement between matter qubits and photons.

Traditionally, qubits have been fabricated using superconducting circuits, trapped atoms and ions, or defects in solids. These qubits encode information in specific physical properties, such as the electronic state of an ion. However, the challenge lies in finding the optimal qubit platform that allows for individual qubit control and interaction with other qubits.

In recent years, rare-earth ion-doped crystals have emerged as a promising platform for quantum information processing. These crystals possess long coherence times and different ground states that can encode qubits. Furthermore, neighboring ions can interact with each other through dipole-dipole interactions, enabling qubit-qubit gates. The key is to find a way to detect and address single ions within the crystal without compromising the density of the ions.

Researchers from ICFO, Institute de Recherche de Chimie de Paris, and Karlsruher Institute fur Technologie have made significant strides in this direction. In an innovative experiment, they coupled single rare-earth ions to a nanoparticle, which in turn was coupled to a fiber-microcavity. This setup allowed for efficient light-matter interaction. By carefully controlling the position of the fiber-microcavity, the researchers were able to address and detect single ions within the nanoparticle.

The researchers grew nanoparticles doped with erbium ions, each containing approximately 1000 Er ions. When cool to a low temperature, these nanoparticles were placed on a mirror and aligned with a curved mirror fabricated on an optical fiber. This arrangement formed an optical cavity, enabling the efficient interaction between the single rare-earth ions and light.

This breakthrough has opened up new possibilities for quantum information processing with single ions in nano-sized particles. By controlling the position and properties of these ions within the nanoparticle, it is now within reach to create a small quantum information processing system. This research not only furthers our understanding of quantum systems but also brings us a step closer to the realization of a functional quantum internet.


Q: What is a qubit?

A: A qubit is the basic unit of quantum information, analogous to a classical bit. However, unlike classical bits that can only store values of 0 or 1, qubits can exist in superpositions of both states simultaneously.

Q: How are qubits typically fabricated?

A: Qubits can be fabricated using various methods, including superconducting circuits, trapped atoms and ions, or defects in solids. Each qubit platform has its own advantages and challenges.

Q: What are rare-earth ion-doped crystals?

A: Rare-earth ion-doped crystals are solid-state matrices in which rare-earth ions are embedded. These crystals possess long coherence times and different ground states that can encode qubits.

Q: What is the significance of the interaction between ions in quantum information processing?

A: The interaction between ions allows for the implementation of qubit-qubit gates, enabling operations and computations with multiple qubits. It is a crucial factor in the development of efficient quantum information processing systems.

Q: What is the potential application of quantum information processing with single ions in nano-sized particles?

A: Quantum information processing with single ions in nanoparticles opens up possibilities for creating small-scale quantum systems. These systems could be used for various applications, including secure communication, simulation of complex quantum systems, and optimization problems.