Scientists are constantly searching for improved qubit platforms to enhance quantum information processing. One of the key goals is to develop a system that can generate entanglement between long-lived matter qubits and photons, enabling efficient communication between quantum nodes. While qubits can be created using various methods, solid-state spins have garnered significant attention in recent years.
However, the requirements for solid-state spins pose challenges. On one hand, single qubits in a solid-state matrix necessitate a low concentration of spins for individual addressing. On the other hand, a low density of spins reduces the interaction between ions, hindering qubit-qubit gates. Researchers have discovered that rare-earth ion-doped crystals offer a promising solution. These ions are trapped in the solid-state matrix, possess long coherence times, and feature different ground states suitable for encoding qubits. Additionally, neighboring ions can interact with each other through dipole-dipole interactions.
In a groundbreaking study published in Optica, researchers at ICFO, in collaboration with other institutions, demonstrated a novel method to address and detect single rare-earth ions within a nanoparticle. They achieved this by coupling the nanoparticle to a fiber-microcavity, enabling efficient light-matter interaction. The team used erbium ions emitting single photons and packed them into a volume two orders of magnitude smaller than previous realizations.
To overcome the challenges of addressing individual ions in an over-dense ensemble, the researchers turned to nanoparticles. By reducing the volume, the density of ions could be increased while still maintaining distinguishability between ion spectra. This allowed for the formation of a constellation of interacting ions within the nanoparticle, potentially creating a small quantum information processing system.
In their experiment, the team grew nanoparticles doped with erbium ions and placed them on a mirror. By aligning an optical fiber with a nanoparticle, a cavity was formed, enabling efficient light-matter interaction. This breakthrough paves the way for further advancements in quantum information processing utilizing nanoparticles and solid-state spins.
What are qubits?
Qubits are the basic building blocks of quantum information that encode quantum states, such as the electronic state of an ion, to perform computational tasks.
What is entanglement?
Entanglement is a quantum phenomenon where two or more qubits become linked in such a way that the state of one qubit is dependent on the state of another qubit, regardless of the physical distance between them.
What are rare-earth ion-doped crystals?
Rare-earth ion-doped crystals are solid-state materials that have been infused with rare-earth ions, which exhibit unique properties for light-matter interaction and quantum information processing.
(Source: ICFO – The Institute of Photonic Sciences)