Revolutionizing Quantum Networking: Scalable Approach Using Rare-Earth Ions Paves Way for Quantum Internet

Scientists from the California Institute of Technology and Stanford University have conducted a study on the Scalable Multipartite Entanglement of Remote Rareearth Ion Qubits, focusing on the development of quantum repeater networks. The research introduces a scalable approach to quantum networking using frequency erasing photon detection and adaptive real-time quantum control. The study also extends this protocol to include a third ion and prepare a tripartite W state. The results provide a practical route to overcoming limitations in solid-state emitters and showcase single rare-earth ions as a scalable platform for the future quantum internet.

What is the Scalable Multipartite Entanglement of Remote Rareearth Ion Qubits?

The Scalable Multipartite Entanglement of Remote Rareearth Ion Qubits is a research study conducted by a team of scientists from the Thomas J Watson Sr Laboratory of Applied Physics, Kavli Nanoscience Institute, Institute for Quantum Information and Matter, Division of Physics Mathematics and Astronomy, all at the California Institute of Technology, and the Department of Electrical Engineering at Stanford University. The study focuses on the development of quantum repeater networks, which are considered promising for the advancement of technologies in communications and sensing.

The research introduces a scalable approach to quantum networking that uses frequency erasing photon detection in conjunction with adaptive real-time quantum control. This approach enables frequency multiplexed entanglement distribution that is also insensitive to deleterious optical frequency fluctuations. The researchers used two 171YbYVO 4ions in remote nanophotonic cavities to herald bipartite entanglement and probabilistically teleport quantum states.

The study also extends this protocol to include a third ion and prepare a tripartite W state, a useful input for advanced quantum networking applications. The results of the research provide a practical route to overcoming universal limitations imposed by nonuniformity and instability in solid-state emitters, while also showcasing single rare-earth ions as a scalable platform for the future quantum internet.

How Does the Quantum Networking Protocol Work?

The quantum networking protocol developed in this study overcomes the challenge of remote entanglement distribution, which arises from both static and fluctuating frequency differences between emitters’ optical transitions. The protocol corrects the random phase in real time for each heralding event via a measurement-conditioned feed-forward operation that consists of two stages.

Firstly, contributions from optical frequency fluctuations are dynamically rephased. Secondly, residual phase from static optical frequency differences is compensated. By eliminating the stochastic phase, this protocol attains two key milestones: optical lifetime-limited entanglement rates and fidelities that are robust against spectral diffusion, and entanglement of optically distinguishable spin qubits without frequency tuning.

This efficient paradigm for quantum networking allows optical inhomogeneity to enable the realization of frequency-multiplexed multi-qubit nodes, which can be robustly entangled.

What is the 171YbYVO 4 Quantum Network Node?

The 171YbYVO 4 Quantum Network Node is a quantum networking platform used in this study. It consists of two separate nanophotonic cavities, each fabricated from an yttrium orthovanadate (YVO 4) crystal which hosts single 171Yb3 ions. These ions fulfill many requirements for quantum network nodes, including a ground state spin which can be initialized, controlled with high fidelity, used for long-term memory, and read out.

The ions also have a coherent optical interface that can be used for entanglement generation, and an auxiliary quantum memory implemented via local nuclei. The researchers used two hyperfine ground states separated by 2 π675 MHz as a qubit and a cycling optical transition at 9845 nm as a coherent optical interface.

How Does the Quantum Network Node Work?

The quantum network node works by using two ions in Device 1, labelled Ion 1 and Ion 3, separated by an optical frequency difference of 2π475 MHz, which have Purcell-enhanced lifetimes of 22µs. Ion 2 in Device 2 has a Purcell-enhanced lifetime of 09µs and is separated by 2π31 MHz from Ion 1.

Each ion has a long-term integrated optical linewidth of 2π1 MHz, defined as the standard deviation of the optical frequency distribution measured via Ramsey spectroscopy. This is roughly ten times broader than the lifetime limit. However, optical echo measurements exhibit near lifetime-limited decay, thereby verifying that the ions are suitable for use in the quantum network node.

What is the Significance of this Research?

The significance of this research lies in its potential to revolutionize the field of quantum networking. The scalable approach to quantum networking introduced in this study could overcome the limitations of current technologies and pave the way for the development of the quantum internet.

The use of single rare-earth ions as a scalable platform for quantum networking is particularly promising, as it could enable the creation of robust, frequency-multiplexed multi-qubit nodes. This could lead to significant advancements in the fields of communications and sensing, among others.

The research also provides valuable insights into the properties and potential applications of rare-earth ions and nanophotonic cavities, which could have far-reaching implications for the field of quantum physics.