Scientists Create a Quantum Information Bridge Between Photonic and Solid-State Quantum Systems

Insider Brief

• Researchers have developed a quantum interface enabling the transfer of quantum information between diamond NV centers and 795nm photonic time-bin qubits, a step that would be aligned with building a quantum internet.
• The study used a two-stage frequency conversion process to match photon properties, achieving quantum teleportation with a fidelity surpassing classical limits.
• Future improvements could include integrating NV centers into optical cavities, exploring group-IV diamond defects for higher photon rates, and enhancing frequency conversion for long-distance quantum networks.

Scientists have created a way to transfer quantum information between different types of quantum systems, a step that could help build a future quantum internet.

A QuTech & Delft University of Technology-led team of researchers report they developed a quantum interface that can transfer quantum information between diamond nitrogen-vacancy (NV) centers and photonic time-bin qubits. This work addresses a significant challenge in quantum computing: interconnecting different types of quantum hardware components, an advance that would be needed for reliable, scalable quantum communication systems.

The study, published in npj Quantum Information, outlines a proof-of-concept experiment demonstrating the feasibility of linking different quantum network devices.

The researchers employed a two-stage quantum frequency conversion process to align the properties of photonic qubits with those of NV center photons. This alignment enabled quantum teleportation of 795nm time-bin qubits into the NV center spin qubit with a fidelity surpassing classical limits.

The 795nm time-bin qubits is a specific type of quantum bit (qubit) used for quantum communication. Breaking it down, 795 nanometers refers to the wavelength of the light used to represent the qubit, a wavelength falls within the near-infrared region of the electromagnetic spectrum. Time-bin qubits are qubits encoded using the time at which a photon arrives. The information is carried by photons that exist in a superposition of being in two different time “bins” or time slots. Time-bin encoding is particularly robust against noise and loss during transmission, which makes it suitable for long-distance quantum communication.

The researchers write that this is significant because significant because this technique bridges different quantum technologies, like photonic communication channels and solid-state quantum memories. These qubits are compatible with quantum memories that operate using atoms like Thulium and Rubidium, facilitating the transfer and storage of quantum information across varied hardware. According to the paper, creating, for example, a future quantum internet — a network that would enable ultra-secure communication, distributed quantum computing and advanced sensing applications — compatibility between photonic and solid state would be essential.

Quantum Interface Development

The interface comprises three primary components: a frequency conversion module, an interference station, and a real-time feedback mechanism. The frequency conversion module uses a two-stage process to convert 795nm photons to 637nm photons, achieving a conversion efficiency of 3%. The interference station combines the converted photons with NV center photons on a beam-splitter, facilitating a Bell state measurement — a fundamental quantum operation. The real-time feedback system applies a correction to the NV spin qubit based on the measurement outcome.

The diamond NV center quantum network node and 795nm photonic time-bin qubits were compatible with Thulium and Rubidium quantum memories. The researchers generated photonic time-bin qubits at 795nm from weak coherent states using intensity and phase modulators, calibrating the intensity modulator to mimic the NV photon’s temporal profile within a 30-nanosecond window. This method produced photonic states compatible with storage and retrieval from Thulium-doped solid-state quantum memories and Rubidium-gas-based quantum memories.

Implications for Quantum Networking

The development of a quantum interface capable of seamlessly connecting different quantum network hardware is crucial for several innovations, including providing numerous ways to advance quantum computing.

Various hardware platforms for quantum memories and network nodes are based on atom-like systems with distinct properties, making it challenging to match their photonic qubits. The researchers’ solution addresses this issue by employing a two-stage frequency conversion process that converts 795nm photons to 637nm photons, aligning with the properties of NV center photons.

Conversion Improvements

There is still a lot of work to do. For example, while the study demonstrates the feasibility of interconnecting different quantum network hardware, the conversion efficiency of 3% indicates room for improvement. Enhancing this efficiency is essential for practical applications in quantum networking.

However, there are also a lot of avenues for future research, the team writes. For example, future research could focus on improving that conversion efficiency and exploring the integration of this interface with other quantum hardware platforms.

In another route, scientists could use synchronized quantum memories with photon emissions from NV centers and integrating NV centers into optical cavities to boost photon emission rates.

Exploring different color center defects in diamonds — such as “group-IV elements,” or elements in the fourth column of the periodic table, such as carbon, silicon and germanium — could also be promising due to their higher photon output and compatibility with nanophotonic structures. Additionally, platforms using defect centers in silicon carbide (SiC), silicon (Si), and optical quantum dots may offer efficient alternatives for quantum processors.

Efforts to improve frequency conversion setups to telecom wavelengths could enable photon transmission over long distances, pushing toward practical quantum networks for global communication.

The research team included Mariagrazia Iuliano, Marie-Christine Slater, Arian J. Stolk, Matthew J. Weaver, Tanmoy Chakraborty, Elsie Loukiantchenko, Gustavo C. do Amaral, Nir Alfasi, Mariya O. Sholkina, and Ronald Hanson from QuTech & Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands. Wolfgang Tittel contributed from the Department of Applied Physics at the University of Geneva, Switzerland.