QuTech Develops Diamond Quantum Emitter Interface

QuTech researchers have achieved a breakthrough in quantum networking by demonstrating a coherent interface between a diamond tin-vacancy (SnV) quantum emitter and a nanophotonic cavity. This critical development enables reliable communication between solid-state qubits, which store information, and photons, which transmit it over long distances. The findings represent a substantial leap towards building scalable and efficient quantum networks.

This advancement provides a pathway for the development of quantum internet infrastructure. Future quantum networks rely on stable interactions between distinct carriers of quantum information: solid-state qubits, which manage data processing and storage, and photons, which facilitate long-range data transmission between nodes. QuTech’s team successfully established an efficient and coherent interface between a diamond-based quantum emitter and photons confined within a nanoscopic optical cavity. This represents a crucial stride toward establishing rapid and dependable connections within future quantum processors. The researchers also showcased near-complete command over transmitted light and confirmed the scalability of their fabrication method across hundreds of cavities, offering a positive outlook for broad implementation. These results are now published in PRX.

Advancing Quantum Internet Infrastructure

Today’s traditional internet transmits information as binary bits. A future quantum internet, however, will distribute quantum information using qubits, enabling entirely new applications in secure communication, blind access to quantum computers, and ultrafast coordination for network traffic management. To realize this vision, each network node requires a highly dependable interface. This interface must connect matter qubits on a chip, which store and process information, with light that creates dynamic, long-range links between nodes.

One promising approach employs color centers in diamond. These are precisely controlled imperfections within the otherwise regular lattice of carbon atoms. A tin-vacancy (SnV) center, for example, integrates a tin atom into the diamond lattice alongside missing carbon atoms. This SnV center behaves like an atom-like quantum system embedded within a solid, offering properties highly beneficial for networking. These properties include the capacity to store and process quantum information, along with an inherent interface to light. Recent research has demonstrated significant progress in utilizing SnV-based systems as network-ready building blocks.

Combining SnV centers with optical cavities, which trap light, unlocks potent protocols for linking network nodes. However, a significant challenge persists. Even if a defect emits light, these protocols demand coherent interaction with light, meaning the photon and the emitter must remain “in step” long enough to execute quantum protocols without being degraded by noise. Achieving such coherence proves particularly difficult in nanophotonic devices. In these systems, the emitter must withstand localized noise, and fabrication methods must consistently produce high-quality structures.

The researchers engineered diamond photonic crystal cavities, which are miniature structures designed to trap and concentrate light. They then investigated SnV centers embedded near the regions where the trapped light intensity is highest. The team reports a scalable fabrication outcome: across two distinct chips, they measured 327 devices, demonstrating a high average quality and yield. This scalability is vital because future quantum networks will require numerous such devices, not just a few.

Demonstrating Coherent Coupling and Control

In two specific devices, the optical cavity significantly enhanced the SnV’s emission of photons into the desired optical mode. When tuned into resonance, a single SnV could almost entirely block light transmission through the cavity, demonstrating that a single quantum emitter can exert strong control over a beam of light particles. By measuring optical linewidths—a method to quantify the “sharpness” and stability of the interaction—the researchers established coherent cooperativities exceeding one. This widely recognized threshold indicates that the system operates in a regime suitable for high-fidelity quantum operations, surpassing merely bright emission.

Achieving above-unity coherent coupling represents a practical milestone in quantum technology. Ronald Hanson, who oversaw the research, explains that this result signifies that useful quantum interactions can now overcome dephasing noise, paving the way for faster and more reliable entanglement generation between distant network nodes. This advancement is particularly important for the ongoing quantum computing collaboration with Fujitsu, as it facilitates the efficient linking of qubit modules into a larger, more powerful computing system. This research received financial support from several key programs and institutions. These include the joint research program “Modular quantum computers” by Fujitsu Limited and Delft University of Technology, co-funded by the Netherlands Enterprise Agency under project number PPS2007. Further backing came from the Dutch Research Council (NWO) through the Spinoza prize 2019 (project number SPI 63-264). Additional contributions were provided by the Dutch Ministry of Economic Affairs and Climate Policy (EZK) as part of the Quantum Delta NL programme, and from the Quantum Internet Alliance through the Horizon Europe program (grant agreement No. 101080128). The Kavli Foundation also contributed through its Kavli Institute Innovation Award, specifically for “Quantum Materials for Broad-Band Quantum Transduction.” These combined efforts underscore a collaborative commitment to advancing quantum technology.