From jewelry stores to quantum labs — diamonds have found a new sparkle in the world of quantum technologies. Their atomic-scale color centers host electron and nuclear spins that can serve as long-lived qubits and bright photon sources, making them powerful candidates for realizing quantum networks. In this talk, I’ll explore how these tiny defects in diamond enable us to connect stationary quantum memories through flying photonic qubits. We’ll look at the fundamental principles, key experimental advances, and ongoing challenges in creating scalable quantum links — and discuss how “shining light on defects” may become the key to the quantum internet.
From jewelry stores to quantum labs — diamonds have found a new sparkle in the world of quantum technologies. Their atomic-scale color centers host electron and nuclear spins that can serve as long-lived qubits and bright photon sources, making them powerful candidates for realizing quantum networks. In this talk, I’ll explore how these tiny defects in diamond enable us to connect stationary quantum memories through flying photonic qubits. We’ll look at the fundamental principles, key experimental advances, and ongoing challenges in creating scalable quantum links — and discuss how “shining light on defects” may become the key to the quantum internet.
Large-scale quantum networks will enable entirely new applications of quantum information science in fields such as quantum communication, distributed quantum computing, sensing, and metrology. To build nodes of such networks, diamond color defects are one of the promising candidates. Their excellent optical properties, fast spin-qubit control, and long spin coherence times make them well-suited for quantum information processing and quantum memory applications. Additionally, recent advances in the heterogeneous integration of diamond nanophotonic structures with photonic integrated circuits have made these systems more efficient and well-suited for scalable quantum processor architectures. In this comprehensive review, we discuss the optical and spin properties of these systems, recent progress in the building blocks of quantum networks, and demonstrations of metropolitan-scale quantum networks, as well as the challenges associated with these systems at both the fundamental and experimental levels, along with potential solutions.
Single defect centers in diamond have emerged as a powerful platform for quantum optics experiments and quantum information processing tasks. Connecting spatially separated nodes via optical photons into a quantum network will enable distributed quantum computing and long-range quantum communication. Initial experiments on trapped atoms and ions as well as defects in diamond have demonstrated entanglement between two nodes over several meters. To realize multi-node networks, additional quantum bit systems that store quantum states while new entanglement links are established are highly desirable. Such memories allow for entanglement distillation, purification and quantum repeater protocols that extend the size, speed and distance of the network. However, to be effective, the memory must be robust against the entanglement generation protocol, which typically must be repeated many times. Here we evaluate the prospects of using carbon nuclear spins in diamond as quantum memories that are compatible with quantum networks based on single nitrogen vacancy (NV) defects in diamond. We present a theoretical framework to describe the dephasing of the nuclear spins under repeated generation of NV spin-photon entanglement and show that quantum states can be stored during hundreds of repetitions using typical experimental coupling parameters. This result demonstrates that nuclear spins with weak hyperfine couplings are promising quantum memories for quantum networks.
Integrated photonic devices in diamond have tremendous potential for many quantum applications, including long-distance quantum communication, quantum information processing, and quantum sensing. These devices benefit from diamond's combination of exceptional thermal, optical, and mechanical properties. Its wide electronic bandgap makes diamond an ideal host for a variety of optical active spin qubits that are key building blocks for quantum technologies. In landmark experiments, diamond spin qubits have enabled demonstrations of remote entanglement, memory-enhanced quantum communication, and multi-qubit spin registers with fault-tolerant quantum error correction, leading to the realization of multinode quantum networks. These advances put diamond at the forefront of solid-state material platforms for quantum information processing. Recent developments in diamond nanofabrication techniques provide a promising route to further scaling of these landmark experiments towards real-life quantum technologies. In this paper, we focus on the recent progress in creating integrated diamond quantum photonic devices, with particular emphasis on spin-photon interfaces, cavity optomechanical devices, and spin-phonon transduction. Finally, we discuss prospects and remaining challenges for the use of diamond in scalable quantum technologies.
A coherent interface between optical photons and long-lived matter qubits can form the basis for a broad range of quantum technologies. I will describe the realization of such an interface using inversion-symmetric color-centers integrated into diamond nanophotonic devices at millikelvin temperatures. The resulting high-cooperativity spin-photon interface can be fabricated en-masse and exhibits a unique combination of long coherence times, high-fidelity control, strong light-matter interactions, and efficient photon out-coupling, establishing it as a leading platform for the construction of a large-scale quantum internet.
Solid-state spin defects, such as color centers in diamond, are among the most promising candidates for scalable and integrated quantum technologies. In particular, the good optical properties of silicon-vacancy centers in diamond combined with naturally occurring and exceptionally coherent nuclear spins serve as a building block for quantum networking applications. Here, we show that leveraging an ultra-high strained silicon-vacancy center inside a nanodiamond allows us to coherently and efficiently control its electron spin, while mitigating phonon-induced dephasing at liquid helium temperature. Moreover, we indirectly control and characterize a 13C nuclear spin and establish a quantum register. We overcome limited nuclear spin initialization by implementing single-shot nuclear spin readout. Lastly, we demonstrate coherent optical control with GHz rates, thus connecting the register to the optical domain. Our work paves the way for future integration of quantum network registers into conventional, well-established photonics and hybrid quantum communication systems.
A key challenge in realizing practical quantum networks for long-distance quantum communication involves robust entanglement between quantum memory nodes connected via fiber optical infrastructure. I will talk about our recent work on utilizing silicon vacancy (SiV) centers in nanophotonic diamond cavities integrated with a telecommunication (telecom) metropolitan quantum network. Specifically, remote entanglement generation is generated by the cavity-enhanced interactions, and long-lived auxiliary memory qubits are used to provide second-long entanglement storage with integrated error detection. By interfacing with efficient bi-directional frequency conversion to telecommunication frequencies, we demonstrate entanglement of two nuclear spin memories through a 35 km long fiber deployed in the Boston urban area, an enabling step towards practical quantum repeaters and large-scale quantum network. I will also talk about an in-progress work on exploring blind and distributed quantum computation through this two-node quantum network.