Quantum network is a secure network using quantum entanglement for the transmission of information. Each point, such as sender, receiver, and quantum repeater, is called quantum network node. Quantum emitters with supirior optical and spin properties are required to construct the quantum network nodes. Diamond quantum emitters are a promising candidate for this purpose.
An NV center is one of the mostly studied solid-state emitters. However, it suffers from a low fraction of zero phonon line and unstable emission line. Thus, a quantum emitter which can solve these problems is required.
In our lab, we have so far created quantum emitters in diamond which are composed of group-IV elements: Germanium-vacancy (GeV) and Tin-vacancy (SnV) centers. Furthermore, recently, we have clarified zero phonon line of Lead-vacancy (PbV) center. The group-IV emitters have an inversion symmetry, leading to high concentrations to the zero phonon line and stable emission. Especially, SnV and PbV centers are expected to show a long spin coherence time at Kelvin temperatures, making them attracttive for quantum network applications.
Acheiving both suprior optical and spin properties are important for the application of group-IV color centers in diamond to quantum network. In general, diamon is annealed at around 1000 degC after ion implanation of impurities to form color centers and recover lattice defects. However, more effective method is necessary to recover the defects for the fromation of SnV and PbV centers due to a larger number of defects generaeted uponion implantation of the heavy elements.
With collaborator, we fabricate high-quality SnV and PbV centers by treating the diamond at over 2000 degC under a high-pressure after ion implantation.
We have succeeded in generating identical photons with nearly same photon frequencies from multiple SnV centers. This results paves the way to achieve quantum entanglement between quantum network nodes based on group-IV diamond quantum emitters.
The properties of diamond quantum emitters are investigated using cryostats and a narrowlinewidth tunable laser. We are working on the development of measurement technologies along the high-quality formation to reveal the optical and spin properties of the group-IV quantum emitters.