Overcoming spectral diffusion in solid-state single-photon emitters

• Applicant: Professor Dr. Andreas Reiserer
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 547245129

The implementation of large distributed quantum systems is among the main research goals in quantum science. Such systems would not only allow novel and precision tests of quantum theory, but also facilitate numerous applications, which include communication with provable security, timekeeping and sensing with unprecedented resolution, as well as the networking of small quantum processors to enhance their computational capabilities. A key step towards the realization of such systems via the connection and entanglement of remote quantum bits is the implementation of an efficient and coherent interface between stationary emitters and optical photons. Because of their comparably low experimental overhead, solid-state systems seem particularly attractive emitters. However, all previous experiments with such systems have been plagued by spectral diffusion, i.e. a change of the frequency of the emitted light over time. This has hindered the entanglement of solid-state spins with high rate and high fidelity, as required for the up-scaling of distributed quantum information processing systems. This proposal aims to fully eliminate this obstacle by a combination of materials optimization with advanced control techniques. We plan to follow a two-fold approach: First, by using ultra-pure crystalline membranes, we will minimize the known sources of spectral diffusion, which are found in "spin noise" from magnetic moments and "charge noise" from interfaces and impurities in previously studied materials. Second, we will minimize the sensitivity of the dopants to perturbations by a specific combination of operating conditions, in which the shift of the energy levels in response to electric and magnetic field fluctuations is dramatically reduced. By combining the mentioned concepts in a new setup that simultaneously minimizes mechanical vibrations as the only known remaining source of spectral instability, we plan to completely eliminate spectral diffusion in spectrally multiplexed C-band single-photon emitters. This would constitute a landmark achievement for distributed quantum-information processing based on solid-state systems. As many of the explored techniques are applicable to several other solid-state emitters, we expect that our work will also find applications in different hardware platforms. However, a key advantage of our system is that the targeted sub-kHz linewidth is extremely narrow, 100-fold narrower than the current record value. This paves the way for the addressing of thousands of qubits in the same resonator by spectral multiplexing. In addition, the new setup will allow us to explore the ultimate limits to the spectral stability of photon emitters in solids.

• DFG Programme: Research Grants