SESSION 3: Qubits in defectsChair: (Kai-Mei Fu (University of Washington))
|Nathalie de Leon, Princeton University
New color centers in diamond for long distance quantum networks
|Abstract. Color centers in diamond are promising candidates for quantum networks, as they can serve as solid state quantum memories with efficient optical transitions. Prior work has focused on the NV- center in diamond, which exhibits long spin coherence times and has narrow, spin-conserving optical transitions. However, the NV- center is prone to spectral diffusion, and over 97% of emission is in an incoherent phonon side band, severely limiting scalability. Alternatively, SiV- exhibits excellent optical properties, with 70% of its emission in the zero phonon line and a narrow inhomogeneous linewidth. However, SiV- suffers from significant interaction with phonons, with spin coherence times limited by an orbital relaxation time (T1) of around 40 ns at 5 K. Informed by the limitations of NV- and SiV-, we have developed new methods to control the diamond Fermi level to stabilize the neutral charge state of SiV, thus accessing a new spin configuration. SiV0 exhibits a spin T1 of around 1 minute at 4 K, coherence time (T2) approaching 1 second, over 90% of emission in the zero phonon line, and near-transform limited optical linewidths, making it a promising candidate for applications in quantum networks.
|Emma Schmidgall, University of Washington
Frequency control of single quantum emitters in integrated photonic circuits
|Abstract. An entangled graph state of qubits is a valuable resource for both universal quantum computation and quantum communication. To date, entanglement generation rates are too low to realize these multi-qubit networks due to photon emission into unwanted spatial and spectral modes. The integration of crystal defect-based qubits with photonic circuits can significantly enhance photon collection efficiency, albeit at the cost of degrading the defect's optical properties, such as an increase in inhomogeneous emission energies (linewidth broadening of GHz vs a few tens of MHz) and decreased spectral stability (spectral diffusion of tens of GHz vs a few hundred MHz). Compensating for this static and dynamic spread in emission energies is of critical importance for scalable on-chip graph state generation. We demonstrate the ability to tune the emission energy of photonic device-coupled near-surface NV centers over a large (200 GHz) tuning range with applied bias voltage. This is larger than the inhomogeneity of implanted NV centers suggesting a viable route for indistinguishable photons from separate emitters. However, measurements on many single waveguide-coupled NV centers highlight the variability in response to an applied bias voltage. Despite this variability, we are able to apply real-time voltage feedback control to partially stabilize the emission energy of a device-coupled NV center.
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