Quantum Simulation of Helium Hydride Cation in a Solid-State Spin Register.

Ab initio computation of molecular properties is one of the most promising applications of quantum computing. While this problem is widely believed to be intractable for classical computers, efficient quantum algorithms exist which have the potential to vastly accelerate research throughput in fields ranging from material science to drug discovery. Using a solid-state quantum register realized in a nitrogen-vacancy (NV) defect in diamond, we compute the bond dissociation curve of the minimal basis helium hydride cation, HeH(+). Moreover, we report an energy uncertainty (given our model basis) of the order of 10(-14) hartree, which is 10 orders of magnitude below the desired chemical precision. As NV centers in diamond provide a robust and straightforward platform for quantum information processing, our work provides an important step toward a fully scalable solid-state implementation of a quantum chemistry simulator.

Efficient photon collection from a nitrogen vacancy center in a circular bullseye grating.

Efficient collection of the broadband fluorescence from the diamond nitrogen vacancy (NV) center is essential for a range of applications in sensing, on-demand single photon generation, and quantum information processing. Here, we introduce a circular "bullseye" diamond grating which enables a collected photon rate of (2.7 ± 0.09) × 10(6) counts per second from a single NV with a spin coherence time of 1.7 ± 0.1 ms. Back-focal-plane studies indicate efficient redistribution of the NV photoluminescence into low-NA modes by the bullseye grating.

High-fidelity spin entanglement using optimal control.

Precise control of quantum systems is of fundamental importance in quantum information processing, quantum metrology and high-resolution spectroscopy. When scaling up quantum registers, several challenges arise: individual addressing of qubits while suppressing cross-talk, entangling distant nodes and decoupling unwanted interactions. Here we experimentally demonstrate optimal control of a prototype spin qubit system consisting of two proximal nitrogen-vacancy centres in diamond. Using engineered microwave pulses, we demonstrate single electron spin operations with a fidelity F≈0.99. With additional dynamical decoupling techniques, we further realize high-quality, on-demand entangled states between two electron spins with F>0.82, mostly limited by the coherence time and imperfect initialization. Crosstalk in a crowded spectrum and unwanted dipolar couplings are simultaneously eliminated to a high extent. Finally, by high-fidelity entanglement swapping to nuclear spin quantum memory, we demonstrate nuclear spin entanglement over a length scale of 25 nm. This experiment underlines the importance of optimal control for scalable room temperature spin-based quantum information devices.

Nanoscale detection of a single fundamental charge in ambient conditions using the NV- center in diamond.

Single charge nanoscale detection in ambient conditions is a current frontier in metrology that has diverse interdisciplinary applications. Here, such single charge detection is demonstrated using two nitrogen-vacancy (NV) centers in diamond. One NV center is employed as a sensitive electrometer to detect the change in electric field created by the displacement of a single electron resulting from the optical switching of the other NV center between its neutral (NV(0)) and negative (NV(-)) charge states. As a consequence, our measurements also provide direct insight into the charge dynamics inside the material.

High-resolution correlation spectroscopy of ¹³C spins near a nitrogen-vacancy centre in diamond.

Spin complexes comprising the nitrogen-vacancy centre and neighbouring spins are being considered as a building block for a new generation of spintronic and quantum information processing devices. As assembling identical spin clusters is difficult, new strategies are being developed to determine individual node structures with the highest precision. Here we use a pulse protocol to monitor the time evolution of the (13)C ensemble in the vicinity of a nitrogen-vacancy centre. We observe long-lived time correlations in the nuclear spin dynamics, limited by nitrogen-vacancy spin-lattice relaxation. We use the host (14)N spin as a quantum register and demonstrate that hyperfine-shifted resonances can be separated upon proper nitrogen-vacancy initialization. Intriguingly, we find that the amplitude of the correlation signal exhibits a sharp dependence on the applied magnetic field. We discuss this observation in the context of the quantum-to-classical transition proposed recently to explain the field dependence of the spin cluster dynamics.

Diamond nanophotonics.

We demonstrate the coupling of single color centers in diamond to plasmonic and dielectric photonic structures to realize novel nanophotonic devices. Nanometer spatial control in the creation of single color centers in diamond is achieved by implantation of nitrogen atoms through high-aspect-ratio channels in a mica mask. Enhanced broadband single-photon emission is demonstrated by coupling nitrogen-vacancy centers to plasmonic resonators, such as metallic nanoantennas. Improved photon-collection efficiency and directed emission is demonstrated by solid immersion lenses and micropillar cavities. Thereafter, the coupling of diamond nanocrystals to the guided modes of micropillar resonators is discussed along with experimental results. Finally, we present a gas-phase-doping approach to incorporate color centers based on nickel and tungsten, in situ into diamond using microwave-plasma-enhanced chemical vapor deposition. The fabrication of silicon-vacancy centers in nanodiamonds by microwave-plasma-enhanced chemical vapor deposition is discussed in addition.