Single Defect Centers Research Articles

Thermoluminescence (TL) and electron paramagnetic resonance (EPR) of dumortierite sensitized by heat treatments

The present study presents the effect of heat treatment on TL and EPR of dumortierite. It was found that applying a heat treatment at 1200 °C for 1h, followed by slow cooling to room temperature, is optimal for improving its TL sensitivity. The glow curves of the sensitized dumortierite sample show TL emission bands centered at 350, 475, and 580 nm. The kinetic parameters of the TL peaks were obtained using the Tm-Tstop and deconvolution methods. In addition, sensitized dumortierite exhibits a linear response with γ-radiation dose and low fading in its TL response. Studies using the technique of EPR were carried out to investigate the defect center EPR signals observed after γ-irradiation. A single defect center with an axially symmetric g-tensor was observed with principal values g∥ = 2.0009 and g⊥ = 2.0017. The center was attributed to an F+ center and appears to correlate with the TL peak at 200 °C.

Comment on “Observation of Fourier transform limited lines in hexagonal boron nitride”

Recently, emission linewidths of single defect centers in layered hexagonal boron nitride down to 50 MHz were reported, close to the lifetime limit. The linewidths were extracted from time traces of laser scanning photoluminescence excitation experiments. At the same time, temporal blinking was affecting the measured time traces even in the absence of a frequency scanning the excitation laser. I argue here that the reported temporal blinking timescale is consistent with the observed transients, implying that the interpretation as spectral shapes and thus the extracted linewidths are invalid.

Observation of Fourier transform limited lines in hexagonal boron nitride

Single defect centers in layered hexagonal boron nitride (hBN) are promising candidates as single photon sources for quantum optics and nanophotonics applications. However, until today spectral instability hinders many applications. Here, we perform resonant excitation measurements and observe Fourier-Transform limited (FL) linewidths down to $\approx 50$ MHz. We investigate optical properties of more than 600 quantum emitters (QE) in hBN. The QEs exhibit narrow zero-phonon lines (ZPL) distributed over a spectral range from 580 nm to 800 nm and with dipole-like emission with high polarization contrast. The emission frequencies can be divided into four main regions indicating distinct families or crystallographic structures of the QEs, in accord with ab-initio calculations. Finally, the emitters withstand transfer to a foreign photonic platform - namely a silver mirror, which makes them compatible with photonic devices such as optical resonators and paves the way to quantum photonics applications including quantum commmunications and quantum repeaters.

Prediction of multiband luminescence due to the gallium vacancy–oxygen defect complex in GaN

Oxygen is the most common unintentional impurity found in GaN. We study the interaction between substitutional oxygen (ON) and the gallium vacancy (VGa) to form a point defect complex in GaN. The formation energy of the gallium vacancy is largely reduced in n-type GaN by complexing with oxygen, while thermodynamic and optical transition levels remain within the bandgap. We study the spectroscopy of this complex using a hybrid quantum-mechanical molecular-mechanical embedded-cluster approach. We reveal how a single defect center can be responsible for multiband luminescence, including possible contributions to the ubiquitous yellow luminescence signatures observed in n-type GaN, owing to the coexistence of diffuse (extended) and compact (localized) holes.

Observation of Effective Pseudospin Scattering in ZrSiS.

3D Dirac semimetals are an emerging class of materials that possess topological electronic states with a Dirac dispersion in their bulk. In nodal-line Dirac semimetals, the conductance and valence bands connect along a closed path in momentum space, leading to the prediction of pseudospin vortex rings and pseudospin skyrmions. Here, we use Fourier transform scanning tunneling spectroscopy (FT-STS) at 4.5 K to resolve quasiparticle interference (QPI) patterns at single defect centers on the surface of the line nodal semimetal zirconium silicon sulfide (ZrSiS). Our QPI measurements show pseudospin conservation at energies close to the line node. In addition, we determine the Fermi velocity to be ℏvF = 2.65 ± 0.10 eV Å in the Γ-M direction ∼300 meV above the Fermi energy EF and the line node to be ∼140 meV above EF. More importantly, we find that certain scatterers can introduce energy-dependent nonpreservation of pseudospin, giving rise to effective scattering between states with opposite pseudospin deep inside valence and conduction bands. Further investigations of quasiparticle interference at the atomic level will aid defect engineering at the synthesis level, needed for the development of lower-power electronics via dissipationless electronic transport in the future.

Resonant Excitation of Quantum Emitters in Hexagonal Boron Nitride

Quantum emitters in layered hexagonal boron nitride (hBN) have recently attracted a great deal of attention as promising single photon sources. In this work, we demonstrate resonant excitation of a single defect center in hBN, one of the most important prerequisites for employment of optical sources in quantum information processing applications. We observe spectral line widths of an hBN emitter narrower than 1 GHz while the emitter experiences spectral diffusion. Temporal photoluminescence measurements reveal an average spectral diffusion time of around 100 ms. An on-resonance photon antibunching measurement is also realized. Our results shed light on the potential use of quantum emitters from hBN in nanophotonics and quantum information processing applications.

Complete coherent control of silicon vacancies in diamond nanopillars containing single defect centers

Arrays of identical and individually addressable qubits lay the foundation for the creation of scalable quantum hardware such as quantum processors and repeaters. Silicon-vacancy (SiV) centers in diamond offer excellent physical properties such as low inhomogeneous broadening, fast photon emission, and a large Debye–Waller factor. The possibility for all-optical ultrafast manipulation and techniques to extend the spin coherence times makes them promising candidates for qubits. Here, we have developed arrays of nanopillars containing single (SiV) centers with high yield, and we demonstrate ultrafast all-optical complete coherent control of the excited state population of a single SiV center at the optical transition frequency. The high quality of the chemical vapor deposition (CVD) grown SiV centers provides excellent spectral stability, which allows us to coherently manipulate and quasi-resonantly read out the excited state population of individual SiV centers on picosecond timescales using ultrafast optical pulses. This work opens new opportunities to create a scalable on-chip diamond platform for quantum information processing and scalable nanophotonics applications.

Proposal for observing dynamic Jahn–Teller effect by single solid-state defects

The Jahn–Teller effect (JTE) widely exists in polyatomic systems including organic molecules, nano-magnets, and solid-state defects. Detecting the JTE at single-molecule level can provide unique properties about the detected individual object. However, such measurements are challenging because of the weak signals associated with a single quantum object. Here, we propose that the dynamic JTE of single defects in solids can be observed with nearby quantum sensors. With numerical simulations, we demonstrate the real-time monitoring of JT axis jumps between different stable configurations of single substitutional nitrogen defect centers (P1 centers) in diamond. This is achieved by measuring the spin coherence of a single nitrogen-vacancy (NV) center near the P1 center with the double electron-electron resonance technique. Our work extends the ability of NV center as a quantum probe to sense the rich physics in various electron-vibrational coupled systems.

(Keynote) Devices Architectures and Technology for Quantum Computing

There have been many reports on quantum computing hardware using various quantum two-level systems. In principle, any quantum two-level system can be used as a basic unit of information in quantum computing, which is called quantum bit (qubit). Many ways for implementing qubits have been studied to date, for example, trapped ions, cavity quantum electrodynamics, single defect centers, single photons, nuclear spin resonances, superconductor circuits, and semiconductor quantum dots (QDs). Among these, solid-state system has an advantage of scalability, which will be required for practical applications of quantum computers. Especially an electron spin in a QD is a well-defined quantum two-level system characterized by a spin-up and a spin-down state, which is one of the most promising candidates for a qubit, because of its long coherence time. Electron spin-based qubits have been studied using QDs in GaAs, which has a relatively small electron effective mass, m* = 0.067 m 0, the QD size required to obtain quantum effects is relatively large (~100 nm) and can be readily obtained using electron beam lithography. However, further research into quantum operations has found difficulties related to decoherence. The main source of the decoherence is hyperfine interaction with the nuclear spins of the Ga and As atoms.To reduce this hyperfine interaction, the use of Si and SiGe has been investigated, since these materials have isotopes with zero nuclear spin. It is also possible to completely remove the hyperfine interaction through controlling the isotopic composition of the host. Si system is advantageous for future applications because of its potential for compatibility with conventional CMOS devices. However, it is necessary to fabricate much smaller QDs in Si in order to obtain quantum effects because of the larger electron effective mass in this material (m* = 0.19 m 0), and so a highly sophisticated fabrication technique is required.To properly apply qubits based on electron spins, it is necessary to observe spin-related tunneling phenomena and to reduce the electron number in individual QDs to only a few, so as to ensure energetically well-defined spin states. To date, single-electron regimes in single QDs and Pauli-spin blockades (PSBs) in coupled QDs have been observed in Si/SiGe heterostructures. Single-electron regimes in Si QDs have also been observed in MOS structures using a double top-gate design, MOS fine-gate structures and nanowire structures. Thus far, the majority of these Si QD devices have had gate-defined QD structures in which confinement potentials are generated by electric fields with fine top gates. In contrast, the physically-defined Si QD devices described below do not require gates to create confinement potentials for the QDs. These devices thus represent a technological simplification owing to the reduced number of gates and may be advantageous with regard to the integration of qubit technology, since common fabrication processes normally used to produce Si MOS technologies may be applied to make the physically-defined Si QDs. Recently, our group was able to obtain high-quality physically-defined Si QD structures by applying fabrication techniques such as electron beam lithography, oxidation and dry-etching. The resulting devices represented physically-defined coupled Si QDs with MOS structures incorporating a top gate for inducing inversion carriers and side gates for controlling potentials in the QDs. We observed spin-related tunneling phenomena [1] and reduced the electron number in the QDs to the few-electron regime [2,3]. Charge detection of change in number of carriers in the QDs, one by one, has also been successfully demonstrated [4]. These achievements are the important steps for realizing quantum computing devices,[1] G. Yamahata, T. Kodera, H. O. H. Churchill, K. Uchida, C. M. Marcus, and S. Oda, Phys. Rev. B 86, 115322 (2012). [2] K. Horibe, T. Kodera, T. Kambara, K. Uchida, and S. Oda, J. Appl. Phys. 111, 093715 (2012). [3] K. Horibe, T. Kodera, and S. Oda, Appl. Phys. Lett. 106, 083111 (2015). [4] K. Horibe, T. Kodera, and S. Oda, Appl. Phys. Lett. 106, 053119 (2015).

Investigation of Line Width Narrowing and Spectral Jumps of Single Stable Defect Centers in ZnO at Cryogenic Temperature.

Finding new solid state defect centers in novel host materials is crucial for realizing integrated hybrid quantum photonic devices. We present a preparation method for defect centers with photostable bright single photon emission in zinc oxide, a material with promising properties in terms of processability, availability, and applications. A detailed optical study reveals a complex dynamic of intensity fluctuations at room temperature. Measurements at cryogenic temperatures show very sharp (<60 GHz) zero phonon lines (ZPLs) at 580 nm to 620 nm (≈ 2.0 eV) with frozen out fast fluctuations. Remaining discrete jumps of the ZPL, which depend on the excitation power, are observed. The low temperature results will narrow down speculations on the origin of visible-near-infrared (NIR) wavelength defect emission in zinc oxide and provide a basis for improved theoretical models.

Towards quantum networks of single spins: analysis of a quantum memory with an optical interface in diamond.

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.

Microscopic diamond solid-immersion-lenses fabricated around single defect centers by focused ion beam milling.

Recent efforts to define microscopic solid-immersion-lenses (SIL) by focused ion beam milling into diamond substrates that are registered to a preselected single photon emitter are summarized. We show how we determine the position of a single emitter with at least 100 nm lateral and 500 nm axial accuracy, and how the milling procedure is optimized. The characteristics of a single emitter, a Nitrogen Vacancy (NV) center in diamond, are measured before and after producing the SIL and compared with each other. A count rate of 1.0 × 10(6) counts/s is achieved with a [111] oriented NV center.

Correction to Single Defect Center Scanning Near-Field Optical Microscopy on Graphene

Correction to Single Defect Center Scanning Near-Field Optical Microscopy on Graphene

Single Defect Center Scanning Near-Field Optical Microscopy on Graphene

We present a scanning-probe microscope based on an atomic-size emitter, a single nitrogen-vacancy center in a nanodiamond. We employ this tool to quantitatively map the near-field coupling between the NV center and a flake of graphene in three dimensions with nanoscale resolution. Further we demonstrate universal energy transfer distance scaling between a point-like atomic emitter and a two-dimensional acceptor. Our study paves the way toward a versatile single emitter scanning microscope, which could image and excite molecular-scale light fields in photonic nanostructures or single fluorescent molecules.

Front Cover: Coupling of single nitrogen‐vacancy defect centers in diamond nanocrystals to optical antennas and photonic crystal cavities (Phys. Status Solidi B 5/2012)

Nitrogen-vacancy (NV) centers in diamond are a promising resource for solid state quantum technology. Wolters et al. (pp. 918–924) demonstrate the ability to integrate single NV centers in diamond nanocrystals into photonic or plasmonic hybrids using state of the art scanning probe lithography. Hereby the emission properties of the single NV centers are strongly modified. The authors review experiments concerning the controlled coupling of single defect centers in nanodiamonds to optical nanoantennas made of gold bowtie structures. By placing one and the same emitter at various locations with high precision, a map of decay rate enhancements is obtained. Furthermore, the authors demonstrate the formation of a hybrid cavity quantum electrodynamics (cQED) system in which a single defect center is coupled to a single mode of a gallium phosphite photonic crystal cavity.

Coupling of single nitrogen‐vacancy defect centers in diamond nanocrystals to optical antennas and photonic crystal cavities

AbstractWe demonstrate the ability to modify the emission properties and enhance the interaction strength of single‐photon emitters coupled to nanophotonic structures based on metals and dielectrics. Assembly of individual diamond nanocrystals, metal nanoparticles, and photonic crystal cavities to meta‐structures is introduced. Experiments concerning controlled coupling of single defect centers in nanodiamonds to optical nanoantennas made of gold bowtie structures are reviewed. By placing one and the same emitter at various locations with high precision, a map of decay rate enhancements was obtained. Furthermore, we demonstrate the formation of a hybrid cavity quantum electrodynamics system in which a single defect center is coupled to a single mode of a gallium phosphite photonic crystal cavity.

Single defect centers in diamond nanocrystals as quantum probes for plasmonic nanostructures

We present two applications of a single nitrogen vacancy center in a nanodiamond as quantum probe for plasmonic nanostructures. Coupling to the nanostructures is achieved in a highly controlled manner by picking up a pre-characterized nanocrystal with an atomic force microscope and placing it at the desired position. Local launching of single excitations into a nanowire with a spatial control of few nanometers is demonstrated. Further, a two dimensional map of the electromagnetic environment of a plasmonic bowtie antenna was derived, resembling an ultimate limit of fluorescence lifetime nanoscopy.

Controling the single-diamond nitrogen-vacancy color center photoluminescence spectrum with a Fabry–Perot microcavity

We present here both theoretical and experimental results on the fluorescence of single defect centers in diamond nanocrystals embedded in a planar dielectric microcavity. From a theoretical point of view, we show that the overall fluorescence collection efficiency using a moderate numerical aperture microscope objective can be enhanced by using a low-quality-factor microcavity. This could be used in particular for low-temperature applications, where the numerical aperture of collection microscope objectives is limited due to the experimental constraints. We experimentally investigate the control of the fluorescence spectrum of the emitted light from a single center. We show the simultaneous narrowing of the room temperature broadband emission spectrum and the increase in the fluorescence spectral density.

Monolithic diamond optics for single photon detection

In this work, we experimentally demonstrate a novel and simple approach that uses off-the-shelf optical elements to enhance the collection efficiency from a single emitter. The key component is a solid immersion lens made of diamond, the host material for single color centers. We improve the excitation and detection of single emitters by one order of magnitude, as predicted by theory.

Control and Coherence of the Optical Transition of Single Nitrogen Vacancy Centers in Diamond

We demonstrate coherent control of the optical transition of single nitrogen-vacancy defect centers in diamond. On applying short resonant laser pulses, we observe optical Rabi oscillations with a half period as short as 1 ns, an order of magnitude shorter than the spontaneous emission time. By studying the decay of Rabi oscillations, we find that the decoherence is dominated by laser-induced spectral jumps. By using a low-power probe pulse as a detuning sensor and applying postselection, we demonstrate that spectral diffusion can be overcome in this system to generate coherent photons.