Single Defect Centers Research Articles

Superconducting cavity bus for single nitrogen-vacancy defect centers in diamond

Circuit-QED has demonstrated very strong coupling between individual microwave photons trapped in a superconducting coplanar resonator and nearby superconducting qubits. In this work we show how, by designing a novel interconnect, one can strongly connect the superconducting resonator, via a magnetic interaction, to a small number (perhaps single), of electronic spins. By choosing the electronic spin to be within a Nitrogen Vacancy centre in diamond one can perform optical readout, polarization and control of this electron spin using microwave and radio frequency irradiation. More importantly, by utilising Nitrogen Vacancy centres with nearby 13C nuclei, using this interconnect, one has the potential build a quantum device where the nuclear spin qubits are connected over centimeter distances via the Nitrogen Vacancy electronic spins interacting through the superconducting bus.

Quantum electrodynamics in a whispering-gallery microcavity coated with a polymer nanolayer

Quasi-transverse-electric and -transverse-magnetic fundamental whispering gallery modes in a polymer-coated silica microtoroid are theoretically investigated and demonstrated to possess very high-quality factors. The existence of a nanometer-thickness layer not only evidently reduces the cavity mode volume but also draws the maximal electric field's position of the mode to the outside of the silica toroid, where single quantum dots or nanocrystals are located. Both effects result in a strongly enhanced coherent interaction between a single dipole (for example, a single defect center in a diamond crystal) and the quantized cavity mode. Since the coated microtoroid is highly feasible and robust in experiments, it may offer an excellent platform to study strong-coupling cavity quantum electrodynamics, quantum information, and quantum computation.

Nanopositioning of a diamond nanocrystal containing a single nitrogen-vacancy defect center

Precise control over the position of a single quantum object is important for many experiments in quantum science and nanotechnology. We report on a technique for high-accuracy positioning of individual diamond nanocrystals. The positioning is done with a home-built nanomanipulator under real-time scanning electron imaging, yielding an accuracy of a few nanometers. This technique is applied to pick up, move, and position a single nitrogen-vacancy (NV) defect center contained in a diamond nanocrystal. We verify that the unique optical and spin properties of the NV center are conserved by the positioning process.

Controlled coupling of a single-diamond nanocrystal to a photonic crystal cavity

We demonstrate the controlled coupling of a single diamond nanocrystal to a planar photonic crystal double-heterostructure cavity. A dip-pen deposition method and subsequent manipulation with an atomic force microscope was used to precisely position the nanocrystal on top of the cavity. The optical properties of this combined system are investigated with regard to changes in the quality factor and resonance wavelength of the cavity mode as a function of the size and relative position of the diamond nanocrystal. These studies represent an important step toward well-controlled cavity-QED experiments with single-defect centers in diamond.

One-by-One Coupling of Single Defect Centers in Nanodiamonds to High-Q Modes of an Optical Microresonator

In this letter, we present the on-demand coupling of single NV(-) defect centers in nanodiamonds to a polystyrene microspherical resonator. From an ensemble on a coverslip, we select single nanodiamonds containing a single defect proven by a pronounced antibunching dip. With the help of a scanning near-field probe, we can attach these nanodiamonds to a microsphere resonator one-by-one. A clearly modulated fluorescence spectrum demonstrates coupling of the single defect centers to high-Q whispering-gallery modes. Our experiments establish a toolbox to assemble complex systems consisting of single quantum emitters and (coupled) microresonators.

Scanning magnetic field microscope with a diamond single-spin sensor

We describe a scanning device where a single spin is used as an ultrasensitive, nanoscale magnetic field sensor. As this “probe spin” we consider a single nitrogen-vacancy defect center in a diamond nanocrystal, attached to the tip of the scanning device. Changes in the local field seen by the probe spin are detected by optically monitoring its electron paramagnetic resonance transition. The room-temperature scanning device may be useful for performing nanoscale magnetic resonance imaging and spectroscopy, and for the characterization of magnetic nanostructures down to the single atom level.

Probing the Role of Single Defects on the Thermodynamics of Electric-Field Induced Phase Transitions

The kinetics and thermodynamics of first order transitions are universally controlled by defects that act as nucleation sites and pinning centers. Here we demonstrate that defect-domain interactions during polarization reversal processes in ferroelectric materials result in a pronounced fine structure in electromechanical hysteresis loops. Spatially resolved imaging of a single defect center in multiferroic BiFeO3 thin film is achieved, and the defect size and built-in field are determined self-consistently from the single-point spectroscopic measurements and spatially resolved images. This methodology is universal and can be applied to other reversible bias-induced transitions including electrochemical reactions.

Temporal Coherence of Photons Emitted by Single Nitrogen-Vacancy Defect Centers in Diamond Using Optical Rabi-Oscillations

Photon interference among distant quantum emitters is a promising method to generate large scale quantum networks. Interference is best achieved when photons show long coherence times. For the nitrogen-vacancy defect center in diamond we measure the coherence times of photons via optically induced Rabi oscillations. Experiments reveal a close to Fourier-transform (i.e., lifetime) limited width of photons emitted even when averaged over minutes. The projected contrast of two-photon interference (0.8) is high enough to envisage applications in quantum information processing. We report 12 and 7.8 ns excited state lifetimes depending on the spin state of the defect.

Generation of single color centers by focused nitrogen implantation

Single defect centers in diamond have been generated via nitrogen implantation. The defects have been investigated by single defect center fluorescence microscopy. Optical and electron paramagnetic resonance spectra unambiguously show that the produced defect is the nitrogen-vacancy color center. An analysis of the nitrogen flux together with a determination of the number of nitrogen-vacancy centers yields that on average one 2MeV nitrogen atom need to be implanted per defect center.

Experimental Test of the Fluctuation Theorem for a Driven Two-Level System with Time-Dependent Rates

A single defect center in diamond periodically excited by a laser is shown to provide a simple realization for a system obeying a fluctuation theorem for nonthermal noise. The distribution of these fluctuations is distinctly non-Gaussian, which has also been verified by numerical calculation. For driving protocols symmetric under time reversal a more restricted form of the theorem holds, which is also known from entropy fluctuations caused by thermal noise.

A Quantum Computer Based on NV Centers in Diamond: Optically Detected Nutations of Single Electron and Nuclear Spins

In an effort to realize a two-bit processor for a quantum computer on the basis of single nitrogen-vacancy defect centers (NV centers) in diamond, the optically detected nutations of the electron spin of a single NV center in the ground state and of the nuclear spin of a 13C atom located at a diamond lattice site nearest to the NV center are studied. The photodynamics of NV and NV + 13C centers under different temperatures and optical excitation conditions is discussed. A seven-level model of a center excited by radiation from an Ar+ laser at room temperature is proposed. On the basis of this model, the experimental spectra of optically detected electron paramagnetic and electron-nuclear double resonances of single NV and NV + 13C centers in diamond nanocrystals, as well as experimental data on the optically detected nutations of the electron and nuclear spins of these centers caused by the actions of pulsed microwave and radiofrequency fields, respectively, are interpreted.

Energy levels and decoherence properties of single electron and nuclear spins in a defect center in diamond

The coherent behavior of the single electron and single nuclear spins of a defect center in diamond and a $^{13}\mathrm{C}$ nucleus in its vicinity, respectively, are investigated. The energy levels associated with the hyperfine coupling of the electron spin of the defect center to the $^{13}\mathrm{C}$ nuclear spin are analyzed. Methods of magnetic resonance, together with the optical readout of single defect centers, have been applied in order to observe the coherent dynamics of the electron and nuclear spins. Long coherence times, in the order of microseconds for electron spins and tens of microseconds for nuclear spins, recommend the studied system as a good experimental approach for implementing a two-qubit gate.

Observation of Coherent Oscillation of a Single Nuclear Spin and Realization of a Two-Qubit Conditional Quantum Gate

Rabi nutations of a single nuclear spin in a solid have been observed. The experiments were carried out on a single electron and a single 13C nuclear spin of a single nitrogen-vacancy defect center in diamond. The system was used for implementation of quantum logical NOT and a conditional two-qubit gate (CROT). Density matrix tomography of the CROT gate shows that the gate fidelity achieved in our experiments is up to 0.9, good enough to be used in quantum algorithms.

Observation of coherent oscillations in a single electron spin.

Rabi nutations and Hahn echo modulation of a single electron spin in a single defect center have been observed. The coherent evolution of the spin quantum state is followed via optical detection of the spin state. Coherence times up to several microseconds at room temperature have been measured. Optical excitation of the spin states leads to decoherence. Quantum beats between electron spin transitions in a single spin Hahn echo experiment are observed. A closer analysis reveals that beats also result from the hyperfine coupling of the electron spin to a single 14N nuclear spin. The results are analyzed in terms of a density matrix approach of an electron spin interacting with two oscillating fields.

Defect physics of the ordered defect compound CuIn 3Se 5

The activation energies of acceptor and donor defect states in the ordered defect compound CuIn 3Se 5 are calculated by using a simple model based on the effective-mass theory for single, double and triple point defect centers. It is found that the values of these energies for both shallow and moderately deep levels are in reasonable agreement with those determined from experimental data. From the analysis of the results, a tentative assignment of the origins of these centers has been made.

Quantum computation using the 13C nuclear spins near the single NV defect center in diamond

We discuss the possibility of realizing quantum computation on the basis of a cluster of single interacting nuclear spins in solids. This idea seems to be feasible because of the combination of two techniques—Single Molecule Spectroscopy and Optically Detected Electron Nuclear Double Resonance. Compared to the well-known bulk Nuclear Magnetic Resonance (NMR), the proposed method of quantum computation has the advantage that quantum computation is performed with pure spin states and the quantum processor is more easily scalable. At the same time, the advantages of NMR quantum computation are kept: long coherence time and easy construction of quantum gates. As a specific system to implement the above idea, we discuss the 13C-nuclear spins in the nearest vicinity of a single nitrogen-vacancy (NV) defect center in diamond, which can be optically detected using the technique of scanning confocal microscopy. Owing to the hyperfine coupling of the ground state electron paramagnetic spin S=1 of the center to 13C nuclear spins in a diamond lattice, the states of nuclear spins in the vicinity of the defect-center can be addressed individually. Preliminary consideration shows that it should be possible to address up to 12 individual 13C nuclear spins. The dephasing time of the nuclear spin states at low temperatures allows realization up to 105 gates.

Fluorescence Correlation and Low Temperature Linewidth of Single Defect Centers in Diamond

Low temperature fluorescence excitation spectroscopy was carried out on single , nitrogen vacancy defect centers. At temperatures below 90, K; the fluorescence intensity of individual centers drastically diminishes because of the population of a metastable singlet state in near resonance with the . optically excited state. Low temperature fluorescence excitation spectroscopy , down to 5 K becomes possible via deshelving of this state with a second laser source. Surprisingly individual centers reveal low temperature fluorescence excitation line widths around 0.6 meV. PACS numbers: 78.20.—e, 42.30.Yc

Low-temperature microscopy and spectroscopy on single defect centers in diamond

Individual nitrogen-vacancy defect centers have been investigated by low-temperature confocal microscopy and fluorescence excitation spectroscopy. At temperatures below 90 K the fluorescence intensity of individual centers drastically diminishes because of the population of a metastable singlet state in near resonance with the optically excited state. Low-temperature fluorescence excitation spectroscopy down to 5 K becomes possible via deshelving of this state with a second laser source. Surprisingly individual centers reveal low-temperature fluorescence excitation line widths around 0.6 meV, more than two orders of magnitude larger than expected from previous high resolution laser spectroscopy on bulk samples.

Defect physics of the CuInSe 2 chalcopyrite semiconductor

The activation energies of acceptor E A and donor levels E D in the chalcopyrite compound CuInSe 2 are calculated by using a simpler model based in the effective-mass theory for the case of single, double and triple point defect centers. Despite of the simplicity of this model, it is found that the values of E A and E D thus calculated for shallow and deep levels are in reasonable agreement with those reported from the experimental data. In the case of not shallow donor levels values of E D in good agreement with these data are calculated by using the free electron mass m 0 instead of the effective electron mass. From the analysis of the results, most of these levels have been identified as due to the presence of several native point defects.

Scanning Confocal Optical Microscopy and Magnetic Resonance on Single Defect Centers

The fluorescence of individual nitrogen-vacancy defect centers in diamond was observed with room-temperature scanning confocal optical microscopy. The centers were photostable, showing no detectable change in their fluorescence emission spectrum as a function of time. Magnetic resonance on single centers at room temperature was shown to be feasible. The magnetic resonance spectra revealed marked changes in zero-field splitting parameters among different centers. These changes were attributed to strain-induced differences in the symmetry of the centers.