Coupling of single color centers in diamond to micro- and nano-photonic cavities
Christoph Becher

Fachrichtung 7.2 (Experimentalphysik), Universitaet des Saarlandes, Campus E2.6,
66123 Saarbruecken, Germany

Many proposals for diamond-based quantum information technologies such as cavity enhanced single photon sources, spin-photon interfaces and distributed quantum networks rely on the deterministic coupling of single color centers to optical cavities. We here present two routes for the coupling of single color centers to optical cavities at the micro- and nano-scale: The first approach employs a fiber-based Fabry-Perot cavity which is easily tunable, automatically fiber-coupled and achieves high quality factors at moderate mode volumes. We demonstrate the coupling of a single NV center in a diamond nanocrystal to the fiber micro-cavity and observe single photon emission with high spectral brightness (photons / bandwidth) at the cavity output. The cavity emission is described using a theoretical model taking into account the pure phonon dephasing of the NV zero phonon line and sidebands. As second approach we use photonic crystal nano-cavities directly fabricated at the predetermined position of single Silicon-Vacancy (SiV) centers in a single crystal diamond membrane. Here, the tiny mode volume together with the moderate quality factor leads to an efficient emitter-cavity coupling and Purcell enhancement of the spontaneous emission. Furthermore, we investigate the deterministic implantation of NV centers into photonic crystal cavities with high spatial precision.


Basic physics of NV centers in diamond with applications to ensemble sensing
Dmitry Budker

I will discuss recent results on the spectroscopy of the singlet states, bulk nuclear polarization, T1 and T2 studies, light narrowing of ODMR resonances, etc., with applications to magnetometry and rotation sensing.


The Diamond Bionic Eye
Steven Prawer

The diseases of age related macular degeneration and retinitis pigemntosa are one of the main causes of blindness and cause untold suffering for those afflicted with these conditions. Electrical stimulation of the retina has already been shown to restore partial vision in some patients, albeit at low resolution. Higher resolution may be achievable by taking advantage of modern nanofabrication techniques to build stimulating arrays with hundreds or even thousands of electrodes that will allow patients to read large print and recognize faces of loved ones. However, formidable challenges remain in the fabrication of such devices. I will describe the work of Bionic Vision Australia in meeting these challenges and in particular the use of diamond for the direct stimulation of the retina and for the encapsulation of the bionic implant. Having established that diamond is an excellent material for neural stimulation, we consider how diamond can be used in a range of neural prostheses.


Solid State Quantum Computation with NV Center
Jiangfeng Du

The nitrogen-vacancy defect center (N-V center) is a promising candidate for quantum information processing due to the possibility of coherent manipulation of individual spins in the absence of the cryogenic requirement. Our research mainly focuses on basic theory and experiment fields of quantum computation on solid state spins with NV Center. We concern on several respects such as decoherence regime, dynamical decoupling methods for suppressing decoherence, Initialize the quantum spin state, quantum operation and readout, and seek possible ways for scalable quantum computation.


Quantum engineering using diamond cavity-Quantum ElectroDynamics
Jason Twamley

It is natural to consider the use of ensembles of neutral atoms interacting with light to perform novel quantum operations on flying "photonic qubits". However, using neutral atomic gasses it is difficult to achieve strong coupling and to design robust implementations. Instead we describe how one can couple individual Nitrogen-Vacancy (NV) defects in diamond to high-Q optical cavities to engineer various novel, nonlinear quantum operations. Using an individual NV-defect strongly coupled to a high-Q cavity we describe to protocols: to perform deterministic intra-cavity near-pi phase gates between two individual photons, and how to deterministically synthesise photonic Fock states with a preset target number of photons.


Kilian Singer

Novel ion trap geometries for deterministic high resolution ion implantation are presented which are obtained by highly efficient field calculation methods [1]. I will present our recent progress with a segmented ion trap with mK laser cooled ions which serves as a high resolution deterministic single ion source. It can operate with a huge range of sympathetically cooled ion species, isotopes or ionic molecules. We have deterministically extracted a predetermined number of ions on demand [2], performed transport operations [3] without exciting any motional quanta. These results a first step in the realization of an atomic nano assembler, a novel device capable of placing an exactly defined number of atoms or molecules into solid state substrates with sub nano meter precision in depth and lateral position. Current state of the art production techniques do not offer these possibilities and pose a major production problem for the realization of scaled solid state quantum devices. The project is motivated by the quest for novel tailored solid state quantum materials generated by deterministic high resolution ion implantation. The major goals are the deterministic generation of colour centers or quantum dots, placing them in special geometries in order to exploit the mutual coupling for the realization of macroscopic functional systems and interfacing them to the macroscopic world with the help of electrode structures, single electron transistors and optical micro cavities. Targeted applications range from quantum repeater, correlated triggered multi photon sources, calibrated single photon sources, quantum computation circuits and sensors with unprecedented sensitivity.
[1] K. Singer, U. G. Poschinger, M. Murphy, P. A. Ivanov, F. Ziesel, T. Calarco, F. Schmidt- Kaler, Rev. Mod. Phys. 82, 2609 (2010).
[2] W. Schnitzler, N. M. Linke, R. Fickler, J. Meijer, F. Schmidt-Kaler, and K. Singer, Phys. Rev. Lett. 102, 070501 (2009).
[3] A. Walther, F. Ziesel, T. Ruster, S. T. Dawkins, K. Ott, M. Hettrich, K. Singer, F. Schmidt-Kaler, U. G. Poschinger, Phys. Rev. Lett. 109, 080501 (2012).


Spin noise: Quantum physics and imaging
Joerg Wrachtrup

J. Wrachtrup, F. Reinhardt, H. Fedder, P. Neumann
3rd Institute of Physics, Stuttgart University, Stuttgart, Germany
Noise usually leads to relaxation and decoherence of quantum systems and as such is a rather unwanted phenomenon. Traditionally a wealth of methods has been developed to eliminate or mitigate its impact on the system under study. In diamond central spin systems however there is now an increasingly detailed understanding about the noise characteristics of the spin impurities surrounding the central electron spin. Its quantum versus classical properties has been explored and currently non-classical correlations in the 'bath' magnetic field are used to generate entanglement in multi spin clusters. When using diamond spins as imaging devices under ambient conditions magnetic field noise proves to be an excellent contrast mechanism allowing for efficient visualization of paramagnetic impurities in complex media such as cells.


Towards a large-scale quantum simulator on diamond surface at room temperature
Jianming Cai

We propose a new architecture for a scalable quantum simulator that can operate at room temperature. It consists of strongly-interacting nuclear spins attached to the diamond surface by its direct chemical treatment, or by means of a functionalized graphene sheet. The initialization, control and read-out of this quantum simulator can be accomplished with nitrogen-vacancy centers implanted in diamond. The system can be engineered to simulate a wide variety of interesting strongly-correlated models with long-range dipole-dipole interactions which show very rich quantum phases. I will also report our recent development of concatenated continuous dynamical decoupling schemes (robust against both magnetic noise and microwave fluctuations), which can find applications in controlling and sensing single external nuclear spins outside diamond.


Detecting and polarizing nuclear spins with nuclear double resonance on a single electron spin
Paz London

Measurements of nuclear spin moments are essential to numerous modern fields including medicine, chemistry, metrology, and QIP. But the sensitivity and application of these measurements suffer from poor signal to noise ratio (SNR) which hinders the ability to detect and manipulate nuclear spins at the nanometer scale. Recently, the nitrogen-vacancy color center in diamond has emerged as promising candidate to tackle this outstanding challenge. This is due to its sensitivity to the mesoscopic magnetic environment. As state of the art demonstrations, dynamical decoupling of the NV from its environment can enhance the signal from a single nuclear spin, otherwise not noticeable[1]. In the talk I will present an additional approach to detect weakly coupled nuclear spins in diamond. We utilize an electron-nuclear double resonance technique, known as Hartmann-Hahn double resonance, to transfer populations between the two spin species[2,3]. Most important, we show that by carefully tuning the control protocol, nearby nuclei can not only be sensed and characterized, but can also be polarized directly. Such control of weakly coupled distant spins may play a significant role in quantum sensing, such as reconstructing the spatial structure of single molecules in biological samples. In addition to quantum sensing prospects, this work opens various possibilities for QIP protocols using microwave-dressed qubits and nuclear spins?, and mesoscopic spin baths.
1. Zhao, N. et al., Sensing single remote nuclear spins, Nature Nanotechnology 7, 657 (2012)
2. Hartmann, S.R. & Hahn, E.L. Nuclear double resonance in the rotating frame, Physical Review 128, 5 (1962).
3. Cai, J.M. et al. Diamond based single molecule magnetic resonance spectroscopy, (2012)


Quantum information processing with NV-centers in micro cavities
Joerg Schmiemdayer

One of the grand challenges in building quantum information devices is to find efficient ways to scale up to large and larger systems from small building blocks. Here we present such an approach based on single nitrogen vacancy centers in diamond embedded in an optical cavity. Nodes are connected by photons, the optical transitions act as a transducer between the electron spin and the photon, the nuclear spin as a quantum memory. We show that our modular approach overcomes many of the inherent problems associated with scaling up. Requirements on the single components and their connections for realistic operating conditions up to a large scale device will be discussed in the context of the current status of experimental implementations.


The Nitrogen Vacancy Centre for Quantum Photonics
Jeremy O'Brien

Jake Kennard, J.P. Hadden, Sebastian Knauer, Luca Marseglia, Alberto Politi
Jonathan C. F. Matthews, Brian Patton, John G. Rarity, and Jeremy L. O'Brien

The negatively charged nitrogen vacancy (NV-) centre in diamond is a leading candidate for single photon emission due to its extreme photo stability even at room temperature. The centre further allows manipulation and optical readout of its electron spin2 which has important applications in nanoscale magnetometry and solid state quantum computing4. However the dificulty of photon collection from colour centres in bulk diamond severely reduces their practical use in such applications. By etching 5m diameter hemispherical solid immersion lenses into the surface of bulk diamond using a gallium focussed ion beam (FIB) we measured a factor of 10 improvement in photon collection efficiency from a single NV- centre
However, in order to fully realise the potential of this system as a spin-photon interface it is necessary to couple the NV- centres to cavities which enhance the photonic interaction. Here we present the latest fabrication results of cavity structures with the FIB and discuss current challenge of creating cavities around single NV- centres. Part of this challenge is to accurately determine the position of the target NV centre in order to accurately fabricate a cavity around it. Recently, techniques such as stimulated emission depletion have allowed lateral position determination exceeding the difraction bounds by several orders of magnitude. However axial (depth) determination is still difficult due in part to the high refractive index of diamond, which induces signicant spherical aberrations. We demonstrate how to overcome these problems by using self interference spectroscopy of single NV- defects several microns from a diamond-air interface. Over the relatively wide NV- centre emission spectrum, interference of the direct and re ectedportions show constructive and destructive interference, encoding the distance of the emitter to the surface. Spectral analysis allows axial position determination with nanometre scale accuracy.
Integrated waveguide circuits represent a leading approach to quantum photonics. Recent work has demonstrated implementations of linear optical quantum algorithms10, two particle quantum walks and quantum metrology. Coupling integrated waveguide circuits to spin-photon interfaces represents one approach to creating a hybrid quantum network. Here we demonstrate a single integrated waveguide chip comprising of directional couplers and a recongurable thermal phase controller used to observe both a wave-like interference pattern and a particle-like sub poissionian autocorrelation function of single photons emitted from a Chromium defect in diamond.


Stable Three-Axis Nuclear Spin Gyroscope in Diamond
Paola Cappellaro

Department of Nuclear Science and Engineering and Research Laboratory of Electronics,
Massachusetts Institute of Technology, Cambridge, MA, USA

Gyroscopes find wide application in everyday life, from navigation and inertial sensing, to jerk sensors in hand-held devices and automobiles. Current devices, based on either atomic or solid-state systems, impose a choice between long-time stability and high sensitivity in a miniaturize system. In this talk I will present a novel sensor based on the Nitrogen-Vacancy (NV) center in diamond, which overcomes these limitations by providing a sensitive and stable three-axis gyroscope in a solid-state package.
I will show how we can achieve high sensitivity by exploiting the long coherence time of the N14 nuclear spin associated with the NV center, combined with the e?cient polarization and measurement of its electronic spin. While the gyroscope is based on a simple Ramsey interferometry scheme, coherent control of the quantum sensor improves its coherence time and robustness against long-time drifts. Such a sensor can achieve sensitivity of 0.5mdeg/s/ (Hz mm3)^(1/2) , while o?ering enhanced stability in a small footprint. In addition, I will show how to exploit the four axes of delocalization of the Nitrogen-Vacancy center to measure not only the rate of rotation, but also its direction, thus obtaining a compact three-axis gyroscope.


It's not all in the lattice - the role and reactivity of the diamond surface
Anke Krueger

Institute for Organic Chemistry, Julius-Maximilians University Wuerzburg, Germany
Diamond is an attractive material for a variety of applications due to its chemical inertness, mechanical resistance and biocompatible behaviour. Recently, functionalized nanoscale diamond particles have come into the focus as well. They can be used for composite materials, catalyst immobilization, drug delivery, for the detection of bioactive molecules or for in vitro and in vivo imaging. For most of these applications a suitable surface termination is required.
In this presentation the surface reactivity of nanodiamond and related materials will be discussed in detail. Depending on the production method and surface treatment diamond exhibits an oxidized, hydrogenated or reconstructed (i.e. covered with sp2-carbon) surface that is accessible for a variety of organic reactions.[1] Here, methods for the production of nanoscale diamond from different macroscopic and micrometer-sized diamond sources and their influence on the resulting diamond nanoparticles will be presented. Furthermore, the influence of different chemical and other treatments on the homogeneity of the particle surface will be discussed.
Surface transformations include conventional coupling chemistry using peptide ligation or click reactions as well as techniques such as cycloadditions, arylation of extended pi systems or methods derived from fullerene chemistry.[2,3] Taking all experimental evidence into consideration the diamond nanoparticle can be seen as a conventional organic compound that is neither inert nor different from other carbon-rich hydrocarbons with sp3-hybridized carbon atoms.
[1] A. Krueger, D. Lang, Adv. Funct. Mater. 2012, 22, 890.
[2] G. Jarre, Y. Liang, P. Betz, D. Lang, A. Krueger, Chem. Commun. 2011, 47, 544.
[3] a) T. Meinhardt, D. Lang, H. Dill, A. Krueger, Adv. Funct. Mater. 2011, 21, 494; b) Y. Liang, M. Ozawa, A. Krueger, ACS Nano 2009, 3, 2288; c) P. Betz, A. Krueger, Chem. Phys. Chem. 2012, 13, 2578.


Neil Manson



Applications of Single Photon Emitters based on Defect Centers in Nanodiamonds
Janik Wolters

Nitrogen-vacency (NV) centers [1] in nanodiamonds are versatile single photon emitters. They are optically stable even under ambient conditions at room temperature and large enough (10nm-100nm) to be manipulated by scanning probe techniques [2,3]. We discuss several applications of these 'movable atoms'.
A first example concerns a fundamental quantum optical experiment which demonstrates the non-classicality of light in a most simplified setup using only a single light source and a single detector [4].
In a second experiment we show how an incoherent conversion process can generate single photons of arbitrary wavelength starting from a bright diamond single photon source [5].
Finally, we critically discuss the application of diamond nanocrystals for quantum information processing and show their integration in novel 3D nanophotonic devices.
[1] 'Single defect centres in diamond: A review', F. Jelezko, and J. Wrachtrup, Phys. Stat. Sol. A 203, 3207 (2006); 'Diamond photonics', I. Aharonovich, A. D. Greentree and S. Prawer, Nature Phys. 5, 397 (2011).
[2] 'Assembly of hybrid photonic architectures from nanophotonic constituents', O. Benson, Nature 480, 193 (2011);
[3] 'A scanning probe-based pick-and-place procedure for assembly of integrated quantum optical hybrid devices', A. W. Schell, G. Kewes, T. Hanke, A. Leitenstorfer, R. Bratschitsch, O. Benson, and T. Aichele, Opt. Expr. 19, 7914 (2011).
[4] 'Quantum Nature of Light Measured With a Single Detector', G. A. Steudle, S. Schietinger, D. Hoeckel, S. N. Dorenbos, V. Zwiller, and O. Benson, arXiv:1107.1353.
[5] 'Incoherent photon conversion in selectively infiltrated hollow-core photonic crystal fibers for single photon generation in the near infrared', P. Jiang, T. Schroeder, M. Barth, V. Lesnyak, N. Gaponik, A. Eychmueller, and O. Benson, Opt. Expr. 20, 11536-11547 (2012).


Characterization of color centers in diamond from first principles
Adam Gali

Nitrogen-vacancy center in diamond is the most favorite color center in diamond because of the robust optically detected magnetic resonance (ODMR) signal at room temperature, and its ODMR signal is sufficiently strong for single center detection. While breakthrough in different applications ranging from quantum optics to bioimaging could be achieved by nitrogen-vacancy center there is an on-going need to seek for alternative color centers where either the color of the emitted light or the broadening of the emission spectrum or the magneto-optical properties suit better to the actual application than those of nitrogen-vacancy center. Recently, the combination of group theory and first principles calculations could strongly contribute in understanding the underlying processes of the excitation and other phenomena in nitrogen-vacancy center. We apply this methodology on color centers involving other impurities than nitrogen in diamond that are even much less understood. In this talk, we will briefly show the most important recent results on this topic.


Entanglement of quantum registers in diamond
Tim Hugo Taminiau

The nitrogen vacancy (NV) center in diamond is one of the most promising candidates for solid state quantum information processing. To realize its full potential we require both excellent control over local electron-nuclear spin quantum registers and robust scalable methods to couple multiple NV centers over long distances.
Here I will present our recent progress in realizing these goals. We use two complementary approaches: decoherence protected gates and projective measurements. First, by protecting gates between the electron and nuclear spins from decoherence due to the environment [1], we show that the size of the electron-nuclear quantum register can be extended to include weakly coupled nuclear spins that are embedded in the bath of spins surrounding the NV center [2]. Second, we exploit a non-destructive parity measurement to project two nuclear spins into highly-entangled states and use them to demonstrate a violation of Bells inequality [3]. Because we do not assume fair sampling, this result provides strong proof of a pure entangled state of nuclear spins and of the implementation of three key requirements for quantum information: Initialization, universal control and readout. Finally, we present the entanglement of two distant NV centers through a robust method based on two-photon interference. This combination of an increased local quantum register, measurement-based control, and entanglement over long distances provides a path towards quantum networks based on the NV center.
[1] T. van der Sar et al., Nature 484, 82 (2012)
[2] T. H. Taminiau et al., Phys. Rev. Lett. 109, 137602 (2012)
[3] W. Pfaff et al., Nature Physics (2012), doi:10.1038/nphys2444


Long-lived driven solid-state quantum memory
Nadav Katz

We investigate the performance of inhomogeneously broadened spin ensembles as quantum memories under continuous dynamical decoupling. The role of the continuous driving field is twofold: firstly, it decouples individual spins from magnetic noise; secondly, and more importantly, it suppresses and reshapes the spectral inhomogeneity of spin ensembles. We show that a continuous driving field, which itself may also be inhomogeneous over the ensemble, can considerably enhance the decay of the tails of the inhomogeneous broadening distribution. This fact enables a spin-ensemble-based quantum memory to exploit the effect of cavity protection and achieve a much longer storage time. In particular, for a spin ensemble with a Lorentzian spectral distribution, our calculations demonstrate that continuous dynamical decoupling has the potential to improve its storage time by orders of magnitude for the state-of-the-art experimental parameters.


Selective Imaging and Observation of Fluorescent Diamond introduced in living biological samples
Yohsuke Yoshinari

Single molecule fluorescence measurements of biological samples frequently suffer from luminous autofluorescence background originated from biochemical activity in living samples, and from unstable photo-physical properties of fluorescent labeling materials. They prevent us from conducting observation of the target fluorescent dyes for a long period of time and quantitative analysis. We demonstrate a new protocol to completely exclude obstacle fluorescence in real-time scope-view observation by combination of optically detected magnetic resonance (ODMR) and a promising fluorescent color center, nitrogen-vacancy center (NVC) in diamond fine particles (DFPs)[1]. The extracted background-free fluorescence image was further used to measure a minute change in orientation of DFP introduced into a living Caenorhabditis elegans (C. elegans). The time-course of DFP orientations reveals a rolling motion likely caused by biophysical activity in the intestine. We will also discuss a potential of NVC containing DFP for quantitative analysis of local dynamics and fluctuations.
[1] R. Igarashi, et al., Nano Lett. 2012, 12, 5726 ? 5732.


Electrical control of single photon emission by NV center in diamond
Norikazu Mizuochi

The NV centre in diamond has attracted significant interest as a resource of devices for quantum information processing and communication. Previously, we investigated the quantum entanglement generation in multi-qubit system [1], manipulation of the single spins in multi-qubit system [2], spin coherence properties in isotopically engineered diamond [2-3], and demonstrated strong coupling between a quantum processing unit (a flux-qubit) and a dedicated quantum memory (NV centers) [4]. Here we present the realization of electrically driven single photon source at room temperature by using the NV centre [5].
Single-photon sources that provide non-classical light states on demand have a broad range of application in quantum communication, quantum computing, and metrology. Single-photon emission has been demonstrated using single atoms, ions, molecules, diamond colour centers, and semiconductor quantum dots. Recently, significant progresses have been shown in semiconductor quantum-dots. However, a major obstacle is the requirement of cryogenic temperatures. Here we show the realization of a stable room temperature electrically driven single-photon source based on a single NV centre in a diode structure. Remarkably the generation of electroluminescence follows a fundamentally different kinetics than photoluminescence. This suggests electroluminescence is generated by electron-hole recombination at the defect. Our results prove that functional single defects can be integrated into electronic control structures, which is a crucial step towards elaborated quantum information devices.
[1] P. Neumann, N. Mizuochi, et al., Science, 320, 1326 (2008).
[2] N. Mizuochi, et al., Phys. Rev. B, 80, 041201(R) (2009).
[3] G. Balasubramanian, et al., Nature materials, 8, 383 (2009).
[4] X. Zhu, et al., Nature, 478, 221 (2011).
[5] N. Mizuochi, T. Makino, H. Kato, D. Takeuchi, M. Ogura, H. Okushi, M. Nothaft, P. Neumann, A. Gali, F. Jelezko, J. Wrachtrup, S. Yamasaki, Nature Photonics, 6, 299-303 (2012).

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