Nir Bar-Gill
 
Optimized dynamical decoupling and potential for plasmonically enhanced optical readout



I will present our recent results on extending the coherence time of arbitrary quantum states of NVs using optimized dynamical decoupling. We identify concatenated XY sequences as advantageous for preserving arbitrary states, and achieve coherence times of ms at a temperature of 77K. We then demonstrate improved magnetic field sensitivity using these sequences. In addition, I will describe our investigations into potential enhancements of the optical readout signal-to-noise ratio, using plasmonic nanostructures coupled to the NV center. We find realistic parameters for significantly enhanced SNR, which are now being tested with relevant nanofabricated devices.

 

Joerg Wrachtrup
 
Spin quantum memories and their use in sensing and quantum communication.

Memories have a central role in various quantum techniques. Scalable communication and quantum repeater schemes for example require memories to store single photon states and e.g. robustness against multiple readout as well as local processing capabilities for e.g. error correction of entanglement purification. Less prominent is the use in sensing application. Here, robust memories are central for e.g. high resolution NMR. The talk shall discuss the physics of nuclear spin memory qubits under relevant operation conditions, e.g. multiple optical excitations or electron spin flips and demonstrate applications.

 

Prawer
 
Scalable fabrication of high quality, ultrathin, single crystal diamond membranes.

We demonstrate a new method for the fabrication of high quality, large size (?4 4 mm) and low surface roughness, low strain, ultra-thin SCD membranes which can be fabricated without deformations such as breakage, bowing or bending. These membranes are easy to handle making them particularly suitable for fabrication of optical and mechanical quantum devices. On such suspended diamond membranes we demonstrate a suite of photonic components as building blocks for nanophotonic circuits. Monolithic grating couplers are used to efficiently couple light between photonic circuits and optical fibers. In waveguide coupled optical ring resonators we find loaded quality factors up to 66 000 at a wavelength of 1550 nm which illustrate that low propagation loss is maintained. Our approach holds promise for the scalable implementation of future diamond quantum photonic technologies and all-diamond photonic metrology tools.

 

Ren-Bao Liu
 
Wavefuntion fingerprint quantum sensing for atomic-scale MRI

Transition frequencies (i.e., frequency fingerprints) of nuclear spins are the key to nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). The frequency gradients set the fundamental limit on the resolution of MRI. Recently nanoscale NMR and MRI have been enabled by dynamical decoupling (DD) based quantum sensing. The current DD-based quantum sensing, however, cannot resolve different nuclear spins that have the same noise frequency or identify different types of correlations in nuclear spin clusters. Thus the quantum sensing based MRI is still limited by the frequency gradients due to the magnetic field from a nano-tip or the hyperfine interaction with a sensor electron spin (such as the NV centers in diamond). Here we show that this limitation can be overcome by using ?wavefunction fingerprints? of target nuclear spins, which is much more sensitive than the "frequency fingerprints" to weak hyperfine interaction between the targets and a sensor under resonant DD control. We demonstrate a scheme of angstrom-resolution MRI that is capable of counting and individually localising single nuclear spins of the same frequency and characterizing correlations in nuclear spin clusters. A nitrogen-vacancy centre spin sensor near a diamond surface, provided that the coherence time is improved by surface-engineering in the near future, may be employed to determine, with angstrom-resolution, the positions and conformation of single molecules that are isotope-labelled. Furthermore, the correlations between nuclear spins can be fully characterized by two-dimensional quantum sensing based on the wavefunction fingerprints. The schemes in this work, using the quantum nature of target nuclear spins, offer an approach to breaking the resolution limit set by "frequency gradients" in conventional MRI and to reaching the angstrom-scale resolution. This work was supported by Hong Kong RGC/CRF CUHK4/CRF/12G & CUHK VC?s One-off Discretionary Fund.
References:
1. W. L. Ma & R. B. Liu, ?Scheme of angstrom-resolution magnetic resonance imaging of single molecules via dynamical decoupling enhanced quantum sensing?, arXiv:1510.04081.
2. W. L. Ma & R. B. Liu, ?Multi-dimensional quantum sensing?, arXiv:1512.03548.

 

Adam Gali
 
Dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide

Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point defects in semiconductors is a key resource for both initializing nuclear quantum memories and producing nuclear hyperpolarization. DNP is therefore an important process in the field of quantum-information processing, sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based spintronics. DNP based on optical pumping of point defects has been demonstrated by using the electron spin of nitrogen-vacancy (NV) center in diamond, and more recently, by using divacancy and related defect spins in hexagonal silicon carbide (SiC). Here, we describe a general model for these optical DNP processes that allows the effects of many microscopic processes to be integrated. Applying this theory, we gain a deeper insight into dynamic nuclear spin polarization and the physics of diamond and SiC defects. We discuss how the new insights from our analysis may harness DNP in different applications.

 

Jean-Philippe Tetienne
 
T1-based spectroscopy and imaging using NV centres in diamond

Most magnetic sensing techniques based on NV centres in diamond to date have exploited the decoherence (T2) of the NV electronic spin and its sensitivity to the environment. In the first part of the talk, I will present our recent progress towards the use of spin relaxation (T1) to perform sensing, spectroscopy and imaging, using both NV ensembles and single NVs. In particular, we demonstrate a T1-based technique for performing nanoscale magnetic resonance spectroscopy of spin species. The intrinsic broadband nature of the technique allows us to address both electronic and nuclear spin transitions. The technique is demonstrated on P1 centres within the diamond [1]. Extension to spectroscopy of nuclear spins external to the diamond is discussed. In the second part of the talk, I will present new approaches to NV-based imaging. First, using a scanning nano-spin ensemble microscope, we characterise and image clusters of magnetic nanoparticles via T1 sensing and ODMR spectroscopy [2]. We also perform thermal imaging of photo-heated gold nanoparticles in a liquid environment. Finally, using a wide-field diamond microscope, we demonstrate magnetic imaging of solid-state samples with sub-micron resolution [3].
References
[1] L. T. Hall, P. Kehayias, D. A. Simpson, A. Jarmola, A. Stacey, D. Budker, and L. Hollenberg, ?Detection of nanoscale electron spin resonance spectra demonstrated using nitrogen-vacancy centre probes in diamond?, Nat. Commun. 7, 10211 (2016).
[2] J.-P. Tetienne, A. Lombard, D. A. Simpson, C. Ritchie, J. Lu, P. Mulvaney, and L. Hollenberg, ?A scanning nano-spin ensemble microscope for nanoscale magnetic and thermal imaging?, Nano Letters 16, 326 (2016).
[3] D. A. Simpson, J.-P. Tetienne, J. McCoey, K. Ganesan, L. T. Hall, S. Petrou, R. Scholten, and L. Hollenberg, ?Magneto-optical imaging of thin magnetic films using spins in diamond?, Scientific Reports 6, 22797 (2016).

 

Fedor Jelezko
 
Light-matter interface based on single colour centers

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Martin Plenio
 
Manipulating nuclear spins for hyperpolarisation, sensing and quantum computation

In this talk I will discuss our recent work on hyperpolarisation of nuclear spins inside and outside of diamond structures. Furthermore, I will discuss asymmetric AXY decoupling sequences and their application in sensing and computation.

 

Milos Nesladek
 
Beyond Optical Detection of Spins in Diamond

The aim of the talk is to report on the photoelectrical detection schemes of NV-spin resonances. Spin properties of Nitrogen-Vacancy centres (NV-) are being exploited mainly using Optically Detected Magnetic Resonance (ODMR) leading to bemchamrk applications in the field of solid?state quantum information processing, nanoscale sensing and single spin imaging, photonics and opto-mechanics. Recently we have employed photoelectric detection method for the detection of NV- magnetic resonances (PDMR), based on the direct electric detection of electrons promoted to the conduction band of diamond by ionization of NV . This technique could make easier the integration of NV- centres to electronic chips and allow independent readout of NV- centres situated closer than the diffraction limit. It might also lead to high detection efficiency since every photon has the ability to generate more than one electron?hole pair (photoelectric gain mechanism). In this talk we discuss the current state-of?the-art of photoelectric detection and benchmark its potential with optical detection techniques for quantum sensing and technology applications.

 

Viktor Perunicic
 
Roadmap to full 3D molecular imaging using single spin probes

We present a general methodology for magnetic resonance imaging (MRI) of individual molecules using an electron-spin probe, such as the NV centre in diamond or phosphorus donor in silicon. Compared to conventional MRI, the role of the classical magnetic gradient is assumed by the probe?s quantum dipole field, while the probe?s spin state serves as the MRI sensor. We carefully integrate solid-state NMR decoupling sequences into the quantum gradient field context to develop a protocol for selective control of nuclear spins situated in a particular gradient slice. Structural information of a molecular target in proximity to the probe is extracted by encoding the projection of the nuclear density onto gradient slices on the quantum state of the probe. The signal is transformed into Cartesian-space, producing a 3D image of the molecule?s nuclear density. To test the protocol we simulate its application to the 1kD rapamycin molecule (C51H79NO13), and show that highly dense hydrogen(1) and carbon(13) molecular structures can be imaged in full at sub-Angstrom level using currently accessible spin probe technology. We further outline a pathway specifically tailored to applications using the NV centre in diamond as a quantum probe.

 

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