Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P52: NV Centers and Spin EnsemblesFocus
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Sponsoring Units: GQI Chair: Trond Andersen, Harvard University Room: 399 |
Wednesday, March 15, 2017 2:30PM - 3:06PM |
P52.00001: Controlling geometric phase optically in a single spin in diamond Invited Speaker: Christopher G. Yale Geometric phase, or Berry phase, is an intriguing quantum mechanical phenomenon that arises from the cyclic evolution of a quantum state. Unlike dynamical phases, which rely on the time and energetics of the interaction, the geometric phase is determined solely by the geometry of the path travelled in parameter space. As such, it is robust to certain types of noise that preserve the area enclosed by the path, and shows promise for the development of fault-tolerant logic gates. Here, we demonstrate the optical control of geometric phase within a solid-state spin qubit, the nitrogen-vacancy center in diamond\footnote{C. G. Yale*, F. J. Heremans*, B. B. Zhou,* A. Auer, G. Burkard, D. D. Awschalom, \textit{Nature Photonics}, \textbf{10}, 184 (2016).}. Using stimulated Raman adiabatic passage (STIRAP), we evolve a coherent dark state along `tangerine slice' trajectories on the Bloch sphere and probe these paths through time-resolved state tomography. We then measure the accumulated geometric phase through phase reference to a third ground spin state. In addition, we examine the limits of this control due to adiabatic breakdown as well as the longer timescale effect of far-detuned optical fields. Finally, we intentionally introduce noise into the experimental control parameters, and measure the distributions of the resulting phases to probe the resilience of the phase to differing types of noise. We also examine this robustness as a function of traversal time as well as the noise amplitude. Through these studies, we demonstrate that geometric phase is a promising route toward fault-tolerant quantum information processing. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:42PM |
P52.00002: Controlling spin relaxation with a cavity Invited Speaker: Audrey Bienfait Spontaneous emission of radiation is one of the fundamental relaxation mechanisms for a quantum system. For spins, however, it is negligible compared to non-radiative relaxation-processes due to their weak coupling to the electromagnetic field. In 1946, Purcell realized [1] that spontaneous emission is strongly enhanced when the quantum system is placed in a resonant cavity - an effect now used to control the lifetime of systems with an electrical dipole [2]. Here, by coupling donor spins in silicon to a high quality factor superconducting microwave cavity of small mode volume, we reach the regime where spontaneous emission constitutes the dominant spin relaxation channel [3]. The relaxation rate is shown to depend on the cavity quality factor, on the spin-cavity coupling and on the spin-cavity frequency detuning, proving that the quantum fluctuations of the cavity field are indeed responsible for the spin relaxation. Moreover, the spin relaxation rate is increased by three orders of magnitude when the spins are tuned to the cavity resonance, showing it can be engineered and controlled on-demand. Our results provide a novel way to initialize any spin into its ground state, with applications in magnetic resonance and quantum information processing. They also show for the first time an alteration of spin dynamics by quantum fluctuations; as such they represent a step towards the coherent magnetic coupling of a spin to microwave photons. [1] E. M. Purcell, Phys. Rev. 1946, 69, 681. [2] P. Goy et al., PRL. 50, 1983. [3] A. Bienfait et al., Nature, 2016, 531(7592):74--77. [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 3:54PM |
P52.00003: Exploring the potential of hybrid two-qubit solid-state nodes for quantum networks Peter Humphreys, Norbert Kalb, Andreas Reiserer, Jacob Bakermans, Sten Kamerling, Naomi Nickerson, Earl Campbell, Matthew Markham, Daniel Twitchen, Simon Benjamin, Tim Taminiau, Ronald Hanson We demonstrate an elementary quantum network consisting of a pair of hybrid two-qubit quantum nodes. These nodes combine nitrogen-vacancy defects in diamond as spin-photon interfaces for entanglement generation, state manipulation and measurement along with coupled carbon nuclear-spin quantum memories. We utilise this network to investigate different quantum information protocols for establishing links over few-qubit quantum networks in the near term. We find that the ability to coherently store quantum information during attempts to generate network links may increase the rate at which entanglement can be generated. [Preview Abstract] |
Wednesday, March 15, 2017 3:54PM - 4:06PM |
P52.00004: A coherent electronic spin cluster in diamond Helena Knowles, Dhiren Kara, Mete Atature An optically active spin in solid state coherently coupled to a dark spin cluster has been at the heart of many exciting proposals in recent years, from implementations of spin chains to environment-assisted schemes that enhance the performance of a single-spin magnetic field sensor. Dark electron spins, with magnetic moments compared with nuclear spins, are particularly interesting as they enable fast dipolar coupling and exhibit strong interactions with target fields. Realised in a nanodiamond such a cluster could transform the performance of a unique sensing device that enables temperature and magnetic field measurements inside living cells. Experimental progress on this front has been promising, albeit hindered by the limited ability to polarise, control and readout dark spins. We use a nitrogen-vacancy centre (NV) in a nanodiamond to polarize and readout a cluster formed of three dark nitrogen (N) spins. We also demonstrate an interferometric method to probe each N spin individually and extract their coupling strengths and degrees of polarisation. This enables us to locate the spins to within a few lattice sites. Moreover, we report the first observation of coherent spin exchange between NV and N electron spins, essential for any exploitation of such multi-spin systems. [Preview Abstract] |
Wednesday, March 15, 2017 4:06PM - 4:18PM |
P52.00005: Double quantum spin relaxation limits to coherence of near-surface diamond nitrogen vacancy centers Amila Ariyaratne, Bryan Myers, Ania Jayich The diamond nitrogen vacancy (NV) center is an emerging quantum technology, with applications in atomic-scale magnetic resonance imaging and quantum information. These applications require the NVs to be located within nanometers of the diamond surface; however, near-surface NVs undergo significantly higher decoherence than bulk NVs. For a two-level qubit, the coherence time T2 is limited by the spin relaxation time T1: T2$\le $2T1. However, for shallow NVs, T2s only up to 0.1T1 have been reported. We identify an additional decoherence channel that must be accounted for to explain these prior results. The NV ground state is a 3-level system and hence a proper definition of T1 must consider all relaxation channels in the system, rather than just those between two qubit levels. We show that relaxation between the NV ($+$1,-1) levels lowers the effective T1 of the (0, $+$1) qubit, making the upper limit of T2$\le $2T1 attainable. Further, we utilize all relaxation channels of the qutrit to spectroscopically probe surface-induced noise, discriminating between electric and magnetic field noise. Identifying origins of surface-induced noise has important implications across many qubit platforms. [Preview Abstract] |
Wednesday, March 15, 2017 4:18PM - 4:30PM |
P52.00006: Tunneling-driven nanoscale clustering of trapped charge in diamond under ambient conditions. S. Dhomkar, P.R. Zangara, M.W. Doherty, N.B. Manson, A. Alkauskas, J. Henshaw, C.A. Meriles Negatively charged nitrogen-vacancy (NV) centers in diamond are emerging as versatile resources for applications in quantum information processing and high-resolution metrology. In the case of samples with relatively high defect concentration, it is of great interest to understand the physical processes that affect charge and spin dynamics of ensembles of NV centers. Here, we utilize two color confocal microscopy to investigate electron tunneling processes between NV and surrounding nitrogen centers in type 1b diamond. We present the results of various protocols which involve sequential illumination and/or scanning with green (532 nm) and/or red (633 nm) laser beams at various intensities. To explain the experimental data, we develop a model that incorporates the effects of tunneling processes during laser illumination and in the dark. We demonstrate that although tunneling effects modify the charge distribution on a nanometer scale, their consequences can be observed macroscopically, giving rise to unique patterns in the fluorescence images. [Preview Abstract] |
Wednesday, March 15, 2017 4:30PM - 4:42PM |
P52.00007: Optimizing structure in nanodiamonds using in-situ strain-sensitive Bragg coherent diffraction imaging. Stephan Hruszkewycz, Wonsuk Cha, Andrew Ulvestad, Paul Fuoss, F. Joseph Heremans, Ross Harder, Paolo Andrich, Christopher Anderson, David Awschalom The nitrogen-vacancy center in diamond has attracted considerable attention for nanoscale sensing due to unique optical and spin properties. Many of these applications require diamond nanoparticles which contain large amounts of residual strain due to the detonation or milling process used in their fabrication. Here, we present experimental, in-situ observations of changes in morphology and internal strain state of commercial nanodiamonds during high-temperature annealing using Bragg coherent diffraction imaging to reconstruct a strain-sensitive 3D image of individual sub-micron-sized crystals [1]. We find minimal structural changes to the nanodiamonds at temperatures less than 650 C, and that at higher temperatures up to 750 C, the diamond-structured volume fraction of nanocrystals tend to shrink. The degree of internal lattice distortions within nanodiamond particles also decreases during the anneal. Our findings potentially enable the design of efficient processing of commercial nanodiamonds into viable materials suitable for device design. [1] I. Robinson et al., Nat. Mater. 8, 291 (2009). [Preview Abstract] |
Wednesday, March 15, 2017 4:42PM - 4:54PM |
P52.00008: Towards a large scale simulation of many body ground states by measurement induced back action Johannes N. Greiner, D. D. Bhaktavatsala Rao, J\"org Wrachtrup Singlet pairing is a well-studied physical mechanism in strongly correlated systems. Quantum particles paired in singlets share maximal entanglement and their total vanishing spin renders them robust to external noise. Inducing such pairing in any random spin ensemble has many potential applications in the field of quantum limited sensing$[1,2]$ and quantum information processing$[3]$. We show here how singlet pairing can be generated in an unpolarized nuclear spin ensemble which is dipolar coupled to a Nitrogen Vacancy (NV) center in diamond. Alongside the singlet formation, the long life times of these spins constitute a potential test bed for simulating quantum correlations of dimer compounds crystallizing into singlet pairs.$[4]$\\ $[1]$ Wrachtrup, J. & Finkler, A. Single spin magnetic resonance. Journal of Magnetic Resonance 269, 225–236 (2016).$[2]$ Zaiser, S. et al. Enhancing quantum sensing sensitivity by a quantum memory. Nature Communications 7, 12279 (2016).$[3]$ Waldherr, G. et al. Quantum error correction in a solid-state hybrid spin register. Nature 506, 204–207 (2014).\\ $[4]$ Greiner, J. N., Rao, D. D. B. & Wrachtrup, J. Purification of an unpolarized spin ensemble into entangled singlet pairs. arXiv:1610.08886 [quant-ph] (2016). [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:06PM |
P52.00009: Magnetic resonance with squeezed microwaves Patrice Bertet, Audrey Bienfait, Philippe Campagne-Ibarcq, Alexander Holm-Kiilerich, Xin Zhou, Sebastian Probst, Jarryd Pla, Thomas Schenkel, Denis Vion, Daniel Esteve, John Morton, Klaus Moelmer Although vacuum fluctuations appear to represent a fundamental limit to the sensitivity of electromagnetic field measurements, it is possible to overcome them by using so-called squeezed states. In such states, the noise in one field quadrature is reduced below the vacuum level while the other quadrature becomes correspondingly more noisy, as required by Heisenberg's uncertainty principle. At microwave frequencies, cryogenic temperatures are required for the electromagnetic field to be in its vacuum state and reach the quantum limit of sensitivity. Here we report the use of squeezed microwave fields to enhance the sensitivity of magnetic resonance spectroscopy of an ensemble of electronic spins beyond the standard quantum limit. Our scheme consists in sending a squeezed vacuum state to the input of a cavity containing the spins while they are emitting an echo, with the phase of the squeezed quadrature aligned with the phase of the echo. We demonstrate a total noise reduction of 1.2dB at the spectrometer output due to the squeezing. These results provide a motivation to examine the application of the full arsenal of quantum metrology to magnetic resonance detection. [Preview Abstract] |
Wednesday, March 15, 2017 5:06PM - 5:18PM |
P52.00010: Optical magnetometry of superconductors using nitrogen - vacancy centers in diamond films K.R. Joshi, N. M. NUSRAN, KYUIL CHO, M. A. TANATAR, S. L. BUD'KO, P. C. CANFIELD, R. PROZOROV Spin-dependent fluorescence of nitrogen - vacancy (NV) centers in diamond has emerged as a promising tool for non-invasive sensitive magnetometry with excellent sensitivity. In this work, we employ ensembles of NV centers implanted at the surface of a diamond film to study magnetic induction as the function of position, magnetic field and temperature in superconductors after different cooling/heating protocols and magnetic history. One of the motivations of our work is to study the structure of the Meissner expulsion upon field cooling, where we observe significant deviations from the simple, textbook example. Another is to determine the lower superconducting critical field, H$_c$$_1$. Conventional Nb is compared with borocarbides (LuNi$_2$B$_2$C) and iron-pnictides (CaKFe$_4$As$_4$). [Preview Abstract] |
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