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. 2016 Jul 18:7:12232.
doi: 10.1038/ncomms12232.

Room temperature manipulation of long lifetime spins in metallic-like carbon nanospheres

Bálint Náfrádi  1 , Mohammad Choucair  2 , Klaus-Peter Dinse  3 , László Forró  1
Affiliations

Room temperature manipulation of long lifetime spins in metallic-like carbon nanospheres

Bálint Náfrádi et al. Nat Commun. .

Abstract

The time-window for processing electron spin information (spintronics) in solid-state quantum electronic devices is determined by the spin-lattice and spin-spin relaxation times of electrons. Minimizing the effects of spin-orbit coupling and the local magnetic contributions of neighbouring atoms on spin-lattice and spin-spin relaxation times at room temperature remain substantial challenges to practical spintronics. Here we report conduction electron spin-lattice and spin-spin relaxation times of 175 ns at 300 K in 37±7 nm carbon spheres, which is remarkably long for any conducting solid-state material of comparable size. Following the observation of spin polarization by electron spin resonance, we control the quantum state of the electron spin by applying short bursts of an oscillating magnetic field and observe coherent oscillations of the spin state. These results demonstrate the feasibility of operating electron spins in conducting carbon nanospheres as quantum bits at room temperature.

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Figures

Figure 1
Figure 1. Comparison of itinerant and localized electron-based qubits.
(a) Itinerant spin system of carbon nanospheres (CNS), and localized spin systems of (b) N@C60, (c) N-V nanodiamond and (d) Si:P. The spin information in the CNS is encoded by a delocalized electron spin that spreads over the entire 35-nm diameter (shaded area), making the system more robust against external magnetic field fluctuations and hyperfine interactions enforced by nuclear spins. Consequently, high qubit density can be achieved without enhanced decoherence. (e) The sphere diameters comparing the required volume for different types of qubits with scale bar, 100 nm.
Figure 2
Figure 2. Carbon nanosphere structure and size.
(a) TEM image of carbon nanospheres on a carbon support. (b) High-resolution TEM of discrete carbon nanospheres. (c–e) TEM three-dimensional tomography reconstruction of the carbon nanospheres. The particles are spherical and also distort slightly to an ellipsoidal shape, with coalescence. Spheres appear transparent due to the high image contrast with the sputtered gold substrate, small sphere size and extremely thin sphere layers. (f–h) In situ variable temperature high-resolution TEM images of the non-crystalline carbon nanosphere structure within regions of various spheres. The spheres remain non-crystalline upon heating to 583 K. A high contrast is applied to the images to allow the graphite planes to be distinguished with a black outline. Arrows indicate direction towards the centre of the sphere. Scale bars, 200 nm (a), 5 nm (b), 10 nm (c), were omitted for clarity (d), 5 nm (e), 1 nm (f–h).
Figure 3
Figure 3. Sample processing of carbon nanospheres.
(a) A 300 mg of carbon nanospheres collected as a solid powder in a sample tube and 10 mg on a glass slide, stable in air. (b) Carbon nanospheres directly deposited during synthesis onto a 2.5 × 2.5 cm quartz slide. (c) A small amount of carbon nanospheres dispersed in 2 ml of ethanol by sonication. (d) SEM image of an individual ∼50 nm carbon nanosphere physically positioned on a Si substrate using a 200-nm tungsten manipulator tip. Scale bar, 200 nm (d).
Figure 4
Figure 4. Characterization of the spin system of the carbon spheres by ESR.
(a)Temperature dependence of T1 and T2 at νZ=9.5 GHz. (b)Temperature dependence of the spin susceptibility, χspin, measured by ESR at νZ=9.4 GHz with an overlaying Curie−Weiss line, characteristic to small paramagnetic particles. (c) The ESR linewidth is plotted as a function of the Zeeman energy, EZ=hνZ measured by a multi-frequency ESR at 300 K. The linear fit (straight solid line) using equation (1), with T1=T2=175 ns gives δ=1 meV. (d) The temperature-independent g-factor shift Δg relative to the free electron g-value, in good agreement with a material exhibiting very weak spin−orbit coupling. Error bars represent the confidence interval of least square fits to the spectra.
Figure 5
Figure 5. Spin control over electron qubits confined to carbon nanospheres at 300 K.
(a) Rabi oscillations of the electron qubits at 300 K and B0=337 mT for different microwave powers. (b) Fourier transform of the Rabi oscillations, with the signal shifted vertically for clarity. (c) Rabi frequency is proportional with the square root of the power. The value 25 MHz observed for the maximum power is consistent with the previously determined maximum B1 field in the dielectric cavity of 0.9 mT, indicating the presence of an effective spin S=1/2.
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