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ABSTRACT: The study of hyperfine interactions in optically excited fullerenes has recently acquired importance within the context of nuclear spin entanglement for quantum-information technology. We here report a first-principles pseudopotential study of the hyperfine coupling parameters of optically excited fullerene derivatives as well as small organic radicals. The calculations are performed within the gauge-invariant projector-augmented wave method [C. Pickard and F. Mauri, Phys. Rev. B 63, 245101 (2001)]. In order to establish the accuracy of this methodology we compare our results with all-electron calculations and with experiment. In the case of fullerene derivatives we study the hyperfine coupling in the spin-triplet exciton state and compare our calculations with recent electron paramagnetic resonance measurements [M. Schaffry et al., Phys. Rev. Lett. 104, 200501 (2010)]. We discuss our results in light of a recent proposal for entangling remote nuclear spins in photoexcited chromophores.
Phys. Rev. B. 01/2012; 85(11):115430.
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ABSTRACT: Measurement devices could benefit from entangled correlations to yield a measurement sensitivity approaching the physical Heisenberg limit. Building upon previous magnetometric work using pseudoentangled spin states in solution-state NMR, we present two conceptual advancements to better prepare and interpret the pseudoentanglement resource. We apply these to a 13-spin cat state to measure the local magnetic field with a 12.2 sensitivity increase over an equivalent number of isolated spins.
Phys Rev A. 82(2):022330.
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ABSTRACT: Endohedral fullerenes encapsulating a spin-active atom or ion within a carbon cage offer a route to self-assembled arrays such as spin chains. In the case of metallofullerenes the charge transfer between the atom and the fullerene cage has been thought to limit the electron spin phase coherence time (T-2) to the order of a few microseconds. We study electron spin relaxation in several species of metallofullerene as a function of temperature and solvent environment, yielding a maximum T-2 in deuterated o-terphenyl greater than 200 mu s for Y, Sc, and La@C-82. The mechanisms governing relaxation (T-1, T-2) arise from metal-cage vibrational modes, spin-orbit coupling and the nuclear spin environment. The T-2 times are over 2 orders of magnitude longer than previously reported and consequently make metallofullerenes of interest in areas such as spin labeling, spin-tronics, and quantum computing.
Phys. Rev. B. 82(3):033410.
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ABSTRACT: A photo-switchable fullerene dimer and its analogous nitrogen endohedral species have been synthesized and characterized. Irradiation by ultraviolet and visible light has been used to switch between the trans and cis isomers of both the C-60- and N@C-60- based dimers. Environmental perturbations experienced by the encapsulated nitrogen atom upon switching between the two isomers in degassed carbon disulfide has been determined by pulse electron paramagnetic resonance. Both T-1 and T-2 electron spin relaxation times of the two isomers of the endohedral fullerene containing dimer revealed a biexponential decay. Although the zero field splitting parameter D-eff for both isomers in solution was similar, around 13.0 MHz, the molecular rotation correlation time tau(c) of the trans and cis isomers was calculated to be 37.2 +/- 1.6 and 34.8 +/- 2.7 ps, respectively.
J Phys Chem C. 112(8):2802-2804.
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ABSTRACT: Using the graph-state approach to quantum computation, one can avoid the need for complex array nanostructures in which quantum bits (qubits) interact directly. Instead one can employ simple 'atom-like' nanostructures, coupled over macroscopic distances via optical emissions. Here, we describe a robust coupling procedure, which we call brokering, that is especially well suited to nanostructures bearing both nuclear and electron spins. We describe how this approach can be implemented with N-V centre materials.
New J. Phys. 8:141.
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ABSTRACT: The electron paramagnetic resonance (EPR) of spin-active metallofullerenes (MFs) La@C-82 and Sc@C-82 diluted in solid-state C-60 crystalline matrices with molar concentrations varying from 0.4% to 100% are investigated. For dilute concentrations, the hyperfine structure of the MFs is resolved, and as the concentration increases exchange narrowing is observed leading to a single peak in the EPR. Sc@C-82 MFs are inserted into single-walled carbon nanotubes to form peapods with concentrations of 10% and 0.1%, diluted with C-60. For the case of peapods containing 10% Sc@C-82 a strong narrow peak is observed in X-band CW EPR, but not pulsed measurements. Peapods containing Ce@C-82 MFs are prepared and these also show similar CW EPR to the Sc@C-82, indicating the peak arises from charge transfer with the SWNT.
Phys. Rev. B. 81(7):075424.
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J. Chem. Phys. 124(1):014508.
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Eisuke Abe,
Alexei M Tyryshkin,
Shinichi Tojo, John J L Morton,
Wayne M Witzel,
Akira Fujimoto,
Joel W Ager,
Eugene E Haller,
Junichi Isoya,
Stephen A Lyon,
Mike L W Thewalt,
Kohei M Itoh
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ABSTRACT: We report electron paramagnetic resonance (EPR) experiments of phosphorus donors in isotopically controlled silicon single crystals. By varying the concentration of the Si-29 isotope, f, from 0.075% to 99.2%, we systematically study the effect of the environmental nuclear spins on the donor-electron spin. We find excellent agreement between experiment and theory for decoherence times due to nuclear-induced spectral diffusion, clarifying that the nuclear-induced decoherence is dominant in the range of f studied. We also observe that the EPR linewidth shows a transition from the square-root dependence to the linear dependence on f, in agreement with theoretical predictions.
Phys. Rev. B. 82(12):121201.
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Nat Phys. 2(1):40-43.
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ABSTRACT: The field of quantum metrology promisesmeasurement devices that are fundamentally superior to conventional technologies. Specifically, when quantum entanglement is harnessed, the precision achieved is supposed to scale more favorably with the resources employed, such as system size and time required. Here, we consider measurement of magnetic-field strength using an ensemble of spin-active molecules. We identify a third essential resource: the change in ensemble polarization (entropy increase) during the metrology experiment. We find that performance depends crucially on the form of decoherence present; for a plausible dephasing model, we describe a quantum strategy, which can indeed beat the standard strategy.
Phys Rev A. 82(4):042114.
