29 research outputs found
Will spin-relaxation times in molecular magnets permit quantum information processing?
Using X-band pulsed electron spin resonance, we report the intrinsic
spin-lattice () and phase coherence () relaxation times in molecular
nanomagnets for the first time. In Cr heterometallic wheels, with = Ni
and Mn, phase coherence relaxation is dominated by the coupling of the electron
spin to protons within the molecule. In deuterated samples reaches 3
s at low temperatures, which is several orders of magnitude longer than
the duration of spin manipulations, satisfying a prerequisite for the
deployment of molecular nanomagnets in quantum information applications.Comment: 4 pages, 3 figures, in press at Physical Review Letter
Measuring errors in single qubit rotations by pulsed electron paramagnetic resonance
The ability to measure and reduce systematic errors in single-qubit logic
gates is crucial when evaluating quantum computing implementations. We describe
pulsed electron paramagnetic resonance (EPR) sequences that can be used to
measure precisely even small systematic errors in rotations of
electron-spin-based qubits. Using these sequences we obtain values for errors
in rotation angle and axis for single-qubit rotations using a commercial EPR
spectrometer. We conclude that errors in qubit operations by pulsed EPR are not
limiting factors in the implementation of electron-spin based quantum
computers
Electron spin relaxation of N@C60 in CS2
We examine the temperature dependence of the relaxation times of the
molecules N@C60 and N@C70 (which comprise atomic nitrogen trapped within a
carbon cage) in liquid CS2 solution. The results are inconsistent with the
fluctuating zero field splitting (ZFS) mechanism, which is commonly invoked to
explain electron spin relaxation for S > 1/2 spins in liquid solution, and is
the mechanism postulated in the literature for these systems. Instead, we find
a clear Arrhenius temperature dependence for N@C60, indicating the spin
relaxation is driven primarily by an Orbach process. For the asymmetric N@C70
molecule, which has a permanent non-zero ZFS, we resolve an additional
relaxation mechanism caused by the rapid reorientation of its ZFS. We also
report the longest coherence time (T2) ever observed for a molecular electron
spin, being 0.25 ms at 170K.Comment: 6 pages, 6 figures V2: Updated to published versio
Electrochemical Conversion of the Lignin Model Veratryl Alcohol to Veratryl Aldehyde Using Manganese(III)-Schiff Base Homogeneous Catalysts
Lignin and other colored structures need to be bleached after the Kraft process in the pulp industry. Development of environmentally-safe bleaching catalysts or electrocatalysts constitutes an attractive strategy for selective removal of lignin. Seven manganese(III)-complexes with Schiff base ligands 1â7 were synthetized and characterized by different analytical and spectroscopic techniques. The tetragonally elongated octahedral geometry for the manganese coordination sphere and the global ”-aquo dimeric structure were revealed by X-ray diffraction (XRD) studies for 1, Mn2L12(H2O)2(N(CN)2)2 (N(CN)2 = dicyanamide). Complexes 1â4 behave as more efficient peroxidase mimics as compared to 5â7. Electrochemical oxidation of the lignin model veratrylalcohol (VA) to veratrylaldehyde (VAH) is efficiently catalyzed by a type of dimanganese(III) complexes in a chlorine-free medium. The electrocatalytic reaction proceeds through the oxidation of chloride into hypochlorite at alkaline pH along with the formation of hydrogen from water as a subproductThis research was funded by Xunta de Galicia (GRC GI-1584-ED431C2018/13 Suprabioin Research Group, and MetalBIO Network ED431D 2017/01)S
Environmental effects on electron spin relaxation in N@C60
We examine environmental effects of surrounding nuclear spins on the electron
spin relaxation of the N@C60 molecule (which consists of a nitrogen atom at the
centre of a fullerene cage). Using dilute solutions of N@C60 in regular and
deuterated toluene, we observe and model the effect of translational diffusion
of nuclear spins of the solvent molecules on the N@C60 electron spin relaxation
times. We also study spin relaxation in frozen solutions of N@C60 in CS2, to
which small quantities of a glassing agent, S2Cl2 are added. At low
temperatures, spin relaxation is caused by spectral diffusion of surrounding
nuclear 35Cl and 37Cl spins in the S2Cl2, but nevertheless, at 20 K, T2 times
as long as 0.23 ms are observed.Comment: 7 pages, 6 figure
Contactless photoconductivity-detected electron spin resonance of P donors in isotopically purified Si
Coherence times of electron spins bound to phosphorus donors have been
measured, using a standard Hahn echo technique, to be up to 20 ms in
isotopically pure silicon with [P] cm and at temperatures
K. Although such times are exceptionally long for electron spins in
the solid state, they are nevertheless limited by donor electron spin-spin
interactions. Suppressing such interactions requires even lower donor
concentrations, which lie below the detection limit for typical electron spin
resonance (ESR) spectrometers. Here we describe an alternative method for
phosphorus donor ESR detection, exploiting the spin-to-charge conversion
provided by the optical donor bound exciton transition. We characterise the
method and its dependence on laser power and use it to measure a coherence time
of ms for one of the purest silicon samples grown to-date ([P]cm). We then benchmark this result using an alternative
application of the donor bound exciton transition: optically polarising the
donor spins before using conventional ESR detection at 1.7~K for a sample with
[P]cm, and measuring in this case a of 350 ms
A new mechanism for electron spin echo envelope modulation
Electron spin echo envelope modulation (ESEEM) has been observed for the
first time from a coupled hetero-spin pair of electron and nucleus in liquid
solution. Previously, modulation effects in spin echo experiments have only
been described in liquid solutions for a coupled pair of homonuclear spins in
NMR or a pair of resonant electron spins in EPR. We observe low-frequency ESEEM
(26 and 52 kHz) due to a new mechanism present for any electron spin with S>1/2
that is hyperfine coupled to a nuclear spin. In our case these are electron
spin (S=3/2) and nuclear spin (I=1) in the endohedral fullerene N@C60. The
modulation is shown to arise from second order effects in the isotropic
hyperfine coupling of an electron and 14N nucleus.Comment: 15 pages, 4 figure