Bench-top cooling of a microwave mode using an optically pumped spin refrigerator

We experimentally demonstrate the temporary removal of thermal photons from a microwave mode at 1.45 GHz through its interaction with the spin-polarized triplet states of photo-excited pentacene molecules doped within a p-terphenyl crystal at room temperature. The crystal functions electromagnetically as a narrow-band cryogenic load, removing photons from the otherwise room-temperature mode via stimulated absorption. The noise temperature of the microwave mode dropped to 50+18 −32 K (as directly inferred by noise-power measurements) while the metal walls of the cavity enclosing the mode remained at room temperature. Simulations based on the same system’s behavior as a maser (which could be characterized more accurately) indicate the possibility of the mode’s temperature sinking to ∼10 K (corresponding to ∼140 microwave photons).These observations, when combined with engineering improvements to deepen the cooling, identify the system as a narrow-band yet extremely convenient platform —free of cryogenics, vacuum chambers and strong magnets— for realizing low-noise detectors, quantum memory and quantum-enhanced machines (such as heat engines) based on strong spin-photon coupling and entanglement at microwave frequencies

ESR study of spin adducts of the direct electrocatalytic decomposition of light aliphatic alcohols in a polymer electrolyte fuel cell

Spin adducts of methanol and ethanol electrocatalytic oxidation were detected by the spin trap method using a tiny H2/O2 fuel cell (FC) designed for ESR in situ with a Nafion/Pt membrane electrode assembly. Spin adducts of intermediates of the direct electrooxidation of ethanol, which have not been observed earlier, were obtained by the variation of oxidation conditions, in particular, the FC potential. The work of the FC was controlled by monitoring the diagnostic curves potential3-current density, power density3-current density, and efficiency-power density. © 2010 Springer Science+Business Media, Inc

Invasive optical pumping for room-temperature masers, time-resolved EPR, triplet-DNP, and quantum engines exploiting strong coupling

We explore an approach for optically pumping a body of optically dense magnetic material. This challenge arises in time-resolved electron paramagnetic resonance (TREPR), triplet-based dynamic nuclear polarisation (DNP), and cavity QED. Crystals of pentacene-doped p-terphenyl were grown around variously shaped ends of optical waveguides, through which pump light could be injected deeply into the crystal. When incorporated into a maser as the gain medium, we found that, compared to conventional side-pumping, 11 times less pump beam intensity was needed to reach the masing threshold and 54 times more pulse energy could be absorbed by the gain medium without damage, resulting in a record peak output power of -5 dBm

ESR study of spin adducts of the direct electrocatalytic decomposition of light aliphatic alcohols in a polymer electrolyte fuel cell

Spin adducts of methanol and ethanol electrocatalytic oxidation were detected by the spin trap method using a tiny H2/O2 fuel cell (FC) designed for ESR in situ with a Nafion/Pt membrane electrode assembly. Spin adducts of intermediates of the direct electrooxidation of ethanol, which have not been observed earlier, were obtained by the variation of oxidation conditions, in particular, the FC potential. The work of the FC was controlled by monitoring the diagnostic curves potential3-current density, power density3-current density, and efficiency-power density. © 2010 Springer Science+Business Media, Inc

Unraveling the room-temperature spin dynamics of photoexcited pentacene in its lowest triplet state at zero field

Photoexcited pentacene, upon arriving via intersystem crossing into its lowest triplet state, has been extensively studied due to the large and relatively long-lived spin polarization that it exhibits. However, the spin dynamics of these triplets has not hitherto been accurately determined, with glaring inconsistencies between published values. Using zero-field transient electron paramagnetic resonance (ZF-trEPR), we here report the determination of a complete set of depopulation and spin–lattice relaxation rates for the lowest triplet state of pentacene doped at 0.1% into a p-terphenyl host crystal at room temperature in zero applied magnetic field. The rates of spin–lattice relaxation between the triplet’s sublevels are found to be highly anisotropic (i.e., transition-specific) and not negligible compared to the rates of depopulation from the same three sublevels back to pentacene’s ground state. The spin dynamics, as well as the ZF-trEPR technique reported here, can aid the rational, quantitative engineering of applications such as room-temperature masers and triplet dynamic nuclear polarization

ESR study of spin adducts of the direct electrocatalytic decomposition of light aliphatic alcohols in a polymer electrolyte fuel cell

Spin adducts of methanol and ethanol electrocatalytic oxidation were detected by the spin trap method using a tiny H2/O2 fuel cell (FC) designed for ESR in situ with a Nafion/Pt membrane electrode assembly. Spin adducts of intermediates of the direct electrooxidation of ethanol, which have not been observed earlier, were obtained by the variation of oxidation conditions, in particular, the FC potential. The work of the FC was controlled by monitoring the diagnostic curves potential3-current density, power density3-current density, and efficiency-power density. © 2010 Springer Science+Business Media, Inc