Abstract-Giant multiphoton absorption for THz resonances in silicon hydrogenic donors

M. A. W. van Loon, N. Stavrias, Nguyen H. Le, K. L. Litvinenko, P. T. Greenland, C. R. Pidgeon, K. Saeedi, B. Redlich, G. Aeppli,  B. N. Murdin

https://www.nature.com/articles/s41566-018-0111-x

The absorption of multiple photons when there is no resonant intermediate state is a well-known nonlinear process in atomic vapours, dyes and semiconductors. The N-photon absorption (NPA) rate for donors in semiconductors scales proportionally from hydrogenic atoms in vacuum with the dielectric constant and inversely with the effective mass, factors that carry exponents 6N and 4N, respectively, suggesting that extremely large enhancements are possible. We observed 1PA, 2PA and 3PA in Si:P with a terahertz free-electron laser. The 2PA coefficient for 1s–2s at 4.25 THz was 400,000,000 GM (=4 × 10−42 cm4 s), many orders of magnitude larger than is available in other systems. Such high cross-sections allow us to enter a regime where the NPA cross-section exceeds that of 1PA—that is, when the intensity approaches the binding energy per Bohr radius squared divided by the uncertainty time (only 3.84 MW cm−2 in silicon)—and will enable new kinds of terahertz quantum control.

Abstract-Optical response from terahertz to visible light of electronuclear transitions in LiYF4:Ho3+

G. Matmon, S. A. Lynch, T. F. Rosenbaum, A. J. Fisher, and G. Aeppli

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.205132

Because of its role as a model system with tunable quantum fluctuations and quenched disorder, and the desire for optical control and readout of its states, we have used high-resolution optical absorption spectroscopy to measure the crystal-field excitations for Ho3+ ions in LiHoxY1−xF4 from the terahertz to visible regimes. We show that many of the excitations yield very narrow lines visibly split even by the nuclear hyperfine interaction, making Ho3+ in LiHoxY1−xF4 a candidate host for optically addressable electronuclear qubits with quality factors as high as Q=4.7×105, where the higher-lying levels are electronic singlets. Optical transitions in the easily accessible near- and mid-infrared are narrow enough to allow readout of the ground-state electronuclear qubits responsible for the interesting magnetism of LiHoxY1−xF4. While many of the higher-lying states have been observed previously, we also report here detailed spectra of terahertz excitations. The strengths of the electric and magnetic dipole crystal-field transition lines of five of the lowest excited spin-orbit manifolds of dilute LiYF4:Ho3+ were calculated and compared with measurement. The magnitude of the nuclear hyperfine coupling was used to assign the correct upper and lower states to transition lines.

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Abstract-Optical response from the terahertz domain to visible light of electronuclear transitions in LiYF4:Ho3+

G. Matmon, S. A. Lynch, T. F. Rosenbaum, A. J. Fisher, and G. Aeppli

https://journals.aps.org/prb/accepted/f707bK9eF5316d0a710c2a75f5c802098c53e8fb8

Because of its role as a model system with tunable quantum fluctuations and quenched disorder, and the desire for optical control and readout of its states, we have used high resolution optical absorption spectroscopy to measure the crystal field excitations for \mathrm{Ho}3+ ions in \mathrm{LiHo}_x\mathrm{Y}1-x\mathrm{F}_4 from the THz to visible regimes. We show that many of the excitations yield very narrow lines visibly split even by the nuclear hyperfine interaction, making \mathrm{Ho}3+ in \mathrm{LiHo}_x\mathrm{Y}1-x\mathrm{F}_4 a candidate host for optically addressable electro-nuclear qubits with quality factors as high as Q=4.7\times10^5, where the higher lying levels are electronic singlets. Optical transitions in the easily accessible near and mid-infrared are narrow enough to allow readout of the ground state electronuclear qubits responsible for the interesting magnetism of \mathrm{LiHo}_x\mathrm{Y}1-x\mathrm{F}_4. While many of the higher-lying states have been observed previously, we also report here detailed THz domain excitations. The strengths of the electric- and magnetic dipole crystal field transition lines of five of the lowest excited spin-orbit manifolds of dilute LiYF4:Ho3+ were calculated and compared with measurement. The magnitude of the nuclear hyperfine coupling was used to assign the correct upper and lower states to transition lines.