Longitudinal bulk plasmons in an $n$-doped ZnO layer system are studied by two-color femtosecond pump-probe spectroscopy in the midinfrared. The optical bulk plasmon resonance identified in linear reflectivity spectra undergoes a strong redshift and a limited broadening upon intraband excitation of electrons. The nonlinear changes of plasmon absorption decay on a time scale of 2 ps and originate from the intraband redistribution of electrons. Theoretical calculations explain the plasmon redshift by the transient increase of the ensemble-averaged electron mass and the concomitantly reduced plasma frequency in the hot electron plasma. The observed bulk plasmon nonlinearity holds strong potential for applications in plasmonics.

We determine the minimum energy required to control the evolution of any mesoscopic quantum system in the presence of arbitrary Markovian noise processes. This result provides the mesoscopic equivalent of the fundamental cost of refrigeration, sets the minimum power consumption of mesoscopic devices that operate out of equilibrium, and allows one to calculate the efficiency of any control protocol, whether it be open-loop or feedback control. As examples, we calculate the energy cost of maintaining a qubit in the ground state and the efficiency of resolved-sideband cooling of nano-mechanical resonators, and discuss the energy cost of quantum information processing.

In a model metallic glass, we study the relaxation dynamics in both the linear and the nonlinear response regimes by numerical simulations of dynamical mechanical spectroscopy and analyze the atomic displacement statistics. We find that the primary ($\alpha$) relaxation always takes place when the most probable atomic displacement reaches a critical fraction ($\sim 20\%$) of the average interatomic distance, irrespective of whether the relaxation is induced by temperature (linear response) or by mechanical strain (nonlinear response). Such a unified scenario, analogous to the well-known Lindemann criterion for crystal melting, provides insight into the structural origin of the strain-induced glass-liquid transition.

In catalytic methanol oxidation on ultrathin vanadium oxide layers on Rh(111) (${\mathrm{\Theta }}_{\mathrm{V}}\approx 0.2$ monolayer equivalent) we observe a 2D ripening of the ${\mathrm{VO}}_x$ islands that is controlled by the catalytic reaction. Neighboring ${\mathrm{VO}}_x$ islands move under reaction conditions towards each other and coalesce. The motion and the coalescence of the islands are explained by a polymerization-depolymerization equilibrium that is sensitive to gradients in the adsorbate coverages.

We detect the persistence of the solidification and order-disorder first-order transition lines in the phase diagram of nanocrystalline ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_8$ vortex matter down to a system size of less than one hundred vortices. The temperature location of the vortex solidification transition line is not altered by decreasing the sample size although there is a depletion of the entropy jump at the transition with respect to macroscopic vortex matter. The solid order-disorder phase transition field moves upward on decreasing the system size due to the increase of the surface-to-volume ratio of vortices entailing a decrease on the average vortex binding energy.

Lattice QCD calculations of two-nucleon systems are used to isolate the short-distance two-body electromagnetic contributions to the radiative capture process $np\to d\gamma$, and the photo-disintegration processes ${\gamma }^{(*)}d\to np$. In nuclear potential models, such contributions are described by phenomenological meson-exchange currents, while in the present work, they are determined directly from the quark and gluon interactions of QCD. Calculations of neutron-proton energy levels in multiple background magnetic fields are performed at two values of the quark masses, corresponding to pion masses of $m_{\pi }\sim 450$ and 806 MeV, and are combined with pionless nuclear effective field theory to determine the amplitudes for these low-energy inelastic processes. At $m_{\pi }\sim 806\mathrm{MeV}$, using only lattice QCD inputs, a cross section ${\sigma }^{806\mathrm{MeV}}\sim 17\mathrm{mb}$ is found at an incident neutron speed of $v=2,200\mathrm{m}/\mathrm{s}$. Extrapolating the short-distance contribution to the physical pion mass and combining the result with phenomenological scattering information and one-body couplings, a cross section of ${\sigma }^{\text{lqcd}}(np\to d\gamma )=334.9(\begin{array}{c}+5.2\\ -5.4\end{array})\mathrm{mb}$ is obtained at the same incident neutron speed, consistent with the experimental value of ${\sigma }^{\text{expt}}(np\to d\gamma )=334.2(0.5)\mathrm{mb}$.

New technical developments have led to a 2 orders of magnitude improvement of the resolution of the collinear resonance ionization spectroscopy (CRIS) experiment at ISOLDE, CERN, without sacrificing the high efficiency of the CRIS technique. Experimental linewidths of 20(1) MHz were obtained on radioactive beams of francium, allowing us for the first time to determine the electric quadrupole moment of the short lived [$t_{1/2}=22.0(5)\mathrm{ms}$] ${}^{219}\mathrm{Fr}$ $Q_s=-1.21(2)\mathrm{eb}$, which would not have been possible without the advantages offered by the new method. This method relies on a continuous-wave laser and an external Pockels cell to produce narrow-band light pulses, required to reach the high resolution in two-step resonance ionization. Exotic nuclei produced at rates of a few hundred ions/s can now be studied with high resolution, allowing detailed studies of the anchor points for nuclear theories.

Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and $247(73)\mu \mathrm{s}$ have been discovered in the heavy ${}^{254}\mathrm{Rf}$ nucleus. The observation of the shorter-lived isomer was made possible by a novel application of a digital data acquisition system. The isomers were interpreted as the $K^{\pi }=8^{-}$, ${\nu }^2(7/2^{+}[624],9/2^{-}[734])$ two-quasineutron and the $K^{\pi }=16^{+}$, $8^{-}{\nu }^2(7/2^{+}[624],9/2^{-}[734])\otimes 8^{-}{\pi }^2(7/2^{-}[514],9/2^{+}[624])$ four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter $N=150$ isotones. The four-quasiparticle isomer is longer lived than the ${}^{254}\mathrm{Rf}$ ground state that decays exclusively by spontaneous fission with a half-life of $23.2(1.1)\mu \mathrm{s}$. The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.

Spin echo is a powerful technique to extend atomic or nuclear coherence times by overcoming the dephasing due to inhomogeneous broadenings. However, there are disputes about the feasibility of applying this technique to an ensemble-based quantum memory at the single-quanta level. In this experimental study, we find that noise due to imperfections of the rephasing pulses has both intense superradiant and weak isotropic parts. By properly arranging the beam directions and optimizing the pulse fidelities, we successfully manage to operate the spin echo technique in the quantum regime by observing nonclassical photon-photon correlations as well as the quantum behavior of retrieved photons. Our work for the first time demonstrates the feasibility of harnessing the spin echo method to extend the lifetime of ensemble-based quantum memories at the single-quanta level.

We propose a new mechanism to explain the origin of optical gain in the transitions between the excited and ground states of the ionized nitrogen molecule following irradiation of neutral nitrogen molecules with an intense ultrashort laser pulse. An efficient transfer of population to the excited state is achieved via field-induced multiple recollisions. We show that the proposed excitation mechanism must lead to a superradiant emission, a feature that we confirm experimentally.

We present experiments on the driven dynamics of a two-level superconducting artificial atom. The driving strength reaches 4.78 GHz, significantly exceeding the transition frequency of 2.288 GHz. The observed dynamics is described in terms of quasienergies and quasienergy states, in agreement with Floquet theory. In addition, we observe the role of pulse shaping in the dynamics, as determined by nonadiabatic transitions between Floquet states, and we implement subnanosecond single-qubit operations. These results pave the way to quantum control using strong driving with applications in quantum technologies.

We measure ensemble-averaged quantum correlations of path-entangled photons, propagating in a disordered lattice and undergoing Anderson localization. These result in intriguing patterns, which show that quantum interference leads to unexpected dependencies of the location of one particle on the location of the other. These correlations are shared between localized and nonlocalized components of the two-photon wave function, and, moreover, yield information regarding the nature of the disorder itself. Such effects cannot be reproduced with classical waves, and are undetectable without ensemble averaging.

We show electric field control of the spin accumulation at the interface of the oxide semiconductor $\mathrm{Nb}\text{−}{\mathrm{SrTiO}}_3$ with $\mathrm{Co}/{\mathrm{AlO}}_x$ spin injection contacts at room temperature. The in-plane spin lifetime ${\tau }_{\parallel }$, as well as the ratio of the out-of-plane to in-plane spin lifetime ${\tau }_{\perp }/{\tau }_{\parallel }$, is manipulated by the built-in electric field at the semiconductor surface, without any additional gate contact. The origin of this manipulation is attributed to Rashba spin orbit fields (SOFs) at the $\mathrm{Nb}\text{−}{\mathrm{SrTiO}}_3$ surface and shown to be consistent with theoretical model calculations based on SOF spin flip scattering. Additionally, the junction can be set in a high or low resistance state, leading to a nonvolatile control of ${\tau }_{\perp }/{\tau }_{\parallel }$, consistent with the manipulation of the Rashba SOF strength. Such room temperature electric field control over the spin state is essential for developing energy-efficient spintronic devices and shows promise for complex oxide based (spin) electronics.