Nonadiabatic Character Research Articles

Storing short single-photon-level optical pulses in Bose–Einstein condensates for high-performance quantum memory

Large-scale quantum networks require quantum memories featuring long-lived storage of non-classical light together with efficient, high-speed and reliable operation. The concurrent realization of these features is challenging due to inherent limitations of matter platforms and light–matter interaction protocols. Here, we propose an approach to overcome this obstacle, based on the implementation of the Autler–Townes-splitting (ATS) quantum-memory protocol on Bose–Einstein condensate (BEC) platform. We demonstrate a proof-of-principle of this approach by storing short pulses of single-photon-level light as a collective spin-excitation in a rubidium-BEC. For 20 ns long-pulses, we achieve an ultra-low-noise memory with an efficiency of 30% and lifetime of 15 μs. The non-adiabatic character of the ATS protocol (leading to high-speed and low-noise operation) in combination with the intrinsically large atomic densities and ultra-low temperatures of the BEC platform (offering highly efficient and long-lived storage) opens up a new avenue toward high-performance quantum memories.

Electrochemical Investigation of Redox Processes of Labile Cu(II)/Cu(I)-Cl Complexes by Scanning Electrochemical Microscopy.

The studies reported here provide detailed information on the kinetics and reaction mechanism determined by the scanning electrochemical microscopy (SECM) for Cu(II)/Cu(I) redox reactions in a system with excess chloride. In positive feedback mode, the tip voltammograms obtained consist of two partially overlapping reduction waves, not one quasi-reversible process as was always thought. The reduced species of CuIICl42- and [CuIICl3(H2O)]- could coexist during the time scale of SECM measurements, due to the slowness of the ligand substitution reaction of [CuIICl3(H2O)]- to CuIICl42-. The stepwise EC reactions of CuIICl42- have experienced the same electron transfer kinetics as do outer-sphere reactants, while the reactions of [CuIICl3(H2O)]- followed concerted EC pathways and much lower rate constants can be obtained, mainly due to the nonadiabatic character of electron transfer (k0Pt/k0Au = 1.625). The findings of this study can offer valuable insights for analyzing the electrode kinetics of labile complexes of metals in aqueous solutions.

Nonadiabatic effects and excitonlike states during the insulator-to-metal transition in warm dense hydrogen

Transition of molecular hydrogen to atomic ionized state with increase of temperature and pressure poses still unresolved problems for experimental methods and theory. Here we analyze the dynamics of this transition and show its nonequilibrium non-adiabatic character overlooked in both interpreting experimental data and in theoretical models. The non-adiabatic mechanism explains the strong isotopic effect [Zaghoo, Husband, and Silvera, Phys. Rev. B 98, 104102 (2018)] and the large latent heat [Houtput, Tempere, and Silvera, Phys. Rev. B 100, 134106 (2019)] reported recently. We demonstrate the possibility of formation of intermediate exciton-like molecular states at heating of molecular hydrogen that can explain puzzling experimental data on reflectivity and conductivity during the insulator-to-metal transition.

Elucidation of near-resonance vibronic coherence lifetimes by nonadiabatic electronic-vibrational state character mixing

Recent work suggests that the long-lived coherences observed in both natural and artificial light-harvesting systems (such as the Fenna-Matthews-Olson complex) could be attributed to the mixing of the pigments' electronic and vibrational degrees of freedom. To investigate the underlying mechanism of these long coherence lifetimes, a sophisticated description of interactions between the molecular aggregates and the nonequilibrium fluctuations in the surrounding environment is necessary. This is done by implementing the hierarchical equations of motion approach on model homodimers, a method used in the intermediate coupling regime for many molecular aggregates wherein the nonequilibrium environment phonons play nontrivial roles in exciton dynamics. Here we report a character change in the vibronic states-reflective of property mixing between the electronic and vibrational states-induced by an interplay between system coupling parameters within the exciton-vibrational near-resonance regime. This mixing dictates vital aspects of coherence lifetime; by tracking the degree of mixing, we are able to elucidate the relationship between coherence lifetime and both the electronic energy fluctuation and the vibrational relaxation dephasing pathways.

Sequential character of low-energy ternary and quaternary nuclear fission

An analysis of low-energy true ternary (quaternary) nuclear fission leads to the conclusion that these fission modes have a sequential two-step (three-step) character such that the emission of a third particle (third and fourth particles) and the separation of fission fragments occur at distinctly different instants, in contrast to the simultaneous emergence of all fission products in the case of onestep ternary (quaternary) fission. This conclusion relies on the following arguments. First, the emission of a third particle (third and fourth particles) from a fissile nucleus is due to a nonevaporative mechanism associated with a nonadiabatic character of the collective deformation motion of this nucleus at the stages preceding its scission. Second, the axial symmetry of the deformed fissile compound nucleus and the direction of its symmetry axis both remain unchanged at all stages of ternary (quaternary) fission. This circumstancemakes it possible to explain themechanism of the appearance of observed anisotropies and T — odd asymmeries in the angular distributions of products of ternary (quaternary) nuclear fission. Third, the T —odd asymmetry discovered experimentally in ternary nuclear fission induced by cold polarized neutrons obeys the T —invariance condition only in the case of a sequential two-step (three-step) character of true ternary (quaternary) nuclear fission. At the same time, this asymmetry is not a T —invariant quantity in the case of the simultaneous emission of products of true ternary (quaternary) nuclear fission from the fissile compound nucleus.

Experimental investigation of non-ideality and non-adiabatic effects under high pressure releases

This paper presents experimental studies involving high pressure gaseous releases with specific attention to the non-adiabatic character of the process approaching cryogenic temperatures, especially when the influence of heat exchange with ambient air becomes important. A small-scale facility is designed and constructed to simulate the transient blow-down of a cryogenic fluid through a small break. Gaseous and liquid nitrogen were planned to be used as a surrogate material for GH2 and LH2. The experimental results complement the quasi-stationary safety regulation tests and provide time-dependent data for verification of the theoretical models. Different orifice sizes (0.5, 1, 2, 3, 4 mm) and initial vessel (over-) pressures 30–200 bar are used in the tests. The measured time-dependent data for vessel discharge pressure, thrust, discharge mass flow rate, and gas temperatures are compared with a theoretical model for high pressure nitrogen release. This verification for nitrogen also assures the equation of state for hydrogen, which is based on the same methodology.

Properties of true quaternary fission of nuclei with allowance for its multistep and sequential character

An analysis of basicmechanisms of binary and ternary fission of nuclei led to the conclusion that true ternary and quaternary fission of nuclei has a sequential two-step (three-step) character, where, at the first step, a fissile nucleus emits a third light particle (third and fourth light particles) under shakeup effects associated with a nonadiabatic character of its collective deformation motion, whereupon the residual nucleus undergoes fission to two fission fragments. Owing to this, the formulas derived earlier for the widths with respect to sequential two- and three-step decays of nuclei in constructing the theory of two-step twoproton decays and multistep decays in chains of genetically related nuclei could be used to describe the relative yields and angular and energy distributions of third and fourth light particles emitted in (α, α), (t, t), and (α, t) pairs upon the true quaternary spontaneous fission of 252Cf and thermal-neutron-induced fission of 235U and 233U target nuclei. Mechanisms that explain a sharp decrease in the yield of particles appearing second in time and entering into the composition of light-particle pairs that originate from true quaternary fission of nuclei in relation to the yields of analogous particles in true ternary fission of nuclei are proposed.

The antikick strikes back: Recoil velocities for nearly extremal binary black hole mergers in the test-mass limit

Gravitational waves emitted from a generic binary black-hole merger carry away linear momentum anisotropically, resulting in a gravitational recoil, or "kick", of the center of mass. For certain merger configurations the time evolution of the magnitude of the kick velocity has a local maximum followed by a sudden drop. Perturbative studies of this "antikick" in a limited range of black hole spins have found that the antikick decreases for retrograde orbits as a function of negative spin. We analyze this problem using a recently developed code to evolve gravitational perturbations from a point-particle in Kerr spacetime driven by an effective-one-body resummed radiation reaction force at linear order in the mass ratio $\nu\ll 1$. Extending previous studies to nearly-extremal negative spins, we find that the well-known decrease of the antikick is overturned and, instead of approaching zero, the antikick increases again to reach $\Delta v/(c\nu^{2})=3.37\times10^{-3}$ for dimensionless spin $\hat{a}=-0.9999$. The corresponding final kick velocity is $v_{end}/(c\nu^{2})=0.076$. This result is connected to the nonadiabatic character of the emission of linear momentum during the plunge. We interpret it analytically by means of the quality factor of the flux to capture quantitatively the main properties of the kick velocity. The use of such quality factor of the flux does not require trajectories nor horizon curvature distributions and should therefore be useful both in perturbation theory and numerical relativity.

Quantum size effects in chemicurrent measurements during low-temperature oxidation of Mg(0001) epilayers

The reactivity of Mg epilayers on Si(111)-7 × 7 towards molecular oxygen is investigated as a function of the metal film thickness in the range between 7 and 45 monolayers. Quantum well and surface states are characterized with ultraviolet photoelectron spectroscopy demonstrating the epitaxial and single-crystalline structure of the Mg films. The oxidation rate is monitored during the reaction by measuring chemicurrents at 110 K in the Mg/p-Si(111) Schottky diodes due to the non-adiabatic character of at least one step in the reaction chain. For film thicknesses around 9 and 13 monolayers the chemicurrent transients demonstrate that the reaction rate is strongly enhanced by a factor of more than two. With Mg 2p core level spectroscopy, a similar enhancement can be found for the total oxygen uptake for long exposures indicating that the chemicurrent increase measures solely a quantum size effect on the reactivity and no device-related effects. The enhanced reactivity can be explained by the increased first charge transfer into the affinity level of the approaching molecule when a quantum well state appears at the Fermi level and increases the density of electronic states. A linear relationship between the photoelectron intensity at the Fermi level and the maximum chemicurrent is clearly observed. On the other hand, the surface work function and the Schottky barrier height exhibit almost no correlation with the enhanced reactivity.

Signature of nonadiabatic coupling in excited-state vibrational modes.

Using analytical excited-state gradients, vibrational normal modes have been calculated at the minimum of the electronic excited-state potential energy surfaces for a set of extended conjugated molecules with different coupling between them. Molecular model systems composed of units of polyphenylene ethynylene (PPE), polyphenylenevinylene (PPV), and naphthacene/pentacene (NP) have been considered. In all cases except the NP model, the influence of the nonadiabatic coupling on the excited-state equilibrium normal modes is revealed as a unique highest frequency adiabatic vibrational mode that overlaps with the coupling vector. This feature is removed by using a locally diabatic representation in which the effect of NA interaction is removed. Comparison of the original adiabatic modes with a set of vibrational modes computed in the locally diabatic representation demonstrates that the effect of nonadiabaticity is confined to only a few modes. This suggests that the nonadiabatic character of a molecular system may be detected spectroscopically by identifying these unique state-specific high frequency vibrational modes.

Electron-transfer studies of a peroxide dianion.

A peroxide dianion (O2(2-)) can be isolated within the cavity of hexacarboxamide cryptand, [(O2)⊂mBDCA-5t-H6](2-), stabilized by hydrogen bonding but otherwise free of proton or metal-ion association. This feature has allowed the electron-transfer (ET) kinetics of isolated peroxide to be examined chemically and electrochemically. The ET of [(O2)⊂mBDCA-5t-H6](2-) with a series of seven quinones, with reduction potentials spanning 1 V, has been examined by stopped-flow spectroscopy. The kinetics of the homogeneous ET reaction has been correlated to heterogeneous ET kinetics as measured electrochemically to provide a unified description of ET between the Butler-Volmer and Marcus models. The chemical and electrochemical oxidation kinetics together indicate that the oxidative ET of O2(2-) occurs by an outer-sphere mechanism that exhibits significant nonadiabatic character, suggesting that the highest occupied molecular orbital of O2(2-) within the cryptand is sterically shielded from the oxidizing species. An understanding of the ET chemistry of a free peroxide dianion will be useful in studies of metal-air batteries and the use of [(O2)⊂mBDCA-5t-H6](2-) as a chemical reagent.

Time-dependent exchange-correlation functional for a Hubbard dimer: Quantifying nonadiabatic effects

We address and quantify the role of non-adiabaticity ("memory effects") in the exchange-correlation (xc) functional of time-dependent density functional theory (TDDFT) for describing non-linear dynamics of many-body systems. Time-dependent resonant processes are particularly challenging for available TDDFT approximations, due to their strong non-linear and non-adiabatic character. None of the known approximate density functionals are able to cope with this class of problems in a satisfactory manner. In this work we look at the prototypical example of the resonant processes by considering Rabi oscillations within the exactly soluble 2-site Hubbard model. We construct the exact adiabatic xc functional and show that (i) it does not reproduce correctly resonant Rabi dynamics, (ii) there is a sizable non-adiabatic contribution to the exact xc potential, which turns out to be small only at the beginning and at the end of the Rabi cycle when the ground state population is dominant. We then propose a "two-level" approximation for the time-dependent xc potential which can capture Rabi dynamics in the 2-site problem. It works well both for resonant and for detuned Rabi oscillations and becomes essentially exact in the linear response regime. This new, fully non-adiabatic and explicit density functional constitutes one of the main results of the present work.

On the adiabaticity of electrode processes: Effect of the supporting electrolyte cation on the kinetics of electroreduction of 3-nitrophenolate

The comparative analysis of voltammetric responses at different temperatures through the asymmetric Marcus–Hush theory provides physical insight into the changes upon the electron transfer mechanism and the electronic interaction between the electrode and the electroactive species. Herein this approach is applied to the assessment of the influence of the nature of the supporting electrolyte on the kinetics of electrode processes.In particular, the electroreduction of the 3-nitrophenolate anion is studied in dimethylsulfoxide solutions via the use of a mercury hemispherical working microelectrode. Three different tetra-alkyl-ammonium perchlorates are employed as supporting electrolyte: tetraethylammonium, tetrabutylammonium and tetrahexylammonium. From these kinetic studies undertaken at different temperatures the reorganization energy, force constant symmetry and the strength of the electronic coupling are determined and analyzed for the different conditions. The results presented show a significant effect of the identity of the supporting electrolyte cation on the electrode kinetics that can be attributed to the change of the distance of closest approach between the electroactive species and the electrode as well as to ion-pairing effects. The experimental behavior observed suggests that the process has a non-adiabatic character.

Probabilities for the emission of light particles and their energy and angular distributions for true quaternary nuclear fission

On the basis of quantum-mechanical fission theory, the features of true quaternary nuclear fission are studied by treating this fission process as a sequence of three processes following one another in the course of time. The first two processes are the escape of the first and then the second of the two light particles emitted from the neck of a fissioning nucleus because of a nonadiabatic character of the collective deformation motion of this nucleus. Finally, the third process is the separation of the fissioning nucleus into two rather heavy fission fragments. The differences that arise in the emission probabilities and in the angular and energy distributions upon going over from the first emitted to the second emitted prescission third and fourth particles are analyzed by invoking experimental data on the spontaneous and thermalneutron-induced fission of nuclei, and it is shown that these differences are caused by the changes both in the geometric configuration of the fissioning nucleus and in the shell structure of its neck after the first prescission particle is emitted from it.

Multiple-site concerted proton-electron transfer reactions of hydrogen-bonded phenols are nonadiabatic and well described by semiclassical Marcus theory.

Photo-oxidations of hydrogen-bonded phenols using excited-state polyarenes are described to derive fundamental understanding of multiple-site concerted proton-electron transfer reactions (MS-CPET). Experiments have examined phenol bases having -CPh(2)NH(2), -Py, and -CH(2)Py groups ortho to the phenol hydroxyl group and tert-butyl groups in the 4,6-positions for stability (HOAr-NH(2), HOAr-Py, and HOAr-CH(2)Py, respectively; Py = pyridyl; Ph = phenyl). The photo-oxidations proceed by intramolecular proton transfer from the phenol to the pendent base concerted with electron transfer to the excited polyarene. For comparison, 2,4,6-(t)Bu(3)C(6)H(2)OH, a phenol without a pendent base and tert-butyl groups in the 2,4,6-positions, has also been examined. Many of these bimolecular reactions are fast, with rate constants near the diffusion limit. Combining the photochemical k(CPET) values with those from prior thermal stopped-flow kinetic studies gives data sets for the oxidations of HOAr-NH(2) and HOAr-CH(2)Py that span over 10(7) in k(CPET) and nearly 0.9 eV in driving force (ΔG(o)'). Plots of log(k(CPET)) vs ΔG(o)', including both excited-state anthracenes and ground state aminium radical cations, define a single Marcus parabola in each case. These two data sets are thus well described by semiclassical Marcus theory, providing a strong validation of the use of this theory for MS-CPET. The parabolas give λ(CPET) ≅ 1.15-1.2 eV and H(ab) ≅ 20-30 cm(-1). These experiments represent the most direct measurements of H(ab) for MS-CPET reactions to date. Although rate constants are available only up to the diffusion limit, the parabolas clearly peak well below the adiabatic limit of ca. 6 × 10(12) s(-1). Thus, this is a very clear demonstration that the reactions are nonadiabatic. The nonadiabatic character slows the reactions by a factor of ~45. Results for the oxidation of HOAr-Py, in which the phenol and base are conjugated, and for oxidation of 2,4,6-(t)Bu(3)C(6)H(2)OH, which lacks a base, show that both have substantially lower λ and larger pre-exponential terms. The implications of these results for MS-CPET reactions are discussed.

Propagation of the ultrashort laser pulses through the quantum nonlinear medium with resonant properties

The propagation of ultrashort few-cycle laser pulses through a quantum nonlinear medium with resonant properties is studied using the method of slowly varying amplitudes with allowance for dispersion effects. A self-consistent system of nonlinear wave equation for the evolution of laser field and the nonstationary Schrodinger equation that determines the material polarization response is numerically solved. Specific features of the propagation of laser pulse caused by a relatively large spectral width and the nonadiabatic character of the laser pulse are established. The rise of the slowly dumping polarization at the eigenfrequency of the medium and the consequent stretching of the laser pulse are observed. The role of the resonant absorption of the laser energy in the medium is analyzed. The nonlinear spectral broadening is demonstrated for the laser pulse propagating through the medium.

Breakdown of the dipole blockade with a zero-area phase-jump pulse

We theoretically investigate the effect of a zero-area pulse on the excitations of interacting Rydberg atoms. The unexpected breakdown of dipole blockade occurs in the strong Rydberg blockade regime, which results from the nonadiabatic character of a phase-jump pulse interacting with the atoms. We also check the effect of the modulation on the final probability of double excitations and find that the switching time should be short enough to observe the breakdown of dipole blockade.

Comparative study of the pressure effects on the magnetic penetration depth in electron-and hole-doped cuprate superconductors

The effect of pressure on the magnetic penetration depthλ was tested for the hole-doped superconductorYBa2Cu3O7−δ and in theelectron-doped one Sr0.9La0.1CuO2 by means of magnetization measurements. Whereas a large change ofλ wasfound in YBa2Cu3O7−δ, confirming the non-adiabatic character of the electron–phonon coupling in hole-dopedsuperconductors, the same quantity is not affected by pressure in electron-dopedSr0.9La0.1CuO2, suggesting a close similarity of the latter to conventional adiabaticBardeen–Cooper–Schrieffer superconductors. The present results imply a remarkabledifference between the electronic properties of hole-doped cuprates and electron-dopedSr0.9La0.1CuO2, giving a strong contribution to the long debated asymmetric consequences of hole andelectron doping in cuprate superconductors.

Bandgaps, surface states and the anomalous neutralization of Li+ on (111) surfaces of noble metals

The effect of progressive changes in the electronic structure of (111) surfaces of noble metals on neutralization of Li+ ions is studied in relation to recent study on electron transfer on nanoclusters dealing with electronic effects. Strong differences in electron transfer probabilities are revealed and the trends in these changes are related to the progressive changes of the band structure of Ag, Cu and Au surfaces. Experimental data reveal an anomalously high neutralization of ions on these high workfunction surfaces and an unusual ion energy dependence, suggesting a pronounced non-adiabatic character of the electron transfer process, not accountable in a ‘jellium’ model of resonant electron capture. We suggest a mechanism of capture involving non-resonant charge exchange from occupied surface states as well as a strongly reduced loss due to the presence of the L-bandgap.

Anomalous electron-phonon coupling probed on the surface of superconductorZrB12

Magnetization measurements under hydrostatic pressure up to $10.5\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$ in zirconium dodecaboride $\mathrm{Zr}{\mathrm{B}}_{12}$ superconductor (${T}_{c}\ensuremath{\simeq}6.0\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ at $p=0$) were carried out. A negative pressure effect on ${T}_{c}$ with $d{T}_{c}∕dp=\ensuremath{-}0.0225(3)\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{kbar}$ was observed. The electron-phonon coupling constant ${\ensuremath{\lambda}}_{\mathrm{el}\text{\ensuremath{-}}\mathrm{ph}}$ decreases with increasing pressure with $d\phantom{\rule{0.2em}{0ex}}\mathrm{ln}\phantom{\rule{0.2em}{0ex}}{\ensuremath{\lambda}}_{\mathrm{el}\text{\ensuremath{-}}\mathrm{ph}}∕dp\ensuremath{\simeq}\ensuremath{-}0.20%∕\mathrm{kbar}$. The magnetic field penetration depth $\ensuremath{\lambda}$ was studied in the Meissner state and, therefore, probes mainly the surface of the sample. The absolute values of $\ensuremath{\lambda}$ and the superconducting energy gap at ambient pressure and zero temperature were found to be $\ensuremath{\lambda}(0)=140(30)\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and ${\ensuremath{\Delta}}_{0}=1.251(9)\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, respectively. ${\ensuremath{\Delta}}_{0}$ scales linearly with ${T}_{c}$ as $2{\ensuremath{\Delta}}_{0}∕{k}_{B}{T}_{c}=4.79(1)$. The studies of the pressure effect on $\ensuremath{\lambda}$ reveal that ${\ensuremath{\lambda}}^{\ensuremath{-}2}$ increases with pressure with $d\phantom{\rule{0.2em}{0ex}}\mathrm{ln}\phantom{\rule{0.2em}{0ex}}{\ensuremath{\lambda}}^{\ensuremath{-}2}(0)∕dp=0.60(23)%∕\mathrm{kbar}$. This effect cannot be explained within the framework of conventional adiabatic electron-phonon pairing, suggesting the possibility that close to the surface an unconventional nonadiabatic character of the electron-phonon coupling takes place.