Resonant Excitation Scheme Research Articles

Probing the dynamics and coherence of a semiconductor hole spin via acoustic phonon-assisted excitation

Spins in semiconductor quantum dots (QDs) are promising local quantum memories to generate polarization-encoded photonic cluster states, as proposed in the pioneering Lindner and Rudolph scheme (2009 Phys. Rev. Lett. 103 113602). However, harnessing the polarization degree of freedom of the optical transitions is hindered by resonant excitation schemes that are widely used to obtain high photon indistinguishability. Here we show that acoustic phonon-assisted excitation, a scheme that preserves high indistinguishability, also allows to fully exploit the polarization selective optical transitions to initialise and measure single spin states. We access the coherence of hole spin systems in a low transverse magnetic field and directly monitor the spin Larmor precession both during the radiative emission process of an excited state or in the QD ground state. We report a spin state detection fidelity of granted by the optical selection rules and a ns hole spin coherence time, demonstrating the potential of this scheme and system to generate linear cluster states with a dozen of photons.

Electronic ring current and magnetic field generation induced by current-carrying states of ring molecules in intense fields

The generation of electronic currents and magnetic fields by and molecules with current-carrying states under circularly polarized (CP) and linearly polarized (LP) laser pulses is investigated. Results show that the electronic currents and magnetic fields induced by CP pulses are higher than those by LP pulses for both molecules in the resonance excitation scheme. This can be attributed to the switchable dipole moment of the laser pulses, inducing selective state-to-state electronic transitions. Moreover, it was found that magnetic fields are sensitive to different initial states of the molecules in the ionization scheme. In particular, the magnetic fields induced by the current-carrying states are much higher than that induced by the ground state, which is because the current-carrying states have a stable electronic ring current and the induced magnetic field is contributed by the current-carrying state itself and the laser field. These findings provide a scheme for generating ring-shaped currents and magnetic fields in molecular systems for future research in ultrafast magneto-optics.

Production and characterization of standard particles for rL-SNMS

In this work, uranium-and plutonium-baring particles were produced by fast iron co-precipitation for the purpose of creating homogeneous multi-element standards. A set of single isolated particles showing no inhomogeneities in the element distribution were selected. These particles were used to determine the maximal achievable suppression ratios for uranium in Resonant Laser Secondary Neutral Mass Spectrometry (rL-SNMS) measurements of plutonium. It was shown for the first time directly that suppression-ratios in the order of three magnitudes are achievable with a resonant two-step excitation scheme for non-destructive measurements.

SUPER Scheme in Action: Experimental Demonstration of Red-Detuned Excitation of a Quantum Emitter.

The quest for the perfect single-photon source includes finding the optimal protocol for exciting the quantum emitter. Coherent optical excitation was, up until now, achieved by tuning the laser pulses to the transition frequency of the emitter, either directly or in average. Recently, it was theoretically discovered that an excitation with two red-detuned pulses is also possible where neither of which would yield a significant upper-level population individually. We show that the so-called swing-up of quantum emitter population (SUPER) scheme can be implemented experimentally with similar properties to existing schemes by precise amplitude shaping of a broadband pulse. Because of its truly off-resonant nature, this scheme has the prospect of powering high-purity photon sources with superior photon count rate.

Nonstationary spin waves in a single rectangular permalloy microstrip under uniform magnetic excitation

Ferromagnetic resonance modes in a single rectangular ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ microstrip were directly imaged using time-resolved scanning transmission x-ray microscopy combined with a phase-locked ferromagnetic resonance excitation scheme, and the findings were corroborated by micromagnetic simulations. Although under uniform excitation in a single confined microstructure typically standing spin waves are expected, all imaged spin waves showed a nonstationary character both at and off resonance, the latter being additionally detected with microantenna-based ferromagnetic resonance. The effect of the edge quality on the spin waves was observed in micromagnetic simulations.

Exploration and Realization of Novel High-Q Bulk Modes Using Support Transducer Topology

This work reports an exploratory study of novel high quality factor acoustic modes that can be excited using the support transducer topology. The removal of the piezoelectric transducer layer from the high energy confinement mode eliminates the charge cancellation bottleneck. To excite the targeted modes, a frequency match between the thin film piezoelectric on substrate (TPoS) transducer arm and the central Silicon based high quality factor (Q) resonant tank is necessary. The concept of scaling up the frequency without shrinking the device dimensions by exciting higher-order modes has been verified using a third-order Lamé mode. The device exhibits a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> of 21,632 for a resonant frequency of 58.5MHz. Unexplored modes such as the combination of a square extension mode and a radial contour mode operating in an out-of-phase manner, multiple new higher-order modes, etc. exhibiting very high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> have been realized. The average <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> values of these new resonator designs range between 15,000 and 50,000, which is exceptional for piezoelectric transduction-based Microelectromechanical resonators. The idea of excitation of degenerate modes using silicon aligned along non-<100> and non-<110> crystalline axes has also been verified. The proof-of-concept of going beyond the traditional approach of resonance excitation scheme will pave the way to the investigation of unexplored modes that hold immense potential across various sectors of MEMS. [2021-0075]

Structure and electron dynamics of planetary states of Sr below the Sr+ 7d and 8p thresholds

In a combined experimental and theoretical study we investigate the $7dnl$ and $8pnl$ ($n\ensuremath{\ge}11, l=9--12$) doubly excited planetary states of Sr. The experimental spectrum was obtained using a five-photon resonant excitation scheme. The method of configuration interaction with exterior complex scaling was used to compute the energy-level structure and dynamics of the two highly excited electrons from first principles. Good quantitative agreement was obtained with the spectra we recorded, and the theoretical calculations shed light on their complex structure and the signatures of electron correlations therein. The two-electron probability densities we calculated reveal the strongly correlated angular motion of the two electrons in the $7dnl$ and $8pnl$ planetary states, and confirm quantitatively the predictions of the frozen-planet approximation describing electron dynamics as the polarization of the fast inner electron by the electric field of the outer ``frozen'' electron.

Resonant excitation of nanowire quantum dots

GaAs quantum dots in nanowires are one of the most promising candidates for scalable quantum photonics. They have excellent optical properties, can be frequency-tuned to atomic transitions, and offer a robust platform for fabrication of multi-qubit devices that promise to unlock the full technological potential of quantum dots. Coherent resonant excitation is necessary for virtually any practical application because it allows, for instance, for on-demand generation of single and entangled photons, photonic clusters states, and electron spin manipulation. However, emission from nanowire structures under this excitation scheme has never been demonstrated. Here we show, for the first time, biexciton–exciton cascaded emission via resonant two-photon excitation and resonance fluorescence from an epitaxially grown GaAs quantum dot in an AlGaAs nanowire. We also report that resonant excitation schemes, combined with above-bandgap excitation, can be used to clean and enhance the emission of nanowire quantum dots.

Non-standing spin-waves in confined micrometer-sized ferromagnetic structures under uniform excitation

A non-standing characteristic of directly imaged spin-waves in confined micrometer-sized ultrathin Permalloy (Ni80Fe20) structures is reported along with evidence of the possibility to alter the observed state by modifications to the sample geometry. Using micromagnetic simulations, the presence of the spin-wave modes excited in the Permalloy stripes along with the quasi-uniform modes was observed. The predicted spin-waves were imaged in direct space using time resolved scanning transmission x-ray microscopy, combined with a ferromagnetic resonance excitation scheme (STXM-FMR). STXM-FMR measurements revealed a non-standing characteristic of the spin-waves. Also, it was shown by micromagnetic simulations and confirmed using STXM-FMR results that the observed characteristic of the spin-waves can be influenced by the local magnetic fields in different sample geometries.

On the double resonance activation of electrostatically actuated microbeam based resonators

Electrostatically actuated microelectromechanical system (MEMS) devices have shown prominent potential in various applications. However, despite their low power consumption, they do require high input voltages to be actuated. This is even worse if these devices are driven around their mechanical resonant state. Assuming a double resonance excitation scheme, both electrically and mechanically, activates the system’s mechanical and electrical resonances simultaneously. This double resonance activation was recently verified experimentally to alleviate the problem of high actuating voltage/displacement near the resonant state. Therefore, in this work, an analytical electro-mechanical coupled model for a double-resonance-driven microbeam, assuming a classical nonlinear beam model combined with an RLC electric circuit model is first proposed and then numerically examined. Good match among the numerical simulations and the experimental data when the electrical resonance frequency band is sufficiently high is demonstrated. The suggested model can be used to further optimize certain MEMS designs and therefore fully benefit from this double resonance activation scheme in improving MEMS sensors and actuators.

Maximized vertical photoluminescence from optical material with losses employing resonant excitation and extraction of photonic crystal modes

Abstract Optical losses of a host material together with the total internal reflection phenomenon can significantly reduce photoluminescence external quantum efficiency of embedded light-emitters. This is not only the case for light-emitting color centers in thin layers of nanocrystalline diamond, but also for silicon nanocrystals in silica dioxide matrices and for some types of perovskite materials. Here, we show that a significant boost (more than 100-fold enhancement) of the directional light emission efficiency from light-emitters in diamond can be achieved by using two-dimensional photonic crystal slabs (PhCs) to extract the light emission into vertical direction (resonant extraction) and at the same time to couple the excitation beam into the structure (resonant excitation). We have further shown that this so-called resonant extraction and excitation scheme provides the highest enhancement when the overlap between the electric field distribution of extraction leaky mode and the region of the excited light-emitters is maximized. This can be achieved by using the same type of the photonic mode for both extraction and excitation, and by optimizing the thickness of a diamond layer. The usage of the same type of modes appears to be more significant than tuning of the Q-factors of the excitation and extraction leaky modes individually. The results of our measurements are supported by the outputs of computer simulations. Our findings may be helpful in designing future PhCs for extraction of luminescence originating from various optoelectronic and sensor devices making use of the unique properties of the diamond. Moreover, our concept can be easily extended to other light-emitting materials with optical losses.

Interaction-enhanced flow of a polariton superfluid current in a ring

We study the quantum hydrodynamical features of exciton-polaritons flowing circularly in a ring-shaped geometry. We consider a resonant-excitation scheme in which the spinor polariton fluid is set into motion in both components by spin-to-orbital angular momentum conversion. We show that this scheme allows to control the winding number of the fluid, and to create two circulating states differing by two units of the angular momentum. We then consider the effect of a disorder potential, which is always present in realistic nanostructures. We show that a smooth disorder is efficiently screened by the polariton-polariton interactions, yielding a signature of polariton superfluidity. This effect is reminiscent of supercurrent in a superconducting loop.

Quantum-optical spectroscopy of a two-level system using an electrically driven micropillar laser as a resonant excitation source

Two-level emitters are the main building blocks of photonic quantum technologies and are model systems for the exploration of quantum optics in the solid state. Most interesting is the strict resonant excitation of such emitters to control their occupation coherently and to generate close to ideal quantum light, which is of utmost importance for applications in photonic quantum technology. To date, the approaches and experiments in this field have been performed exclusively using bulky lasers, which hinders the application of resonantly driven two-level emitters in compact photonic quantum systems. Here we address this issue and present a concept for a compact resonantly driven single-photon source by performing quantum-optical spectroscopy of a two-level system using a compact high-β microlaser as the excitation source. The two-level system is based on a semiconductor quantum dot (QD), which is excited resonantly by a fiber-coupled electrically driven micropillar laser. We dress the excitonic state of the QD under continuous wave excitation, and trigger the emission of single photons with strong multi-photon suppression (, g^{(2)}(0) = 0.02) and high photon indistinguishability (V = 57±9%) via pulsed resonant excitation at 156 MHz. These results clearly demonstrate the high potential of our resonant excitation scheme, which can pave the way for compact electrically driven quantum light sources with excellent quantum properties to enable the implementation of advanced quantum communication protocols.

New Formulation of Magnetization Equation for Flowing Nuclear Spin Under Nuclear Magnetic Resonance/Magnetic Resonance Imaging Excitation

We have obtained from the Bloch nuclear magnetic resonance (NMR) equations the correct dependence of the single component My and Mz at resonance (NMR/magnetic resonance imaging (MRI)) on relaxation times, rf B1 field (pulsed or continuous), blood(nuclear spin) flow velocity, etc., in the rotating frame of reference. We find that the new formulation for the first time uniquely describes the true relationship between individual single component My or Mz of magnetization of flowing nuclear spin with the above quantities (excluding diffusion and gradient fields) during NMR/MRI excitation. The equations are applicable for both continuous wave (CW) and pulsed NMR experiments with or without flow of spins. Our approaches can be extended easily to include gradient fields and diffusion of spins, if needed in NMR/MRI experiments. We also discuss the application of our equations to a specific case of magnetic resonance (MR) excitation scheme: Free induction decay. The new equations and further equations that can be derived with the methodologies used here can advance the techniques of noninvasive blood flow estimation by MR and also accurate extraction of parameters of clinical importance by enabling accurate simulation of the MR images (of blood flow and tissue) and comparison with experimental MR images. The detailed simulations from the equations will be published in the next paper.

Clocking the Ultrafast Electron Cooling in Anatase Titanium Dioxide Nanoparticles

The recent identification of strongly bound excitons in room-temperature anatase TiO2 single crystals and nanoparticles underscores the importance of bulk many-body effects in samples used for applications. Here, for the first time, we unravel the interplay between many-body interactions and correlations in highly excited anatase TiO2 nanoparticles using ultrafast two-dimensional deep-ultraviolet spectroscopy. With this approach, under nonresonant excitation, we disentangle the optical nonlinearities contributing to the bleach of the lowest direct exciton peak. This allows us to clock the ultrafast time scale of the hot electron thermalization in the conduction band with unprecedented temporal resolution, which we determine to be <50 fs, due to the strong electron–phonon coupling in the material. Our findings call for the design of alternative resonant excitation schemes in photonics and nanotechnology.

Phonon-Assisted Two-Photon Interference from Remote Quantum Emitters.

Photonic quantum technologies are on the verge of finding applications in everyday life with quantum cryptography and quantum simulators on the horizon. Extensive research has been carried out to identify suitable quantum emitters and single epitaxial quantum dots have emerged as near-optimal sources of bright, on-demand, highly indistinguishable single photons and entangled photon-pairs. In order to build up quantum networks, it is essential to interface remote quantum emitters. However, this is still an outstanding challenge, as the quantum states of dissimilar “artificial atoms” have to be prepared on-demand with high fidelity and the generated photons have to be made indistinguishable in all possible degrees of freedom. Here, we overcome this major obstacle and show an unprecedented two-photon interference (visibility of 51 ± 5%) from remote strain-tunable GaAs quantum dots emitting on-demand photon-pairs. We achieve this result by exploiting for the first time the full potential of a novel phonon-assisted two-photon excitation scheme, which allows for the generation of highly indistinguishable (visibility of 71 ± 9%) entangled photon-pairs (fidelity of 90 ± 2%), enables push-button biexciton state preparation (fidelity of 80 ± 2%) and outperforms conventional resonant two-photon excitation schemes in terms of robustness against environmental decoherence. Our results mark an important milestone for the practical realization of quantum repeaters and complex multiphoton entanglement experiments involving dissimilar artificial atoms.

In Situ Raman Analysis of CO₂-Assisted Drying of Fruit-Slices.

This work explores the feasibility of applying in situ Raman spectroscopy for the online monitoring of the supercritical carbon dioxide (SC-CO2) drying of fruits. Specifically, we investigate two types of fruits: mango and persimmon. The drying experiments were carried out inside an optical accessible vessel at 10 MPa and 313 K. The Raman spectra reveal: (i) the reduction of the water from the fruit slice and (ii) the change of the fruit matrix structure during the drying process. Two different Raman excitation wavelengths were compared: 532 nm and 785 nm. With respect to the quality of the obtained spectra, the 532 nm excitation wavelength was superior due to a higher signal-to-noise ratio and due to a resonant excitation scheme of the carotenoid molecules. It was found that the absorption of CO2 into the fruit matrix enhances the extraction of water, which was expressed by the obtained drying kinetic curve.

High efficiency resonance ionization of palladium with Ti:sapphire lasers

This work presents the development and testing of highly efficient excitation schemes for resonance ionization of palladium. To achieve the highest ionization efficiencies, a high-power, high repetition rate Ti:sapphire laser system was used and 2-step, 3-step and 4-step schemes were investigated and compared. Starting from different excited steps, the frequencies of the final ionization steps were tuned across the full accessible spectral range of the laser system, revealing several autoionizing Rydberg series, which converge towards the energetically higher lying state of the Pd+ ion ground state configuration. Through proper choice of these excitation steps, we developed a highly efficient, fully resonant 3-step excitation scheme, which lead to overall efficiencies of % and %, measured at two independent mass separator setups. To our knowledge, these are presently the highest efficiency values ever achieved with a resonance ionization laser ion source.

Experimental realization of a polariton beam amplifier

In this report we demonstrate a novel concept for a planar cavity polariton beam amplifier using non-resonant excitation. In contrast to resonant excitation schemes, background carriers are injected which form excitons, providing both gain and a repulsive potential for a polariton condensate. Using an attractive potential environment induced by a locally elongated cavity layer, the repulsive potential of the injected background carriers is compensated and a significant amplification of polariton beams is achieved without beam distortion.

Single-photon emission at a rate of 143 MHz from a deterministic quantum-dot microlens triggered by a mode-locked vertical-external-cavity surface-emitting laser

We report on the realization of a quantum dot (QD) based single-photon source with a record-high single-photon emission rate. The quantum light source consists of an InGaAs QD which is deterministically integrated within a monolithic microlens with a distributed Bragg reflector as back-side mirror, which is triggered using the frequency-doubled emission of a mode-locked vertical-external-cavity surface-emitting laser (ML-VECSEL). The utilized compact and stable laser system allows us to excite the single-QD microlens at a wavelength of 508 nm with a pulse repetition rate close to 500 MHz at a pulse width of 4.2 ps. Probing the photon statistics of the emission from a single QD state at saturation, we demonstrate single-photon emission of the QD-microlens chip with g(2)(0) &amp;lt; 0.03 at a record-high single-photon flux of (143 ± 16) MHz collected by the first lens of the detection system. Our approach is fully compatible with resonant excitation schemes using wavelength tunable ML-VECSELs, which will optimize the quantum optical properties of the single-photon emission in terms of photon indistinguishability.