Coherent Transfer Research Articles

Frequency comb-to-comb stabilization over a 1.3-km free-space atmospheric optical link

Stabilizing a frequency comb to an ultra-stable optical frequency reference requires a multitude of optoelectronic peripherals that have to operate under strict ambient control. Meanwhile, the frequency comb-to-comb stabilization aims to synchronize a slave comb to a well-established master comb with a substantial saving in required equipment and efforts. Here, we report an utmost case of frequency comb-to-comb stabilization made through a 1.3 km free-space optical (FSO) link by coherent transfer of two separate comb lines along with a feedback suppression control of atmospheric phase noise. The FSO link offers a transfer stability of 1.7 × 10–15 at 0.1 s averaging, while transporting the master comb’s stability of 1.2 × 10–15 at 1.0 s over the entire spectrum of the slave comb. Our remote comb-to-comb stabilization is intended to expedite diverse long-distance ground-to-ground or ground-to-satellite applications; as demonstrated here for broadband molecular spectroscopy over a 6 THz bandwidth as well as ultra-stable microwaves generation with phase noise of -80 dBc Hz–1 at 1 Hz.

Decoherence and Revival in Attosecond Charge Migration Driven by Non-adiabatic Dynamics.

Attosecond charge migration is a periodic evolution of the charge density at specific sites of a molecule on a time scale defined by the energy intervals between the electronic states involved. Here, we report the observation of charge migration in neutral silane (SiH4) in 690 as, its decoherence within 15 fs, and its revival after 40-50 fs, using X-ray attosecond transient absorption spectroscopy. We observe the migration of charge as pairs of quantum beats with a characteristic spectral phase in the transient spectrum, in agreement with theory. The decay and revival of the degree of electronic coherence is found to be a result of both adiabatic and non-adiabatic dynamics in the populated Rydberg and valence states. The experimental results are supported by fully quantum-mechanical ab-initio calculations that include both electronic and nuclear dynamics, which additionally support the experimental evidence that conical intersections can mediate the transfer of electronic coherence from an initial superposition state to another one involving a different lower-lying state.

Environment-Driven Coherent Population Transfer Governs the Ultrafast Photophysics of Tryptophan.

By combining UV transient absorption spectroscopy with sub-30-fs temporal resolution and CASPT2/MM calculations, we present a complete description of the primary photoinduced processes in solvated tryptophan. Our results shed new light on the role of the solvent in the relaxation dynamics of tryptophan. We unveil two consecutive coherent population transfer events involving the lowest two singlet excited states: a sub-50-fs nonadiabatic La → Lb transfer through a conical intersection and a subsequent 220 fs reverse Lb → La transfer due to solvent-assisted adiabatic stabilization of the La state. Vibrational fingerprints in the transient absorption spectra provide compelling evidence of a vibronic coherence established between the two excited states from the earliest times after photoexcitation and lasting until the back-transfer to La is complete. The demonstration of response to the environment as a driver of coherent population dynamics among the excited states of tryptophan closes the long debate on its solvent-assisted relaxation mechanisms and extends its application as a local probe of protein dynamics to the ultrafast time scales.

Sub-molecular diagnostics of coherent energy transfer.

Sub-molecular diagnostics of coherent energy transfer.

Molecular Vibrational Polaritons Towards Quantum Technologies

AbstractMolecular vibrational polaritons (MVPs)—a hybrid molecular‐photon quasiparticle—and the development of a proof‐of‐principle quantum technology platform are discussed to simulate coherence transfer, for use at room temperature. It is shown that MVPs can form qubits, coherence, and have nonlinear interactions, all at room temperature. Some new insights, such as polaritonic nonlinearity dependence on macroscopic properties including cavity thickness and molecular concentrations are also uncovered. It is hoped that these advances can stimulate more research in developing this system into a quantum technology platform free from the constraints imposed by the requirement of cryogenic conditions.

Nonadiabatic Molecular Dynamics with Extended Density Functional Tight-Binding: Application to Nanocrystals and Periodic Solids.

In this work, we report a new methodology for nonadiabatic molecular dynamics calculations within the extended tight-binding (xTB) framework. We demonstrate the applicability of the developed approach to finite and periodic systems with thousands of atoms by modeling "hot" electron relaxation dynamics in silicon nanocrystals and electron-hole recombination in both a graphitic carbon nitride monolayer and a titanium-based metal-organic framework (MOF). This work reports the nonadiabatic dynamic simulations in the largest Si nanocrystals studied so far by the xTB framework, with diameters up to 3.5 nm. For silicon nanocrystals, we find a non-monotonic dependence of "hot" electron relaxation rates on the nanocrystal size, in agreement with available experimental reports. We rationalize this relationship by a combination of decreasing nonadiabatic couplings related to system size and the increase of available coherent transfer pathways in systems with higher densities of states. We emphasize the importance of proper treatment of coherences for obtaining such non-monotonic dependences. We characterize the electron-hole recombination dynamics in the graphitic carbon nitride monolayer and the Ti-containing MOF. We demonstrate the importance of spin-adaptation and proper sampling of surface hopping trajectories in modeling such processes. We also assess several trajectory surface hopping schemes and highlight their distinct qualitative behavior in modeling the excited-state dynamics in superexchange-like models depending on how they handle coherences between nearly parallel states.

Nuclear coherent population transfer to the Th229m isomer using x-ray pulses

Population of the 8 eV $^{229m}$Th isomer via the second nuclear excited state at 29.19 keV by means of coherent x-ray pulses is investigated theoretically. We focus on two nuclear coherent population transfer schemes using partially overlapping x-ray pulses known from quantum optics: stimulated Raman adiabatic passage (STIRAP), and successive $\pi$ pulses. Numerical results are presented for three possible experimental setups. Our results identify the Gamma Factory as the most promising scenario, where two ultraviolet pulses combined with relativistically accelerated ions deliver the required intensities for efficient isomer population. Our simulations require knowledge of the in-band and cross-band nuclear transition probabilities. We give theoretically predicted values for the latter and discuss them in the context of recent experiments.

Nonlinear Computational Edge Detection Metalens

AbstractOptical image processing and computing systems provide supreme information processing rates by utilizing parallel optical architectures. Existing optical analog processing techniques require multiple devices for projecting images and executing computations. In addition, those devices are typically limited to linear operations due to the time‐invariant optical responses of the building materials. In this work, a single metalens with an illumination intensity dependent coherent transfer function (CTF) is proposed and experimentally demonstrated, which performs varying computed imaging without requiring any additional optical components. The metalens consisting of nanoantenna structures with a static geometric phase and a nonlinear metallic quantum well layer offering an intensity‐dependent dynamic phase results in a continuously tunable CTF. The approach allows for a weighted summation of two designed functions based on the metalens design, which potentially enables all optical computations of complex functions. The nonlinear metalens may lead to important applications in optical neural networks and parallel analog computing.

Coherent population transfer of Rydberg atoms in a dual-microwave driven five-level configuration

We report the coherent population transfer (CPT) of Rydberg atoms with a 5S1/2-5P3/2-57D5/2-58P3/2-58S1/2 level configuration of 85Rb using a dual-microwave driven four-step excitation scheme. The electromagnetically induced transparency, Autler–Townes splitting, and CPT are experimentally observed with different energy level configurations. The effects of power and frequency detuning of microwave fields are investigated to demonstrate plentiful population dynamics. To comprehend the entire coherent mechanism, a theoretical model based on the density-matrix is proposed and numerically solved with the steady-state condition. Compared with the mono-microwave-assisted coherent process of Rydberg atoms, dual-microwave results, which are the optimal coherent transfer evolution of atom population with multiple tunable parameters, are presented in this scheme. This work lays the foundation for studying multi-level coherence effects and manufacturing multi-channel quantum sensors.

Enhanced Nuclear Magnetic Resonance Spectroscopy with Isotropic Mixing as a Pseudodimension.

Chemical analysis based on liquid-state nuclear magnetic resonance spectroscopy exploits numerous observables, mainly chemical shifts, relaxation rates, and internuclear coupling constants. Regarding the latter, the efficiencies of internuclear coherence transfers may be encoded in spectral peak intensities. The dependencies of these intensities on the experimental parameter that influences the transfer, for example, mixing time, are an important source of structural information. Yet, they are costly to measure and difficult to analyze. Here, we show that peak intensity build-up curves in two-dimensional total correlation spectroscopy (2D TOCSY) experiments may be quickly measured by employing nonuniform sampling and that their analysis can be effective if supported by quantum mechanical calculations. Thus, such curves can be used to form a new, third pseudodimension of the TOCSY spectrum. Similarly to the other two frequency dimensions, this one also resolves ambiguities and provides characteristic information. We show how the approach supports the analysis of a fragment of protein Tau Repeat-4 domain. Yet, its potential applications are far broader, including the analysis of complex mixtures or other polymers.

Coherent frequency transfer with < 5*10-21 stability via a multi-branch comb with noise cancellation.

We demonstrate a multi-branch frequency comb for spectral purity transfer incorporating hardware enabled noise cancellation based on a cw noise transfer laser. We verify coherent frequency transfer at stabilities ≈ 2×10-18 in 1 second and < 5×10-21 in 10,000 seconds without any reference cavity.

Wavelike electronic energy transfer in donor-acceptor molecular systems through quantum coherence.

Quantum-coherent intermolecular energy transfer is believed to play a key role in light harvesting in photosynthesis and photovoltaics. So far, a direct, real-space demonstration of quantum coherence in donor-acceptor systems has been lacking because of the fragile quantum coherence in lossy molecular systems. Here, we precisely control the separations in well-defined donor-acceptor model systems and unveil a transition from incoherent to coherent electronic energy transfer. We monitor the fluorescence from the heterodimers with subnanometre resolution through scanning tunnelling microscopy induced luminescence. With decreasing intermolecular distance, the dipole coupling strength increases and two new emission peaks emerge: a low-intensity peak blueshifted from the donor emission, and an intense peak redshifted from the acceptor emission. Spatially resolved spectroscopic images of the redshifted emission exhibit a σ antibonding-like pattern and thus indicate a delocalized nature of the excitonic state over the whole heterodimer due to the in-phase superposition of molecular excited states. These observations suggest that the exciton can travel coherently through the whole heterodimer as a quantum-mechanical wavepacket. In our model system, the wavelike quantum-coherent transfer channel is three times more efficient than the incoherent channel.

Magnetic coherence effects in the spectroscopy of transitions between energy levels with total angular momenta J = 1/2 and J = 1 using unidirectional waves

The physical processes that form the spectra of saturated absorption resonances at atomic transitions between energy levels with angular momenta J = 1/2 and J = 1 in the field of two unidirectional linearly polarised laser waves are studied analytically and numerically. It is shown that the specific features of the resonance spectra are formed in the Λ-schemes of transitions and manifest themselves in the form of narrow coherent structures – dips due to the magnetic coherence (optical orientation) of the transition levels induced by the optical fields. In this case, the energy levels of the lower state make the main contribution, and the contribution of the transfer of magnetic coherence from the sublevels of the upper state to the lower ones in the resonance amplitude manifests itself as an additive. Conditions are found under which the nonlinear resonance is exclusively coherent. The effect of the saturating wave field on the shape of coherent resonance structures is studied.

Quantum frequency conversion with coherent transfer of time-bin encoding

Time-bin encoding of photons offers a robust kind of long-distance quantum communication over lossy channels. The diversity of material nodes in quantum networks operating at natural frequencies requires coherent frequency and wave-form conversion of information-carrying photons to provide an efficient quantum interface with optical fibers and various quantum memories, which has been extensively studied. However, the quantum frequency conversion with transfer of time-bin encoding between single photons of different wavelengths has not yet been explored. In this paper, we present a method for efficiently exchanging time-bin encoding in the conversion process between two photons propagating in cold tripod atoms driven by a strong laser field. The latter is designed to slow down photons and suppress their absorption due to electromagnetically induced transparency. Photons interact parametrically through modified atomic coherence, which is utilized also to achieve equal group velocities of photons. We demonstrate the ability of our model to generate entanglement between distant atoms that equally share the original quantum information stored in the ground-state polarization qubits of both atoms. The proposed method for frequency conversion based on modified atomic coherence is promising because it can simplify the implementation of reliable and high-speed quantum communication protocols based on single-photon entanglement.

Immersive Storytelling in Creative Media, Smart Manufacturing and Healthcare

The paper explores interactive storytelling in Augmented and Virtual Reality. It is based on the project ANONYMIZED that bridges the gap between technological developments and their application and aims to combine art, economy and science. Five use cases employ an interdisciplinary research design in the areas of Creative Media, Smart Manufacturing and Healthcare. They all develop prototypical applications but also attend to their contextualization with focus on narrative elements: Each use case defines a ”story” in its own context, the purpose of its narration, and its media specificity. Due to their increased availability, virtual and immersive technologies have not only led to a resurgence of their popularity but also to intriguing new perspectives regarding their use in different contexts. Our research project employs state-of-the art AR and VR technology in five use cases about VR Interaction, Motion Tracking in Artistic VR, Auditory AR for Industry, AR Interfaces for Industry and AR Education for Patients. All of them inquire prototypical applications but relate to the central concept of interactive storytelling. The project addresses three distinct dimensions of storytelling in each use case: the production of a coherent story, the collection and transfer of knowledge, and the specificity of the used technology. Those dimensions are widely known and employed. However, they are seldomly intertwined in one interdisciplinary project focusing on immersive media. Furthermore, the notions of interactivity and immersion play significant roles in the study of storytelling in conjunction with VR an AR. Following papers about immersive storytelling are significant: John Bucher (2017) e. g. examines the timeless principles of storytelling and how they are applied, transformed, and transcended in VR. Marie-Laure Ryan (2015) combines the concepts of immersion and interactive storytelling into a Poetics of Immersion including spatial, temporal and emotional categories. She highlights underlying interactive structures such as the Complete Graph, the Network, the Flowchart. Moya Baldry (2018) discusses the role of the author in complex narratives of immersive environments. Covering the areas of Creative Media, Smart Manufacturing and Healthcare leads to a very specific research design, as each area is connected to different research contexts. Therefore, the paper focuses on the above-mentioned dimensions of storytelling and addresses the following questions: How is the “story” defined in each context and what is its purpose? Which methods and technologies are used to convey it? Which narrative elements show potential and how can they be developed further for future applications? The paper reflects on the outcome of the use cases and potential future applications of interactive storytelling in immersive media.

Coherent manipulation of trapped Rb atoms by overlapping frequency-chirped laser pulses: theory and experiment

We present results of experimental and theoretical studies of coherent momentum transfer to rubidium atoms in a magneto-optical trap by pairs of counter-propagating frequency-modulated (chirped) laser pulses. The counter-propagating pulse pairs partially overlap each other leading to multiphoton interaction processes. We show experimentally that the mechanical momentum transferred to atoms in this scheme of interaction is larger than in the case of non-overlapping pulse pairs acting separately on the atoms. Results of numerical simulations that take into account all relevant hyperfine energy states of Rb along with the influence of relaxation and re-pumping processes are in good agreement with obtained experimental results.Graphical abstract

NMR Assignment of Methyl Groups in Immobilized Proteins Using Multiple-Bond 13C Homonuclear Transfers, Proton Detection, and Very Fast MAS.

In nuclear magnetic resonance spectroscopy of proteins, methyl protons play a particular role as extremely sensitive reporters on dynamics, allosteric effects, and protein–protein interactions, accessible even in high-molecular-weight systems approaching 1 MDa. The notorious issue of their chemical shift assignment is addressed here by a joint use of solid-state 1H-detected methods at very fast (nearly 100 kHz) magic-angle spinning, partial deuteration, and high-magnetic fields. The suitability of a series of RF schemes is evaluated for the efficient coherence transfer across entire 13C side chains of methyl-containing residues, which is key for establishing connection between methyl and backbone 1H resonances. The performance of ten methods for recoupling of either isotropic 13C–13C scalar or anisotropic dipolar interactions (five variants of TOBSY, FLOPSY, DIPSI, WALTZ, RFDR, and DREAM) is evaluated experimentally at two state-of-the-art magic-angle spinning (55 and 94.5 kHz) and static magnetic field conditions (18.8 and 23.5 T). Model isotopically labeled compounds (alanine and Met-Leu-Phe tripeptide) and ILV-methyl and amide-selectively protonated, and otherwise deuterated chicken α-spectrin SH3 protein are used as convenient reference systems. Spin dynamics simulations in SIMPSON are performed to determine optimal parameters of these RF schemes, up to recently experimentally attained spinning frequencies (200 kHz) and B 0 field strengths (28.2 T). The concept of linearization of 13C side chain by appropriate isotope labeling is revisited and showed to significantly increase sensitivity of methyl-to-backbone correlations. A resolution enhancement provided by 4D spectroscopy with non-uniform (sparse) sampling is demonstrated to remove ambiguities in simultaneous resonance assignment of methyl proton and carbon chemical shifts.

Customizable Quantum Control via Stimulated Raman User-Defined Passage

Adiabatic quantum-control schemes are widely used in the areas of quantum-information processing and quantum sensing. The very requirement of adiabaticity in these schemes often leads to problems of low efficiency and being sensitive to decoherence. To address such issues, various methods have been developed for accelerating adiabatic processes, but they often need to be designed on an $ad\phantom{\rule{0.2em}{0ex}}hoc$ basis. Here we propose and experimentally demonstrate an inverse-engineering approach, where a parameterized state of the Schr\"odinger equation is employed for constructing desired evolutions. Within a single and simple frame, the user-defined passages can be flexibly customized for different objectives and systems. To experimentally benchmark its performance, we implement this approach in a task of coherent state transfer in a superconducting Xmon device. We find that our method completed the transfer with the fastest speed and highest efficiency (&gt;99.5%) among all recent experiments performed in similar configurations.

Laser-Controlled Charge Transfer in a Two-Dimensional Organic/Inorganic Optical Coherent Nanojunction

Understanding the fundamental mechanisms ruling laser-induced coherent charge transfer in hybrid organic/inorganic interfaces is of paramount importance to exploit these systems in next-generation opto-electronic applications. In a first-principles work based on real-time time-dependent density-functional theory, we investigate the ultrafast charge-carrier dynamics of a prototypical two-dimensional vertical nanojunction formed by a MoSe$_2$ monolayer with adsorbed pyrene molecules. The response of the system to the incident pulse, set in resonance with the frequency of the lowest-energy transition in the physisorbed moieties, is clearly nonlinear. Under weak pulses, charge transfer occurs from the molecules to the monolayer while for intensities higher than 1000 GW/cm$^{2}$, the direction of charge transfer is reverted, with electrons being transferred from MoSe$_2$ to pyrene. This finding is explained by Pauli blocking: laser-induced (de)population of (valence) conduction states saturates for intensities beyond 200 GW/cm$^{2}$. Evidence of multi-photon absorption is also provided by our results. A thorough analysis of electronic current density, excitation energy, and number of excited electrons supports the proposed rationale and suggests the possibility to create an inorganic/organic coherent optical nanojunction for ultrafast electronics.

Coherent Optical Frequency Transfer via a 490 km Noisy Fiber Link

We demonstrate the coherent transfer of an ultrastable optical frequency reference over a 490 km noisy field fiber link. The fiber-induced phase noise power spectrum density per-unit-length at 1 Hz offset frequency can reach up to 510 rad2⋅Hz−1⋅km−1, which is much higher than the fiber noise observed in previous reports. This extreme level of phase noise is mainly due to the fiber link laying underground along the highway. Appropriate phase-locked loop parameters are chosen to complete the active compensation of fiber noise by measuring the intensity fluctuation of additional phase noise and designing a homemade digital frequency division phase discriminator with a large phase detection range of 212 π rad. Finally, a noise suppression intensity of approximately 40 dB at 1 Hz is obtained, with fractional frequency instability of 1.1 × 10−14 at 1 s averaging time, and 3.7 × 10−19 at 10000 s. The transfer system will be used for remote atomic clock comparisons and optical frequency distribution over a long-distance communication network established in China.