Periodic Reporting for period 1 - ULISSES (Ultrafast molecular chirality: twisting light to twist electrons on ultrafast time scale)
Berichtszeitraum: 2022-10-01 bis 2025-03-31
An object is called chiral if it cannot be superimposed with its mirror image. Two non-superimposable mirror twins of the same molecule are called enantiomers. Chirality is a feature of leaving matter as it enables metabolic reactions and stability of proteins. Distinguishing molecular enantiomers is extremely important for medicine, pharmacology and drug industry, agriculture and food industry. Exquisite methods for detecting and separating molecular enantiomers using e.g. gas and liquid chromatography are rooted in thermodynamics and kinetics, operating at the equilibrium state of matter and involving inherently slow processes. However today one desires a combination of high efficiency and detection speed.
Light is the fastest agent in mediating electric signals. However, since the early 19-th century, the chiral light-matter coupling was believed to require the interaction with the magnetic field component of light. For medium-sized molecules such interaction is inefficient in the optical range as it scales with the ratio of the molecular size to the light wavelength, making chiral discrimination with light challenging.
ERC project ULISSES (Ultrafast chirality: twisting light to twist electrons) follows an alternative route exploring local chiral interactions and non-equilibrium state of matter. Local chirality may sound as an oxymoron, since chirality is a geometric property of an extended object defined by mutual orientations of its parts. The appeal to non-equilibrium state of matter solves the apparent controversy: temporal evolution of any local vectorial observable can substitute the missing spatial dimensions. For example, the molecular handedness maps into the vector of induced polarization or current, which trace a chiral trajectory in time. These vectors can be followed in time to discriminate enantiomers. One can also create light with electric field vector tracing a chiral trajectory within a single cycle of temporal evolution. Non-linear light matter interactions couple temporal chirality of light and temporal chirality of molecular currents yielding strong enantio-sensitive response.
Our Odyssey into the world of local chirality has both fundamental and practical goals. We progress from establishing the concepts associated with geometry of temporal structures in light and matter to identifying new enantio-sensitive observables stemming from these concepts to developing new highly efficient methods of enantio-discrimination.
Light is the fastest agent in mediating electric signals. However, since the early 19-th century, the chiral light-matter coupling was believed to require the interaction with the magnetic field component of light. For medium-sized molecules such interaction is inefficient in the optical range as it scales with the ratio of the molecular size to the light wavelength, making chiral discrimination with light challenging.
ERC project ULISSES (Ultrafast chirality: twisting light to twist electrons) follows an alternative route exploring local chiral interactions and non-equilibrium state of matter. Local chirality may sound as an oxymoron, since chirality is a geometric property of an extended object defined by mutual orientations of its parts. The appeal to non-equilibrium state of matter solves the apparent controversy: temporal evolution of any local vectorial observable can substitute the missing spatial dimensions. For example, the molecular handedness maps into the vector of induced polarization or current, which trace a chiral trajectory in time. These vectors can be followed in time to discriminate enantiomers. One can also create light with electric field vector tracing a chiral trajectory within a single cycle of temporal evolution. Non-linear light matter interactions couple temporal chirality of light and temporal chirality of molecular currents yielding strong enantio-sensitive response.
Our Odyssey into the world of local chirality has both fundamental and practical goals. We progress from establishing the concepts associated with geometry of temporal structures in light and matter to identifying new enantio-sensitive observables stemming from these concepts to developing new highly efficient methods of enantio-discrimination.
We aim to establish: 1) novel, highly efficient, all-optical ways of enantio-discrimination, 2) enantio-resolved movies of chiral electronic dynamics, 3) chiral topological light – a new tool for chiral interactions, and 4) bridges between light-driven electron dynamics in chiral gases and topological effects in solids, with the goal of establishing new efficient and robust enantio-sensitive observables, where efficiency comes from local chirality and robustness comes from topological concepts.
1) We have established two new efficient methods of enantio-discrimination based on local chirality: Enantio-sensitive Free Induction Decay (Khokhlova et al, Science Advances 2022) and Enantio-sensitive Sum-Frequency Generation (Vogwell et al, Science Advances 2023). Sum frequency generation (SFG) is an example of non-invasive and versatile technique, but its application to chiral sensing was limited to the phase of the emitted SFG light. Locally chiral light overcomes this limitation by inducing interference between chiral SFG and achiral third harmonic generation, achieving ultimate enantio-sensitivity: one enantiomer remains dark, while the other emits a bright SFG signal.
2) We have introduced a concept of enantio-sensitive charge directed reactivity and conditions for its observation (Ordonez et al Communications Physics 2023). We uncovered the fundamental link between the direction of electron current and direction of motion of molecular fragments in chiral molecules and demonstrated that its enantio-sensitivity can reach 40 % -- extremely high value in comparison with sub-percent enantio-sensitivity of standard methods. These concepts contributed to the experimental (Callegari group, DESY) movies of ultrafast chiral currents excited in chiral molecules (Wanie et al, Nature 2024).
3) We have created a new type of structured light which is both locally chiral and has topological properties (Mayer et al, Nature Photonics 2024). Our set-up involves a combination of two-color tightly focused counter-rotating circularly polarised vortex beams such that light polarization vector draws a trefoil knot in time and forms a vortex with controlled topological charge in space. Our calculations show that such light enables robust detection of sub-percent values of enantiomeric excess. Topological robustness is due to conservation of topological charge –which remains unchanged under e.g. light intensity fluctuations. The major challenge was to extend our concepts to the situation when several topological charges co-exist. Such situation emerges due to the lack of control over circularity of incoming beams. Our work has been highlighted in the News and Views commentary (D. Smirnova et al Nature Photonics 2024).
4) Temporal geometry is recorded on sub-laser cycle time -scale. Is it possible to excite and detect temporal geometry in solids? Theoretically we have found a way to record and characterise the sub-cycle correlated charge dynamics in a model high temperature superconductor (Valmispild et al, Nature Photonics 2024) and also in a context of experiment (Biegert group, ICFO) on light driven topology in a two-dimensional material (Tulnev et al, Nature 2024). Thus the concepts of temporal geometry can be extended to correlated materials and chiral solids.
1) We have established two new efficient methods of enantio-discrimination based on local chirality: Enantio-sensitive Free Induction Decay (Khokhlova et al, Science Advances 2022) and Enantio-sensitive Sum-Frequency Generation (Vogwell et al, Science Advances 2023). Sum frequency generation (SFG) is an example of non-invasive and versatile technique, but its application to chiral sensing was limited to the phase of the emitted SFG light. Locally chiral light overcomes this limitation by inducing interference between chiral SFG and achiral third harmonic generation, achieving ultimate enantio-sensitivity: one enantiomer remains dark, while the other emits a bright SFG signal.
2) We have introduced a concept of enantio-sensitive charge directed reactivity and conditions for its observation (Ordonez et al Communications Physics 2023). We uncovered the fundamental link between the direction of electron current and direction of motion of molecular fragments in chiral molecules and demonstrated that its enantio-sensitivity can reach 40 % -- extremely high value in comparison with sub-percent enantio-sensitivity of standard methods. These concepts contributed to the experimental (Callegari group, DESY) movies of ultrafast chiral currents excited in chiral molecules (Wanie et al, Nature 2024).
3) We have created a new type of structured light which is both locally chiral and has topological properties (Mayer et al, Nature Photonics 2024). Our set-up involves a combination of two-color tightly focused counter-rotating circularly polarised vortex beams such that light polarization vector draws a trefoil knot in time and forms a vortex with controlled topological charge in space. Our calculations show that such light enables robust detection of sub-percent values of enantiomeric excess. Topological robustness is due to conservation of topological charge –which remains unchanged under e.g. light intensity fluctuations. The major challenge was to extend our concepts to the situation when several topological charges co-exist. Such situation emerges due to the lack of control over circularity of incoming beams. Our work has been highlighted in the News and Views commentary (D. Smirnova et al Nature Photonics 2024).
4) Temporal geometry is recorded on sub-laser cycle time -scale. Is it possible to excite and detect temporal geometry in solids? Theoretically we have found a way to record and characterise the sub-cycle correlated charge dynamics in a model high temperature superconductor (Valmispild et al, Nature Photonics 2024) and also in a context of experiment (Biegert group, ICFO) on light driven topology in a two-dimensional material (Tulnev et al, Nature 2024). Thus the concepts of temporal geometry can be extended to correlated materials and chiral solids.
The key principle of enantio-discrimination employed in ULISSES is exciting and following non-equilibrium dynamics in electronic states of chiral molecules via non-linear electronic or optical response, which goes beyond standard linear static chiroptical methods such as optical rotation and circular dichroism.
Practical impacts of our work depend on implementation of our methods into devices capable to sense chirality. By the end of the project we aim to identify the optimal approach among several proposed methods in ULISSES and consider ways towards its practical implementation. Fundamental impact of our work is in exploring geometric properties of photodynamic processes in chiral molecules and establishing new functionalities associated with chiral dynamics such as enantio-sensitive molecular orientation (Ordonez et al Communications Physics 2023) and its extension to spin degree of freedom.
Practical impacts of our work depend on implementation of our methods into devices capable to sense chirality. By the end of the project we aim to identify the optimal approach among several proposed methods in ULISSES and consider ways towards its practical implementation. Fundamental impact of our work is in exploring geometric properties of photodynamic processes in chiral molecules and establishing new functionalities associated with chiral dynamics such as enantio-sensitive molecular orientation (Ordonez et al Communications Physics 2023) and its extension to spin degree of freedom.