- Nanoscience Center and Department of Chemistry, University of Jyväskylä, P.O. Box 35, 40014, Jyväskylä, Finland
- Departamento de Fisica Teorica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid, Spain
The strong light-matter coupling regime, in which excitations of materials hybridize with excitations of confined light modes into polaritons, holds great promise in various areas of science and technology, including low-threshold lasing , energy transfer [2,3] and photochemical catalysis [4,5]. To understand the effects of strong light-matter coupling on the molecular dynamics in these processes, we developed a multiscale quantum mechanics/molecular mechanics (QM/MM) simulation model that we implemented for massive parallel computations on modern high-performance computing (HPC) platforms [6-8]. With our model we have carried out simulations with thousands of molecules strongly coupled to the confined light modes of optical cavities, to investigate in atomic detail (i) how polaritons relax, (ii) how polaritons propagate and (iii) how collective strong coupling affects photochemistry.
- Kéna-Cohen, S.; Forrest, S. R. Room-temperature polariton lasing in an organic single-crystal microcavity. Nat. Photonics 2010, 4, 371–37
- Rozenman, G. G.; Akulov, K.; Golombek, A.; Schwartz, T. Long-Range Transport of Organic Exciton-Polaritons Revealed by Ultrafast Microscopy. ACS Photonics 2018, 5, 105–110
- Berghuis, M. A.; Tichauer, R. H.; de Jong, L.; Sokolovskii, I.; Bai, P.; Ramezani, M.; Murai, S.; Groenhof, G.; Gómez Rivas, J. Controlling Exciton Propagation in Organic Crystals through Strong Coupling to Plasmonic Nanoparticle Arrays. ACS Photonics 2022, https://doi.org/10.1021/acsphotonics.2c00007
- Hutchison, J. A.; Schwartz, T.; Genet, C.; Devaux, E.; Ebbesen, T. W. Modifying Chemical Landscapes by Coupling to Vacuum Fields. Angew. Chem. Int. Ed. 2012, 51, 1592–1596
- Stranius, K.; Herzog, M.; Börjesson, K. Selective manipulation of electronically excited states through strong light-matter interactions. Nat. Comm. 2018, 9, 2273
- Luk, H.-L.; Feist, J.; Toppari, J. J.; Groenhof, G. Multiscale Molecular Dynamics Simulations of Polaritonic Chemistry. J. Chem. Theory Comput. 2017, 13, 4324–4335
- Groenhof, G.; Climent, C.; Feist, J.; Morozov, D.; Toppari, J. J. Tracking Polariton Relaxation with Multiscale Molecular Dynamics Simulations. J. Chem. Phys. Lett. 2019, 10, 5476–5483
- Tichauer, R. H.; Feist, J.; Groenhof, G. Multiscale simulations of molecular polaritons: the effect of multiple cavity modes on polariton relaxation. J. Chem. Phys. 2021, 154, 104112
When an open quantum system is strongly coupled to a structured environment, describing the dynamics of that system becomes a challenging problem. Moreover, traditional approaches, based on time evolution of the reduced density matrix are generally not able to correctly calculate higher-order or multi-time correlations. I will review recent progress that addresses both these issues, by showing how the time evolution of the system can be efficiently simulated using tensor network methods . Such a tensor network naturally leads one to consider the process tensor (PT), an object which encodes all multi-time correlations of the reservoir . A key insight is that one can construct efficient MPO representations of the PT. This idea makes possible many otherwise challenging tasks, including optimisation of non-Markovian systems  (requiring repeated simulation of the dynamics), and modelling the non-Markovian dynamics of many-body open quantum systems [4,5]. It also prompts identification of alternate algorithms to construct an MPO form of the PT . In particular, I will discuss how this can be used to model the dynamics of molecular polariton condensates , accounting for realistic low-frequency vibrational environments.
The algorithm underpinning this work is publicly available , and we are keen to help support other researchers in using this approach.
- Efficient non-Markovian quantum dynamics using time-evolving matrix product operators. A. Strathearn, P. Kirton, D. Kilda, J. Keeling, B. W. Lovett. Nature Commun. 9, 3322 (2018)
- Exploiting the causal tensor network structure of quantum processes to efficiently simulate non-Markovian path integrals, M. R. Jørgensen and F. A. Pollock, Phys. Rev. Lett. 123, 240602 (2019)
- Efficient exploration of Hamiltonian parameter space for optimal control of non-Markovian open quantum systems. G. E. Fux, E. P. Butler, P. R. Eastham, B. W. Lovett, J. Keeling, Phys. Rev. Lett. 126, 200401 (2021).
- Efficient many-body non-Markovian dynamics of organic polaritons. P. Fowler-Wright, B. W. Lovett, J. Keeling. arXiv:2112.09003
- Thermalization of a spin chain with strong environment coupling. G. E. Fux, D. Kilda, B. W. Lovett, J. Keeling. arXiv:2201.05529
- Numerically-exact simulations of arbitrary open quantum systems using automated compression of environments. M. Cygorek, M. Cosacchi, A. Vagov, V. M. Axt, B. W. Lovett, J. Keeling, E. M. Gauger. Nature Physics 18, 662 (2022)
- The TEMPO collaboration, OQuPy - Open Quantum Systems in Python: A Python 3 package to efficiently compute non-Markovian open quantum systems. (2022). https://oqupy.readthedocs.io/en/latest/
Coherent light-matter interactions provide a powerful means to study and control interacting matter excitations. Using the mature, III-Arsenide semiconductor system, we incoporate a designable photonic crystal mirror to control hybrid light-matter coupled modes (polaritons), and use it to study non-equilibrium quantum orders, including a Bardeen-Cooper-Schrieffer like polariton condensate  and limit cycles self-oscillations  in coupled polariton condensate. The system provides a highly controllable and accessible platform for nonlinear dynamic phenomena and non-equilibrium orders. Using transitional metal dichalcogenides (TMDs) crystals with exceptionally strong light-matter interactions and engineering flexibility, we explore a few interesting opportunities, including strong coupling and exciton lasing in slab photonic crystals [3, 4], bright and tunable moiré excitons , and nonlinear moiré quantum-dot array polaritons . Future development in these materials and integration with innovative photonic structure may open doors to many new scientific and technological opportunities.
- Hu, J. et al. (2021) “Polariton Laser in the Bardeen-Cooper-Schrieffer Regime”, Physical Review X, 11(1), p. 011018.
- Kim, S. et al. (2020) “Emergence of microfrequency comb via limit cycles in dissipatively coupled condensates”, Physical Review B, 101(8), p. 085302.
- Zhang, L. et al. (2018) “Photonic-crystal exciton-polaritons in monolayer semiconductors.” Nature Communications 9, 713
- Paik, E. Y. et al. (2019) “Interlayer exciton laser of extended spatial coherence in atomically thin heterostructures”, Nature, 576(7785), pp. 80–84.
- Zhang, L. et al. (2020) “Twist-angle dependence of moiré excitons in WS 2 /MoSe 2 heterobilayers”, Nature Communications, 11(1), p. 5888.
- Zhang, L. et al. (2021) “Van der Waals Heterostructure Polaritons with Moire-Induced Nonlinearity”, Nature 591, 61–65.
- Universidad Autónoma de Madrid/IFIMAC, Madrid, Spain
- Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany
- Institut für Laserphysik, Universität Hamburg, Hamburg, Germany
In this talk, I discuss several theoretical advances in the field of generating and exploiting squeezeed states. I propose the idea of a squeezed laser , in which a macroscopic photonic occupation powered by stimulated emission develops in a squeezed cavity mode. I discuss possible implementations in the optical regime and the quantum-optical properties of the emission: above the lasing threshold, the emitted light retains both the line narrowing and frequency stabilization characteristic of a laser and the photon correlations characteristic of a photonic mode with squeezed quadratures, which opens news possibilities for applications in quantum metrology and spectroscopy. As an example of future applications, I discuss the quantum advantage that these states provide in the estimation of cross sections of two-photon absorption processes  .
- C. Sánchez Muñoz and D. Jaksch, Phys. Rev. Lett 127, 183603 (2021)
- C. Sánchez Muñoz, G. Frascella and F. Schlawin, Phys. Rev. Research 3, 033250 (2021)
Networks of (interacting) molecular optical dipoles play an important role in natural light harvesting and hold significant promise for designing artificial technologies. Typically, such molecular complexes experience collective interactions with their electromagnetic environment as well as being subject to interactions with local vibrational environments. In this talk, I will aim to give an overview of recent work from my group regarding the conversion of light into matter excitations (1-4), enabling efficient long-range energy transport (5), as well as methodological advances allowing modelling of systems that are strongly coupled to more than one non-additive environment (6).
- Brown and Gauger, J. Phys. Chem. Lett., 10, 15, 4323–4329 (2019)
- Tomasi et al, J. Phys. Chem. Lett., 12, 26, 6143–6151 (2021)
- Werren, Brown and Gauger, in preparation (2022)
- Quach et al, Science Advances (2022)
- Scott, Pollock and Gauger, arXiv:2201.13442; to appear in PRX Quantum (2022)
- Cygorek et al, Nature Physics (2022)
- Max-Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany
- IPCF-CNR, Pisa, Italy
- Chalmers University, Goeteborg, Sweden
- Flatiron Institute, New York, USA
We present how to solve the (minimal-coupling) Pauli-Fierz Hamiltonian for realistic chemical systems using quantum-electrodynamical density-functional theory and discuss under which conditions an approximate modeling (dipole approximation, discarding dissipation and decoherence,…) becomes reasonable . We then show how various important observables depend crucially on the detailed description of the individual molecule  and highlight that a collectively-coupled (perfect) ensemble leads to strong local effects at an impurity . Further we show that treating the full mesosocopic ensemble quantum-coherently leads to unphysical results . From these findings we propose a semi-classical and more local/impurity-driven perspective on polaritonic chemistry, where the collective coupling induces a non-canonical equilibrium, and which allows for the first time to qualitatively describe the modification of ground-state chemical reactions as observed in experiment .
- R. Jestädt et al., Advances in Physics 68, 225 (2019).
- D. Sidler et al., J. Phys. Chem. Lett. 11, 7525 (2020).
- D. Sidler etal., J. Phys. Chem. Lett. 12, 508 (2020).
- D. Sidler et al., J. Chem. Phys. in press.
- C. Schäfer, arXiv preprint arXiv:2104.12429.
- University of Kassel, Kassel, Germany
- University of Freiburg, Freiburg, Germany
Quantum electrodynamics has long predicted that the electromagnetic field exhibits fluctuations even in its ground state, the so-called quantum vacuum. Only very recently, these have been observed directly by means of electro-optic sampling [1,2]. We present a theory of such novel quantum-vacuum detectors  and its use in the demonstration of field correlations between causally disconnected regions .
Prior to the advent of electro-optic sampling, vacuum fluctuations were only accessible indirectly via their impact on inter- and intra-molecular energy loss and transfer processes such as spontaneous or Auger decay, (Förster) resonance energy transfer, or interatomic Coulombic decay. We describe how environments can be used to modify the quantum vacuum and hence engineer said processes [5,6].
- C. Riek, D. V. Seletskiy, A. S. Moskalenko, J. F. Schmidt, P. Krauspe, S. Eckart, S. Eggert, G. Burkhardt, and A. Leitenstorfer, Science 350, 420 (2015).
- I. C. Benea-Chelmus, F. F. Settembrini, G. Scalari, and J. Faist, Nature 568, 202 (2019).
- F. Lindel, R. Bennett, and S. Y. Buhmann, Phys. Rev. A 102, 041701(R) (2020).
- F. F. Settembrini, F. Lindel, A. M. Herter, S. Y. Buhmann, and J. Faist, Nature Commun., in press (2022).
- J. L. Hemmerich, R. Bennett, and S. Y. Buhmann, Nature Commun. 9, 1 (2018).
- J. Franz and S. Y. Buhmann, New J. Phys. 24, 043002 (2022).
- Department of Engineering Physics, Polytechnique Montréal, Montreal, Canada
- Center for Organic Photonics and Electronics Research (OPERA) and Department of Applied Chemistry, Kyushu University, Japan
- Department of Physics, Universidad de Santiago de Chile, Santiago, Chile
Compared to their inorganic counterparts, organic polariton condensates hold several advantages: room-temperature operation, tunability across the visible through various possible emitter choices and ease of fabrication. However, for many practical applications, the lasing threshold remains several orders of magnitude too high. The lasing threshold depends principally on the polariton lifetime and the rate with which initially created excitons (electrically or through non-resonant pumping) can form polariton states. Within a perturbative picture, polariton formation has been interpreted as originating from either vibrational relaxation or radiative pumping. More recently, non-perturbative Master equation approaches have been introduced that include these mechanisms implicitly. However, until now there has been very little comparison of such models with experiment. We will present a simple method used to calculate the polariton scattering rate and then compare this rate to a simple theoretical model for radiative relaxation. We will show that the agreement is excellent for very negative detunings, but that when the detuning becomes more positive such that the polariton modes overlap with the inhomogeneously broadened lineshapes, the model fails drastically and the observed rate is much slower than that calculated from the model. This appears to be mostly due to the effect of disorder, which has until now been ignored in describing the relaxation process.
The interplay of electrons, photons, and nuclei makes the theoretical simulation of polaritonic phenomena a challenging one. For realistic modeling, approximations are required. A classical treatment of nuclei can be justified based on their relatively large mass, while a classical treatment of photons can be justified from the harmonic nature of the zeroth order Hamiltonian. While such approximations have been applied to realistic systems, extending traditional mixed quantum-classical methods such as Ehrenfest and surface-hopping to polaritonic systems, a question is whether the underlying force and coupling terms in these approaches are well-approximated. The exact factorization approach offers a relatively new perspective to dynamics of correlated between coupled quantum subsystems, answering exactly this question. It provides definitions of potentials acting on the nuclei that contain exactly the effect of coupling to electrons and photons, and likewise for the photonic system and electronic system. Here we study some model systems that show how these potentials exactly contain the photon-matter correlation, compare with traditional approximations used, and apply practical mixed quantum-classical methods derived from the exact factorization to polaritonic dynamics.
- L. Lacombe, N. M. Hoffmann, and N. T. Maitra, Phys. Rev. Lett. 123, 083201 (2019)
- B. Rosenzweig, N. M. Hoffmann, L. Lacombe, and N. T. Maitra J. Chem. Phys. 156, 054101 (2022)
- E. Villaseco Arribas, F. Agostini, N. T. Maitra, Molecules 27, 4002 (2022)
We discuss our experimental and theoretical work on the role of strong coupling in plasmonic lasing and Bose-Einstein condensation phenomena [1,2], including long-range coherence  and condensate phase formation . We point to remaining theoretical and experimental challenges. We also briefly report on our latest results related to topological photonics [5,6].
- T.K. Hakala, A.J. Moilanen, A.I. Väkeväinen, R. Guo, J.-P. Martikainen, K.S. Daskalakis, H.T. Rekola, A. Julku, P. Törmä, Nature Phys. 14, 739 (2018); A.I. Väkeväinen, A.J. Moilanen, M. Necada, T.K. Hakala, P. Törmä, Nature Commun. 11, 3139 (2020).
- K.B. Arnardottir, A.J. Moilanen, A. Strashko, P. Törmä, and J Keeling, Phys. Rev. Lett. 125, 233603 (2020).
- A.J. Moilanen, K.S. Daskalakis, J.M. Taskinen, P. Törmä, Phys. Rev. Lett. 127, 255301 (2021).
- J.M. Taskinen, P. Kliuiev, A.J. Moilanen, P. Törmä, Nano Letters 21, 5202 (2021).
- R. Heilmann, G. Salerno, J. Cuerda, T.K. Hakala, P. Törmä, ACS Photonics 9, 224 (2022).
- F. Freire-Fernandez, J. Cuerda, K.S. Daskalakis, S. Perumbilavil, J.-P. Martikainen, K. Arjas, P. Törmä, S. van Dijken, Nature Phot. 16, 27 (2022).
The problem of self-alignment of anisotropic medium, such as molecular dipoles or plasmonic nanorods, inside an optical cavity by vacuum-field effects is of fundamental interest, as a way to visualize the Casimir force similarly to the classical Faraday’s experiment with iron filings showing the direction of magnetic field lines. A necessary condition for observing this phenomenon is that the change of the ground-state energy of the system due to the alignment must be greater than the energy of temperature fluctuations. This change, coming from the interaction of any kind of dipoles with the vacuum fluctuations in the cavity, can be estimated with both macroscopic and microscopic ways. Microscopically, one can consider the QED light-matter Hamiltonian and find the ground-state energy shift within second-order perturbation theory . However, this will give the same result that can be obtained directly using the Casimir-Polder formalism , in which there are no problems with choosing a physically realistic interaction constant, but it is only necessary to know the Green’s functions of the cavity. In the macroscopic approach the system of nanorods should be considered as a homogenized medium with an anisotropic dielectric function. Then using the Lifshitz formalism it is easy to calculate the Casimir energy difference for different orientations of the anisotropy axis. Moreover, as Lifshitz showed, such a macroscopic calculation of the Casimir energy can be reduced to the microscopic Casimir-Polder formalism in the rarefied medium approximation . Here we present the calculations of described above problem within both Casimir-Polder and Lifshitz formalisms. Both approaches show the presence of an orientation effect in the ground-state energy shift. We discuss the role of anisotropy in the Casimir self-energies of the films and in counterintuitive increase of the Casimir force between mirrors.
- J. Galego, C. Climent, F. J. Garcia-Vidal, and J. Feist, Phys. Rev. X 9, 021057 (2019).
- H.B.G. Casimir, D. Polder, Phys. Rev. 73, 360 (1948).
- E. M. Lifshitz, Sov. Phys. JETP 2, 73 (1956).
The observed modification of thermal chemical rates in Fabry-Perot cavities remains a poorly understood effect. Mounting evidence supported by theory indicates that the cavity has a small effect on transition state theory rates, suggesting that dynamical corrections may play a prominent role. In this direction, the Grote-Hynes (GH) theory can explain how the cavity introduces friction with the reaction coordinate, thus reducing the transmission coefficient and the rate. The regime of rate enhancement, the observed sharp resonances at varying cavity frequencies, and the survival of these effects in the collective regime are not explained in the GH framework. Here, we will discuss the cis-trans isomerization of HONO atomistically using an ab-initio potential energy surface. We examine the conditions under which the cavity can modify the reactive flux leading to an acceleration of the rate. This occurs in the underdamped, low-friction regime of the reaction coordinate, where the cavity coupling reduces the amount of recrossing, thus increasing the transmission coefficient. In this regime, cavity-enabled energy redistribution channels determine the sharp resonances of the cavity effect with the cavity frequency .
- Jing Sun, Oriol Vendrell; On the Suppression and Enhancement of Thermal ChemicalRates in a Cavity, [arXiv:2204.01522 [physics]]
Nonadiabatic effects arise due to conical intersections (CIs) that are either present naturally in field-free space or induced by a classical laser field in a molecule . Recently, it was demonstrated that conical intersections in a molecular system can also be created in an optical cavity . Here, the quantized radiation field mixes the nuclear and electronic degrees of freedom creating hybrid light-matter polariton states which can form light-induced conical intersection (LICI). In a single molecule situation it is called “individual” (LICI). However, if many molecules are present in a cavity a novel type of “collective” LICIs and also collective CIs involving nuclear motion on separate molecules is formed within the dark states of the system. In this case the degeneracy is lifted along collective displacements of the molecules in the ensemble [3,4]. During the talk, our latest theoretical results on the role of “individual” LICIs, [5,6] as well as “collective” LICIs and CIs on the dynamics of diatomic  and polyatomic systems will be discussed.
- G.J. Halász, Á. Vibók, and L.S. Cederbaum, JPCL 6, 348, (2015)
- A. Csehi, M. Kowalewski, G.J. Halász, and Á. Vibók, New. J. Phys. 21, 093040 (2019)
- J. Feist, J. Galego, and F.J. Garcia-Vidal, ACS Photonics, 5, 205 (2018)
- O. Vendrell, PRL 121, 253001 (2018)
- C. Fabri, G.J. Halász, and Á. Vibók, JPCL 13, 1172 (2022)
- C. Fabri, G.J. Halász, L.S. Cederbaum and Á. Vibók, arXiv:2206.04998v1
- A. Csehi, O. Vendrell, G.J. Halász, Á. Vibók, New. J. Phys. 24, 073022 (2022)
Many of the intriguing phenomena observed in the field of molecular polaritonics over the last years are a consequence of the collective enhancement of the vacuum Rabi splitting proportional to the square root of the number of molecules N. While this scaling results from the hybridization of a single bright superposition state with light, there exists a large number (N-1) of dark states indirectly coupled to light, e.g. owing to disorder, which are thought to have a crucial impact on some observed properties. We take an open quantum system approach to describe the loss of energy from polaritonic states into the dark state manifold . In the mesoscopic limit of large N, we show how this approach can be used to derive simple scaling laws for the decay rate into the dark reservoir. Furthermore, we propose a model where the combined effects of dipole-dipole interactions, vibronic coupling and vibrational relaxation are incorporated into an effective Förster-type migration of excitation within the molecular ensemble. We also illustrate analogies of cavity-coupled molecular ensembles to free-space coupled molecules, where similar interactions between collective radiation states occur .
- C. Sommer, M. Reitz, F. Mineo, and C. Genes, Phys. Rev. Research 3, 033141 (2021)
- R. Holzinger, S. A. Oh, M. Reitz, H. Ritsch, and C. Genes, arXiv:2203.04998 (2021)
- Department of Physics, Universidad De Santiago de Chile, Santiago, Chile.
- Millennium Institute for Research in Optics (MIRO), Concepción, Chile.
- IPCMS (UMR 7504), CNRS, 67000, Strasbourg, France.
- Chemistry Division, U.S. Naval Research Laboratory, Washington, DC 20375, United States.
Reaction rate modifications for chemical processes have been reported to occur in infrared cavities due to strong coupling between reactant molecular vibrations with the cavity vacuum. However, there are no accepted mechanisms that would enable the observations. We use an open quantum system approach to model recent experiments on the alcoholysis of phenyl isocyanate (PHI) with cyclohexanol monomers in a liquid-phase Fabry-Perot cavity . We focus on the resonant suppression of the NCO stretching mode of PHI molecules due to strong vibrational coupling at normal incidence with one of the cavity modes. Taking into account inhomogeneous broadening, cavity photon losses, intramolecular vibrational coupling, vibrational relaxation, thermalization, and many-particle effects, we show that stationary resonant modifications of chemical reactivity with a molecular ensemble are possible via light-matter quantum coherences, thus suggesting fundamental links between chemistry and quantum science that can be further explored at room temperature.
- W. Ahn, F. Herrera, B. Simpkins, Modification of urethane addition reaction via vibrational strong coupling, chemrxiv doi:10.26434/chemrxiv-2022-wb6vs, (2022)
- Universidad Autónoma de Madrid, Madrid, Spain
- University of Jyväskylä, Jyväskylä, Finland
Strong coupling between material excitations and confined light modes found in a variety of photonic nanostructures has the potential to open a new era in energy harvesting  and transport [2,3], catalysis  and in the design of polaritonic optical devices . The large binding energy of Frenkel excitons makes organic materials promising candidates for future applications as polariton formation takes place at ambient conditions. However, the complexity of individual molecules and their collective dynamics in ensembles poses significant difficulties for exploiting the remarkable properties of polaritons [4,6].
To understand how material properties affect the structure and dynamics of strongly coupled systems, a model that includes both the chemical details of the molecules and the details of the electromagnetic environment created by the light-confining device is needed. While we achieved the first requirement of such a model by adopting an atomistic QM/MM representation of the material part of the strongly coupled system [7,8], the description of cavity modes was limited to the structure of simple optical Fabry-Pérot resonators . Here, we go beyond the latter and introduce an explicit description of the quantised electromagnetic field for arbitrary light confining structure such as plasmonic or hybrid metallodieletric nanocavities [10,11]. In the talk, I will present the model and share ongoing work aimed at investigating the properties of a few chromophores strongly coupled to a plasmonic nanocavity .
- J.Q. Quach et al., Sci. Adv., 8, eabk3160 (2022)
- G.G. Rozenman et al., ACS Photonics, 5, 105 (2018)
- A.M. Berghuis et al., ACS Photonics, (2022)
- J. Fregoni et al., ACS Photonics. 9, 1096 (2022)
- D. Sanvitto and S. Kéna-Cohen, Nat. Materials, 15, 1061 (2016)
- F.J. García-Vidal et al., Science, 373, eabd0336 (2021)
- H.L. Luk et al., J. Chem. Theory Comput., 13, 4324 (2017)
- G. Groenhof et al., J. Phys. Chem. Lett., 10, 5476 (2019)
- R.H. Tichauer et al., J. Chem. Phys., 154, 104112 (2021)
- I. Medina et al., Phys. Rev. Lett. 126, 093601 (2021)
- M. Sánchez-Barquilla et al., Nanophotonics, doi:10.1515/nanoph-2021-0795 (2022)
- J. Heintz et al., ACS Nano., 15, 14732 (2021)
The collective strong light-matter coupling regime differs from the single-molecule case in that there is an abundance of ~N so-called dark-modes per polariton mode (here, N ranges from 10^3 to 10^10 in the IR and UV-visible regimes). What that means is that polariton formation in optical microcavities in principle yield negligible changes in the per-molecule energetics. If this is the case, are there any hopes of explaining experiments reporting drastic changes in the chemical kinetics of molecules under collective strong light-matter coupling?
In this talk, I will discuss theoretical challenges addressing what we term “the large N problem.” We showcase experimental and theoretical evidence of this problem in the photophysical dynamics of organic chromophores under electronic strong coupling [2-4], theoretical challenges to explain vibropolaritonic chemistry , a possible resolution of these issues using weak optical pumping as well as polariton condensation .
References:L. Martínez-Martínez, R. Ribeiro, J. Campos-González-Angulo, J. Yuen-Zhou, ACS Photonics, 5, 167-176 (2017)E. Eizner, L. Martínez-Martínez, J. Yuen-Zhou, S. Kéna-Cohen, Sci. Adv., 5, (2019)L. Martínez-Martínez, E. Eizner, S. Kéna-Cohen, J. Yuen-Zhou, J. Chem. Phys., 151, 054106 (2019)D. Polak, R. Jayaprakash, T. Lyons, L. Martínez-Martínez, A. Leventis, K. Fallon, H. Coulthard, D. Bossanyi, K. Georgiou, A. Petty, II, J. Anthony, H. Bronstein, J. Yuen-Zhou, A. Tartakovskii, J. Clark, A. Musser, Chem. Sci., 11, 343-354 (2020)J. Campos-Gonzalez-Angulo, R. Ribeiro, J. Yuen-Zhou, Nat. Commun., 10, 4685 (2019)S. Pannir-Sivajothi, J. Campos-Gonzalez-Angulo, L. Martínez-Martínez, S. Sinha, J. Yuen-Zhou, Nat. Commun., 13, 1645 (2022)
During the past decades, strong coupling of matter excitations with confined electromagnetic modes have been shown to greatly modify material properties. Notably, polaritonic excitations are known to exhibit long-range energy transport characteristics. Moreover, while Anderson localization suppresses transport in one-dimensional systems with short-range interaction , such hybrid light-matter excitations have been proven robust against disorder . Surprisingly, in recent studies of disordered polaritonic systems [3,4], an improvement of the transport characteristics has been observed when increasing the disorder strength, instead of the expected suppression. The interplay between disorder and strong light-matter coupling is then highly nontrivial, and its understanding is of primary importance, since disorder is always present in experimental setups.
In this work, we study such interplay by considering a disordered one-dimensional chain of lossy dipoles coupled to a multimode optical cavity through a microscopically-derived Hamiltonian. Such a disordered system hosting polaritonic excitations may be realized experimentally in a wide range of systems with strong light-matter coupling, from plasmonic and dielectric nanoparticles to ultracold atoms or molecules embedded in a photonic cavity.
By analyzing both the eigenspectrum and the driven-dissipative transport properties of our system, we find that in the strong-coupling regime, increasing disorder leads uncoupled dark states to acquire a photonic part, allowing them to inherit polaritonic long-range transport characteristics. Crucially, we show that this disorder-enhanced transport mechanism is increasingly noticeable when the considered dipoles are lossier.
References: P. W. Anderson, [Phys. Rev. 109, 1492-1505 (1958)] (https://doi.org/10.1103/PhysRev.109.1492). R. Houdré, R. P. Stanley, and M. Ilegem, [Phys. Rev. A 53, 2711 (1996)] (https://doi.org/10.1103/PhysRevA.53.2711). N. C. Chavez, F. Mattiotti, J. A. Méndez-Bermudez, F. Borgonovi, and G. L. Celardo, [Phys. Rev. Lett. 126, 153201 (2021)] (https://doi.org/10.1103/PhysRevLett.126.153201). J. Dubail, T. Botzung, J. Schachenmayer, G. Pupillo, and D. Hagenmüller, [Phys. Rev. A 105, 023714 (2022)] (https://doi.org/10.1103/PhysRevA.105.023714).
Single-photon sources play a vital role in light-based quantum-information systems. One well-known design for such sources is a coupled emitter-cavity system. Single-photon emission is then achieved through two mechanisms: the destructive interference between the emitter and the cavity decays (unconventional antibunching [1,2]) and the photon blockade phenomenon (conventional antibunching [2.3]). While the destructive interference mechanism commonly emerges in the weak-coupling regime, the photon blockade mechanism requires a strong emitter-cavity coupling. Such strong coupling induces a breakdown of the harmonicity of the system and as a result prevents the absorption of subsequent photons. We here propose a novel non-Hermitian photon blockade mechanism, which stems from the anharmonicity of the system but works in the weak-coupling regime. We demonstrate an implementation of this idea using hybrid metallodielectric cavities that incorporate photon modes with different loss rates, and show that high-purity single-photon emission at high repetition rates could be achievable in such systems.
- M. Bamba, A. Imamoğlu, I. Carusotto, and C. Ciuti, Phys. Rev. A83, 021802(R) (2011).
- E. Zubizarreta Casalengua, J. C. López Carreño, F.P. Laussy, and E. D. Valle, Laser & Photonics Reviews, 14(6), 1900279 (2020).
- A. Verger, C. Ciuti, I. Carusotto, Phys. Rev. B 73, 193306 (2006).
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA
- Department of Chemistry and 4D LABS, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA
Contemporary nanophotonics research has focused recently on the ability of non-linear optical processes to mediate and transform optical signals in a myriad of novel devices, including optical modulators, transducers, color filters, photodetectors, photon sources, and ultrafast optical switches. The inherent weakness of optical nonlinearity at smaller-scales (e.g., nano- to micro-meter) has, however, hindered the realization of efficient miniaturized devices, and strategies for enhancing their throughput via nanoengineering remain limited. Here, we demonstrate a novel mechanism by which second harmonic generation, a prototypical non-linear optical phenomenon, from individual lithium niobate particles can be significantly enhanced through nonradiative coupling to the plasmon resonances of embedded gold nanoparticles. A single-particle experimental investigation of mesoporous lithium niobate particles coated with a dispersed layer of $\sim$10 nm diameter gold nanoparticles, together with a theoretical exploration of the energy exchange between the constituents of the hybrid structures, shows that a $\sim$32-fold enhancement of SHG response can be achieved without introducing large, lossy plasmonic nanoantennas to mediate photon transfer to or from the non-linear material. This work highlights the limitations of current Purcell-type strategies for enhancing non-linear optical phenomena and proposes a route through which a new class of smaller-size non-linear optical platforms can be designed to maximize non-linear efficiencies through near-field energy exchange.
References:R. Faryad Ali, Jacob A. Busche, Saied Kamal, David J. Masiello, Byron D. Gates., [In preparation]
Disorder is an intrinsic attribute of any realistic molecular system; recently it was suggested that in molecular ensembles strongly coupled to photonic cavities, disorder may lead to delocalization , and modification of transport  and chemical reaction rates . When the coupling strength largely exceeds the molecular inhomogeneity, polaritons are unaffected by the disorder . However, in many realizations, such homogeneous limit does not apply. We investigated vibrational polaritons in an open cavity involving localized molecular ensembles with a systematically modified disorder. Experimental spectroscopic results are in a good agreement with the numerical model involving a generalized Tavis-Cummings-like Hamiltonian accounting for molecular disorder. We observed an increase in Rabi-splitting and modification of the polariton bandwidths, suggesting that enhanced delocalization of the reservoir states occurs via an admixture of the cavity mode. Another manifestation of the delocalization within the reservoir is observed in third-order nonlinear two-dimensional spectroscopic experiments, where ultrafast quantum dynamics of vibrational polaritons is measured . In contrast to localized states, where polariton-to-reservoir excitation transfer is expected to be the dominant relaxation pathway , we observed strong reservoir-to-polariton transfer, suggesting a collective process involving correlated many-body states [7,8]. Our results provide new exciting insights into dynamics of polaritons involving disordered molecules.
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- University of Debrecen
- University of Heidelberg
Light-induced nonadiabatic phenomena arise when molecules or molecular ensembles are exposed to resonant external electromagnetic fields. The latter can either be classical laser or quantized cavity radiation fields, which can couple to either the electronic, nuclear or rotational degrees of freedom of the molecule. In the case of quantized radiation fields, the light-matter coupling results in the formation of two new hybrid light-matter states, namely the upper and lower “polaritons”. Light-induced avoided crossings and light-induced conical intersections between polaritons exist as a function of the vibrational and rotational coordinates of single molecules . For ensembles of N molecules, the N − 1 dark states between the two optically active polaritons feature, additionally, so-called collective conical intersections, involving the coordinates of more than one molecule to form . Here, we study the competition between intramolecular and collective light-induced nonadiabatic phenomena by comparing the escape rate from the Franck-Condon region of a single molecule and of a molecular ensemble coupled to a cavity mode . In situations where the polaritonic gap would be large and the dark-state decay channels could not be reached effectively, the presence of a seam of light-induced conical intersection between the polaritons facilitates again the participation of the dark manifold, resulting in a cooperative effect that determines the overall non-radiative decay rate from the upper into the lower polaritonic states.
- A. Csehi, M. Kowalewski, G. J. Halász, and Á. Vibók, New Journal of Physics, 2019, 21(9).
- O. Vendrell, Physical Review Letters, 2018, 121(25).
- A. Csehi, O. Vendrell, G.J. Halász, Á. Vibók, submitted to New Journal of Physics.
Common quantum-mechanical models for polaritonic chemistry lack mechanisms that populate dark states. In this work we explicitly model a process that does; disorder from stochastic energy variations the in matter systems inside the optical cavity. Such fluctuations typically arise due to local environment interactions, and the effect enters into the equations of motion as dephasing operators. Viewed through the lens of polaritonic states, a reservoir of previously inaccessible states has thus been opened up, and basic entropic arguments would imply that the remaining polaritonic states have less population to share. In other words, excess energy will be trapped in dark states, which would (e.g.) inhibit cavity output. On the other hand, in a product-basis of the sub-systems, before polaritonic diagonalisation, it is hard to see how small phase shifts would trap energy. In this work we investigate this tension, and we find that the analysis from the polaritonic perspective provides the correct intuition.
- Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Spain
The interaction of an atom with the electromagnetic environment supported by a macroscopic body affects its structure and induces both spontaneous emission and Casimir-Polder energy shifts of the atomic levels. The possibility to control the properties of the atom by tuning the parameters of the macroscopic body has drawn attention recently . Usually, the effects of the environment are treated separately for each atomic level. However, for groups of near-degenerate states, the induced shifts can become comparable to the energy differences between levels. In that case, the standard approach fails and it becomes necessary to treat the environment-induced interaction between the levels, leading to off-diagonal terms in the field-induced decay and energy shifts. We here present a way to treat such systems and show that the dynamics of an atom close to a macroscopic structure can noticeably deviate from those predicted by the standard diagonal formulation of the theory. Our approach is based on the framework of macroscopic quantum electrodynamics , together with a recent Lindblad master equation formalism that can treat near-degenerate levels while avoiding some of the problems of the standard Bloch-Redfield equation, leading to a trace-preserving master equation even without performing a secular approximation . While this method includes the well-known Casimir-Polder potentials in the diagonal energy shifts, it importantly also describes off-diagonal contributions, especially relevant in near-degenerate atomic subspaces. Due to these off-diagonal contributions, the effective atomic eigenstates are linear combinations of the free-space eigenstates. The mixing of the atomic eigenstates has interesting physical consequences on, for instance, the atomic decay rates, and yet, as far as we know, these off-diagonal terms have not been discussed in the literature. We have simulated the fine structure of a hydrogen atom coupled to a silver nanoparticle that supports plasmon-polaritonic resonances. We quantify the amount of Casimir-Polder-induced mixing of the eigenstates through the so-called participation ratio. We can also gauge the impact of the off-diagonal Casimir-Polder terms on the atomic dynamics by obtaining the eigenenergies and decay rates from the master equation and studying them as a function of the distance between the hydrogen atom and the nanoparticle. Noticeably, avoided crossings become a new marked feature of the energy spectrum of the atom, a clear signature of mixed eigenstates. As for the decay rates, the nanoparticle offers new decay channels that become enhanced as the atom approaches it, leading to the naive expectation that the atomic decay rates will increase in a monotonic fashion, closely related to the well-known emission quenching due to nanoparticles. Our results show that the real evolution of the decay rates becomes more complicated as a consequence of the off-diagonal contributions. In particular, for an adequate set of parameters and distance range, some decay rates can be shown to actually decrease as the atom approaches the nanoparticle, again, thanks to the state mixing induced by the off-diagonal Casimir-Polder potential. Such effects are not present at all in traditional Casimir-Polder treatments lacking the off-diagonal terms and are necessary to include in order to properly understand the physics behind quantum state manipulation applications.
- Chang C.-H. et al., ACS Photonics 4, 12, 3098 (2017)
- Scheel, S. and Buhmann S. Y., Acta Physica Slovaca 58, 5, 675 (2008)
- McCauley, G. et al., npj Quantum Inf 6, 74 (2020)
- University of St Andrews, St Andrews, United Kingdom
In this talk I present a method (1) capable of simulating many-body systems with strong coupling to multiple environments. This uses mean-field theory in conjunction with matrix product operator methods. I apply the method to the problem of organic polariton lasing, investigating the phase diagram and spectrum of a model of a cavity coupled to many molecules, with each molecule having a continuous spectrum of vibrational degrees of freedom. I also discuss the nature of the mean-field theory and the role of bright and dark exciton states in this approach.
- P. Fowler-Wright, B. W. Lovett, J. Keeling, arXiv:2112.09003
- Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049, Spain
- Dipartimento di Scienze Chimiche, Università di Padova, 35131, Italy
- Istituto di Nanoscienze, Consiglio Nazionale delle Ricerche CNR-Nano, 41125, Italy
The near-field enhancement in plasmonic platforms can induce strong changes in the molecular electronic density at both the ground and excited state level. These effects are highly non-homogeneous in space, as they depend on both the nanoparticles geometries and the molecular structure, position and orientations with respect to the plasmonic platform. As a consequence, the model descriptions of the electromagnetic field and the molecular dipole approximation are extremely limited tools to grasp the complexity of these systems. In this poster, we firstly present a quantisation strategy for the plasmonic modes building on a polarizable continuum description of the nanoparticle. By these means, we obtain a representation of the plasmonic modes as electrostatic response charges. We then compute the quantum coupling between the quantised plasmons and a molecule described at quantum chemical level, highlighting the changes in the molecular electronic structure induced by the presence of the nanoparticles. Finally, we extend this coupling framework to the case of multiple molecules, investigating the optical properties of molecules collectively coupled to a realistic nanoparticle.
- T. Neuman, R. Esteban, D. Casanova, F. J. García-Vidal and J. Aizpurua, Nano Lett. 18, 2358(2018).
- S. Pipolo and S. Corni, J. Phys. Chem. C 120, 28774 (2016).
- J. Fregoni, T. S. Haugland, S. Pipolo, T. Giovannini, H. Koch and S. Corni, Nano Lett. 21, 6664 (2021).
- J. Kuttruff, M. Romanelli, E. Pedrueza-Villalmanzo et al., arXiv:2205.06358v1, cond-mat.mes-hall.
- Universidad de Antioquia, Medellín, Colombia
- Technical University of Munich, Garching, Germany
- Universidad Autónoma de Madrid, Cantoblanco, Spain
Two-dimensional spectroscopy (2DS) is a tool used for the study of radiation-assisted molecular processes with femtosecond resolution . It is based on the interaction of three delayed pulses (two pump and one probe pulse) with a target system, and can access the third-order polarization response. We theoretically apply 2DS to a polaritonic system of N molecules interacting with a quantized mode of the electromagnetic field within a nanocavity . The hybrid light-matter states (polaritons) in the coupled system are described by the Tavis-Cummings model in the strong coupling regime. Photonic losses are included as a Lindblad term in the master equation, while molecular vibrations are represented using the Bloch-Redfield formalism to appropriately describe the vibration-induced decay and pumping between the system states.
To obtain the 2D spectra we derive a simple and efficient computational procedure based on a set of pseudo-analytical equations obtained by expanding the states of the system in the Liouvillian eigenbasis. These equations are quite general and can be used for any dissipative system with diagonalizable Liouvillian. Our analytical formulas allow us to understand some characteristics of the 2D spectra in terms of both the Liouvillian and the Hamiltonian eigenstates.
Using our approach, we find that 2D spectra recorded at different waiting times T (between the pump and probe pulses) show that the diagonal signal associated with the lower polariton (LP) decreases more rapidly than that of the upper polariton (UP), a counterintuitive effect since the LP has a longer lifetime than the UP and is additionally refilled by vibration-induced decay from molecular dark states (non-radiative eigenstates of the Tavis-Cummings model). Interestingly, this effect also appears in recent experiments on polaritons involving molecular J-aggregates . We explain the physical reason behind these observations through a careful analysis of the different contributions to the 2D spectra, and show that dark states indeed play a crucial (albeit indirect) role. We also discuss the importance of different excited-state manifolds to the observed spectra.
- P. Hamm and M. Zanni. Concepts and methods of 2D infrared spectroscopy. Cambridge University Press (2011)
- J. Fregoni, F. J. Garcia-Vidal and J. Feist, [ACS Photonics, 9, 1096 (2022)] (https://doi.org/10.1021/acsphotonics.1c01749)
- L. Mewes, M. Wang, R. A. Ingle, K. Börjesson and M. Chergui, [Comm. Phys. 3,1 (2020)] (https://doi.org/10.1038/s42005-020-00424-z)
THz quantum optics is seen as a potential powerful tool [1,2] because the THz frequencies are in the same order of magnitude as the transition frequencies in many molecules. The initial hurdle lies in creating a potent source of THz radiation, a THz laser. In this project, we follow the proposal in , where this is achieved with an ensemble of weak-coupling quantum dots. We, however, study a strongly-coupled single colloidal quantum dot confined in a SiC dimer nanocavity. We show that this configuration can function as a laser, but can also exhibit antibunching or superbunching. We therefore prove that our platform acts as a versatile, tunable source of nonclassical THz radition.
- M. Tonouchi, Cutting-edge terahertz technology, Nature Photonics 1, 97 (2007).
- X. C. Zhang, A. Shkurinov, and Y. Zhang, Extreme tera-hertz science, Nature Photonics 11, 16 (2017).
- I. Y. Chestnov, V. A. Shahnazaryan, A. P. Alodjants, and I. A. Shelykh, Terahertz lasing in ensemble of asymmetric quantum dots, ACS Photonics 4, 2726 (2017).
- University of Innsbruck
- University of Erlangen
Dipole-coupled subwavelength quantum emitter arrays respond cooperatively to external light fields as they may host collective delocalized excitations (a form of excitons) with super- or subradiant character. Deeply subwavelength separations typically occur in molecular ensembles, where in addition to photon-electron interactions, electron-vibron couplings and vibrational relaxation processes play an important role. We provide analytical and numerical results on the modification of super- and subradiance in molecular rings of dipoles including excitations of the vibrational degrees of freedom. While vibrations are typically considered detrimental to coherent dynamics, we show that molecular dimers or rings can be operated as platforms for the preparation of long-lived dark superposition states aided by vibrational relaxation. In closed ring configurations, we extend previous predictions for the generation of coherent light from ideal quantum emitters to molecular emitters, quantifying the role of vibronic coupling onto the output intensity and coherence.
- M. Reitz, C. Sommer, and C. Genes, “Langevin approachto quantum optics with molecules,” Phys. Rev. Lett. 122,203602 (2019)
- M. Reitz, C. Sommer, and C. Genes, “Cooperative quantum phenomena in light-matter platforms,” PRX Quantum 3, 010201 (2022).
- R. Holzinger, D. Plankensteiner, L. Ostermann, andH. Ritsch, “Nanoscale coherent light source,” Phys. Rev.Lett. 124, 253603 (2020).
- Department of Engineering Physics, Polytechnique Montréal, Canada
- Department of Chemistry, Kyoto University, Japan
- Center for Organic Photonics and Electronics Research (OPERA) and Department of Applied Chemistry, Kyushu University, Japan
- International Institute for Carbon Neutral Energy Research, Kyushu University, Japan
At high excitation densities, exciton-polaritons in organic microcavities can show Bose-Einstein condensation (BEC) at room temperature , but the thresholds range from Pth ~ 2.2 to 500 μJ cm-2, which are too high for electrical pumping. Recently, it has been demonstrated that maximizing the polariton relaxation rate (Wep) is one way to accumulate efficiently lower polaritons (LPs) and decrease the polariton condensation threshold . However, the currently reported Wep via a radiative pumping of spin-singlets is about Wep = 5 × 107 s-1 , and the use of spin-triplets is essential to further decrease the threshold. If triplet excitons can be efficiently converted to the LP state, the LP density will further increase due to the relaxation from the triplet in addition to the spin-singlets to the LP state (Fig. 1 a). So far, although the dynamics of the reverse intersystem crossing process from the spin-triplet to the LP state have been studied [3, 4], the influence of phosphorescence emission on the polariton relaxation process has not been fully explored. In this study, we focused on the microcavities containing ν-DABNA (Fig. 1 b, c) and discuss the role of phosphorescence emission in the polariton relaxation process through time-resolved emission measurement. As a result, we demonstrated that LPs were directly relaxed from triplet states via a radiative pumping of phosphorescence.
- S. Kéna-Cohen, S. R. Forrest,Nat. Photon. 4, 371 (2010).
- T. Ishii et al.,Adv. Opt. Mater. 10, 2102034 (2022).
- E. Eizner et al.,Sci. Adv. 5, eaax4482 (2019).
- Y. Yu et al.,Nat. Commun. 12, 3255 (2021).
- University of Jyväskylä, Finland
We have developed a stochastic formalism to describe collective reactivity in polaritonic chemistry. In this approach, the stochastic behavior of many bistable systems (toy model for vibrational ground state of a molecule) is modified by the coupling to a single cavity vacuum field. The coupling modifies the reaction rates and, after a certain threshold, causes a spontaneous symmetry breaking in the stationary state. However, this effect is crucially dependent on the distribution of the light-matter couplings. When the values of the couplings greatly vary, the bifurcation shows up as a phase separation, and there is no apparent modification to the reaction rates. We discuss how this rich phenomenology connects to the existing and future experiments in the field.
- K. S. U. Kansanen and T. T. Heikkilä, arXiv:2202.12182
- Department of Physics, Stockholm University
We have investigated a number of molecular systems in the last few years with regard to the strong cavity coupling. While it seems to be widely accepted that collective interactions play a major in strong coupling photochemistry, other effects are less well explored. Our theoretical studies have shown that, for example, limited photon lifetimes, dipole self interactions, or vibrational strong coupling seems to play a role. We will give an overview over our studies and discuss the influence of these effects.
- Chalmers University of Technology, Gothenburg, Sweden
Self-assembled systems can be observed in molecular and biological systems with short range interactions such as van der Waals. It is possible to have stable longer range (100-200 nm separation) self-assembled microcavities with the charged metallic (in this case gold) flakes by creating an equilibrium between attractive Casimir and repulsive electrostatic forces. This system forms a tunable Fabry-Perot microcavities and allow us the modulate the system resonance both in active (laser pressure) and passive (electrostatic screening) ways . Casimir torque is complicated to measure due to its small magnitude; however recently direct measurement is performed by Munday et al.  by using the two anisotropic material and mechanical torque observed which is induced by quantum fluctuations. In our work, we focus on the rotation effect of the lateral Casimir force and realize the self-alignment on the two triangle gold flakes. The gold flake in water solution starts rotating until it reaches the lowest energy state which is the perfect alignment with bottom triangle Au film / or another triangle flake in the solution. Self-alignment of microcavities is sensitive to electrostatic changes in the liquid surrounding media since it changes the electronic screening and breaks the equilibrium between two forces. We experimentally can obtain stable microcavities and investigate the effects of electrostatic on the lateral Casimir force by analyzing the alignment of the two triangle flakes. Self-assembled and self-aligned Casimir microcavities opens a controllable/tunable platform for various applications such as optomechanics , polaritonic chemistry  and nano- and micromechanical systems .
- B. Munkhbat, A. Canales, B. Küçüköz, D. Baranov, T. Shegai, Nature, 597, 214-219 (2021).
- Somers, D.A.T., Garrett, J.L., Palm, K.J. et al.Nature 564, 386-389 (2018).
- Eichenfield, M., Camacho, R., Chan, J., Vahala, K. J. & Painter, O. Nature 459, 550–555 (2009).
- J. Galego, C. Climent, F. Garcia-Vidal, J. Feist, Phys. Rev. X, 9, 021057 (2019).
- J. C. Martinez, X. Chen, and M. B. A. Jalil, AIP Adv. 8(1), 015330 (2018).
- NEST Lab., CNR—Istituto di Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa 56217, Italy
- Dipartimento di Fisica, Università di Pisa, Largo Pontecorvo 3, Pisa 56127, Italy
- Dep. de Física Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
Light-matter interaction between molecules and confined electromagnetic fields is of great interest because it allows the modification of fundamental properties of the coupled system. This effect has been exploited for several different applications, such as low-threshold Bose-Einstein condensation and lasing [1-3], cavity-modified photochemical reactivity , and (long-range) energy transfer between donor and acceptor molecules [5-8]. By placing a donor-acceptor pair in a microcavity, delocalized polariton states are formed if the strong coupling condition is met. In this case, the efficiency of resonant energy transfer from the donor to the acceptor is changed, as a result of the appearance of new relaxation channels.
Here we investigate how a photochemical reaction of donor molecules can affect the efficiency of the energy transfer process. We first demonstrate the strong coupling regime between the chromophores and the cavity mode. Using UV illumination, we drive a photochemical reaction of the donor molecules that allow us to modify the hybrid light-matter states. By tuning the time of UV illumination, we obtain a significant enhancement of the emission intensity from the acceptor excitonic reservoir as compared to the outside-cavity case. We also present a theoretical explanation of the physical mechanism behind this experimental finding and we discuss a new way to achieve controllable modification of cavity-mediated energy transfer based on this fundamental knowledge.
- S. Kena-Cohen and S. R. Forrest, Nat. Photonics, 4, 371. (2010)
- J. D. Plumhof, T. Stöferle, L. Mai, U. Scherf and R. F Mahrt, Nat. Mater., 13, 247. (2013)
- M. Ramezani, A. Halpin, A. I. Fernandez-Domínguez, J. Feist, S. R.-K. Rodriguez, F. J. Garcia-Vidal and J. Gomez Rivas, Optica, 4, 31. (2017)
- J. A. Hutchison, T. Schwartz, C. Genet, E. Devaux, and T. W. Ebbesen, Angew. Chem. Int. Ed. 51, 1592 (2012).
- D. M. Coles, N. Somaschi, P. Michetti, C. Clark, P. G. Lagoudakis, P. G. Savvidis and D. G. Lidzey, Nat. Materials, 13(7), 712–719 (2014)
- X. Zhong, T. Chervy, L. Zhang, A. Thomas, J. George, C. Genet, J. A. Hutchison and T. W. Ebbesen, Angew. Chem., Int. Ed., 56, 9034–9038 (2017)
- K. Georgiou, P. Michetti, L. Gai, M. Cavazzini, Z. Shen and D. G. Lidzey, ACS Photonics, 5(1), 258–266 (2018)
- S. Satapathy, M. Khatoniar, D. K. Parappuram, B. Liu, G. John, J. Feist, F. J. Garcia-Vidal, and V. M. Menon, Science Adv. 7, eabj0997 (2021)
- Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- Universität Kassel, Kassel, Germany
The control of quantum systems lies at the core of many quantum technologies. In the field of coherent control, classical fields coherently drive the quantum system from a given initial state into a target state. Exploiting the quantum nature of the field to improve these control protocols has so far been mostly limited to the weak coupling regime.
In my talk, I will discuss how the quantum statistics of a bosonic field can be optimally tailored to drive an (ultra-)strongly coupled quantum system such as an atom or a molecule. This extends optimal control theory to the realm where control and target systems are both quantized and strongly coupled.
- University of Michigan, Ann Arbor, Michigan, USA
Despite the several demonstrations of molecular chemistry being altered by optical microcavities, a detailed understanding of how this works remains unclear. In particular, the common Travis-Cummings model supposes that for a large number N of molecular modes, there should only be 2 polariton modes and the remaining N-1 dark states, those that are essentially unaffected by the cavity, should dominate in a reaction (1). However, this analysis no longer holds when molecules are coupled to more than a single cavity mode (2). We demonstrate that the molecular coupling to the continuum of cavity modes in the commonly used 2D cavities reduces the dark state to polariton ratio by orders of magnitude.
We derive a qualtiative model of the expected ratio of polariton states to dark states. The figure is an example of our calculated results, showing the molecular positions of one instance of the simulation, and the resulting polariton dispersion. Despite being modeled with fully localized excitons with random positions, the molecular polariton dispersion follows nearly exactly the traditional polariton dispersion of a quantum well in a microcavity.
Furthermore, we compare trends in dark state fraction for different cavity dimensionality (0D, 1D, and 2D). We also investigate the effects of positional disorder and energetic disorder on the polariton to dark state ratio. These results facilitate modeling and understanding of polariton chemistry, clarifying plausibility of controlling chemical reactions with optical cavities.
- R. F. Ribeiro, L. A. Martínez-Martínez, M. Du, J. Campos-Gonzalez-Angulo, and J. Yuen-Zhou, Chem. Sci. 9, 6325-6339 (2018).
- R. F. Ribeiro, Commun. Chem. 5, 48 (2022).
- Departamento de Físíca Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid, Spain
Surface-enhanced Raman scattering (SERS) allows the fingerprinting of single molecules via their vibrational degrees of freedom. Inspired by its analogy with the field of cavity optomechanics , a first model was proposed considering the optomechanical dynamics between plasmonic electric fields and molecular vibrations . This molecular optomechanical approach allowed both, to describe new effects in the field of SERS arising from the dynamical backaction and to offer new possibilities in cavity optomechanics due to the resulting large coupling strengths involved – orders of magnitude larger than in previous configurations. Despite recent experimental works evidencing such optomechanical nature of SERS, large spectral discrepancies have arisen with current theoretical predictions  that call for new mechanisms for its understanding. Inspired by the microscopic molecular Hamiltonian , in this work we propose an optomechanical SERS model that considers the internal mechanisms of the molecule. In this model, the electronic transitions involved in the Raman processes are treated as a set of two-level systems that mediate the interaction between plasmons and molecular vibrations via electron-vibron couplings . Since such electronic levels typically lie in the ultra-violet range, we can adiabatically eliminate them and recover the original optomechanical Hamiltonian . Beyond such adiabatic approximation, we further consider a near-resonant transition coexisting with the off-resonant ones, showing interesting cooperative behaviours such as enhancements of anti-Stokes lines and modifications of spectral widths. For ultrastrong interaction scenarios with electron-vibron couplings close to the mechanical frequency, we consider the resulting phonon-dressed states in the master equation that show incoherent contributions to the anti-Stokes peaks, decisive for understanding the spectrum. Our model shows the importance of treating the molecular degrees of freedom with equal footing in SERS and offers new perspectives of the mechanisms involved in molecular optomechanics.
- M. Aspelmeyer and T. J. Kippenberg and F. Maquardt, Rev. Mod. Phys. 86, 1391 (2014)
- P. Roelli and C. Galland and N. Piro and T. J. Kippenberg, Nature Nanotech. 11, 164-169 (2016)
- F. Benz and M. K. Schmidt and A. Dreismann and R. Chikkaraddy and Y. Zhang and A. Demetriadou and C. Carnegie and H. Ohadi and B. Nijs and R. Esteban and J. Aizpurua and J. J. Baumberg, Science 354, 6313, 726-729 (2016)
- M. Reitz and C. Sommer and B. Gurlek and V. Sandoghdar and D. Martin-Cano and C. Genes, Phys. Rev. Research 2, 033270 (2020)
- LOMA, Talence, France
- Universidad Autónoma de Madrid, Madrid, Spain
We theoretically investigate the circular dichroism of a helicity-preserving Fabry-Pérot cavity made of two dielectric metamirrors. The latter are designed to act, in a narrow frequency range, as efficient polarization cross-converters in transmission for one polarization, and almost perfect reflectors for the other polarization. The resulting cavity mode is circularly polarized and decoupled (at resonance) from the outside of the cavity. Despite this decoupling, a Pasteur medium hosted inside the cavity can still couple efficiently to both the outside of the cavity and the helicity-preserving mode, inheriting a partial chiral character. The consequence of this mechanism is twofold: it increases the intrinsic chiroptical response of the molecules by two orders of magnitude and it allows for the formation of chiral polaritons upon entering the regime of strong light-matter coupling.
* These authors contributed equally.
- B. Semnani, J. Flannery, R. Al Maruf, and M. Bajcsy, Light: Science & Applications 9 (2020)
- K. Voronin, A. S. Taradin, M. V. Gorkunov, and D. G. Baranov, ACS Photonics 2022 9 2652 (2022)
- L. Mauro, J. Fregoni, J. Feist, and R. Avriller, arXiv:2209.00402
- S. Sun, B. Gu, and S. Mukamel, Chem. Sci. 13, 1037 (2022)
- J. Gautier, M. Li, T. W. Ebbesen, and C. Genet, ACS Photonics, 9, 3, 778-783 (2022)
- Universidad Autónoma de Madrid, Madrid, Spain
- Institute of High Performance Computing, Agency for Science, Technology, and Research (A*STAR), Singapore, Singapore
Planar microcavities, formed by dielectric and plasmonic materials, are able to modify material properties under the strong coupling regime which can be described by cavity quantum electrodynamics. Among others, changes in chemical rates, superfluidity, and energy transport have been reported . Recently, magnetic materials came into play by experimental findings showing alterations of magnetic properties . Motivated by them, we report on the theoretical foundation of cavity-mediated spin-spin interactions between magnetic nanoparticles, hosted in the structure shown in Fig. 1(a). By developing novel theoretical and rigorous methodological tools capable to account for the collective strong coupling between many optical modes and matter states, we describe how cavity polaritons can strongly couple with both local phonons and spins, a schematic illustration of which is depicted in Fig. 1(b). Our results indicate, that indeed, cavity photons can generate spin-spin interactions exceeding the conventional nearest- and next-nearest-neighbors ones not only in strength but also in range. At the same time, under appropriate conditions, symmetric Heisenberg-like and antisymmetric Dzyaloshinskii—Moriya-like interaction can be reached.
- Francisco J. Garcia Vidal, Cristiano Ciuti, and Thomas W. Ebbesen, Science 373, abd0336 (2021)
- Anoop Thomas, Eloise Devaux, Kalaivanan Nagarajan, Guillaume Rogez, Marcus Seidel, Fanny Richard, Cyriaque Genet, Marc Drillon, and Thomas W. Ebbesen, Nano Lett. 21, 4365 (2021)
Polaritons are hybrid light-matter states that emerge when the interaction between molecular excitations and the electromagnetic field is comparable to their respective frequencies. Several theoretical and experimental work suggest that polaritons provide a new platform for a variety of chemical applications such as the modification of energy transfer rates, the realization of exciton-polariton condensation, and the control of chemical reactivity. However, some of the most exciting experimental results today remain poorly understood despite all the theoretical work in the last decade. From the theoretical standpoint, the study of molecular polaritons beyond simple models is challenging due to the large dimensionality of these systems. Considering this, a very important question is to what extent single molecule models can be used for interpretation or prediction of such phenomena, given that polaritons are experimentally achieved mostly using a macroscopic number of molecules that collectively couple to light.
Here we use the Multi-Configurational Time-Dependent Hartree (MCTDH) method to study the dynamics of molecular polariton Hamiltonians in the collective strong coupling regime. By finite size-scaling of dynamics involving a few molecules, we numerically extrapolate the dynamics into the regime involving a macroscopic number of molecules
- The University of Adelaide, Adelaide, Australia.
- Politecnico di Milano, Milan, Italy.
- University of Sheffield, Sheffield, UK.
- University of St. Andrews, St. Andrews, UK.
- Heriot-Watt University, Edinrbugh. UK.
The rate at which matter emits or absorbs light can be modified by its environment, as dramatically exemplified by the widely studied phenomenon of superradiance. The reverse process, superabsorption, is harder to demonstrate because of the challenges of probing ultrafast processes, and has only been seen for small numbers of atoms. Its central idea—superextensive scaling of absorption meaning larger systems absorb faster—is also the key idea underpinning quantum batteries. Here we implement experimentally a paradigmatic model of a quantum battery, constructed of a microcavity enclosing a molecular dye . Ultrafast optical spectroscopy allows us to observe charging dynamics at femtosecond resolution to demonstrate superextensive charging rates and storage capacity, in agreement with our theoretical modelling. We find that decoherence plays an important role in stabilising energy storage.
- J. Quach, et al., Science Advances 8 (2), eabk3160 (2022)
Strong light-matter interactions are at the core of many electromagnetic phenomena. In this talk, I will give an overview of several nanophotonic systems which support polaritons - hybrids between light and matter, as well as try to demonstrate their potential usefulness in polaritonic chemistry applications. Specifically, I will show that Fabry-Perot resonators, one of the most important workhorses of nanophotonics, can spontaneously form in an aqueous solution of gold nanoflakes . This effect is possible due to the balance between attractive Casimir-Lifshitz forces and repulsive electrostatic forces acting between the flakes. There is a hope that this technology is going to be useful for future developments in self-assembly, nanomachinery, and polaritonic chemistry. I will also briefly discuss the potential relevance and connection between the Casimir effect and polaritonic chemistry [2-3]. Finally, I will discuss the potential relevance of polaritons naturally existing in nanostructured resonant materials to polaritonic chemistry . Several concrete examples such as a slab of the excitonic material and, most interestingly, a spherical water droplet in vacuum are shown to reach the regime of such polaritons. The abundance of cavity-free polaritons in simple and natural structures points at their relevance and potential practical importance for the emerging field of polaritonic chemistry, exciton transport, and modified material properties.
- B. Munkhbat, A. Canales, B. Küçüköz, D. Baranov, T. Shegai, Nature, 597, 214-219 (2021)
- D. Sheehan, J. Chem. Phys., 131, 104706 (2009)
- J. Galego, C. Climent, F. Garcia-Vidal, J. Feist, Phys. Rev. X, 9, 021057 (2019)
- A. Canales, D. Baranov, T. Antosiewicz, T. Shegai, J. Chem. Phys., 154, 024701 (2021)
- University of Jyvaskyla, Jyvaskyla, Finland
- Universidad Autónoma de Madrid, Madrid, Spain
Transfer of excitation energy is a key step in light harvesting and hence of tremendous technological relevance for solar energy conversion. In bare organic materials energy transfer proceeds via incoherent hops, which restrict propagation lengths to the nanoscale. In contrast, energy transport over several micrometers has been observed in the strong coupling regime where excitations hybridise with confined light modes to form polaritons. Because polaritons inherit the group velocity of the confined light modes, their propagation is ballistic and long-ranged. However, experiments on organic micro-cavities indicate that polaritons propagate in a diffusive manner and much slower than the polariton group velocity. To resolve this controversy, we implemented atomistic multi-scale molecular dynamics simulations of Rhodamine molecules in a Fabry-Perot cavity. Our results suggest that polariton propagation is limited by the cavity lifetime and appears diffusive due to reversible population transfer between bright polaritonic states that propagate ballistically at their group velocities, and dark states that are stationary. Furthermore, because the long-lived dark states can effectively trap the excitation, propagation is observed on timescales far beyond the intrinsic polariton life-time, in particular in low-Q cavities. In addition, we discuss the influence of the cavity quality factor on the polariton propagation distance in the case of the resonant excitation of the upper polariton branch. The atomistic insights from our simulations not only help to better understand and interpret experimental observations, but also pave the way towards rational design of molecule-cavity systems for achieving coherent long-range energy transport.
- Departamento de Física, Universidad de Santiago de Chile, Estación Central, Chile
- ANID-Millennium Institute for Research in Optics, Concepción, Chile
Demonstrations of strong and ultrastrong light-matter interaction in mid-infrared resonators have stimulated the search for control schemes that can be used to prepare target material and photonics states for a variety of applications in chemistry . We propose a scheme for modifying the photon number and field quadrature statistics of a confined mid-IR electromagnetic field by modulating the vacuum frequency with femtosecond UV pulses . The scheme relies on the transient modification of the carrier density of the field-confining materials and strong coupling between the confined field and an ensemble of molecular vibrations. We study variations of the Mandel Q-factor and squeezing over sub-picosecond timescales by modulating the cavity frequency ~15%, resulting in squeezing factors of order ~1 dB for a system initially prepared in the stationary ground and lower polariton states . We relate the predicted variations of quantum field statistics to the type of dipolar structure and anharmonicity of the molecular vibrations. Our work can stimulate the design of novel infrared devices at room temperature for applications in quantum metrology and quantum information processing.
- F. Herrera and J. Owrutsky. J. Chem. Phys. 152, 100902 (2020)
- J.F. Triana, F.J. Hernández and F. Herrera. J. Chem. Phys. 152, 234111 (2020)
- J.F. Triana, F. Herrera. New J. Phys. 24, 023008 (2022)
- NanoScience Center, University of Jyväskylä, Survontie 9 C, 40460 Jyväskylä, Finland
Over the past few years, a completely new way of modifying chemical reactivity has emerged based on creating polaritons between molecular vibrations and confined electromagnetic fields.  This is called vibrational strong coupling (VSC)  and is currently being examined by as new tool to control and catalyze chemical reactions [3-7]. VSC utilized light-matter interaction to modify material properties without the need for light as such.
Several experimental studies have demonstrated the ability of VSC to alter reaction kinetics [3-5], binding constants  and aggregation behavior . One specific example is the 4.5x slow down of the enzymatic activity of pepsin by strongly coupling water.  In another study, ester hydrolysis has been observed to accelerate under VSC, highlighting the prospect of VSC as an alternative to traditional catalysis . This result has however been recently contested . Here, we verify the potential of VSC to catalyze ester cleavage and explore it in greater depth. We find effects of coupling different vibrations of the system and discuss the difficulties and pitfalls of VSC kinetic experiments. This work will help to understand the potential of VSC for both industrial and academic chemistry community.
- Garcia-Vidal et al, Science, 2021 (373), 1-9.
- Shabalney et al, Nat Commun, 2015 (6), 1-6.
- Thomas et al, Angew Chem Intl Ed, 2016 (55), 11462-6.
- Hirai et al, Angew Chem Intl Ed, 2020 (59), 5332-5.
- Vergauwe et al, Angew Chem Intl Ed, 2019 (58), 15324-8.
- Pang et al, Angew Chem Intl Ed, 2020 (59), 10436-40.
- Joseph et al, Angew Chem Intl Ed, 2021 (60), 1-7.
- Lather et al, Angew Chem Intl Ed, 2019 (58), 10635-8.
- Wiesehan et al, J Chem Phys, 2021 (55), 241103.
- Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid, Spain.
In this work we show how driving the two-photon resonance of a system of interacting quantum emitters can be exploited for the generation of cavity-assisted steady-state entanglement. The fact that two interacting emitters can be coherently driven via two-photon processes has been exploited, e.g., to estimate interaction strengths and inter-molecular distances at the nanometer scale . It has also been shown that, under a strong two-photon drive, the emitters can be dressed with photon pairs from the drive, developing a rich family of energy levels that translate into a complex structure in the spectrum of resonance fluorescence . By coupling the dressed system to a cavity in the bad cavity limit, new processes among the two-photon dressed energy levels can be engineered. We show that, by placing particular dressed-state transitions in resonance with the cavity, these novel decay processes can stabilize the system into a highly entangled state. Since the energy of the dressed states can be tuned through the Rabi frequency of the drive, the system can be optically tuned in and out of these resonances. We also show that the stabilization of entanglement translates into particular features in the quantum optical properties of the light emitted by the system at frequencies that are well detuned from the drive, allowing us to isolate the optical signatures of entanglement by simple spectral filtering.
- C. Hettich, Nanometer resolution and coherent optical dipole coupling of two individual molecules, Science 298, 385 (2002).
- A. Vivas-Viana and C. Sánchez Muñoz, Two-photon resonance fluorescence of two interacting nonidentical quantum emitters, Physical Review Research 3, 33136 (2021).
Solvation dynamics, i.e., the interaction of a solute with a surrounding solvent, is one of the most fundamental processes in nature, playing a crucial role in many chemical reactions and charge transfer processes. We derive here a simple phenomenological model for this interaction. We want to apply stochastic methods to describe the interplay between polar molecules (e.g. water) in a surrounding polarizable medium. This builds up on previous developed methods, e.g. for the description of molecules in phononic host environments. We then want to apply the developed formalism for the description of charge transfer processes, cavity-coupled molecules and the nonlinear dynamics.
- V. May and O. Kuhn, Charge and Energy Transfer Dynamics in Molecular Systems, 3rd ed. (John Wiley & Sons, Ltd 2011).
- M. Reitz, C. Sommer, and C. Genes, Phys. Rev. Lett. 122, 203602 (2019).
- M. Reitz, C. Sommer, B. Gurlek, V. Sandoghdar, D. Martin-Cano, and C. Genes, Phys. Rev. Research 2, 033270 (2020).
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- N. Gould, S. Li, H. Cho, H. Landfield, S. Caratzoulas, D. Vlachos, P. Bai, and B. Xu, Nat. Commun. 11, 1060 (2020)