# Publications

2022

Anthony W. Schlimgen, Kade Head-Marsden, LeeAnn M. Sager, Prineha Narang, and David A. Mazziotti. 6/15/2022. “Quantum simulation of the Lindblad equation using a unitary decomposition of operators.” Physical Review Research, 4, 2, Pp. 023216. Publisher's VersionAbstract

Accurate simulation of the time evolution of a quantum system under the influence of an environment is critical to making accurate predictions in chemistry, condensed-matter physics, and materials sciences. Whereas there has been a recent surge in interest in quantum algorithms for the prediction of nonunitary time evolution in quantum systems, few studies offer a direct quantum analog to the Lindblad equation. Here, we present a quantum algorithm—utilizing a decomposition of nonunitary operators approach—that models dynamic processes via the unraveled Lindblad equation. This algorithm is employed to probe both a two-level system in an amplitude damping channel as well as the transverse field Ising model in a variety of parameter regimes; the resulting population dynamics demonstrate excellent agreement with classical simulation, showing the promise of predicting population dynamics utilizing quantum devices for a variety of important systems in molecular energy transport, quantum optics, and other open quantum systems.

Jonathan B. Curtis, Ioannis Petrides, and Prineha Narang. 6/9/2022. “Finite-Momentum Instability of Dynamical Axion Insulator.” arXiv. Publisher's VersionAbstract

The chiral anomaly is a striking signature of quantum effects which lead to the non-conservation of a classically conserved current, specifically the chiral currents in systems of fermions. In condensed matter systems, the chiral anomaly can be realized in Weyl semimetals, which then exhibit a signature electromagnetic response associated to anomaly due to the separation of the Weyl points in momentum space. In the presence of strong interactions however, a Weyl semimetal phase can give rise to an ordered phase, and spontaneously break the chiral symmetry. This then leads to a Goldstone mode which can have intrinsic dynamics and fluctuations, leading to a dynamical chiral anomaly response -- a situation known as a dynamical axion insulator. Here we consider a simple model of this dynamical axion insulator and calculate the equations of motion for the Goldstone mode. Surprisingly, we find that the Goldstone mode appears to exhibit a negative phase stiffness, signalling a further instability of the system towards finite momentum. This is expected to lead to very strong fluctuations of the anomalous response. We suggest a long-wavelength theory of Lifschitz type which may govern the axion dynamics in this system and comment on possible signatures of this model.

Somnath Biswas, Ioannis Petrides, Robert J. Kirby, Catrina Oberg, Sebastian Klemenz, Caroline Weinberg, Austin Ferrenti, Prineha Narang, Leslie Schoop, and Gregory D. Scholes. 6/9/2022. “Photoinduced Band Renormalization Effects in ZrSiS Topological Nodal-line Semimetal.” arXiv. Publisher's VersionAbstract

Out-of-equilibrium effects provide an elegant pathway to probing and understanding the underlying physics of topological materials. Creating exotic states of matter using ultrafast optical pulses in particular has shown promise towards controlling electronic band structure properties. Of recent interest is band renormalization in Dirac and Weyl semimetals as it leads to direct physical observables through the enhancement of the effective mass, or, in the shift of resonant energies. Here we provide experimental and theoretical signatures of photo-induced renormalization of the electronic band structure in a topological nodal line semimetal ZrSiS. Specifically, we show how the change of the transient reflectivity spectra under femtosecond optical excitations is induced by out-of-equilibrium effects that renormalize the kinetic energy of electrons. We associate the observed spectral shift to an enhancement of the effective mass and to a red-shift of the resonant frequency as a function of pump field strength. Finally, we show that the transient relaxation dynamics of the reflectivity is primarily an electronic effect with negligible phononic contribution. Our study presents the modifications of electronic properties in ZrSiS using ultrashort pulses, and demonstrates the potential of this approach in creating photo-induced phases in topological quantum mater through an all-optical route.

Yiping Wang, Ioannis Petrides, Grant McNamara, Md Mofazzel Hosen, Shiming Lei, Yueh-Chun Wu, James L. Hart, Hongyan Lv, Jun Yan, Di Xiao, Judy J. Cha, Prineha Narang, Leslie M. Schoop, and Kenneth S. Burch. 6/8/2022. “Axial Higgs mode detected by quantum pathway interference in RTe

_{3}.” Nature. Publisher's VersionAbstractThe observation of the Higgs boson solidified the standard model of particle physics. However, explanations of anomalies (for example, dark matter) rely on further symmetry breaking, calling for an undiscovered axial Higgs mode. The Higgs mode was also seen in magnetic, superconducting and charge density wave (CDW) systems. Uncovering the vector properties of a low-energy mode is challenging, and requires going beyond typical spectroscopic or scattering techniques. Here we discover an axial Higgs mode in the CDW system RTe

_{3}using the interference of quantum pathways. In RTe_{3}(R = La, Gd), the electronic ordering couples bands of equal or different angular momenta. As such, the Raman scattering tensor associated with the Higgs mode contains both symmetric and antisymmetric components, which are excited via two distinct but degenerate pathways. This leads to constructive or destructive interference of these pathways, depending on the choice of the incident and Raman-scattered light polarization. The qualitative behaviour of the Raman spectra is well captured by an appropriate tight-binding model, including an axial Higgs mode. Elucidation of the antisymmetric component is direct evidence that the Higgs mode contains an axial vector representation (that is, a pseudo-angular momentum) and hints that the CDW is unconventional. Thus, we provide a means for measuring quantum properties of collective modes without resorting to extreme experimental conditions.Zixuan Hu, Kade Head-Marsden, David A. Mazziotti, Prineha Narang, and Sabre Kais. 5/30/2022. “A general quantum algorithm for open quantum dynamics demonstrated with the Fenna-Matthews-Olson complex.” Quantum, 6, Pp. 726. Publisher's VersionAbstract

Using quantum algorithms to simulate complex physical processes and correlations in quantum matter has been a major direction of quantum computing research, towards the promise of a quantum advantage over classical approaches. In this work we develop a generalized quantum algorithm to simulate any dynamical process represented by either the operator sum representation or the Lindblad master equation. We then demonstrate the quantum algorithm by simulating the dynamics of the Fenna-Matthews-Olson (FMO) complex on the IBM QASM quantum simulator. This work represents a first demonstration of a quantum algorithm for open quantum dynamics with a moderately sophisticated dynamical process involving a realistic biological structure. We discuss the complexity of the quantum algorithm relative to the classical method for the same purpose, presenting a decisive query complexity advantage of the quantum approach based on the unique property of quantum measurement. An accurate yet tractable quantum algorithm for the description of complex open quantum systems (like the FMO complex) has a myriad of significant applications from catalytic chemistry and correlated materials physics to descriptions of hybrid quantum systems.

Julian Klein, Benjamin Pingault, Matthias Florian, Marie-Christin Heißenbüttel, Alexander Steinhoff, Zhigang Song, Kierstin Torres, Florian Dirnberger, Jonathan B. Curtis, Thorsten Deilmann, Rami Dana, Rezlind Bushati, Jiamin Quan, Jan Luxa, Zdenek Sofer, Andrea Alù, Vinod M. Menon, Ursula Wurstbauer, Michael Rohlfing, Prineha Narang, Marko Lončar, and Frances M. Ross. 5/26/2022. “The bulk van der Waals layered magnet CrSBr is a quasi-1D quantum material.” arXiv. Publisher's VersionAbstract

Correlated quantum phenomena in one-dimensional (1D) systems that exhibit competing electronic and magnetic orders are of fundamental interest. Interaction effects in low-dimensional systems can lead to fundamental excitations which are completely different from the quasi-particles one would expect in a higher-dimensional counterpart, such as Tomonaga-Luttinger liquids and topological orders and defects. However, clean 1D electronic systems are difficult to realize experimentally, particularly magnetically ordered systems. Here, we show that the van der Waals layered magnetic semiconductor CrSBr behaves like a quasi-1D electronic material embedded in a magnetically ordered environment. The strong 1D electronic character is due to the unique combination of weak interlayer hybridization and anisotropy in effective mass and dielectric screening. The band structure and quasi-particle excitations are dominated by the Cr-S chains and a shallow 1D quantum confinement normal to these chains, manifesting in an anisotropic band with an effective electron mass ratio of m

^{e}_{X}/m^{e}_{Y }∼ 50. Strong quasi-particle interactions and 1D electronic character are indicated by Fano resonances from a van Hove singularity of similar strength as in metallic carbon nanotubes. The spectrally narrow excitons (1 meV) inherit the 1D character and show pronounced exciton-phonon coupling effects. Overall, CrSBr appears to be an experimentally clean candidate for the study of 1D correlated many-body physics in the presence of magnetic order.Anthony W. Schlimgen, Kade Head-Marsden, LeeAnn M. Sager-Smith, Prineha Narang, and David A. Mazziotti. 5/5/2022. “Quantum State Preparation and Non-Unitary Evolution with Diagonal Operators.” arXiv. Publisher's VersionAbstract

Realizing non-unitary transformations on unitary-gate based quantum devices is critically important for simulating a variety of physical problems including open quantum systems and subnormalized quantum states. We present a dilation based algorithm to simulate non-unitary operations using probabilistic quantum computing with only one ancilla qubit. We utilize the singular-value decomposition (SVD) to decompose any general quantum operator into a product of two unitary operators and a diagonal non-unitary operator, which we show can be implemented by a diagonal unitary operator in a 1-qubit dilated space. While dilation techniques increase the number of qubits in the calculation, and thus the gate complexity, our algorithm limits the operations required in the dilated space to a diagonal unitary operator, which has known circuit decompositions. We use this algorithm to prepare random sub-normalized two-level states on a quantum device with high fidelity. Furthermore, we present the accurate non-unitary dynamics of two-level open quantum systems in a dephasing channel and an amplitude damping channel computed on a quantum device. The algorithm presented will be most useful for implementing general non-unitary operations when the SVD can be readily computed, which is the case with most operators in the noisy intermediate-scale quantum computing era.

Georgios Varnavides, Adam S. Jermyn, Polina Anikeeva, and Prineha Narang. 4/12/2022. “Probing carrier interactions using electron hydrodynamics.” arXiv. Publisher's VersionAbstract

Electron hydrodynamics arises when momentum-relaxing scattering processes are slow compared to momentum-conserving ones. While the microscopic details necessary to satisfy this condition are material-specific, experimentally accessible current densities share remarkable similarities. We study the dependence of electron hydrodynamic flows on the rates of momentum-relaxing and momentum-conserving scattering processes in a microscopics-agnostic way. We develop a framework for generating random collision operators which respect crystal symmetries and conservation laws and which have a tunable ratio between the momentum-conserving and momentum-relaxing lifetimes. Using various random instances of these collision operators, we calculate macroscopic electron viscosity tensors and solve the Boltzmann transport equation (BTE) in a channel geometry over a grid of momentum-conserving and momentum-relaxing lifetimes, and for different crystal symmetry groups. We find that different random collision operators using the same lifetimes produce very similar current density profiles, meaning that the current density is primarily a probe of the overall rates of momentum conservation and relaxation. By contrast, the viscosity tensor varies substantially at fixed lifetimes, meaning that properties like channel resistance provide detailed probes of the underlying scattering processes. This suggests that, while details of the scattering process are imprinted in the electronic viscosity tensor, for many applications theoretical calculations of hydrodynamic electron flows can use experimentally-available lifetimes within a spatially-resolved BTE framework rather than requiring the costly computation of ab initio collision operators.

Georgios Varnavides, Yaxian Wang, Philip J.W. Moll, Polina Anikeeva, and Prineha Narang. 4/8/2022. “Mesoscopic finite-size effects of unconventional electron transport in PdCoO

_{2}.” Physical Review Materials, 6, 4, Pp. 045002. Publisher's VersionAbstractA wide range of unconventional transport phenomena have recently been observed in single-crystal delafossite metals. Here, we present a theoretical framework to elucidate electron transport using a combination of first-principles calculations and numerical modeling of the anisotropic Boltzmann transport equation. Using PdCoO

_{2}as a model system, we study different microscopic electron and phonon scattering mechanisms and establish the mean free path hierarchy of quasiparticles at different temperatures. We treat the anisotropic Fermi surface explicitly to numerically obtain experimentally-accessible transport observables, which bridge between the "diffusive", "ballistic", and "hydrodynamic" transport regime limits. We illustrate that distinction between the "quasi-ballistic", and "quasi-hydrodynamic" regimes is challenging and often needs to be quantitative in nature. From first-principles calculations, we populate the resulting transport regime plots, and demonstrate how the Fermi surface orientation adds complexity to the observed transport signatures in micro-scale devices. Our work provides key insights into microscopic interaction mechanisms on open hexagonal Fermi surfaces and establishes their connection to the macroscopic electron transport in finite-size channels.Spyros Tserkis, Kade Head-Marsden, and Prineha Narang. 3/1/2022. “Information back-flow in quantum non-Markovian dynamics and its connection to teleportation.” arXiv. Publisher's VersionAbstract

A quantum process is called non-Markovian when memory effects take place during its evolution. Quantum non-Markovianity is a phenomenon typically associated with the information back-flow from the environment to the principal system, however it has been shown that such an effect is not necessary. In particular, maximum quantum non-Markovianity can be achieved without any physical transmission of information. In this work, it is shown that time-homogeneity is a sufficient condition for a non-Markovian quantum process to originate from an information back-flow effect. As a characteristic example, the protocol of measurement-free teleportation is suggested as a time-homogeneous maximally non-Markovian quantum process, in both discrete and continuous-variable systems. Finally, given the resource-like role of entanglement in teleportation protocol, the relationship between this property and non-Markovianity is elucidated.

Davis M. Welakuh and Prineha Narang. 3/1/2022. “Tunable Nonlinearity and Efficient Harmonic Generation from a Strongly Coupled Light-Matter System.” arXiv. Publisher's VersionAbstract

Strong light-matter coupling within electromagnetic environments provides a promising path to modify and control chemical and physical processes. The origin of the enhancement of nonlinear optical processes such as second-harmonic and third-harmonic generation (SHG and THG) due to strong light-matter coupling is attributed to distinct physical effects which questions the relevance of strong coupling in these processes. In this work, we leverage a first-principles approach to investigate the origins of the experimentally observed enhancement of resonant SHG and THG under strong light-matter coupling. We find that the enhancement of the nonlinear conversion efficiency has its origins in a modification of the associated nonlinear optical susceptibilities as polaritonic resonances emerge in the nonlinear spectrum. Further, we find that the nonlinear conversion efficiency can be tuned by increasing the light-matter coupling strength. Finally, we provide a general framework to compute the harmonic generation spectra from the displacement field as opposed to the standard approach which computes the harmonic spectrum from the matter-only induced polarization. Our results address a key debate in the field, and pave the way for predicting and understanding quantum nonlinear optical phenomena in strongly coupled light-matter systems.

Nicholas R. Poniatowksi, Jonathan B. Curtis, Amir Yacoby, and Prineha Narang. 2/28/2022. “Spectroscopic signatures of time-reversal symmetry breaking superconductivity.” Communications Physics, 5. Publisher's VersionAbstract

The collective mode spectrum of a symmetry-breaking state, such as a superconductor, provides crucial insight into the nature of the order parameter. In this work, we study two collective modes which are unique to unconventional superconductors that spontaneously break time reversal symmetry. We show that these modes are coherent and underdamped for a wide variety of time-reversal symmetry breaking superconducting states. By further demonstrating that these modes can be detected using a number of existing experimental techniques, we propose that our work can be leveraged as a form of “collective mode spectroscopy” that drastically expands the number of experimental probes capable of detecting time-reversal symmetry breaking in unconventional superconductors.

Davis M. Welakuh and Prineha Narang. 2/22/2022. “Nonlinear optical processes in centrosymmetric systems by strong-coupling-induced symmetry breaking.” arXiv. Publisher's VersionAbstract

Nonlinear optical processes associated with even-order nonlinear susceptibilities are critical for both classical and quantum technologies. Inversion symmetry, however, prevents nonlinear optical responses mediated by even-order susceptibilities in several material systems pertinent for applications in nanophotonics. Here, we demonstrate induced nonlinear optical processes, namely second- and fourth-harmonic generation that are naturally forbidden in an inversion symmetric system, by strongly coupling to a photon mode of a high-Q optical cavity. As an illustrative system with an inversion symmetry, we consider a semiconductor quantum ring of GaAs that features a single effective electron. For the coupled system, we control the inversion symmetry breaking by changing the light-matter coupling strength which at the same time allows to tune the nonlinear conversion efficiency. We find that the harmonic generation yield can be significantly increased by increasing the light-matter coupling strength in an experimentally feasible way. In the few-photon limit where the incident pump field is a coherent state with just a few photons, we find that the harmonic conversion efficiency is increased for strong coupling as opposed to using intense pump fields. This new approach is applicable to a wide variety of centrosymmetric systems as the symmetry breaking rest on the properties of the photonic environment used to achieve strong light-matter interaction. Our work constitutes a step forward in the direction of realizing physically forbidden nonlinear optical processes in centrosymmetric materials widely adopted for applications in integrated photonics.

Dominik M. Juraschek, Tomáš Neuman, and Prineha Narang. 2/17/2022. “Giant phonon-induced effective magnetic fields in 4

*f*paramagnets.” Physical Review Research, 4, 1, Pp. 013129. Publisher's VersionAbstractWe present a mechanism by which circularly driven phonon modes in the rare-earth trihalides generate giant effective magnetic fields acting on the paramagnetic 4

*f*spins. With cerium trichloride (CeCl_{3}) as our model system, we calculate the coherent phonon dynamics in response to the excitation by an ultrashort terahertz pulse using a combination of first-principles calculations and phenomenological modeling. We find that effective magnetic fields of over 100 T can possibly be generated that polarize the spins for experimentally accessible pulse energies. This mechanism potentially creates a way to control the magnetic and electrical order of ferromagnets and ferroelectrics through interfacial coupling with the phonon-induced magnetization in heterostructures.Ian MacCormack, Conor Delaney, Alexey Galda, Nidhi Aggarwal, and Prineha Narang. 2/14/2022. “Branching quantum convolutional neural networks.” Physical Review Research, 4, 1, Pp. 013117. Publisher's VersionAbstract

Neural-network-based algorithms have garnered considerable attention for their ability to learn complex patterns from very-high-dimensional data sets towards classifying complex long-range patterns of entanglement and correlations in many-body quantum systems, and towards processing high-dimensional classical data sets. Small-scale quantum computers are already showing potential gains in learning tasks on large quantum and very large classical data sets. A particularly interesting class of algorithms, the quantum convolutional neural networks (QCNNs) could learn features of a quantum data set by performing a binary classification task on a nontrivial phase of quantum matter. Inspired by this promise, we present a generalization of QCNN, the “branching quantum convolutional neural network,” or bQCNN, with substantially higher expressibility. A key feature of bQCNN is that it leverages midcircuit (intermediate) measurement results, realizable on several current quantum devices, obtained in pooling layers to determine which sets of parameters will be used in the subsequent convolutional layers of the circuit. This results in a “branching” structure, which allows for a greater number of trainable variational parameters in a given circuit depth. This is of particular use in current-day noisy intermediate-scale quantum devices, where circuit depth is limited by gate noise. We present an overview of the

*Ansatz*structure and scaling and provide evidence of its enhanced expressibility compared with QCNN. Using artificially constructed large data sets of training states as a proof of concept, we demonstrate the existence of training tasks in which bQCNN far outperforms an ordinary QCNN. We provide an explicit example of such a task in the recognition of the transition from a symmetry protected topological to a trivial phase induced by multiple, distinct perturbations. Finally, we present future directions where the classical branching structure and increased density of trainable parameters in bQCNN would be particularly valuable.Jonathan B. Curtis, Andrey Grankin, Nicholas R. Poniatowksi, Victor M. Galitski, Prineha Narang, and Eugene Demler. 2/10/2022. “Cavity magnon-polaritons in cuprate parent compounds.” Physical Review Research, 4, 1, Pp. 013101. Publisher's VersionAbstract

Cavity control of quantum matter may offer new ways to study and manipulate many-body systems. A particularly appealing idea is to use cavities to enhance superconductivity, especially in unconventional or high-T

_{c}systems. Motivated by this, we propose a scheme for coupling terahertz resonators to the antiferromagnetic fluctuations in a cuprate parent compound, which are believed to provide the glue for Cooper pairs in the superconducting phase. First, we derive the interaction between magnon excitations of the Neél order and polar phonons associated with the planar oxygens. This mode also couples to the cavity electric field, and in the presence of spin-orbit interactions mediates a linear coupling between the cavity and magnons, forming hybridized magnon-polaritons. This hybridization vanishes linearly with photon momentum, implying the need for near-field optical methods, which we analyze within a simple model. We then derive a higher-order coupling between the cavity and magnons, which is only present in bilayer systems, but does not rely on spin-orbit coupling. This interaction is found to be large, but only couples to the bimagnon operator. As a result, we find a strong, but heavily damped, bimagnon-cavity interaction which produces highly asymmetric cavity line shapes in the strong-coupling regime. To conclude, we outline several interesting extensions of our theory, including applications to carrier-doped cuprates and other strongly correlated systems with terahertz-scale magnetic excitations.Jonathan B. Curtis, Nicholas R. Poniatowski, Amir Yacoby, and Prineha Narang. 1/12/2022. “Proximity-induced collective modes in an unconventional superconductor heterostructure.” arXiv. Publisher's VersionAbstract

Unconventional superconductors have been long sought for their potential applications in quantum technologies and devices. A key challenge impeding this effort is the difficulty associated with probing and characterizing candidate materials and establishing their order parameter. In this Letter, we present a platform that allows us to spectroscopically probe unconventional superconductivity in thin-layer materials via the proximity effect. We show that inducing an s-wave gap in a sample with an intrinsic d-wave instability leads to the formation of bound-states of quasiparticle pairs, which manifest as a collective mode in the d-wave channel. This finding provides a way to study the underlying pairing interactions vicariously through the collective mode spectrum of the system. Upon further cooling of the system we observe that this mode softens considerably and may even condense, signaling the onset of time-reversal symmetry breaking superconductivity. Therefore, our proposal also allows for the creation and study of these elusive unconventional states.

2021

Anthony W. Schlimgen, Kade Head-Marsden, LeeAnn M. Sager, Prineha Narang, and David A. Mazziotti. 12/29/2021. “Quantum Simulation of Open Quantum Systems Using a Unitary Decomposition of Operators.” Physical Review Letters, 127, 27, Pp. 270503. Publisher's VersionAbstract

Electron transport in realistic physical and chemical systems often involves the nontrivial exchange of energy with a large environment, requiring the definition and treatment of open quantum systems. Because the time evolution of an open quantum system employs a nonunitary operator, the simulation of open quantum systems presents a challenge for universal quantum computers constructed from only unitary operators or gates. Here, we present a general algorithm for implementing the action of any nonunitary operator on an arbitrary state on a quantum device. We show that any quantum operator can be exactly decomposed as a linear combination of at most four unitary operators. We demonstrate this method on a two-level system in both zero and finite temperature amplitude damping channels. The results are in agreement with classical calculations, showing promise in simulating nonunitary operations on intermediate-term and future quantum devices.

Dominik M. Juraschek and Prineha Narang. 12/23/2021. “Magnetic control in the terahertz.” Science, 374, 6575, Pp. 1555-1556. Publisher's VersionAbstract

Magnetic materials are central to information storage devices, with ongoing research seeking to develop faster and more energy-efficient systems. The individual bits of data, written as 1’s and 0’s, can be stored as different orientations of magnetic moments. Conventionally, an electromagnetic head is used to flip these bits between 1 and 0, and the read and write speeds using this method are currently limited to gigahertz frequencies. A substantial amount of energy is used to drive electric currents that generate the magnetic fields. Instead of manipulating magnetic moments with slow or static magnetic fields, an intriguing alternative involves coupling light from a laser to their quantum mechanical states. On page 1608 of this issue, Mashkovich

*et al.*(*1*) report the coupling of light, magnetism, and the crystal structure of a material, which opens new possibilities for controlling the magnetic state of materials on very short time scales.Davis M. Welakuh and Prineha Narang. 12/9/2021. “Transition from Lorentz to Fano Spectral Line Shapes in Non-Relativistic Quantum Electrodynamics.” arXiv. Publisher's VersionAbstract

Spectroscopic signatures associated with symmetric Lorentzian and asymmetric Fano line shapes are ubiquitous. Distinct features of Fano resonances in contrast with conventional symmetric resonances have found several applications in photonics such as optical switching, sensing, lasing, and nonlinear and slow-light devices. Therefore, it is important to have control over the generation of these resonances. In this work, we show through ab initio simulations of coupled light-matter systems that Fano interference phenomena can be realized in a multimode photonic environment by strong coupling to the electromagnetic continuum. Specifically, we show that by effectively enhancing the light-matter coupling strength to the photon continuum in an experimentally feasible way, we can achieve a transition from Lorentzian to Fano lines shapes for both electronic and polaritonic excitations. An important outcome of switching between these spectral signatures is the possibility to control the Purcell enhancement of spontaneous emission alongside electromagnetically induced transparency which is a special case of Fano resonances. Switching from Fano back to a Lorentzian profile can be achieved by physically reducing the coupling strength to the continuum of modes. Our results hold potential for realizing tunable Fano resonances of molecules and materials interacting with the electromagnetic continuum within multimode photonic environments.