# Publications

2020

Georgios Varnavides, Adam S. Jermyn, Polina Anikeeva, Claudia Felser, and Prineha Narang. 9/18/2020. “Electron hydrodynamics in anisotropic materials.” Nature Communications, 11, Pp. 4710. Publisher's VersionAbstract

Rotational invariance strongly constrains the viscosity tensor of classical fluids. When this symmetry is broken in anisotropic materials a wide array of novel phenomena become possible. We explore electron fluid behaviors arising from the most general viscosity tensors in two and three dimensions, constrained only thermodynamics and crystal symmetries. We find nontrivial behaviors in both two- and three-dimensional materials, including imprints of the crystal symmetry on the large-scale flow pattern. Breaking time-reversal symmetry introduces a non-dissipative Hall component to the viscosity tensor, and while this vanishes for 3D isotropic systems we show it need not for anisotropic materials. Further, for such systems we find that the electronic fluid stress can couple to the vorticity without breaking time-reversal symmetry. Our work demonstrates the anomalous landscape for electron hydrodynamics in systems beyond graphene, and presents experimental geometries to quantify the effects of electronic viscosity.

Yaxian Wang and Prineha Narang. 9/15/2020. “Anisotropic scattering in the goniopolar metal NaSn

_{2}As_{2}.” Physical Review B, 102, 12, Pp. 125122. Publisher's VersionAbstractRecent experimental discoveries in axis-dependent conduction polarity, or

*goniopolarity*, have observed that the charge carriers can conduct like either electrons or holes depending on the crystallographic direction they travel along in layered compounds such as NaSn_{2}As_{2}. The original theoretical proposal is based on the opposite signs of the carrier effective mass, or the curvature of the Fermi surface, without examining the effect of electron lifetimes, thus leaving a crucial question to address. To elucidate this unusual transport behavior, we present an*ab initio*study of electron scattering in such systems. We study different microscopic scattering mechanisms in NaSn_{2}As_{2}, and we present the electron-phonon scattering time distribution on its Fermi surface in momentum space, the open concave shape of which is proposed to be the origin of the axis-dependent conduction polarity. Further, we obtain the overall anisotropic lifetime tensors in real space at different electron chemical potentials and temperatures, and we discuss how they contribute to the macroscopic thermopower. While we find that the contribution of the in-plane and cross-plane lifetimes exhibits a similar trend, the concave portion of the Fermi surface alters the electron motion significantly in the presence of a magnetic field, thus flipping the conduction polarity as measured via the Hall effect. Our calculations and analysis of NaSn_{2}As_{2}, in comparison with similar systems, also suggest the strong possibility of hydrodynamic electron flow in the system. Finally, our work has implications for anisotropic electron lifetimes in a broad class of goniopolar materials and provides key, general insights into electron scattering on open Fermi surfaces.Uri Vool, Assaf Hamo, Georgios Varnavides, Yaxian Wang, Tony X. Zhou, Nitesh Kumar, Yuliya Dovzhenko, Ziwei Qiu, Christina A. C. Garcia, Andrew T. Pierce, Johannes Gooth, Polina Anikeeva, Claudia Felser, Prineha Narang, and Amir Yacoby. 9/9/2020. “Imaging phonon-mediated hydrodynamic flow in WTe2 with cryogenic quantum magnetometry.” arXiv. Publisher's VersionAbstract

In the presence of strong interactions, electrons in condensed matter systems can behave hydrodynamically thereby exhibiting classical fluid phenomena such as vortices and Poiseuille flow. While in most conductors large screening effects minimize electron-electron interactions, hindering the search for possible hydrodynamic candidate materials, a new class of semimetals has recently been reported to exhibit strong interactions. In this work, we study the current flow in the layered semimetal tungsten ditelluride (WTe2) by imaging the local magnetic field above it using a nitrogen-vacancy (NV) defect in diamond. Our cryogenic scanning magnetometry system allows for temperature-resolved measurement with high sensitivity enabled by the long defect spin coherence. We directly measure the spatial current profile within WTe2 and find it differs substantially from the uniform profile of a Fermi liquid, indicating hydrodynamic flow. Furthermore, our temperature-resolved current profile measurements reveal an unexpected non-monotonic temperature dependence, with hydrodynamic effects strongest at ~20 K. We further elucidate this behavior via ab initio calculations of electron scattering mechanisms, which are used to extract a current profile using the electronic Boltzmann transport equation. These calculations show quantitative agreement with our measurements, capturing the non-monotonic temperature dependence. The combination of experimental and theoretical observations allows us to quantitatively infer the strength of electron-electron interactions in WTe2. We show these strong electron interactions cannot be explained by Coulomb repulsion alone and are predominantly phonon-mediated. This provides a promising avenue in the search for hydrodynamic flow and strong interactions in high carrier density materials.

Stefan Krastanov, Kade Head-Marsden, Sisi Zhou, Steven T. Flammia, Liang Jiang, and Prineha Narang. 9/8/2020. “Unboxing Quantum Black Box Models: Learning Non-Markovian Dynamics.” arXiv. Publisher's VersionAbstract

Characterizing the memory properties of the environment has become critical for the high-fidelity control of qubits and other advanced quantum systems. However, current non-Markovian tomography techniques are either limited to discrete superoperators, or they employ machine learning methods, neither of which provide physical insight into the dynamics of the quantum system. To circumvent this limitation, we design learning architectures that explicitly encode physical constraints like the properties of completely-positive trace-preserving maps in a differential form. This method preserves the versatility of the machine learning approach without sacrificing the efficiency and fidelity of traditional parameter estimation methods. Our approach provides the physical interpretability that machine learning and opaque superoperators lack. Moreover, it is aware of the underlying continuous dynamics typically disregarded by superoperator-based tomography. This paradigm paves the way to noise-aware optimal quantum control and opens a path to exploiting the bath as a control and error mitigation resource.

Johannes Flick and Prineha Narang. 9/4/2020. “

*ab initio*polaritonic potential-energy surfaces for excited-state nonphotonics and polaritonic chemistry.” The Journal of Chemical Physics, 153, Pp. 094116. Publisher's VersionAbstractAdvances in nanophotonics, quantum optics, and low-dimensional materials have enabled precise control of light-matter interactions down to the nanoscale. Combining concepts from each of these fields, there is now an opportunity to create and manipulate photonic matter via strong coupling of molecules to the electromagnetic field. Towards this goal, here we introduce a first principles framework to calculate polaritonic excited-state potential-energy surfaces for strongly coupled light-matter systems. In particular, we demonstrate the applicability of our methodology by calculating the polaritonic excited-state manifold of a Formaldehyde molecule strongly coupled to an optical cavity. This proof-of-concept calculation shows how strong coupling can be exploited to alter photochemical reaction pathways by influencing avoided crossings. Therefore, by introducing an ab initio method to calculate excited-state potential-energy surfaces, our work opens a new avenue for the field of polaritonic chemistry.

Kate Reidy, Georgios Varnavides, Joachim Dahl Thomsen, Abinash Kumar, Thang Pham, Arthur M. Blackburn, Polina Anikeeva, Prineha Narang, James M. LeBeau, and Frances M. Ross. 8/27/2020. “Direct Imaging and Electronic Structure Modulation of Double Moiré Superlattices at the 2D/3D Interface.” arXiv. Publisher's VersionAbstract

The atomic structure at the interface between a two-dimensional (2D) and a three-dimensional (3D) material influences properties such as contact resistance, photo-response, and high-frequency performance. Moiré engineering has yet to be explored for tailoring this 2D/3D interface, despite its success in enabling correlated physics at 2D/2D twisted van der Waals interfaces. Using epitaxially aligned MoS

_{2}/Au{111} as a model system, we apply a geometric convolution technique and four-dimensional scanning transmission electron microscopy (4D STEM) to show that the 3D nature of the Au structure generates two coexisting moiré periods (18 Angstroms and 32 Angstroms) at the 2D/3D interface that are otherwise hidden in conventional electron microscopy imaging. We show, via ab initio electronic structure calculations, that charge density is modulated with the longer of these moiré periods, illustrating the potential for (opto-)electronic modulation via moiré engineering at the 2D/3D interface.Andrew H. Poppe, Yuguang C. Li, Alán Aspuru-Guzik, Curtis P. Berlinguette, Christopher J. Chang, Richard Cogdell, Abigail G. Doyle, Johannes Flick, Nathaniel M. Gabor, Rienk van Grondelle, Sharon Hammes-Schiffer, Shaffiq A. Jaffer, Shana O. Kelley, Mario Leclerc, Karl Leo, Thomas E. Mallouk, Prineha Narang, Gabriela S. Schlau-Cohen, Gregory D. Scholes, Aleksandra Vojvodic, Vivian Wing-Wah Yam, Jenny Y. Yang, and Edward H. Sargent. 8/7/2020. “Bioinspiration in light harvesting and catalysis.” Nature Reviews Materials. Publisher's VersionAbstract

Capturing and converting solar energy into fuels and feedstocks is a global challenge that spans numerous disciplines and fields of research. Billions of years of evolution have allowed natural organisms to hone strategies for harvesting light from the sun and storing energy in the form of carbon–carbon and carbon–hydrogen bonds. Photosynthetic antenna proteins capture solar photons and funnel photoexcitations to reaction centres with high yields, and enzymes catalyze multi-electron reactions, facilitating chemical transformations not yet efficiently implemented using artificially engineered catalysts. Researchers in renewable energy often look to nature to understand the mechanisms at work and, if possible, to explore their translation into artificial systems. Here, we review advances in bioinspiration across the fields of biological light harvesting and chemical energy conversion. We examine how multi-photon and multi-electron reactions in biology can inspire new methods in photoredox chemistry to achieve novel, selective and complex organic transformations; how carbonic-dehydrogenase-inspired design principles enable catalytic reactions such as the conversion of CO

_{2}into useful products such as fuels; and how concepts from photosynthetic antenna complexes and reaction centres can benefit artificial light-harvesting materials. We then consider areas in which bioinspiration could enable advances in the rational design of molecules and materials, the expansion of the synthetic capabilities of catalysts and the valorization of molecular building blocks. We highlight the challenges that must be overcome to realize these advances and propose new directions that may use bioinspiration to achieve them.Chitraleema Chakraborty, Christopher J. Ciccarino, and Prineha Narang. 7/28/2020. “Dynamic modulation of phonon-assisted transitions in quantum defects in monolayer transition-metal dichalcogenide semiconductors.” arXiv. Publisher's VersionAbstract

Quantum localization via atomic point defects in semiconductors is of significant fundamental and technological importance. Quantum defects in monolayer transition-metal dichalcogenide semiconductors have been proposed as stable and scalable optically-addressable spin qubits. Yet, the impact of strong spin-orbit coupling on their dynamical response, for example under optical excitation, has remained elusive. In this context, we study the effect of spin-orbit coupling on the electron-phonon interaction in a single chalcogen vacancy defect in monolayer transition metal dichalcogenides, molybdenum disulfide (MoS

_{2}) and tungsten disulfide (WS_{2}). From ab initio electronic structure theory calculations, we find that spin-orbit interactions tune the magnitude of the electron-phonon coupling in both optical and charge-state transitions of the defect, modulating their respective efficiencies. This observation opens up a promising scheme of dynamically modulating material properties to tune the local behavior of a quantum defect.Ravishankar Sundararaman, Thomas Christensen, Yuan Ping, Nicholas Rivera, John D. Joannopoulos, Marin Soljačić, and Prineha Narang. 7/24/2020. “Plasmonics in Argentene.” Physical Review Materials, 4, 074011. Publisher's VersionAbstract

Merging concepts from the fields of

*ab initio*materials science and nanophotonics, there is now an opportunity to engineer new photonic materials whose optical, transport, and scattering properties are tailored to attain thermodynamic and quantum limits. Here we present first-principles calculations predicting that*Argentene*, a single-crystalline hexagonal close-packed monolayer of Ag, can dramatically surpass the optical properties and electrical conductivity of conventional plasmonic materials. In the low-frequency limit, we show that the scattering rate and resistivity reduce by a factor of 3 compared to the bulk three-dimensional metal. Most importantly, the low scattering rate extends to optical frequencies in sharp contrast to, e.g., graphene, whose scattering rate increase drastically in the near-infrared range due to optical-phonon scattering. Combined with an intrinsically high carrier density, this facilitates highly confined surface plasmons extending to visible frequencies. We evaluate Argentene across three distinct figures of merit, in each outperforming the state-of-the-art, making it a valuable addition to the two-dimensional heterostructure toolkit for quantum optoelectronics.Tomáš Neuman, Derek S. Wang, and Prineha Narang. 7/22/2020. “Nanomagnonic cavities for strong spin-magnon coupling.” arXiv. Publisher's VersionAbstract

We present a theoretical approach to use ferro- or ferrimagnetic nanoparticles as microwave nanomagnonic cavities to concentrate microwave magnetic fields into deeply subwavelength volumes ∼10

^{−13}mm^{3}. We show that the field in such nanocavities can efficiently couple to isolated spin emitters (spin qubits) positioned close to the nanoparticle surface reaching the single magnon-spin strong-coupling regime and mediate efficient long-range quantum state transfer between isolated spin emitters. Nanomagnonic cavities thus pave the way towards magnon-based quantum networks and magnon-mediated quantum gates.Dominik M. Juraschek and Prineha Narang. 7/21/2020. “Giant phonon-induced effective magnetic fields in 4

*f*paramagnets.” arXiv. 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.Gavin B. Osterhoudt, Vincent M. Plisson, Yaxian Wang, Christina A. C. Garcia, Johannes Gooth, Claudia Felser, Prineha Narang, and Kenneth S. Burch. 7/20/2020. “Evidence for dominant phonon-electron scattering in Weyl semimetal WP

_{2}.” arXiv. Publisher's VersionAbstractTopological semimetals have revealed a wide array of novel transport phenomena, including electron hydrodynamics, quantum field theoretic anomalies, and extreme magnetoresistances and mobilities. However, the scattering mechanisms central to these behaviors remain largely unexplored. Here we reveal signatures of significant phonon-electron scattering in the type-II Weyl semimetal WP

_{2}via temperature-dependent Raman spectroscopy. Over a large temperature range, we find that the decay rates of the lowest energy A_{1 }modes are dominated by phonon-electron rather than phonon-phonon scattering. In conjunction with first-principles calculations, a combined analysis of the momentum, energy, and symmetry-allowed decay paths indicates this results from intraband scattering of the electrons. The excellent agreement with theory further suggests that such results could be true for the acoustic modes. We thus provide evidence for the importance of phonons in the transport properties of topological semimetals and identify specific properties that may contribute to such behavior in other materials.Dominik M. Juraschek and Prineha Narang. 6/22/2020. “Shaken not strained.” Nature Physics. Publisher's VersionAbstract

Experiments show how the magnetic order in antiferromagnets can be manipulated through lattice vibrations excited by a laser. This induces a large and reversible magnetic moment at very high speed.

Tomáš Neuman, Matthew Trusheim, and Prineha Narang. 5/28/2020. “Selective control of photon-mediated qubit-qubit interactions.” Physical Review A, 101, 5, Pp. 052342. Publisher's VersionAbstract

Quantum technologies such as quantum sensing, quantum imaging, quantum communications, and quantum computing rely on the ability to actively manipulate the quantum state of light and matter. Quantum emitters, such as color centers trapped in solids, are a useful platform for the realization of elementary building blocks (qubits) of quantum information systems. In particular, the modular nature of such solid-state devices opens up the possibility to connect them into quantum networks and create non-classical states of light shared among many qubits. The function of a quantum network relies on efficient and controllable interactions among individual qubits. In this context, we present a scheme where optically active qubits of differing excitation energies are mutually coupled via a dispersive interaction with a shared mode of an optical cavity. This generally off-resonant interaction is prohibitive of direct exchange of information among the qubits. However, we propose a scheme in which by acoustically modulating the qubit excitation energies it is in fact possible to tune to resonance a pre-selected pair of qubits and thus open a communication channel between them. This method potentially enables fast (∼ns) and parallelizable on-demand control of a large number of physical qubits. We develop an analytical and a numerical theoretical model demonstrating this principle and suggest feasible experimental scenarios to test the theoretical predictions.

Gabriele Grosso, Hyowon Moon, Christopher J. Ciccarino, Johannes Flick, Noah Mendelson, Milos Toth, Igor Aharonovich, Prineha Narang, and Dirk R. Englund. 5/8/2020. “Low-temperature electron-phonon interaction of quantum emitters in hexagonal Boron Nitride.” ACS Photonics. Publisher's VersionAbstract

Quantum emitters based on atomic defects in layered hexagonal Boron Nitride (hBN) have emerged as promising solid state 'artificial atoms' with atom-like photophysical and quantum optoelectronic properties. Similar to other atom-like emitters, defect-phonon coupling in hBN governs the characteristic single-photon emission and provides an opportunity to investigate the atomic and electronic structure of emitters as well as the coupling of their spin- and charge-dependent electronic states to phonons. Here, we investigate these questions using photoluminescence excitation (PLE) experiments at T=4K on single photon emitters in multilayer hBN grown by chemical vapor deposition. By scanning up to 250 meV from the zero phonon line (ZPL), we can precisely measure the emitter's coupling efficiency to different phonon modes. Our results show that excitation mediated by the absorption of one in-plane optical phonon increases the emitter absorption probability ten-fold compared to that mediated by acoustic or out-of-plane optical phonons. We compare these measurements against theoretical predictions by first-principles density-functional theory of four defect candidates, for which we calculate prevalent charge states and their spin-dependent coupling to bulk and local phonon modes. Our work illuminates the phonon-coupled dynamics in hBN quantum emitters at cryogenic temperature, with implications more generally for mesoscopic quantum emitter systems in 2D materials and represents possible applications in solid-state quantum technologies.

Kade Head-Marsden, Stefan Krastanov, David A. Mazziotti, and Prineha Narang. 4/30/2020. “Capturing Non-Markovian Dynamics on Near-Term Quantum Computers.” arXiv. Publisher's VersionAbstract

With the rapid progress in quantum hardware, there has been an increased interest in new quantum algorithms to describe complex many-body systems searching for the still-elusive goal of 'useful quantum advantage'. Surprisingly, quantum algorithms for the treatment of open quantum systems (OQSs) have remained under-explored, in part due to the inherent challenges of mapping non-unitary evolution into the framework of unitary gates. Evolving an open system unitarily necessitates dilation into a new effective system to incorporate critical environmental degrees of freedom. In this context, we present and validate a new quantum algorithm to treat non-Markovian dynamics in OQSs built on the Ensemble of Lindblad's Trajectories approach, invoking the Sz.-Nagy dilation theorem. Here we demonstrate our algorithm on the Jaynes-Cummings model in the strong coupling and detuned regimes, relevant in quantum optics and driven quantum systems studies. This algorithm, a key step towards generalized modeling of non-Markovian dynamics on a noisy-quantum device, captures a broad class of dynamics and opens up a new direction in OQS problems.

Derek S. Wang, Tomáš Neuman, and Prineha Narang. 4/28/2020. “Dipole-Coupled Defect Pairs as Deterministic Entangled Photon Pair Sources.” arXiv. Publisher's VersionAbstract

Scalable quantum systems require deterministic entangled photon pair sources. Here, we demonstrate a scheme that uses a dipole-coupled defect pair to deterministically emit polarization-entangled photon pairs. Based on this scheme, we predict spectroscopic signatures and quantify the entanglement with physically realizable system parameters. We describe how the Bell state fidelity and efficiency can be optimized by precisely tuning transition frequencies. A defect-based entangled photon pair source would offer numerous advantages including flexible on-chip photonic integration and tunable emission properties via external fields, electromagnetic environments, and defect selection.

Tomáš Neuman, Matt Eichenfield, Matthew Trusheim, Lisa Hackett, Prineha Narang, and Dirk Englund. 3/18/2020. “A Phononic Bus for Coherent Interfaces Between a Superconducting Quantum Processor, Spin Memory, and Photonic Quantum Networks.” arXiv. Publisher's VersionAbstract

We introduce a method for high-fidelity quantum state transduction between a superconducting microwave qubit and the ground state spin system of a solid-state artificial atom, mediated via an acoustic bus connected by piezoelectric transducers. Applied to present-day experimental parameters for superconducting circuit qubits and diamond silicon vacancy centers in an optimized phononic cavity, we estimate quantum state transduction with fidelity exceeding 99\% at a MHz-scale bandwidth. By combining the complementary strengths of superconducting circuit quantum computing and artificial atoms, the hybrid architecture provides high-fidelity qubit gates with long-lived quantum memory, high-fidelity measurement, large qubit number, reconfigurable qubit connectivity, and high-fidelity state and gate teleportation through optical quantum networks.

Dominik M. Juraschek, Quintin N. Meier, and Prineha Narang. 3/16/2020. “Parametric excitation of an optically silent Goldstone-like phonon mode.” Physical Review Letters, 124, 117401. Publisher's VersionAbstract

It has recently been indicated that the hexagonal manganites exhibit Higgs- and Goldstone-like phonon modes that modulate the amplitude and phase of their primary order parameter. Here, we describe a mechanism by which a silent Goldstone-like phonon mode can be coherently excited, which is based on nonlinear coupling to an infrared-active Higgs-like phonon mode. Using a combination of first-principles calculations and phenomenological modeling, we describe the coupled Higgs-Goldstone dynamics in response to the excitation with a terahertz pulse. Besides theoretically demonstrating coherent control of crystallographic Higgs and Goldstone excitations, we show that the previously inaccessible silent phonon modes can be excited coherently with this mechanism.

Xuezeng Tian, Dennis S. Kim, Shize Yang, Christopher J. Ciccarino, Yongji Gong, Yongsoo Yang, Yao Yang, Blake Duschatko, Yakun Yuan, Pulickel M. Ajayan, Juan-Carlos Idrobo, Prineha Narang, and Jianwei Miao. 3/9/2020. “Correlating the three-dimensional atomic defects and electronic properties of two-dimensional transition metal dichalcogenides.” Nature Materials. Publisher's VersionAbstract

The electronic, optical and chemical properties of two-dimensional transition metal dichalcogenides strongly depend on their three-dimensional atomic structure and crystal defects. Using Re-doped MoS

_{2}as a model system, here we present scanning atomic electron tomography as a method to determine three-dimensional atomic positions as well as positions of crystal defects such as dopants, vacancies and ripples with a precision down to 4 pm. We measure the three-dimensional bond distortion and local strain tensor induced by single dopants. By directly providing these experimental three-dimensional atomic coordinates to density functional theory, we obtain more accurate electronic band structures than derived from conventional density functional theory calculations that relies on relaxed three-dimensional atomic coordinates. We anticipate that scanning atomic electron tomography not only will be generally applicable to determine the three-dimensional atomic coordinates of two-dimensional materials, but also will enable ab initio calculations to better predict the physical, chemical and electronic properties of these materials.