# Publications

2020

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.

Yaxian Wang and Prineha Narang. 5/4/2020. “Anisotropic Scattering in Goniopolar Metal NaSn

_{2}As_{2}.” arXiv. 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}. 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 present the electron-phonon scattering time distribution on its Fermi surface in momentum space, the anisotropy 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 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 NaSn2As2 also suggests 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.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.Fariah Hayee, Leo Yu, Jingyuan Linda Zhang, Christopher J. Ciccarino, Minh Nyugen, Ann F. Marshall, Igor Aharonovich, Jelena Vučković, Prineha Narang, Tony F. Heinz, and Jennifer A Dionne. 2/24/2020. “Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated optical and electron microscopy.” Nature Materials, 19, Pp. 534-539. Publisher's VersionAbstract

Color-centers in solids have emerged as promising candidates for quantum photonic computing, communications, and sensing applications. Defects in hexagonal boron nitride(hBN) possess high-brightness, room-temperature quantum emission, but their large spectral variability and unknown local structure significantly challenge their technological utility. Here, we directly correlate hBN quantum emission with its local, atomic-scale crystalline structure using correlated photoluminescence (PL) and cathodoluminescence (CL) spectroscopy. Across 20 emitters, we observe zero phonon lines (ZPLs) in PL and CL ranging from 540-720 nm. CL mapping reveals that multiple defects and distinct defect species located within an optically-diffraction-limited region can each contribute to the observed PL spectra. Through high resolution transmission electron imaging, we find that emitters are located in regions with multiple fork-like dislocations. Additionally, local strain maps indicate that strain is not responsible for observed ZPL spectral range, though it can enable spectral tuning of particular emitters. While many emitters have identical ZPLs in CL and PL, others exhibit reversible but distinct CL and PL peaks; density functional calculations indicate that defect complexes and charge-state transitions influence such emission spectra. Our results highlight the sensitivity of defect-driven quantum emission to the surrounding crystallography, providing a foundation for atomic-scale optical characterization.

Derek S. Wang, Tomáš Neuman, Johannes Flick, and Prineha Narang. 2/24/2020. “Weak-to-Strong Light-Matter Coupling and Dissipative Dynamics from First Principles.” arXiv. Publisher's VersionAbstract

Cavity-mediated light-matter coupling can dramatically alter opto-electronic and physico-chemical properties of a molecule. Ab initio theoretical predictions of these systems need to combine non-perturbative, many-body electronic structure theory-based methods with cavity quantum electrodynamics and theories of open quantum systems. Here we generalize quantum-electrodynamical density functional theory to account for dissipative dynamics and describe coupled cavity-molecule interactions in the weak-to-strong-coupling regimes. Specifically, to establish this generalized technique, we study excited-state dynamics and spectral responses of benzene and toluene under weak-to-strong light-matter coupling. By tuning the coupling we achieve cavity-mediated energy transfer between electronic excited states. This generalized ab initio quantum-electrodynamical density functional theory treatment can be naturally extended to describe cavity-mediated interactions in arbitrary electromagnetic environments, accessing correlated light-matter observables and thereby closing the gap between electronic structure theory and quantum optics.

Georgios Varnavides, Adam S. Jermyn, Polina Anikeeva, Claudia Felser, and Prineha Narang. 2/20/2020. “Generalized Electron Hydrodynamics, Vorticity Coupling, and Hall Viscosity in Crystals.” arXiv. Publisher's VersionAbstract

Theoretical and experimental studies have revealed that electrons in condensed matter can behave hydrodynamically, exhibiting fluid phenomena such as Stokes flow and vortices. Unlike classical fluids, preferred directions inside crystals lift isotropic restrictions, necessitating a generalized treatment of electron hydrodynamics. We explore electron fluid behaviors arising from the most general viscosity tensors in two and three dimensions, constrained only by thermodynamics and crystal symmetries. Hexagonal 2D materials such as graphene support flows indistinguishable from those of an isotropic fluid. By contrast 3D materials including Weyl semimetals, exhibit significant deviations from isotropy. Breaking time-reversal symmetry, for example in magnetic topological materials, introduces a non-dissipative Hall component to the viscosity tensor. While this vanishes by isotropy in 3D, anisotropic materials can exhibit nonzero Hall viscosity components. We show that in 3D anisotropic materials 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.

Bo Zhao, Cheng Guo, Christina A. C. Garcia, Prineha Narang, and Shanhui Fan. 2/19/2020. “Axion-Field-Enabled Nonreciprocal Thermal Radiation in Weyl Semimetals.” Nano Letters. Publisher's VersionAbstract

Objects around us constantly emit and absorb thermal radiation. The emission and absorption processes are governed by two fundamental radiative properties: emissivity and absorptivity.For reciprocal systems, the emissivity and absorptivity are restricted to be equal by Kirchhoff's law of thermal radiation. This restriction limits the degree of freedom to control thermal radiation and contributes to an intrinsic loss mechanism in photonic energy harvesting systems such assolar cells. Existing approaches to violate Kirchhoff's law typically utilize conventional magneto-optical effects in the presence of an external magnetic field. However, these approaches require either a strong magnetic field (~3T), or narrow-band resonances under a moderate magnetic field (~0.3T), because the non-reciprocity in conventional magneto-optical effects isusually weak in the thermal wavelength range. Here, we show that the axion electrodynamics in magnetic Weyl semimetals can be used to construct strongly nonreciprocal thermal emitters that near completely violate Kirchhoff's law over broad angular and frequency ranges, without requiring any external magnetic field. The non-reciprocity moreover is strongly temperature tunable, opening new possibilities for active non-reciprocal devices in controlling thermal radiation.

Stefan Krastanov, Mikkel Heuck, Jeffrey H. Shapiro, Prineha Narang, Dirk R. Englund, and Kurt Jacobs. 2/17/2020. “Room-Temperature Photonic Logical Qubits via Second-Order Nonlinearities.” arXiv. Publisher's VersionAbstract

Recent progress in nonlinear optical materials and microresonators has brought quantum computing with bulk optical nonlinearities into the realm of possibility. This platform is of great interest, not only because photonics is an obvious choice for quantum networks, but also because it may be the only feasible route to quantum information processing at room temperature. We introduce a paradigm for room-temperature photonic quantum logic that significantly simplifies the realization of various quantum circuits, and in particular, of error correction. It uses only the strongest available bulk nonlinearity, namely the χ

^{(2) }nonlinear susceptibility. The key element is a three-mode resonator that implements programmable bosonic quantum logic gates. We show that just two of these elements suffice for a complete, compact error-correction circuit on a bosonic code, without the need for measurement or feed-forward control. An extrapolation of current progress in nonlinear optical materials and photonic circuits indicates that such circuitry should be achievable within the next decade.Christina A. C. Garcia, Jennifer Coulter, and Prineha Narang. 1/23/2020. “Optoelectronic Response of Type-I Weyl Semimetals TaAs and NbAs from First Principles.” Physical Review Research, 2, 013073. Publisher's VersionAbstract

Weyl semimetals are materials with topologically nontrivial band structure both in the bulk and on the surface, hosting chiral nodes which are sinks and sources of Berry curvature. Weyl semimetals have been predicted, and recently measured, to exhibit large nonlinear optical responses. This discovery, along with their high mobilities, makes Weyl semimetals relevant to a broad spectrum of applications in optoelectronic, nanophotonic and quantum optical devices. While there is growing interest in understanding and characterizing the linear and nonlinear behavior of Weyl semimetals, an ab initio calculation of the linear optical and optoelectronic responses at finite temperature remains largely unexplored. Here, we specifically address the temperature dependence of the linear optical response in type-I Weyl semimetals TaAs and NbAs. We evaluate from first principles the scattering lifetimes due to electron-phonon and electron-electron interaction and incorporate these lifetimes in evaluating an experimentally relevant frequency-, polarization- and temperature-dependent complex dielectric function for each semimetal. From these calculations we present linear optical conductivity predictions which agree well where experiment exists (for TaAs) and guide the way for future measurements of type-I Weyl semimetals. Importantly, we also examine the optical conductivity's dependence on the chemical potential, a crucial physical parameter which can be controlled experimentally and can elucidate the role of the Weyl nodes in optoelectronic response. Through this work, we present design principles for Weyl optoelectronic devices that use photogenerated carriers in type-I Weyl semimetals.

Christopher J. Ciccarino, Johannes Flick, Isaac B. Harris, Matthew E. Trusheim, Dirk R. Englund, and Prineha Narang. 1/21/2020. “Strong Spin-Orbit Quenching via the Product Jahn-Teller Effect in Neutral Group IV Artificial Atom Qubits in Diamond.” arXiv. Publisher's VersionAbstract

Artificial atom qubits in diamond have emerged as leading candidates for a range of solid-state quantum systems, from quantum sensors to repeater nodes in memory-enhanced quantum communication. Inversion-symmetric group IV vacancy centers, comprised of Si, Ge, Sn and Pb dopants, hold particular promise as their neutrally charged electronic configuration results in a ground-state spin triplet, enabling long spin coherence above cryogenic temperatures. However, despite the tremendous interest in these defects, a theoretical understanding of the electronic and spin structure of these centers remains elusive. In this context, we predict the ground- and excited-state properties of the neutral group IV color centers from first principles. We capture the product Jahn-Teller effect found in the excited state manifold to second order in electron-phonon coupling, and present a non-perturbative treatment of the effect of spin-orbit coupling. Importantly, we find that spin-orbit splitting is strongly quenched due to the dominant Jahn-Teller effect, with the lowest optically-active

^{3}E_{u}state weakly split into m_{s}-resolved states. The predicted complex vibronic spectra of the neutral group IV color centers are essential for their experimental identification and have key implications for use of these systems in quantum information science.2019

Jennifer Coulter, Gavin B. Osterhoudt, Christina A. C. Garcia, Yiping Wang, Vincent Plisson, Bing Shen, Ni Ni, Kenneth S. Burch, and Prineha Narang. 12/24/2019. “Uncovering Electron-Phonon Scattering and Phonon Dynamics in Type-I Weyl Semimetals.” Physical Review B, 100, 220301(R). Publisher's VersionAbstract

Weyl semimetals are 3D phases of matter with topologically protected states that have remarkable macroscopic transport behaviors. As phonon dynamics and electron-phonon scattering play a critical role in the electrical and thermal transport, we pursue a fundamental understanding of the origin of these effects in type-I Weyl semimetals NbAs and TaAs. In the temperature-dependent Raman spectra of NbAs, we reveal a previously unreported Fano lineshape, a signature stemming from the electron-phonon interaction. Additionally, the temperature dependence of the A

_{1}phonon linewidths in both NbAs and TaAs strongly deviate from the standard model of anharmonic decay. To capture the mechanisms responsible for the observed Fano asymmetry and the atypical phonon linewidth, we present first principles calculations of the phonon self-energy correction due to the electron-phonon interaction. Finally, we investigate the relationship between Fano lineshape, electron-phonon coupling, and locations of the Weyl points in these materials. Through this study of the phonon dynamics and electron-phonon interaction in these Weyl semimetals, we consider specific microscopic pathways which contribute to the nature of their macroscopic transport.Dominik M. Juraschek, Tomáš Neuman, Johannes Flick, and Prineha Narang. 11/30/2019. “Cavity control of nonlinear phononics.” arXiv. Publisher's VersionAbstract

Nonlinear interactions between phonon modes govern the behavior of vibrationally highly excited solids and molecules. Here, we demonstrate theoretically that optical cavities can be used to control the redistribution of energy from a highly excited coherent infrared-active phonon state into the other vibrational degrees of freedom of the system. The hybridization of the infrared-active phonon mode with the fundamental mode of the cavity induces a polaritonic splitting that we use to tune the nonlinear interactions with other vibrational modes in and out of resonance. We show that not only can the efficiency of the redistribution of energy be enhanced or decreased, but also the underlying scattering mechanisms may be changed. This work introduces the concept of cavity control to the field of nonlinear phononics, enabling nonequilibrium quantum optical engineering of new states of matter.

Dominik M. Juraschek, Prineha Narang, and Nicola A. Spaldin. 11/30/2019. “Phono-magnetic analogs to opto-magnetic effects.” arXiv. Publisher's VersionAbstract

The magneto-optical and opto-magnetic effects describe the interaction of light with a magnetic medium. The most prominent examples are the Faraday and Cotton-Mouton effects that modify the transmission of light through a medium, and the inverse Faraday and inverse Cotton-Mouton effects that can be used to coherently excite spin waves. Here, we introduce the phenomenology of the analog magneto-phononic and phono-magnetic effects, in which coherently excited vibrational quanta take the place of the light quanta. We show, using a combination of density functional theory and phenomenological modeling, that the effective magnetic fields exerted by these phono-magnetic effects on the spins of antiferromagnetic nickel oxide yield magnitudes comparable or larger than those of the opto-magnetic effects.

Prineha Narang, Christopher J. Ciccarino, Johannes Flick, and Dirk Englund. 9/30/2019. “Quantum Materials with Atomic Precision: Artificial Atoms in Solids: Ab Initio Design, Control, and Integration of Single Photon Emitters in Artificial Quantum Materials.” Advanced Functional Materials. Publisher's VersionAbstract

This Progress Report explores advances and opportunities in the atomic‐scale design, fabrication, and imaging of quantum materials toward creating artificial atoms in solids with tailored optoelectronic and quantum properties. The authors outline an “ab initio” approach to quantitatively linking first‐principles calculations and atomic imaging with atomic patterning, setting the stage for new designer quantum nanomaterials.