Tobias Helbig

All Publications

• How pairing mechanism dictates topology in valley-polarized superconductors with Berry curvature NPJ QUANTUM MATERIALS May-Mann, J., Helbig, T., Devakul, T. 2026; 11 (1)

  View details for DOI 10.1038/s41535-026-00878-4

  View details for Web of Science ID 001797832700001

• Room-temperature quantum nanoplasmonic coherent perfect absorption NATURE COMMUNICATIONS Lai, Y., Clarke, D. D. A., Grimm, P., Devi, A., Wigger, D., Helbig, T., Hofmann, T., Thomale, R., Huang, J., Hecht, B., Hess, O. 2024; 15 (1): 6324

  Abstract

  Light-matter superposition states obtained via strong coupling play a decisive role in quantum information processing, but the deleterious effects of material dissipation and environment-induced decoherence inevitably destroy coherent light-matter polaritons over time. Here, we propose the use of coherent perfect absorption under near-field driving to prepare and protect the polaritonic states of a single quantum emitter interacting with a plasmonic nanocavity at room temperature. Our scheme of quantum nanoplasmonic coherent perfect absorption leverages an inherent frequency specificity to selectively initialize the coupled system in a chosen plasmon-emitter dressed state, while the coherent, unidirectional and non-perturbing near-field energy transfer from a proximal plasmonic waveguide can in principle render the dressed state robust against dynamic dissipation under ambient conditions. Our study establishes a previously unexplored paradigm for quantum state preparation and coherence preservation in plasmonic cavity quantum electrodynamics, offering compelling prospects for elevating quantum nanophotonic technologies to ambient temperatures.

  View details for DOI 10.1038/s41467-024-50574-9

  View details for Web of Science ID 001279103300004

  View details for PubMedID 39060227

  View details for PubMedCentralID PMC11282272

• Realizing efficient topological temporal pumping in electrical circuits PHYSICAL REVIEW RESEARCH Stegmaier, A., Brand, H., Imhof, S., Fritzsche, A., Helbig, T., Hofmann, T., Boettcher, I., Greiter, M., Lee, C., Bahl, G., Szameit, A., Kiessling, T., Thomale, R., Upreti, L. K. 2024; 6 (2)

  View details for DOI 10.1103/PhysRevResearch.6.023010

  View details for Web of Science ID 001207555200003

• Observation of cnoidal wave localization in nonlinear topolectric circuits PHYSICAL REVIEW RESEARCH Hohmann, H., Hofmann, T., Helbig, T., Imhof, S., Brand, H., Upreti, L. K., Stegmaier, A., Fritzsche, A., Mueller, T., Schwingenschloegl, U., Lee, C., Greiter, M., Molenkamp, L. W., Kiessling, T., Thomale, R. 2023; 5 (1)

  View details for DOI 10.1103/PhysRevResearch.5.L012041

  View details for Web of Science ID 000959867000005

• Hyperbolic matter in electrical circuits with tunable complex phases NATURE COMMUNICATIONS Chen, A., Brand, H., Helbig, T., Hofmann, T., Imhof, S., Fritzsche, A., Kieling, T., Stegmaier, A., Upreti, L. K., Neupert, T., Bzdusek, T., Greiter, M., Thomale, R., Boettcher, I. 2023; 14 (1): 622

  Abstract

  Curved spaces play a fundamental role in many areas of modern physics, from cosmological length scales to subatomic structures related to quantum information and quantum gravity. In tabletop experiments, negatively curved spaces can be simulated with hyperbolic lattices. Here we introduce and experimentally realize hyperbolic matter as a paradigm for topological states through topolectrical circuit networks relying on a complex-phase circuit element. The experiment is based on hyperbolic band theory that we confirm here in an unprecedented numerical survey of finite hyperbolic lattices. We implement hyperbolic graphene as an example of topologically nontrivial hyperbolic matter. Our work sets the stage to realize more complex forms of hyperbolic matter to challenge our established theories of physics in curved space, while the tunable complex-phase element developed here can be a key ingredient for future experimental simulation of various Hamiltonians with topological ground states.

  View details for DOI 10.1038/s41467-023-36359-6

  View details for Web of Science ID 001024149400021

  View details for PubMedID 36739281

  View details for PubMedCentralID PMC9899218

• Simulating hyperbolic space on a circuit board NATURE COMMUNICATIONS Lenggenhager, P. M., Stegmaier, A., Upreti, L. K., Hofmann, T., Helbig, T., Vollhardt, A., Greiter, M., Lee, C., Imhof, S., Brand, H., Kiessling, T., Boettcher, I., Neupert, T., Thomale, R., Bzdusek, T. 2022; 13 (1): 4373

  Abstract

  The Laplace operator encodes the behavior of physical systems at vastly different scales, describing heat flow, fluids, as well as electric, gravitational, and quantum fields. A key input for the Laplace equation is the curvature of space. Here we discuss and experimentally demonstrate that the spectral ordering of Laplacian eigenstates for hyperbolic (negatively curved) and flat two-dimensional spaces has a universally different structure. We use a lattice regularization of hyperbolic space in an electric-circuit network to measure the eigenstates of a 'hyperbolic drum', and in a time-resolved experiment we verify signal propagation along the curved geodesics. Our experiments showcase both a versatile platform to emulate hyperbolic lattices in tabletop experiments, and a set of methods to verify the effective hyperbolic metric in this and other platforms. The presented techniques can be utilized to explore novel aspects of both classical and quantum dynamics in negatively curved spaces, and to realise the emerging models of topological hyperbolic matter.

  View details for DOI 10.1038/s41467-022-32042-4

  View details for Web of Science ID 000833074200010

  View details for PubMedID 35902574

  View details for PubMedCentralID PMC9334621

• Topological Defect Engineering and <i>PT</i> Symmetry in Non-Hermitian Electrical Circuits PHYSICAL REVIEW LETTERS Stegmaier, A., Imhof, S., Helbig, T., Hoefmann, T., Lee, C., Kremer, M., Fritzsche, A., Feichtner, T., Klembt, S., Hofling, S., Boettcher, I., Fulga, I., Ma, L., Schmidt, O. G., Greiter, M., Kiessling, T., Szameit, A., Thomale, R. 2021; 126 (21): 215302

  Abstract

  We employ electric circuit networks to study topological states of matter in non-Hermitian systems enriched by parity-time symmetry PT and chiral symmetry anti-PT (APT). The topological structure manifests itself in the complex admittance bands which yields excellent measurability and signal to noise ratio. We analyze the impact of PT-symmetric gain and loss on localized edge and defect states in a non-Hermitian Su-Schrieffer-Heeger (SSH) circuit. We realize all three symmetry phases of the system, including the APT-symmetric regime that occurs at large gain and loss. We measure the admittance spectrum and eigenstates for arbitrary boundary conditions, which allows us to resolve not only topological edge states, but also a novel PT-symmetric Z_{2} invariant of the bulk. We discover the distinct properties of topological edge states and defect states in the phase diagram. In the regime that is not PT symmetric, the topological defect state disappears and only reemerges when APT symmetry is reached, while the topological edge states always prevail and only experience a shift in eigenvalue. Our findings unveil a future route for topological defect engineering and tuning in non-Hermitian systems of arbitrary dimension.

  View details for DOI 10.1103/PhysRevLett.126.215302

  View details for Web of Science ID 000655930100005

  View details for PubMedID 34114871

• Imaging nodal knots in momentum space through topolectrical circuits NATURE COMMUNICATIONS Lee, C., Sutrisno, A., Hofmann, T., Helbig, T., Liu, Y., Ang, Y., Ang, L., Zhang, X., Greiter, M., Thomale, R. 2020; 11 (1): 4385

  Abstract

  Knots are intricate structures that cannot be unambiguously distinguished with any single topological invariant. Momentum space knots, in particular, have been elusive due to their requisite finely tuned long-ranged hoppings. Even if constructed, probing their intricate linkages and topological "drumhead" surface states will be challenging due to the high precision needed. In this work, we overcome these practical and technical challenges with RLC circuits, transcending existing theoretical constructions which necessarily break reciprocity, by pairing nodal knots with their mirror image partners in a fully reciprocal setting. Our nodal knot circuits can be characterized with impedance measurements that resolve their drumhead states and image their 3D nodal structure. Doing so allows for reconstruction of the Seifert surface and hence knot topological invariants like the Alexander polynomial. We illustrate our approach with large-scale simulations of various nodal knots and an experiment which maps out the topological drumhead region of a Hopf-link.

  View details for DOI 10.1038/s41467-020-17716-1

  View details for Web of Science ID 000569891500012

  View details for PubMedID 32873794

  View details for PubMedCentralID PMC7463261

• Reciprocal skin effect and its realization in a topolectrical circuit PHYSICAL REVIEW RESEARCH Hofmann, T., Helbig, T., Schindler, F., Salgo, N., Brzezinska, M., Greiter, M., Kiessling, T., Wolf, D., Vollhardt, A., Kabasi, A., Lee, C., Bilusic, A., Thomale, R., Neupert, T. 2020; 2 (2)

  View details for DOI 10.1103/PhysRevResearch.2.023265

  View details for Web of Science ID 000603592100005

• Generalized bulk-boundary correspondence in non-Hermitian topolectrical circuits NATURE PHYSICS Helbig, T., Hofmann, T., Imhof, S., Abdelghany, M., Kiessling, T., Molenkamp, L. W., Lee, C. H., Szameit, A., Greiter, M., Thomale, R. 2020; 16 (7): 747-+

  View details for DOI 10.1038/s41567-020-0922-9

  View details for Web of Science ID 000537039500002

• Topological funneling of light SCIENCE Weidemann, S., Kremer, M., Helbig, T., Hofmann, T., Stegmaier, A., Greiter, M., Thomale, R., Szameit, A. 2020; 368 (6488): 311-+

  Abstract

  Dissipation is a general feature of non-Hermitian systems. But rather than being an unavoidable nuisance, non-Hermiticity can be precisely controlled and hence used for sophisticated applications, such as optical sensors with enhanced sensitivity. In our work, we implement a non-Hermitian photonic mesh lattice by tailoring the anisotropy of the nearest-neighbor coupling. The appearance of an interface results in a complete collapse of the entire eigenmode spectrum, leading to an exponential localization of all modes at the interface. As a consequence, any light field within the lattice travels toward this interface, irrespective of its shape and input position. On the basis of this topological phenomenon, called the "non-Hermitian skin effect," we demonstrate a highly efficient funnel for light.

  View details for DOI 10.1126/science.aaz8727

  View details for Web of Science ID 000526525400051

  View details for PubMedID 32217752

• Tomonaga-Luttinger liquid in the edge channels of a quantum spin Hall insulator NATURE PHYSICS Stuehler, R., Reis, F., Mueller, T., Helbig, T., Schwemmer, T., Thomale, R., Schaefer, J., Claessen, R. 2020; 16 (1): 47-+

  View details for DOI 10.1038/s41567-019-0697-z

  View details for Web of Science ID 000508800600016

• Chiral Voltage Propagation and Calibration in a Topolectrical Chern Circuit PHYSICAL REVIEW LETTERS Hofmann, T., Helbig, T., Lee, C., Greiter, M., Thomale, R. 2019; 122 (24): 247702

  Abstract

  We propose an electric circuit array with topologically protected unidirectional voltage modes at its boundary. Instead of external bias fields or Floquet engineering, we employ negative impedance converters with current inversion (INICs) to accomplish a nonreciprocal, time-reversal symmetry-broken electronic network we call a topolectrical Chern circuit (TCC). The TCC features an admittance bulk gap fully tunable via the resistors used in the INICs, along with a chiral voltage boundary mode reminiscent of the Berry flux monopole present in the admittance band structure. The active circuit elements in the TCC can be calibrated to compensate for dissipative loss.

  View details for DOI 10.1103/PhysRevLett.122.247702

  View details for Web of Science ID 000473034200018

  View details for PubMedID 31322409

• Band structure engineering and reconstruction in electric circuit networks PHYSICAL REVIEW B Helbig, T., Hofmann, T., Lee, C., Thomale, R., Imhof, S., Molenkamp, L. W., Kiessling, T. 2019; 99 (16)

  View details for DOI 10.1103/PhysRevB.99.161114

  View details for Web of Science ID 000466402200001