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Perfect elliptic dichroism: Probing the metric of anisotropic quantum Hall droplets
Authors:
Bruno Mera,
Alberto Nardin,
Anaïs Defossez,
Baptiste Bermond,
Tomoki Ozawa,
Nathan Goldman
Abstract:
Understanding the geometry of quantum Hall systems is a central challenge in modern condensed matter physics. We introduce a framework for probing the geometric structure of quantum Hall droplets by engineering the geometry of a dichroic probe and identifying the onset of "perfect elliptic dichroism", a regime in which the system responds exclusively to an elliptically polarized drive of a given c…
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Understanding the geometry of quantum Hall systems is a central challenge in modern condensed matter physics. We introduce a framework for probing the geometric structure of quantum Hall droplets by engineering the geometry of a dichroic probe and identifying the onset of "perfect elliptic dichroism", a regime in which the system responds exclusively to an elliptically polarized drive of a given chirality. This phenomenon provides a direct diagnostic of the droplet's intrinsic metric, and we show that it extends naturally to ideal Chern bands, where holomorphicity of the occupied states guarantees the vanishing of one chiral absorption rate with a quantized response for the other. In lattice realizations, such as the Harper-Hofstadter model, finite lattice-spacing corrections break the exact continuum metric description and give rise to a renormalized, emergent Landau-orbit metric; the probe ellipticity at which perfect dichroism is achieved then shifts accordingly, offering a direct spectroscopic window onto this lattice-induced geometric renormalization. Our results illuminate the rich geometric structure of quantum Hall phases and offer concrete pathways for observing these effects in quantum-engineered platforms.
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Submitted 11 July, 2026; v1 submitted 29 June, 2026;
originally announced June 2026.
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Hall viscosity from metric-sensitive dichroic probes
Authors:
Alberto Nardin,
Bruno Mera,
Anaïs Defossez,
Baptiste Bermond,
Tomoki Ozawa,
Nathan Goldman
Abstract:
Hall viscosity characterizes the geometric response of a quantum Hall droplet to deformations of the underlying metric, yet it has remained difficult to measure directly. We propose a spectroscopic probe based on circular dichroism, using chiral metric-sensitive drives -- implemented as rotating quadrupolar ("saddle") perturbations -- that effectively modulate the metric and couple to the generato…
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Hall viscosity characterizes the geometric response of a quantum Hall droplet to deformations of the underlying metric, yet it has remained difficult to measure directly. We propose a spectroscopic probe based on circular dichroism, using chiral metric-sensitive drives -- implemented as rotating quadrupolar ("saddle") perturbations -- that effectively modulate the metric and couple to the generators of area-preserving deformations. The resulting dichroic signal directly measures the Hall viscosity, while frequency-resolved spectroscopy disentangles it from other excitations. A local formulation further enables spatially resolved markers of Hall viscosity applicable to both continuum and lattice systems. Our results open a direct route to measuring Hall viscosity in quantum-engineered platforms such as cold atoms in optical lattices.
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Submitted 11 July, 2026; v1 submitted 29 June, 2026;
originally announced June 2026.
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Energy-Resolved Quantum Geometry from Středa Response: Driven-Dissipative Bosonic Lattices and Disordered Systems
Authors:
Anaïs Defossez,
Baptiste Bermond,
Lucila Peralta Gavensky,
Nathan Goldman
Abstract:
The Středa formula links the Hall conductivity of an insulator to the magnetic-field response of its particle density, providing a local and universal probe of the topological Chern number. Beyond this quantized response, an energy-resolved Středa marker can be defined from the magnetic response of the density of states, revealing detailed features of the quantum geometry of Bloch bands. We show t…
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The Středa formula links the Hall conductivity of an insulator to the magnetic-field response of its particle density, providing a local and universal probe of the topological Chern number. Beyond this quantized response, an energy-resolved Středa marker can be defined from the magnetic response of the density of states, revealing detailed features of the quantum geometry of Bloch bands. We show that driven-dissipative bosonic lattices provide direct access to both the integrated and energy-resolved Středa responses. Our scheme uses controlled pumping with uniform strength and random phases across the lattice, together with uniform loss, to yield a Lorentzian filter of eigenmode occupations. For generic dispersive bands, this enables reconstruction of a coarse-grained energy-resolved Středa response, establishing these platforms as versatile probes of anomalous spectral flow and energy-resolved quantum geometry. As a striking application, we show that this marker elucidates the fate of topological bands under strong disorder, capturing the quantum-geometric structure underlying topological Anderson insulators.
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Submitted 8 May, 2026;
originally announced May 2026.
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Dichroism from Chiral Thermoelectric Probes: Generalized Sum Rules for Orbital and Heat Magnetizations
Authors:
Baptiste Bermond,
Lucila Peralta Gavensky,
Anaïs Defossez,
Nathan Goldman
Abstract:
We introduce a unified framework that relates orbital and heat magnetizations to experimentally accessible excitation spectra, through thermoelectric probes and generalized sum rules. By analyzing zero-temperature transport coefficients and applying Kramers-Kronig relations, we derive spectral representations of magnetization densities from thermoelectric correlation functions. Excitation rates un…
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We introduce a unified framework that relates orbital and heat magnetizations to experimentally accessible excitation spectra, through thermoelectric probes and generalized sum rules. By analyzing zero-temperature transport coefficients and applying Kramers-Kronig relations, we derive spectral representations of magnetization densities from thermoelectric correlation functions. Excitation rates under chiral thermoelectric drives then naturally emerge as direct probes of these Kubo-type correlators, placing orbital and heat magnetizations on equal footing with the topological Chern number. As a direct consequence of our formalism, we introduce a hierarchical construction that organizes orbital and heat magnetizations into distinct physical contributions accessible through sum rules, and also naturally obtain real-space markers of these magnetizations. Besides, non-chiral thermal probes identify a heat quantum metric, which is defined over the space of gravitomagnetic deformations. From an experimental standpoint, we propose concrete implementations of thermoelectric dichroic measurements in quantum-engineered platforms based on modulated strain fields. These results establish thermoelectric dichroic measurements as a versatile route to access and disentangle fundamental ground-state properties.
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Submitted 2 April, 2026; v1 submitted 26 November, 2025;
originally announced November 2025.
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Controlled Buildup of Half-Quantized Thermal Conductance in an Engineered Chiral Spin Liquid Platform
Authors:
Bo-Ye Sun,
Baptiste Bermond,
Lucila Peralta Gavensky,
Marin Bukov,
Zheng-Wei Zhou,
Nathan Goldman
Abstract:
We study thermal transport along the edge of a small chiral-spin-liquid device coupled to two Ising-chain reservoirs, a platform suitable for quantum-engineered systems. Adiabatically switching on the tunnel couplings to the reservoirs generates a thermal current that dynamically builds up and reaches a quasi-steady-state regime. In this time window, the two-terminal thermal conductance can approa…
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We study thermal transport along the edge of a small chiral-spin-liquid device coupled to two Ising-chain reservoirs, a platform suitable for quantum-engineered systems. Adiabatically switching on the tunnel couplings to the reservoirs generates a thermal current that dynamically builds up and reaches a quasi-steady-state regime. In this time window, the two-terminal thermal conductance can approach half-quantized values -- a hallmark of Majorana-mediated transport -- under finely tuned conditions. The results agree with a steady-state Landauer-Büttiker description for sufficiently large reservoirs, where energy-resolved transmission rates help identify the optimal parameters to achieve the half-quantized conductance. This work provides a controllable platform to investigate topological thermal transport in engineered spin systems, such as realized in cold-atom and Rydberg-atom settings.
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Submitted 3 September, 2025;
originally announced September 2025.
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A local quantized marker for topological magnons from circular dichroism
Authors:
Baptiste Bermond,
Anaïs Defossez,
Gregor Jotzu,
Nathan Goldman
Abstract:
The low-energy excitations of a spin system can display Bloch bands with non-trivial topological properties. While topological magnons can be identified through the detection of chiral propagating modes at the sample's edge, an intriguing approach would be to directly probe their topological nature via localized measurements deep within the bulk. In this work, we introduce a quantized topological…
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The low-energy excitations of a spin system can display Bloch bands with non-trivial topological properties. While topological magnons can be identified through the detection of chiral propagating modes at the sample's edge, an intriguing approach would be to directly probe their topological nature via localized measurements deep within the bulk. In this work, we introduce a quantized topological marker suitable for topological spin systems, which can be experimentally accessed by combining a local driven-dissipative preparation scheme with a circular-dichroic measurement. Demonstrated on a 2D ferromagnetic Heisenberg spin system incorporating Dzyaloshinskii-Moriya interactions, this method effectively maps a local Chern marker with single-site resolution while inherently accounting for magnon losses. Our work offers a general strategy to access local topological markers in bosonic settings within a driven-dissipative framework.
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Submitted 17 July, 2026; v1 submitted 24 April, 2025;
originally announced April 2025.
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Giant quantum oscillations in thermal transport in low-density metals via electron absorption of phonons
Authors:
B. Bermond,
R. Wawrzynczak,
S. Zherlitsyn,
T. Kotte,
T. Helm,
D. Gorbunov,
G. D. Gu,
Q. Li,
F. Janasz,
T. Meng,
F. Menges,
C. Felser,
J. Wosnitza,
Adolfo G. Grushin,
David Carpentier,
J. Gooth,
S. Galeski
Abstract:
Oscillations of conductance observed in strong magnetic fields are a striking manifestation of the quantum dynamics of charge carriers in solids. The large charge carrier density in typical metals sets the scale of oscillations in both electrical and thermal conductivity, which characterize the Fermi surface. In semimetals, thermal transport at low-charge carrier density is expected to be phonon d…
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Oscillations of conductance observed in strong magnetic fields are a striking manifestation of the quantum dynamics of charge carriers in solids. The large charge carrier density in typical metals sets the scale of oscillations in both electrical and thermal conductivity, which characterize the Fermi surface. In semimetals, thermal transport at low-charge carrier density is expected to be phonon dominated, yet several experiments observe giant quantum oscillations in thermal transport. This raises the question of whether there is an overarching mechanism leading to sizable oscillations that survives in phonon-dominated semimetals. In this work, we show that such a mechanism exists. It relies on the peculiar phase-space allowed for phonon scattering by electrons when only a few Landau levels are filled. Our measurements on the Dirac semimetal ZrTe5 support this counter-intuitive mechanism through observation of pronounced thermal quantum oscillations, since they occur in similar magnitude and phase in directions parallel and transverse to the magnetic field. Our phase-space argument applies to all low-density semimetals, topological or not, including graphene and bismuth. Our work illustrates that phonon absorption can be leveraged to reveal degrees of freedom through their imprint on longitudinal thermal transport.
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Submitted 26 February, 2024;
originally announced February 2024.
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Anomalous Casimir effect in an expanding ring
Authors:
Baptiste Bermond,
Adolfo G. Grushin,
David Carpentier
Abstract:
The Casimir effect is a macroscopic evidence of the quantum nature of the vacuum. On a ring, it leads to a finite size correction to the vacuum energy. In this work, we show that this vacuum's energy and pressure acquire additional, sizable corrections, when the ring's radius is increased fast enough, an experimentally accessible model of an expanding universe. This effect is distinct from the dyn…
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The Casimir effect is a macroscopic evidence of the quantum nature of the vacuum. On a ring, it leads to a finite size correction to the vacuum energy. In this work, we show that this vacuum's energy and pressure acquire additional, sizable corrections, when the ring's radius is increased fast enough, an experimentally accessible model of an expanding universe. This effect is distinct from the dynamical Casimir effect: it is a manifestation of the conformal anomaly, originating from the spacetime curvature induced by the increase of the ring's radius. This anomalous dynamical Casimir effect is measurable through the work necessary to increase the ring size, which becomes non-monotonous in time.
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Submitted 19 July, 2024; v1 submitted 13 February, 2024;
originally announced February 2024.
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Anomalous Luttinger equivalence between temperature and curved spacetime: From black hole's atmosphere to thermal quenches
Authors:
Baptiste Bermond,
Maxim Chernodub,
Adolfo G. Grushin,
David Carpentier
Abstract:
Building on the idea of Tolman and Ehrenfest that heat has weight, Luttinger established a deep connection between gravitational fields and thermal transport. However, this relation does not include anomalous quantum fluctuations that become paramount in strongly curved spacetime. In this work, we revisit the celebrated Tolman-Ehrenfest and Luttinger relations and show how to incorporate the quant…
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Building on the idea of Tolman and Ehrenfest that heat has weight, Luttinger established a deep connection between gravitational fields and thermal transport. However, this relation does not include anomalous quantum fluctuations that become paramount in strongly curved spacetime. In this work, we revisit the celebrated Tolman-Ehrenfest and Luttinger relations and show how to incorporate the quantum energy scales associated with these fluctuations, captured by gravitational anomalies of quantum field theories. We point out that such anomalous fluctuations naturally occur in the quantum atmosphere of a black hole. Our results reveal that analogous fluctuations are also observable in thermal conductors in flat-space time provided local temperature varies strongly. As a consequence, we establish that the gravitational anomalies manifest themselves naturally in non-linear thermal response of a quantum wire. In addition, we propose a systematic way to identify thermal analogues of black hole's anomalous quantum fluctuations associated to gravitational anomalies. We identify their signatures in propagating energy waves following a thermal quench, as well as in the energy density of heating Floquet states induced by repeated quenches.
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Submitted 10 October, 2023; v1 submitted 17 June, 2022;
originally announced June 2022.