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Physique de l'exciton, du photon et du spin
(9) Production(s) de l'année 2024
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Quantum thermodynamics of boundary time-crystals
Auteur(s): Carollo Federico, Lesanovsky Igor, Antezza M., De Chiara G.
(Article) Publié:
-Quantum Science And Technology, vol. 9 p.035024 (2024)
DOI: 10.1088/2058-9565/ad3f42
Résumé: Time-translation symmetry breaking is a mechanism for the emergence of non-stationary many-body phases, so-called time-crystals, in Markovian open quantum systems. Dynamical aspects of time-crystals have been extensively explored over the recent years. However, much less is known about their thermodynamic properties, also due to the intrinsic nonequilibrium nature of these phases. Here, we consider the paradigmatic boundary time-crystal system, in a finite-temperature environment, and demonstrate the persistence of the time-crystalline phase at any temperature. Furthermore, we analyze thermodynamic aspects of the model investigating, in particular, heat currents, power exchange and irreversible entropy production. Our work sheds light on the thermodynamic cost of sustaining nonequilibrium time-crystalline phases and provides a framework for characterizing time-crystals as possible resources for, e.g. quantum sensing. Our results may be verified in experiments, for example with trapped ions or superconducting circuits, since we connect thermodynamic quantities with mean value and covariance of collective (magnetization) operators.
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Spontaneous breaking of time-reversal symmetry and time-crystal states in chiral atomic systems
Auteur(s): Antezza M.
(Séminaires)
Università di Roma - La Sapienza (Rome, IT), 2024-04-10
Résumé: We will present a theoretical study of the interaction between an atom characterized by a degenerate ground state and a reciprocal environment, such as a semiconductor nanoparticle, without the presence of external bias. We show that the combined influence of the electron's intrinsic spin magnetic moment on the environment and the chiral atomic dipolar transitions may lead to either the spontaneous breaking of time-reversal symmetry or the emergence of time-crystal-like states with remarkably long relaxation times. The different behavior is ruled by the handedness of the precession motion of the atom's spin vector, which is induced by virtual chiral-dipolar transitions. Specifically, when the relative orientation of the precession angular velocity and the electron spin vector is as in a spinning top, the system manifests time-crystal-like states. Conversely, with the opposite relative orientation, the system experiences spontaneous symmetry breaking of time reversal symmetry. Our findings introduce a mechanism for the spontaneous breaking of time-reversal symmetry in atomic systems, and unveil an exciting opportunity to engineer a nonreciprocal response at the nanoscale, exclusively driven by the quantum vacuum fluctuations.
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Nuclear spin-spin interactions in CdTe probed by zero and ultra-low-field optically detected NMR
Auteur(s): Litvyak V. M., Bazhin P., André Régis, Vladimirova M., Kavokin K. V.
(Document sans référence bibliographique) 2024-03-26Texte intégral en Openaccess :
Ref HAL: hal-04525413_v1
Ref Arxiv: 2403.17593
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: Nuclear magnetic resonance (NMR) is particularly relevant for studies of internuclear spin coupling at zero and ultra-low fields (ZULF), where spin-spin interactions dominate over Zeeman ones. Here we report on ZULF NMR in CdTe. In this semiconductor all magnetic isotopes have spin $I = 1/2$, so that internuclear interactions are never overshadowed by quadrupole effects. Our experiments rely on warm-up spectroscopy, a technique that combines optical pumping, additional cooling via adiabatic demagnetisation, and detection of the oscillating magnetic field-induced warm-up of the nuclear spin system via Hanle effect. We show that NMR spectra exhibit a rich fine structure, consistent with the low abundance of magnetic isotopes in CdTe, their zero quadrupole moments, as well as direct and indirect interactions between them. A model assuming that the electromagnetic radiation is absorbed by nuclear spin clusters composed of up to 5 magnetic isotopes allows us to reproduce the shape of a major part of the measured spectra.
Commentaires: 9 pages, 7 figures, 2 tables
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Graphene conductivity: Kubo model versus QFT-based model
Auteur(s): Rodriguez-Lopez Pablo, Antezza M.
(Document sans référence bibliographique) Texte intégral en Openaccess :
Ref HAL: hal-04523215_v1
Ref Arxiv: 2403.02279
Ref INSPIRE: 2765291
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We compare three available models of graphene conductivity: a non-local Kubo model, a local model derived by Fialkovsky, and finally a non-local Quantum Field Theory based (QFT-b) model. The first two models are extensively used in the nanophotonic community. All these models are not ab-initio since they contain phenomenological parameters (like chemical potential and/or mass gap parameters), and are supposed to provide coherent results since they are derived from the same starting Hamiltonian. While we confirm that the local model is a proper limit of the non-local Kubo model, we find some inconsistencies in the QFT-b model as derived and used in literature. In particular, differently from the Kubo model, the QFT-b model does not satisfy the required Gauge invariance, and as a consequence it shows a plasma-like behavior for the interband transversal conductivity at low frequencies instead of the expected behavior (an almost constant conductivity as a function of frequency $\omega$ with a gap for frequencies $\hbar\omega < \sqrt{(\hbar v_{F}q)^{2} + 4m^{2}}$). The inconsistencies of QFT-b model predictions are due to a non-correct regularization-scheme which allows for the gauge invariance violation. We show how to correctly regularize the QFT-b model in order to satisfy the gauge invariance and, once also losses are correctly included, we show that the Kubo and QFT-b model exactly coincide. Our finding can be of relevant interest for both theory predictions and experimental tests in both the nanophotonic and Casimir effect communities.
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The normal Casimir-Lifshitz force for laterally moving graphene
Auteur(s): Antezza M., Emelianova N., Khusnutdinov N.
(Article) Publié:
Nanotechnology, vol. 35 p.235001 (2024)
DOI: 10.1088/1361-6528/ad2f1c
Résumé: We consider the system of two parallel sheets of graphene which are moving with relative parallel velocity $\vec{v}$ and calculate the Casimir energy by using the scattering approach. We analyze in detail the normal (perpendicular to the planes) Casimir force for two systems—graphene/graphene and ideal metal/graphene. In the non-relativistic case v ≪ vF, the relative correction to the Casimir energy $({{ \mathcal E }}_{v}-{{ \mathcal E }}_{0})/{{ \mathcal E }}_{0}$ is proportional to the (v/c)2 (the maximum value is 0.0033 for the gapeless case and v = vF) for the first system, and it is zero up to the Fermi velocity v = vF for system ideal metal/graphene.
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Photon mediated transport of energy, linear momentum, and angular momentum in fullerene and graphene systems beyond local equilibrium
Auteur(s): Wang Jian-sheng, Antezza M.
(Article) Publié:
Physical Review B, vol. 109 p.125105 (2024)
DOI: 10.1103/PhysRevB.109.125105
Résumé: Based on a tight-binding model for the electron system, we investigate the transfer of energy, momentum, and angular momentum mediated by electromagnetic fields among buckminsterfullerene (
C
60
) and graphene nanostrips. Our nonequilibrium Green's function approach enables calculations away from local thermal equilibrium where the fluctuation-dissipation theorem breaks down. For example, the forces between
C
60
and current-carrying nanostrips are predicted. It is found that the presence of current enhances the van der Waals attractive forces. For two current-carrying graphene strips rotated at some angle, the fluctuational force and torque are much stronger at the nanoscale compared to that of the static Biot-Savart law.
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Measurement of near-field thermal radiation between multilayered metamaterials
Auteur(s): Zhang Sen, Dang Yongdi, Li Xinran, Iqbal Naeem, Jin Yi, Choudhury Pankaj k, Antezza M., Xu Jianbin, Yungui Ma
(Article) Publié:
Physical Review Applied, vol. 21 p.024054 (2024)
DOI: 10.1103/PhysRevApplied.21.024054
Résumé: The near-field radiative heat transfer (NFRHT) between one-dimensional metamaterials comprised of phonon dielectric multilayers was investigated experimentally. Large-size (1 × 1
cm
2
) near-field samples were fabricated using
Si
C
,
Si
O
2
, and
Ge
layers at a certain gap distance, and the effects of layer-stacking order and phonon-resonance quality on NFRHT were examined. The measured results show good agreement with the theoretical results obtained by employing the transmission-matrix method. Super-Planckian thermal radiation was observed between emitters and receivers with identical structures. The failure of effective-medium theory (EMT) at predicting the near-field heat flux has been evidenced by measurements, particularly in the presence of bounded surface modes, such as the epsilon-near-zero mode. Additionally, analyses have shown that, in specific scenarios, the EMT can offer reasonable physical insights into the underlying coupling process from the perspective of homogenized media. Furthermore, the conditions for applying the EMT in the near-field regime were also touched upon.
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