248 research outputs found
Casimir torque and force on gratings
No full textInternational audienceWe will discuss recent results: (i) on the theory of the Casimir torque between two gratingsrotated by an angle θ with respect to each other [1]; and (ii) on the theory and experimenton the Casimir force between interpenetrating gratings [2]. These findings pave the way tothe design of contactless quantum vacuum torsional spring and sensors with possiblerelevance to micro and nanomechanical devices.References[1] Mauro Antezza, H. B. Chan, Brahim Guizal, V.N. Marachevsky, Riccardo Messina,Mingkang Wang, Phys. Rev. Lett. 124, 013903 (2020)[2] Mingkang Wang, L. Tang, C.Y. Ng, Riccardo Messina, Brahim Guizal, J. A. Crosse,Mauro Antezza, C.T. Chan, H.B. Chan, Nature Communication 12, 600 (2021
Elementary quantum systems out of thermal equilibrium: From quantum thermalization to entanglement
No full textInternational audienceWe study the internal dynamics, the quantum thermalization and the entanglementof elementary quantum systems (one or two atoms) placed close to a body held at atemperature different from that of the surrounding radiation.Concerning the single atom dynamics [1,2], we derive general expressions for lifetimeand density matrix valid for bodies of arbitrary geometry and dielectric permittivity.Out of equilibrium, the thermalization process and steady states become both qualitativelyand quantitatively significantly different from the case of radiation at thermalequilibrium. For the case of a three-level atom close to a slab of finite thickness, wepredict the occurrence of population inversion and an efficient cooling mechanism forthe quantum system, whose effective internal temperature can be driven to values muchlower than both involved temperatures. Our results show that non-equilibrium configurationsprovide new promising ways to control the state of an atomic system.We also consider two two-level atomic quantum systems (qubits) [3]. While at thermalequilibrium the two-qubit dynamics is characterized by not entangled steady thermalstates, we show that absence of thermal equilibrium may bring to the generationof entangled steady states. Remarkably, this entanglement emerges from the two-qubitdissipative dynamic itself, without any further external action on the two qubits, suggestinga new protocol to produce and protect entanglement which is intrinsically robustto environmental effects.======================[1] Bruno Bellomo, Riccardo Messina, and Mauro Antezza, Europhys. Lett. 100, 20006(2012).[2] Bruno Bellomo, Riccardo Messina, Didier Felbacq, and Mauro Antezza, Phys. Rev.A 87, 012101 (2013).[3] Bruno Bellomo, and Mauro Antezza, arXiv:1304.2864 (2013)
Spontaneous breaking of time-reversal symmetry and time-crystal states in chiral atomic systems
No full textInternational audiencee 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 [1]. Our analysis reveals 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. 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.[1] Mario G. Silveirinha, Hugo Terças, and Mauro Antezza, Phys. Rev. B 108, 235154 (2023
Effect of top metallic contacts on energy conversion performances for near-field thermophotovoltaics
No full textInternational audienceWe study Effect of top metallic contacts on energy conversion performances for near-field thermophotovoltaics. We find behaviors differing substantially from those predicted by previous simplistic approaches, with significant impact on the net radiative power absorbed by the cell and, consequently, on the generated electrical power. The design of metallic contact grids on the front side of thermophotovoltaic cells is critical since it can cause significant optical and electrical resistive losses, particularly in the near field. However, from the theoretical point of view, this effect has been either discarded or studied by means of extremely simplified models like the shadowing methods, that consist in simply ignoring the fraction of the semiconductor surface covered by metal. Our study [1], based on a rigorous three-body theoretical framework and implemented using the scattering matrix approach with the Fourier modal method augmented with adaptive spatial resolution, provides deeper insight into the influence of the front metal contact grid. This approach allows direct access to the radiative power absorbed by the semiconductor, enabling the proposal of an alternative definition for the thermophotovoltaic cell efficiency. By modeling this grid as a metallic grating, we demonstrate its significant impact on the net radiative power absorbed by the cell and, consequently, on the generated electrical power. Our analysis reveals behaviors differing substantially from those predicted by previous simplistic approaches. References1.Youssef Jeyar, Kevin Austry, Minggang Luo, Brahim Guizal, Yi Zheng, Riccardo Messina, Rodolphe Vaillon, and Mauro Antezza, arXiv:2412.04258 (2024
Spontaneous breaking of time-reversal symmetry and time-crystal states in chiral atomic systems
No full textInternational audienceWe 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 [1]. Our analysis reveals 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.[1] Mario G. Silveirinha, Hugo Terças, and Mauro Antezza, Phys. Rev. B 108, 235154 (2023)
Giant Casimir Torque And Theta=0 Anomaly + Genuinely Quantum Thermal Machine Out of Thermal Equilibrium
No full textInternational audienceIn the first part of my talk I discuss the prediction and physical consequences of a new geometric zero-th order critical transition occurring to the Casimir torque at Theta=0 rotation angle between diffraction gratings. In the second part I discuss the theory predictions and proposal for the realization of a genuinely quantum thermal machine to be realized in systems out of thermal equilibrium. Here the recorded video: "https://online.kitp.ucsb.edu/online/flectro22/antezza/"
Giant Casimir Torque And Theta=0 Anomaly + Genuinely Quantum Thermal Machine Out of Thermal Equilibrium
No full textInternational audienceIn the first part of my talk I discuss the prediction and physical consequences of a new geometric zero-th order critical transition occurring to the Casimir torque at Theta=0 rotation angle between diffraction gratings. In the second part I discuss the theory predictions and proposal for the realization of a genuinely quantum thermal machine to be realized in systems out of thermal equilibrium. Here the recorded video: "https://online.kitp.ucsb.edu/online/flectro22/antezza/"
Macroscopic Effects of Fluctuations in Quantum and Classical Electrodynamics: Casimir Forces and Radiative Heat Transfer
No full textInternational audienceThis is a broad-audience public lecture names "KITP Blackboard Lunch" I gave at the Kavli Institute of Theoreical Physics (KITP) at the University of California at Santa Barbara (UCSB) to discuss the physical basis of the core subjects of the KITP 7-week program "Emerging Regimes and Implications of Quantum and Thermal Fluctuational Electrodynamics" I organized at KITP. This lecture was devoted to the KITP permanent staff and to all the participants to the several KITP programs. Here the recorded video: "https://online.kitp.ucsb.edu/online/bblunch/antezza
Macroscopic Effects of Fluctuations in Quantum and Classical Electrodynamics: Casimir Forces and Radiative Heat Transfer
No full textInternational audienceThis is a broad-audience public lecture names "KITP Blackboard Lunch" I gave at the Kavli Institute of Theoreical Physics (KITP) at the University of California at Santa Barbara (UCSB) to discuss the physical basis of the core subjects of the KITP 7-week program "Emerging Regimes and Implications of Quantum and Thermal Fluctuational Electrodynamics" I organized at KITP. This lecture was devoted to the KITP permanent staff and to all the participants to the several KITP programs. Here the recorded video: "https://online.kitp.ucsb.edu/online/bblunch/antezza
Casimir-lifshitz force out of thermal equilibrium and asymptotic nonadditivity
Get PDFWe investigate the force acting between two parallel plates held at different temperatures. The force reproduces, as limiting cases, the well-known Casimir-Lifshitz surface-surface force at thermal equilibrium and the surface-atom force out of thermal equilibrium recently derived by M. Antezza et al., Phys. Rev. Lett. 95, 113202 (2005). The asymptotic behavior of the force at large distances is explicitly discussed. In particular when one of the two bodies is a rarefied gas the force is not additive, being proportional to the square root of the density. Nontrivial crossover regions at large distances are also identified
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