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Serge Reynaud

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Papers by Serge Reynaud

Statistical approach to Casimir-Polder potentials in heterogeneous media

Physical Review A, Oct 26, 2015

We explore the statistical properties of the Casimir-Polder potential between a dielectric sphere... more We explore the statistical properties of the Casimir-Polder potential between a dielectric sphere and a three-dimensional heterogeneous medium, by means of extensive numerical simulations based on the scattering theory of Casimir forces. The simulations allow us to confirm recent predictions for the mean and standard deviation of the Casimir potential, and give us access to its full distribution function in the limit of a dilute distribution of heterogeneities. These predictions are compared with a simple statistical model based on a pairwise summation of the individual contributions of the constituting elements of the medium.

Quantum reflection of antihydrogen from a liquid helium film

EPL, Aug 1, 2017

We study the quantum reflection of ultracold antihydrogen atoms bouncing on the surface of a liqu... more We study the quantum reflection of ultracold antihydrogen atoms bouncing on the surface of a liquid helium film. The Casimir-Polder potential and quantum reflection are calculated for different thicknesses of the film supported by different substrates. Antihydrogen can be protected from annihilation for as long as 1.3s on a bulk of liquid 4 He, and 1.7s for liquid 3 He. These large lifetimes open interesting perspectives for spectroscopic measurements of the free fall acceleration of antihydrogen. Variation of the scattering length with the thickness of a film of helium shows interferences which we interpret through a Liouville transformation of the quantum reflection problem.

Casimir-Polder shifts on quantum levitation states

Physical review, Mar 6, 2017

An ultracold atom above a horizontal mirror experiences quantum reflection from the attractive Ca... more An ultracold atom above a horizontal mirror experiences quantum reflection from the attractive Casimir-Polder interaction, which holds it against gravity and leads to quantum levitation states. We analyze this system by using a Liouville transformation of the Schrödinger equation and a Langer coordinate adapted to problems with a classical turning point. Reflection on the Casimir-Polder attractive well is replaced by reflection on a repulsive wall and the problem is then viewed as an ultracold atom trapped inside a cavity with gravity and Casimir-Polder potentials acting respectively as top and bottom mirrors. We calculate numerically Casimir-Polder shifts of the energies of the cavity resonances and propose a new approximate treatment which is precise enough to discuss spectroscopy experiments aiming at tests of the weak equivalence principle on antihydrogen. We also discuss the lifetimes by calculating complex energies associated with cavity resonances.

GRASIAN: towards the first demonstration of gravitational quantum states of atoms with a cryogenic hydrogen beam

European Physical Journal D, Mar 1, 2023

At very low energies, a light neutral particle above a horizontal surface can experience quantum ... more At very low energies, a light neutral particle above a horizontal surface can experience quantum reflection. The quantum reflection holds the particle against gravity and leads to gravitational quantum states (gqs). So far, gqs were only observed with neutrons as pioneered by Nesvizhevsky and his collaborators at ill. However, the existence of gqs is predicted also for atoms. The Grasian collaboration pursues the first observation and studies of gqs of atomic hydrogen. We propose to use atoms in order to exploit the fact that orders of magnitude larger fluxes compared to those of neutrons are available. Moreover, recently the q-Bounce collaboration, performing gqs spectroscopy with neutrons, reported a discrepancy between theoretical calculations and experiment which deserves further investigations. For this purpose, we set up a cryogenic hydrogen beam at 6 K. We report on our preliminary results, characterizing the hydrogen beam with pulsed laser ionization diagnostics at 243 nm.

Casimir effect and quantum reflection

arXiv (Cornell University), Nov 12, 2015

The GBAR experiment will time the free fall of cold antihydrogen atoms dropped onto an annihilati... more The GBAR experiment will time the free fall of cold antihydrogen atoms dropped onto an annihilation plate to test the universality of free fall on antimatter. In this contribution, we study the quantum reflection of the anti-atom resulting from the Casimir-Polder attraction to the plate. We evaluate the Casimir-Polder potential and the associated quantum reflection amplitudes and find that reflection is enhanced for weaker potentials. A Liouville transformation of the Schrödinger equation is used to map the quantum reflection problem onto an equivalent problem of scattering on a barrier, leading to an intuitive understanding of the phenomenon.

Universal Casimir Interactions in the Sphere–Sphere Geometry

WORLD SCIENTIFIC eBooks, Dec 1, 2022

We study universal Casimir interactions in two configurations which appear as dual to each other.... more We study universal Casimir interactions in two configurations which appear as dual to each other. The first involves spheres described by the Drude model and separated by vacuum while the second involves dielectric spheres immersed in a salted solution at distances larger than the Debye screening length. In both cases, the long-distance limit, equivalently the high-temperature limit, is dominated by the effect of low-frequency transverse magnetic thermal fluctuations. They are independent of the details of dielectric functions of materials, due to the finite conductivity of metals in the former case and of salted water in the latter one. They also show universality properties in their dependence on geometric dimensions, in relation to an approximate conformal invariance of the reduced free energy. A. High-temperature limit Within the scattering approach [25], the Casimir free energy at a temperature T is given as a sum over the imaginary Matsubara frequencies [26, 27] F = k B T 2 ∞ n=−∞ tr log (1 − M(|ξ n |)) , ξ n = 2πnk B T .

The Casimir Force Between Metallic Mirrors

World Scientific Publishing Company eBooks, Dec 1, 2002

In order to compare recent experimental results with theoretical predictions we study the influen... more In order to compare recent experimental results with theoretical predictions we study the influence of finite conductivity of metals on the Casimir effect. The correction to the Casimir force and energy due to imperfect reflection and finite temperature are evaluated for plane metallic plates where the dielectric functions of the metals are modeled by a plasma model. The results are compared with the common approximation where conductivity and thermal corrections are evaluated separately and simply multiplied.

Proposal to measure the Gravitational Behaviour of Antihydrogen at Rest

Exploring the foundations of the physical universe with space tests of the equivalence principle

Experimental Astronomy, 2021

We present the scientific motivation for future space tests of the equivalence principle, and in ... more We present the scientific motivation for future space tests of the equivalence principle, and in particular the universality of free fall, at the 10− 17 level or better. Two possible mission scenarios, one based on quantum technologies, the other on electrostatic accelerometers, that could reach that goal are briefly discussed. This publication is a White Paper written in the context of the Voyage 2050 ESA Call for White Papers.

Prospects for Studies of the Free Fall and Gravitational Quantum States of Antimatter

Advances in High Energy Physics, 2015

Different experiments are ongoing to measure the effect of gravity on cold neutral antimatter ato... more Different experiments are ongoing to measure the effect of gravity on cold neutral antimatter atoms such as positronium, muonium, and antihydrogen. Among those, the project GBAR at CERN aims to measure precisely the gravitational fall of ultracold antihydrogen atoms. In the ultracold regime, the interaction of antihydrogen atoms with a surface is governed by the phenomenon of quantum reflection which results in bouncing of antihydrogen atoms on matter surfaces. This allows the application of a filtering scheme to increase the precision of the free fall measurement. In the ultimate limit of smallest vertical velocities, antihydrogen atoms are settled in gravitational quantum states in close analogy to ultracold neutrons (UCNs). Positronium is another neutral system involving antimatter for which free fall under gravity is currently being investigated at UCL. Building on the experimental techniques under development for the free fall measurement, gravitational quantum states could als...

Vacuum fluctuations, accelerated motion and conformal frames

Quantum and Semiclassical Optics: Journal of the European Optical Society Part B, 1995

Radiation from a mirror moving in vacuum electromagnetic fields is shown to vanish in the case of... more Radiation from a mirror moving in vacuum electromagnetic fields is shown to vanish in the case of a uniformly accelerated motion. Such motions are related to conformal coordinate transformations, which preserve correlation functions characteristic of vacuum fluctuations. As a result, vacuum fluctuations remain invariant under reflection upon a uniformly accelerated mirror, which therefore does not radiate and experiences no radiation reaction force. Mechanical effects of vacuum fluctuations thus exhibit an invariance with respect to uniformly accelerated motions.

Negative entropies in Casimir and Casimir‐Polder interactions

Fortschritte der Physik, 2016

It has been increasingly becoming clear that Casimir and Casimir‐Polder entropies may be negative... more It has been increasingly becoming clear that Casimir and Casimir‐Polder entropies may be negative in certain regions of temperature and separation. In fact, the occurrence of negative entropy seems to be a nearly ubiquitous phenomenon. This is most highlighted in the quantum vacuum interaction of a nanoparticle with a conducting plate or between two nanoparticles. It has been argued that this phenomenon does not violate physical intuition, since the total entropy, including the self‐entropies of the plate and the nanoparticle, should be positive. New calculations, in fact, seem to bear this out at least in certain cases.

Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic mirrors

Physical Review E, 2016

We examine the conditions of validity for the Lifshitz-Matsubara sum formula for the Casimir pres... more We examine the conditions of validity for the Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic plane mirrors. As in the previously studied case of non-magnetic materials (Guérout et al, Phys. Rev. E 90 042125), we recover the usual expression for the lossy model of optical response, but not for the lossless plasma model. We also show that the modes associated with the Foucault currents play a crucial role in the limit of vanishing losses, in contrast to expectations.

Quantum reflection and Liouville transformations from wells to walls

EPL (Europhysics Letters), 2015

Liouville transformations map in a rigorous manner one Schrödinger equation into another, with a ... more Liouville transformations map in a rigorous manner one Schrödinger equation into another, with a changed scattering potential. They are used here to transform quantum reflection of an atom on an attractive well into reflection of the atom on a repulsive wall. While the scattering properties are preserved, the corresponding semiclassical descriptions are completely different. A quantitative evaluation of quantum reflection probabilities is deduced from this method.

Measurement of Short Range Forces Using Cold Atoms

Frequency Standards and Metrology, 2009

We describe the new project FORCA-G, which aims at studying the short range interactions between ... more We describe the new project FORCA-G, which aims at studying the short range interactions between a surface and atoms trapped in its vicinity. Using cold atoms confined in the wells of an optical standing wave, the atom-surface potential will be measured with high sensitivity using atom interferometry techniques. The experiment will allow a test of gravity at short distances, which will put stringent bounds on a possible deviation from the known laws of physics. FORCA-G will also allow a measurement of the Casimir Polder interaction (QED vacuum fluctuations) with unprecedented accuracy.

Gravitational waves, diffusion and decoherence

The quite different behaviors exhibited by microscopic and macroscopic systems with respect to qu... more The quite different behaviors exhibited by microscopic and macroscopic systems with respect to quantum interferences suggest that there may exist a naturally frontier between quantum and classical worlds. The value of the Planck mass (22$\mu$g) may lead to the idea of a connection between this borderline and intrinsic fluctuations of spacetime. We show that it is possible to obtain quantitative answers to these questions by studying the diffusion and decoherence mechanisms induced on quantum systems by gravitational waves generated at the galactic or cosmic scales. We prove that this universal fluctuating environment strongly affects quantum interferences on macroscopic systems, while leaving essentially untouched those on microscopic systems. We obtain the relevant parameters which, besides the ratio of the system's mass to Planck mass, characterize the diffusion constant and decoherence time. We discuss the feasibility of experiments aiming at observing these effects in the co...

Geometric origin of negative Casimir entropies: A scattering-channel analysis

Physical review. E, Statistical, nonlinear, and soft matter physics, 2015

Negative values of the Casimir entropy occur quite frequently at low temperatures in arrangements... more Negative values of the Casimir entropy occur quite frequently at low temperatures in arrangements of metallic objects. The physical reason lies either in the dissipative nature of the metals as is the case for the plane-plane geometry or in the geometric form of the objects involved. Examples for the latter are the sphere-plane and the sphere-sphere geometry, where negative Casimir entropies can occur already for perfect metal objects. After appropriately scaling out the size of the objects, negative Casimir entropies of geometric origin are particularly pronounced in the limit of large distances between the objects. We analyze this limit in terms of the different scattering channels and demonstrate how the negativity of the Casimir entropy is related to the polarization mixing arising in the scattering process. If all involved objects have a finite zero-frequency conductivity, the channels involving transverse electric modes are suppressed and the Casimir entropy within the large-d...

Kelvin probe force microscopy of metallic surfaces used in Casimir force measurements

Physical Review A, 2014

Kelvin probe force microscopy at normal pressure was performed by two different groups on the sam... more Kelvin probe force microscopy at normal pressure was performed by two different groups on the same Au-coated planar sample used to measure the Casimir interaction in a sphere-plane geometry. The obtained voltage distribution was used to calculate the separation dependence of the electrostatic pressure Pres(D) in the configuration of the Casimir experiments. In the calculation it was assumed that the potential distribution in the sphere has the same statistical properties as the measured one, and that there are no correlation effects on the potential distributions due to the presence of the other surface. The result of this calculation, using the currently available knowledge, is that Pres(D) does not explain the magnitude or the separation dependence of the difference ∆P (D) between the measured Casimir pressure and the one calculated using a Drude model for the electromagnetic response of Au. We discuss in the conclusions the points which have to be checked out by future work, including the influence of pressure and a more accurate determination of the patch distribution, in order to confirm these results.

Transverse Effects on Squeezing with Atoms

Journal de Physique II, 1996

We evaluate the squeezing of a probe beam with a transverse Gaussian structure interacting with a... more We evaluate the squeezing of a probe beam with a transverse Gaussian structure interacting with an ensemble of two-level atoms in a cavity. We use the linear input-output formalism where the effect of atoms is described by susceptibility and noise functions, and show that the transverse structure is accounted for by averaging these atomic functions over the intensity profile. The results of the plane-wave and Gaussian-wave theories are compared. We find that, when a large squeezing is predicted, the prediction of the plane-wave model is not reliable outside the Kerr domain. We give an estimate of the squeezing degradation due to the Gaussian transverse structure.

Quantum Decoherence and Gravitational Waves

Beyond the Quantum, 2007

Statistical approach to Casimir-Polder potentials in heterogeneous media

Physical Review A, Oct 26, 2015

We explore the statistical properties of the Casimir-Polder potential between a dielectric sphere... more We explore the statistical properties of the Casimir-Polder potential between a dielectric sphere and a three-dimensional heterogeneous medium, by means of extensive numerical simulations based on the scattering theory of Casimir forces. The simulations allow us to confirm recent predictions for the mean and standard deviation of the Casimir potential, and give us access to its full distribution function in the limit of a dilute distribution of heterogeneities. These predictions are compared with a simple statistical model based on a pairwise summation of the individual contributions of the constituting elements of the medium.

Quantum reflection of antihydrogen from a liquid helium film

EPL, Aug 1, 2017

We study the quantum reflection of ultracold antihydrogen atoms bouncing on the surface of a liqu... more We study the quantum reflection of ultracold antihydrogen atoms bouncing on the surface of a liquid helium film. The Casimir-Polder potential and quantum reflection are calculated for different thicknesses of the film supported by different substrates. Antihydrogen can be protected from annihilation for as long as 1.3s on a bulk of liquid 4 He, and 1.7s for liquid 3 He. These large lifetimes open interesting perspectives for spectroscopic measurements of the free fall acceleration of antihydrogen. Variation of the scattering length with the thickness of a film of helium shows interferences which we interpret through a Liouville transformation of the quantum reflection problem.

Casimir-Polder shifts on quantum levitation states

Physical review, Mar 6, 2017

An ultracold atom above a horizontal mirror experiences quantum reflection from the attractive Ca... more An ultracold atom above a horizontal mirror experiences quantum reflection from the attractive Casimir-Polder interaction, which holds it against gravity and leads to quantum levitation states. We analyze this system by using a Liouville transformation of the Schrödinger equation and a Langer coordinate adapted to problems with a classical turning point. Reflection on the Casimir-Polder attractive well is replaced by reflection on a repulsive wall and the problem is then viewed as an ultracold atom trapped inside a cavity with gravity and Casimir-Polder potentials acting respectively as top and bottom mirrors. We calculate numerically Casimir-Polder shifts of the energies of the cavity resonances and propose a new approximate treatment which is precise enough to discuss spectroscopy experiments aiming at tests of the weak equivalence principle on antihydrogen. We also discuss the lifetimes by calculating complex energies associated with cavity resonances.

GRASIAN: towards the first demonstration of gravitational quantum states of atoms with a cryogenic hydrogen beam

European Physical Journal D, Mar 1, 2023

At very low energies, a light neutral particle above a horizontal surface can experience quantum ... more At very low energies, a light neutral particle above a horizontal surface can experience quantum reflection. The quantum reflection holds the particle against gravity and leads to gravitational quantum states (gqs). So far, gqs were only observed with neutrons as pioneered by Nesvizhevsky and his collaborators at ill. However, the existence of gqs is predicted also for atoms. The Grasian collaboration pursues the first observation and studies of gqs of atomic hydrogen. We propose to use atoms in order to exploit the fact that orders of magnitude larger fluxes compared to those of neutrons are available. Moreover, recently the q-Bounce collaboration, performing gqs spectroscopy with neutrons, reported a discrepancy between theoretical calculations and experiment which deserves further investigations. For this purpose, we set up a cryogenic hydrogen beam at 6 K. We report on our preliminary results, characterizing the hydrogen beam with pulsed laser ionization diagnostics at 243 nm.

Casimir effect and quantum reflection

arXiv (Cornell University), Nov 12, 2015

The GBAR experiment will time the free fall of cold antihydrogen atoms dropped onto an annihilati... more The GBAR experiment will time the free fall of cold antihydrogen atoms dropped onto an annihilation plate to test the universality of free fall on antimatter. In this contribution, we study the quantum reflection of the anti-atom resulting from the Casimir-Polder attraction to the plate. We evaluate the Casimir-Polder potential and the associated quantum reflection amplitudes and find that reflection is enhanced for weaker potentials. A Liouville transformation of the Schrödinger equation is used to map the quantum reflection problem onto an equivalent problem of scattering on a barrier, leading to an intuitive understanding of the phenomenon.

Universal Casimir Interactions in the Sphere–Sphere Geometry

WORLD SCIENTIFIC eBooks, Dec 1, 2022

We study universal Casimir interactions in two configurations which appear as dual to each other.... more We study universal Casimir interactions in two configurations which appear as dual to each other. The first involves spheres described by the Drude model and separated by vacuum while the second involves dielectric spheres immersed in a salted solution at distances larger than the Debye screening length. In both cases, the long-distance limit, equivalently the high-temperature limit, is dominated by the effect of low-frequency transverse magnetic thermal fluctuations. They are independent of the details of dielectric functions of materials, due to the finite conductivity of metals in the former case and of salted water in the latter one. They also show universality properties in their dependence on geometric dimensions, in relation to an approximate conformal invariance of the reduced free energy. A. High-temperature limit Within the scattering approach [25], the Casimir free energy at a temperature T is given as a sum over the imaginary Matsubara frequencies [26, 27] F = k B T 2 ∞ n=−∞ tr log (1 − M(|ξ n |)) , ξ n = 2πnk B T .

The Casimir Force Between Metallic Mirrors

World Scientific Publishing Company eBooks, Dec 1, 2002

In order to compare recent experimental results with theoretical predictions we study the influen... more In order to compare recent experimental results with theoretical predictions we study the influence of finite conductivity of metals on the Casimir effect. The correction to the Casimir force and energy due to imperfect reflection and finite temperature are evaluated for plane metallic plates where the dielectric functions of the metals are modeled by a plasma model. The results are compared with the common approximation where conductivity and thermal corrections are evaluated separately and simply multiplied.

Proposal to measure the Gravitational Behaviour of Antihydrogen at Rest

Exploring the foundations of the physical universe with space tests of the equivalence principle

Experimental Astronomy, 2021

We present the scientific motivation for future space tests of the equivalence principle, and in ... more We present the scientific motivation for future space tests of the equivalence principle, and in particular the universality of free fall, at the 10− 17 level or better. Two possible mission scenarios, one based on quantum technologies, the other on electrostatic accelerometers, that could reach that goal are briefly discussed. This publication is a White Paper written in the context of the Voyage 2050 ESA Call for White Papers.

Prospects for Studies of the Free Fall and Gravitational Quantum States of Antimatter

Advances in High Energy Physics, 2015

Different experiments are ongoing to measure the effect of gravity on cold neutral antimatter ato... more Different experiments are ongoing to measure the effect of gravity on cold neutral antimatter atoms such as positronium, muonium, and antihydrogen. Among those, the project GBAR at CERN aims to measure precisely the gravitational fall of ultracold antihydrogen atoms. In the ultracold regime, the interaction of antihydrogen atoms with a surface is governed by the phenomenon of quantum reflection which results in bouncing of antihydrogen atoms on matter surfaces. This allows the application of a filtering scheme to increase the precision of the free fall measurement. In the ultimate limit of smallest vertical velocities, antihydrogen atoms are settled in gravitational quantum states in close analogy to ultracold neutrons (UCNs). Positronium is another neutral system involving antimatter for which free fall under gravity is currently being investigated at UCL. Building on the experimental techniques under development for the free fall measurement, gravitational quantum states could als...

Vacuum fluctuations, accelerated motion and conformal frames

Quantum and Semiclassical Optics: Journal of the European Optical Society Part B, 1995

Radiation from a mirror moving in vacuum electromagnetic fields is shown to vanish in the case of... more Radiation from a mirror moving in vacuum electromagnetic fields is shown to vanish in the case of a uniformly accelerated motion. Such motions are related to conformal coordinate transformations, which preserve correlation functions characteristic of vacuum fluctuations. As a result, vacuum fluctuations remain invariant under reflection upon a uniformly accelerated mirror, which therefore does not radiate and experiences no radiation reaction force. Mechanical effects of vacuum fluctuations thus exhibit an invariance with respect to uniformly accelerated motions.

Negative entropies in Casimir and Casimir‐Polder interactions

Fortschritte der Physik, 2016

It has been increasingly becoming clear that Casimir and Casimir‐Polder entropies may be negative... more It has been increasingly becoming clear that Casimir and Casimir‐Polder entropies may be negative in certain regions of temperature and separation. In fact, the occurrence of negative entropy seems to be a nearly ubiquitous phenomenon. This is most highlighted in the quantum vacuum interaction of a nanoparticle with a conducting plate or between two nanoparticles. It has been argued that this phenomenon does not violate physical intuition, since the total entropy, including the self‐entropies of the plate and the nanoparticle, should be positive. New calculations, in fact, seem to bear this out at least in certain cases.

Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic mirrors

Physical Review E, 2016

We examine the conditions of validity for the Lifshitz-Matsubara sum formula for the Casimir pres... more We examine the conditions of validity for the Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic plane mirrors. As in the previously studied case of non-magnetic materials (Guérout et al, Phys. Rev. E 90 042125), we recover the usual expression for the lossy model of optical response, but not for the lossless plasma model. We also show that the modes associated with the Foucault currents play a crucial role in the limit of vanishing losses, in contrast to expectations.

Quantum reflection and Liouville transformations from wells to walls

EPL (Europhysics Letters), 2015

Liouville transformations map in a rigorous manner one Schrödinger equation into another, with a ... more Liouville transformations map in a rigorous manner one Schrödinger equation into another, with a changed scattering potential. They are used here to transform quantum reflection of an atom on an attractive well into reflection of the atom on a repulsive wall. While the scattering properties are preserved, the corresponding semiclassical descriptions are completely different. A quantitative evaluation of quantum reflection probabilities is deduced from this method.

Measurement of Short Range Forces Using Cold Atoms

Frequency Standards and Metrology, 2009

We describe the new project FORCA-G, which aims at studying the short range interactions between ... more We describe the new project FORCA-G, which aims at studying the short range interactions between a surface and atoms trapped in its vicinity. Using cold atoms confined in the wells of an optical standing wave, the atom-surface potential will be measured with high sensitivity using atom interferometry techniques. The experiment will allow a test of gravity at short distances, which will put stringent bounds on a possible deviation from the known laws of physics. FORCA-G will also allow a measurement of the Casimir Polder interaction (QED vacuum fluctuations) with unprecedented accuracy.

Gravitational waves, diffusion and decoherence

The quite different behaviors exhibited by microscopic and macroscopic systems with respect to qu... more The quite different behaviors exhibited by microscopic and macroscopic systems with respect to quantum interferences suggest that there may exist a naturally frontier between quantum and classical worlds. The value of the Planck mass (22$\mu$g) may lead to the idea of a connection between this borderline and intrinsic fluctuations of spacetime. We show that it is possible to obtain quantitative answers to these questions by studying the diffusion and decoherence mechanisms induced on quantum systems by gravitational waves generated at the galactic or cosmic scales. We prove that this universal fluctuating environment strongly affects quantum interferences on macroscopic systems, while leaving essentially untouched those on microscopic systems. We obtain the relevant parameters which, besides the ratio of the system's mass to Planck mass, characterize the diffusion constant and decoherence time. We discuss the feasibility of experiments aiming at observing these effects in the co...

Geometric origin of negative Casimir entropies: A scattering-channel analysis

Physical review. E, Statistical, nonlinear, and soft matter physics, 2015

Negative values of the Casimir entropy occur quite frequently at low temperatures in arrangements... more Negative values of the Casimir entropy occur quite frequently at low temperatures in arrangements of metallic objects. The physical reason lies either in the dissipative nature of the metals as is the case for the plane-plane geometry or in the geometric form of the objects involved. Examples for the latter are the sphere-plane and the sphere-sphere geometry, where negative Casimir entropies can occur already for perfect metal objects. After appropriately scaling out the size of the objects, negative Casimir entropies of geometric origin are particularly pronounced in the limit of large distances between the objects. We analyze this limit in terms of the different scattering channels and demonstrate how the negativity of the Casimir entropy is related to the polarization mixing arising in the scattering process. If all involved objects have a finite zero-frequency conductivity, the channels involving transverse electric modes are suppressed and the Casimir entropy within the large-d...

Kelvin probe force microscopy of metallic surfaces used in Casimir force measurements

Physical Review A, 2014

Kelvin probe force microscopy at normal pressure was performed by two different groups on the sam... more Kelvin probe force microscopy at normal pressure was performed by two different groups on the same Au-coated planar sample used to measure the Casimir interaction in a sphere-plane geometry. The obtained voltage distribution was used to calculate the separation dependence of the electrostatic pressure Pres(D) in the configuration of the Casimir experiments. In the calculation it was assumed that the potential distribution in the sphere has the same statistical properties as the measured one, and that there are no correlation effects on the potential distributions due to the presence of the other surface. The result of this calculation, using the currently available knowledge, is that Pres(D) does not explain the magnitude or the separation dependence of the difference ∆P (D) between the measured Casimir pressure and the one calculated using a Drude model for the electromagnetic response of Au. We discuss in the conclusions the points which have to be checked out by future work, including the influence of pressure and a more accurate determination of the patch distribution, in order to confirm these results.

Transverse Effects on Squeezing with Atoms

Journal de Physique II, 1996

We evaluate the squeezing of a probe beam with a transverse Gaussian structure interacting with a... more We evaluate the squeezing of a probe beam with a transverse Gaussian structure interacting with an ensemble of two-level atoms in a cavity. We use the linear input-output formalism where the effect of atoms is described by susceptibility and noise functions, and show that the transverse structure is accounted for by averaging these atomic functions over the intensity profile. The results of the plane-wave and Gaussian-wave theories are compared. We find that, when a large squeezing is predicted, the prediction of the plane-wave model is not reliable outside the Kerr domain. We give an estimate of the squeezing degradation due to the Gaussian transverse structure.

Quantum Decoherence and Gravitational Waves

Beyond the Quantum, 2007