European Laboratory for Nonlinear Spectroscopy

Sesto Fiorentino, Italy

European Laboratory for Nonlinear Spectroscopy

Sesto Fiorentino, Italy
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Kreula J.M.,University of Oxford | Valtolina G.,National Research Council Italy | Valtolina G.,European Laboratory for Nonlinear Spectroscopy | Torma P.,Aalto University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2017

The spin-asymmetric Josephson effect is a proposed quantum-coherent tunneling phenomenon where Cooper-paired fermionic spin-12 particles, which are subjected to spin-dependent potentials across a Josephson junction, undergo frequency-synchronized alternating-current Josephson oscillations with spin-dependent amplitudes. Here, in line with present-day techniques in ultracold Fermi gas setups, we consider the regime of small Josephson oscillations and show that the Josephson plasma oscillation amplitude becomes spin dependent in the presence of spin-dependent potentials, while the Josephson plasma frequency is the same for both spin components. Detecting these spin-dependent Josephson plasma oscillations provides a possible means to establish the yet-unobserved spin-asymmetric Josephson effect with ultracold Fermi gases using existing experimental tools. © 2017 American Physical Society.


Horsley S.A.R.,University of Exeter | Artoni M.,European Laboratory for Nonlinear Spectroscopy | Artoni M.,CNR Institute of Acoustics and Sensors Orso Mario Corbino | La Rocca G.C.,Normal School of Pisa
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2016

Wave propagation through rapidly but continuously varying media is surprisingly subtle, and in a pair of recent papers [Horsley, J. Opt. 18, 044016 (2016)2040-897810.1088/2040-8978/18/4/044016; Longhi, Eur. Phys. Lett. 112, 64001 (2015)EULEEJ0295-507510.1209/0295-5075/112/64001] it was found that planar media with a spatially varying permittivity ϵ(x) obeying the spatial Kramers-Kronig relations do not reflect waves incident from one side, however rapid the changes in ϵ(x). Within this large class of media there are some examples where the dissipation or gain is not asymptotically negligible and it has been pointed out [Longhi, Eur. Phys. Lett. 112, 64001 (2015)EULEEJ0295-507510.1209/0295-5075/112/64001] that it is impossible to define meaningful reflection and transmission coefficients in such cases. Here we show - using an exactly soluble example - that despite the lack of any meaningful reflection and transmission coefficients, these profiles are still reflectionless from one side in the sense that the profile generates no counterpropagating wave for incidence from one side. This finding is demonstrated through examining the propagation of pulses through the profile, where from one side we find that no second reflected pulse is generated, while from the other there is. We conclude with a discussion of the effect of truncating these infinitely extended profiles, illustrating how the reflectionless behavior may be retained over a wide range of incident angles. © 2016 American Physical Society.


Wu J.-H.,Jilin University | Horsley S.A.R.,University of Exeter | Artoni M.,European Laboratory for Nonlinear Spectroscopy | Artoni M.,CNR Institute of Acoustics and Sensors Orso Mario Corbino | La Rocca G.C.,Normal School of Pisa
Light: Science and Applications | Year: 2013

The typically tiny effect of radiation damping on a moving body can be amplified to a favorable extent by exploiting the sharp reflectivity slope at one edge of an optically induced stop-band in atoms loaded into an optical lattice. In this paper, this phenomenon is demonstrated for the periodically trapped and coherently driven cold 87Rb atoms, where radiation damping might be much larger than that anticipated in previous proposals and become comparable with radiation pressure. Such an enhancement could be observed even at speeds of only a few meters per second with less than 1.0% absorption, making radiation damping experimentally accessible. © 2013 CIOMP. All rights reserved.


Wu J.-H.,Jilin University | Artoni M.,European Laboratory for Nonlinear Spectroscopy | Artoni M.,University of Brescia | La Rocca G.C.,Normal School of Pisa
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

Elaborating versatile strategies for new lasing schemes is important for both fundamental research and realistic applications. By using atomic photonic crystals, two-color distributed feedback lasing can be shown to occur in a nonlinear regime of balanced optical gain. Within the context of a simple model based on coupled-wave theory and applied to alkali-metal-atom crystals, we find that the two-color lasing threshold in cold atoms is within state-of-the-art experimental reach. © 2013 American Physical Society.


Wu J.-H.,Jilin University | Artoni M.,CNR Institute of Acoustics and Sensors Orso Mario Corbino | Artoni M.,European Laboratory for Nonlinear Spectroscopy | La Rocca G.C.,Normal School of Pisa
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

Fourier-expanded Maxwell-Liouville equations are employed to study the light pulse dynamics in atomic samples coherently driven by a standing-wave light field. Solutions are obtained by a suitable truncation of the Maxwell-Liouville equations that contain the number of spin and optical Fourier coherence components appropriate to the sample temperature. This approach is examined here for cold but thermal atoms where the Doppler broadening is still not negligible and familiar secular approximations no longer hold. In this temperature regime higher-order momentum Fourier coherence components are shown to be important for achieving excellent agreement with a recent experiment done in cold Rb87 clouds at several hundred microkelvins. © 2010 The American Physical Society.


Horsley S.A.R.,University of Exeter | Artoni M.,University of Brescia | Artoni M.,European Laboratory for Nonlinear Spectroscopy | La Rocca G.C.,Normal School of Pisa
Nature Photonics | Year: 2015

When a planar dielectric medium has a permittivity profile that is an analytic function in the upper or lower half of the complex position plane x=x'+ix'' then the real and imaginary parts of its permittivity are related by the spatial Kramers-Kronig relations. We find that such a medium will not reflect radiation incident from one side, whatever the angle of incidence. Using the spatial Kramers-Kronig relations, one can derive a real part of a permittivity profile from some given imaginary part (or vice versa) such that the reflection is guaranteed to be zero. This result is valid for both scalar and vector wave theories and may have relevance for designing materials that efficiently absorb radiation or for the creation of a new type of anti-reflection surface. © 2015 Macmillan Publishers Limited.


Horsley S.A.R.,University of St. Andrews | Horsley S.A.R.,University of York | Artoni M.,European Laboratory for Nonlinear Spectroscopy | Artoni M.,University of Brescia | La Rocca G.C.,Normal School of Pisa
Physical Review Letters | Year: 2011

The force exerted on a material by an incident beam of light is dependent upon the material's velocity in the laboratory frame of reference. This velocity dependence is known to be difficult to measure, as it is proportional to the incident optical power multiplied by the ratio of the material velocity to the speed of light. Here we show that this typically tiny effect is greatly amplified in multilayer systems composed of resonantly absorbing atoms exhibiting ultranarrow photonic band gaps. The amplification effect for optically trapped Rb87 is shown to be as much as 3 orders of magnitude greater than for conventional photonic-band-gap materials. For a specific pulsed regime, damping remains observable without destroying the system and significant for material velocities of a few ms⊃-1. © 2011 American Physical Society.


Horsley S.A.R.,University of Exeter | Horsley S.A.R.,European Laboratory for Nonlinear Spectroscopy | Artoni M.,European Laboratory for Nonlinear Spectroscopy | Artoni M.,CNR Institute of Acoustics and Sensors Orso Mario Corbino | La Rocca G.C.,Normal School of Pisa
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

A general theory of optical forces on moving bodies is here developed in terms of generalized 4×4 transfer and scattering matrices. Results are presented for a planar dielectric of arbitrary refractive index placed in an otherwise empty space and moving parallel and perpendicular to the slab-vacuum interface. In both regimes of motion the resulting force comprises lateral and normal velocity-dependent components, which may depend in a subtle way on the Doppler effect and s-p-polarization mixing. For lateral displacements in particular, polarization mixing, which is here interpreted as an effective magnetoelectric effect due to the reduced symmetry induced by the motion of the slab, gives rise to a velocity-dependent force contribution that is sensitive to the phase difference between the two polarization amplitudes. This term gives rise to a rather peculiar optical response on the moving body, and specific cases are illustrated for incident radiation of arbitrarily directed linear polarization. The additional force due to polarization mixing may cancel to first order in V/c with the first order Doppler contribution yielding an overall vanishing of the velocity-dependent component of the force on the body. The above findings bear some relevance to modern developments of nano-optomechanics and to the problem of the frictional component of the Casimir force. © 2012 American Physical Society.


Horsley S.A.R.,University of St. Andrews | Artoni M.,European Laboratory for Nonlinear Spectroscopy | Artoni M.,CNR Institute of Acoustics and Sensors Orso Mario Corbino | La Rocca G.C.,Normal School of Pisa
Journal of the Optical Society of America B: Optical Physics | Year: 2012

The dependence of macroscopic radiation pressure on the velocity of the object being pushed is commonly attributed to the Doppler effect. This need not be the case, and here we highlight velocity-dependent radiation pressure terms that have their origins in the mixing of s and p polarizations brought about by the Lorentz transformation between the lab and the material rest frame, rather than in the corresponding transformation of frequency and wavevector. The theory we develop may be relevant to the nano-optomechanics of moving bodies. © 2012 Optical Society of America.


Wu J.-H.,Northeast Normal University | Artoni M.,European Laboratory for Nonlinear Spectroscopy | Artoni M.,University of Brescia | La Rocca G.C.,Normal School of Pisa
Physical Review Letters | Year: 2014

Light propagation in optical lattices of driven cold atoms exhibits non-Hermitian degeneracies when the first-order modulation amplitudes of real and imaginary parts of the probe susceptibility are manipulated to be balanced. At these degeneracies, one may observe complete unidirectional reflectionless light propagation. This strictly occurs with no gain and can be easily tuned and fully reversed as supported by the transfer-matrix calculations and explained via a coupled-mode analysis. © 2014 American Physical Society.

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