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J Tempere - One of the best experts on this subject based on the ideXlab platform.
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leggett Collective Excitations in a two band fermi superfluid at finite temperatures
New Journal of Physics, 2019Co-Authors: S N Klimin, Hadrien Kurkjian, J TempereAbstract:The Leggett Collective Excitations for a two-band Fermi gas with s-wave pairing and Josephson interband coupling in the BCS-BEC crossover at finite temperatures are investigated within the Gaussian pair fluctuation approach. Eigenfrequencies and damping factors for Leggett modes are determined in a nonperturbative way, using the analytic continuation of the fluctuation propagator through a branch cut in the complex frequency plane, as in Phys. Rev. Lett. 122, 093403 (2019). The treatment is performed beyond the low-energy expansion, which is necessary when the Collective Excitation energy reaches the pair-breaking continuum edge. The results are applied in particular to cold atomic gases at the orbital Feshbach resonance and in a regime far from BEC, which can be relevant for future experiments.
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pair breaking Collective branch in bcs superconductors and superfluid fermi gases
Physical Review Letters, 2019Co-Authors: Hadrien Kurkjian, J Tempere, S N Klimin, Yvan CastinAbstract:We demonstrate the existence of a Collective Excitation branch in the pair-breaking continuum of superfluid Fermi gases and BCS superconductors. At zero temperature, we analytically continue the equation on the Collective mode energy in Anderson's Random Phase Approximation or Gaussian fluctuations through its branch cut associated with the continuum, and obtain the full complex dispersion relation, including in the strong coupling regime. The branch exists as long as the chemical potential μ is positive and the wave number below sqrt[2mμ]/ℏ (with m the fermion mass). In the long wavelength limit, the branch varies quadratically with the wave number, with a complex effective mass that we compute analytically for an arbitrary interaction strength.
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absorption and emission of a Collective Excitation by a fermionic quasiparticle in a fermi superfluid
New Journal of Physics, 2017Co-Authors: Hadrien Kurkjian, J TempereAbstract:We study the process of absorption or emission of a bosonic Collective Excitation by a fermionic quasiparticle in a superfluid of paired fermions. From the RPA equation of motion of the bosonic Excitation annihilation operator, we obtain an expression of the coupling amplitude of this process which is limited neither to resonant processes nor to the long wavelength limit. We confirm our result by independently deriving it in the functional integral approach using the gaussian fluctuation approximation, and by comparing it in the long wavelength limit to the quantum hydrodynamic result. Last, we give a straightforward application of the coupling amplitude we obtain by calculating the lifetime of the bosonic Excitations of arbitrary wave number. We find a mode quality factor that decreases from its maximum at low wave numbers and vanishes when the bosonic branch hits the pair-breaking continuum.
Hadrien Kurkjian - One of the best experts on this subject based on the ideXlab platform.
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leggett Collective Excitations in a two band fermi superfluid at finite temperatures
New Journal of Physics, 2019Co-Authors: S N Klimin, Hadrien Kurkjian, J TempereAbstract:The Leggett Collective Excitations for a two-band Fermi gas with s-wave pairing and Josephson interband coupling in the BCS-BEC crossover at finite temperatures are investigated within the Gaussian pair fluctuation approach. Eigenfrequencies and damping factors for Leggett modes are determined in a nonperturbative way, using the analytic continuation of the fluctuation propagator through a branch cut in the complex frequency plane, as in Phys. Rev. Lett. 122, 093403 (2019). The treatment is performed beyond the low-energy expansion, which is necessary when the Collective Excitation energy reaches the pair-breaking continuum edge. The results are applied in particular to cold atomic gases at the orbital Feshbach resonance and in a regime far from BEC, which can be relevant for future experiments.
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Collective Excitation branch in the continuum of pair condensed fermi gases analytical study and scaling laws
arXiv: Quantum Gases, 2019Co-Authors: Yvan Castin, Hadrien KurkjianAbstract:The pair-condensed unpolarized spin-$1/2$ Fermi gases have a Collective Excitation branch in their pair-breaking continuum (VA Andrianov, VN Popov, 1976). We study it at zero temperature, with the eigenenergy equation deduced from the time-dependent BCS theory and extended analytically to the lower half complex plane through its branch cut, calculating both the dispersion relation and the spectral weights (quasiparticle residues) of the branch. In the case of BCS superconductors, so called because the effect of the ion lattice is replaced by a short-range electron-electron interaction, we also include the Coulomb interaction and we restrict ourselves to the weak coupling limit $\Delta/\mu\to 0^+$ ($\Delta$ is the order parameter, $\mu $ the chemical potential) and to wavenumbers $q=O(1/\xi)$ where $\xi$ is the size of a pair; when the complex energy $z_q$ is expressed in units of $\Delta$ and $q$ in units of $1/\xi$, the branch follows a universal law insensitive to the Coulomb interaction. In the case of cold atoms in the BEC-BCS crossover, only a contact interaction remains, but the coupling strength $\Delta/\mu$ can take arbitrary values, and we study the branch at any wave number. At weak coupling, we predict three scales, that already mentioned $q\approx 1/\xi$, that $q\approx(\Delta/\mu)^{-1/3}/\xi$ where the real part of the dispersion relation has a minimum and that $q\approx(\mu/\Delta)/\xi\approx k_{\rm F}$ ($k_{\rm F}$ is the Fermi wave number) where the branch reaches the edge of its existence domain. Near the point where the chemical potential vanishes on the BCS side, $\mu/\Delta\to 0^+$, where $\xi\approx k_{\rm F}$, we find two scales $q\approx(\mu/\Delta)^{1/2}/\xi$ and $q\approx 1/\xi$. In all cases, the branch has a limit $2\Delta$ and a quadratic start at $q=0$. These results were obtained for $\mu>0$, where the eigenenergy equation admits at least two branching points $\epsilon_a(q)$ and $\epsilon_b(q)$ on the positive real axis, and for an analytic continuation through the interval $[\epsilon_a(q),\epsilon_b(q)] $. We find new continuum branches by performing the analytic continuation through $[\epsilon_b(q),+\infty[$ or even, for $q$ low enough, where there is a third real positive branching point $\epsilon_c(q)$, through $[\epsilon_b(q),\epsilon_c(q)]$ and $[\epsilon_c(q),+\infty[$. On the BEC side $\mu 0$, some of these new branches have a low-wavenumber exotic hypoacoustic $z_q\approx q^{3/2}$ or hyperacoustic $z_q\approx q^{4/5}$ behavior. For $\mu<0$, we find a hyperacoustic branch and a nonhypoacoustic branch, with a limit $2\Delta$ and a purely real quadratic start at $q=0$ for $\Delta/|\mu|<0,222$.
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pair breaking Collective branch in bcs superconductors and superfluid fermi gases
Physical Review Letters, 2019Co-Authors: Hadrien Kurkjian, J Tempere, S N Klimin, Yvan CastinAbstract:We demonstrate the existence of a Collective Excitation branch in the pair-breaking continuum of superfluid Fermi gases and BCS superconductors. At zero temperature, we analytically continue the equation on the Collective mode energy in Anderson's Random Phase Approximation or Gaussian fluctuations through its branch cut associated with the continuum, and obtain the full complex dispersion relation, including in the strong coupling regime. The branch exists as long as the chemical potential μ is positive and the wave number below sqrt[2mμ]/ℏ (with m the fermion mass). In the long wavelength limit, the branch varies quadratically with the wave number, with a complex effective mass that we compute analytically for an arbitrary interaction strength.
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absorption and emission of a Collective Excitation by a fermionic quasiparticle in a fermi superfluid
New Journal of Physics, 2017Co-Authors: Hadrien Kurkjian, J TempereAbstract:We study the process of absorption or emission of a bosonic Collective Excitation by a fermionic quasiparticle in a superfluid of paired fermions. From the RPA equation of motion of the bosonic Excitation annihilation operator, we obtain an expression of the coupling amplitude of this process which is limited neither to resonant processes nor to the long wavelength limit. We confirm our result by independently deriving it in the functional integral approach using the gaussian fluctuation approximation, and by comparing it in the long wavelength limit to the quantum hydrodynamic result. Last, we give a straightforward application of the coupling amplitude we obtain by calculating the lifetime of the bosonic Excitations of arbitrary wave number. We find a mode quality factor that decreases from its maximum at low wave numbers and vanishes when the bosonic branch hits the pair-breaking continuum.
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concavity of the Collective Excitation branch of a fermi gas in the bec bcs crossover
Physical Review A, 2016Co-Authors: Hadrien Kurkjian, Yvan Castin, Alice SinatraAbstract:We study the concavity of the dispersion relation $q\mapsto \omega_{\mathbf{q}}$ of the bosonic Excitations of a three-dimensional spin-$1/2$ Fermi gas in the Random Phase Approximation (RPA). In the limit of small wave numbers $q$ we obtain analytically the spectrum up to order $5$ in $q$. In the neighborhood of $q=0$, a change in concavity between the convex BEC limit and the concave BCS limit takes place at $\Delta/\mu\simeq0.869$ [$1/(k_F a)\simeq-0.144$], where $a$ is the scattering length between opposite spin fermions, $k_F$ is the Fermi wave number and $\Delta$ the gap according to BCS theory, and $\mu$ is the chemical potential. At that point the branch is concave due to a negative fifth-order term. Our results are supplemented by a numerical study which shows the evolution of the border between the zone of the $(q,\Delta)$ plane where $q\mapsto \omega_{\mathbf{q}}$ is concave and the zone where it is convex.
Julien Laurat - One of the best experts on this subject based on the ideXlab platform.
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waveguide coupled single Collective Excitation of atomic arrays
arXiv: Quantum Physics, 2019Co-Authors: Neil V. Corzo, Jérémy Raskop, Aveek Chandra, Baptiste Gouraud, A. S. Sheremet, Julien LauratAbstract:Considerable efforts have been recently devoted to combining ultracold atoms and nanophotonic devices to obtain not only better scalability and figures of merit than in free-space implementations, but also new paradigms for atom-photon interactions. Dielectric waveguides offer a promising platform for such integration because they enable tight transverse confinement of the propagating light, strong photon-atom coupling in single-pass configurations and potentially long-range atom-atom interactions mediated by the guided photons. However, the preparation of non-classical quantum states in such atom-waveguide interfaces has not yet been realized. Here, by using arrays of individual caesium atoms trapped along an optical nanofibre, we observe a single Collective atomic Excitation coupled to a nanoscale waveguide. The stored Collective entangled state can be efficiently read out with an external laser pulse, leading to on-demand emission of a single photon into the guided mode. We characterize the emitted single photon via the suppression of the two-photon component and confirm the single character of the atomic Excitation, which can be retrieved with an efficiency of about 25%. Our results demonstrate a capability that is essential for the emerging field of waveguide quantum electrodynamics, with applications to quantum networking, quantum nonlinear optics and quantum many-body physics.
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Waveguide-coupled single Collective Excitation of atomic arrays
Nature, 2019Co-Authors: Neil V. Corzo, Jérémy Raskop, Aveek Chandra, Baptiste Gouraud, A. S. Sheremet, Julien LauratAbstract:Considerable efforts have been recently devoted to combining ultracold atoms and nanophotonic devices^ 1 – 4 to obtain not only better scalability and figures of merit than in free-space implementations, but also new paradigms for atom–photon interactions^ 5 . Dielectric waveguides offer a promising platform for such integration because they enable tight transverse confinement of the propagating light, strong photon–atom coupling in single-pass configurations and potentially long-range atom–atom interactions mediated by the guided photons. However, the preparation of non-classical quantum states in such atom–waveguide interfaces has not yet been realized. Here, by using arrays of individual caesium atoms trapped along an optical nanofibre^ 6 , 7 , we observe a single Collective atomic Excitation^ 8 , 9 coupled to a nanoscale waveguide. The stored Collective entangled state can be efficiently read out with an external laser pulse, leading to on-demand emission of a single photon into the guided mode. We characterize the emitted single photon via the suppression of the two-photon component and confirm the single character of the atomic Excitation, which can be retrieved with an efficiency of about 25%. Our results demonstrate a capability that is essential for the emerging field of waveguide quantum electrodynamics, with applications to quantum networking, quantum nonlinear optics and quantum many-body physics^ 10 , 11 .Waveguide quantum electrodynamics is used to couple a single Collective Excitation of an atomic array to a nanoscale waveguide; the Excitation is stored and later read out, generating guided single photons on demand.
Yvan Castin - One of the best experts on this subject based on the ideXlab platform.
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Collective Excitation branch in the continuum of pair condensed fermi gases analytical study and scaling laws
arXiv: Quantum Gases, 2019Co-Authors: Yvan Castin, Hadrien KurkjianAbstract:The pair-condensed unpolarized spin-$1/2$ Fermi gases have a Collective Excitation branch in their pair-breaking continuum (VA Andrianov, VN Popov, 1976). We study it at zero temperature, with the eigenenergy equation deduced from the time-dependent BCS theory and extended analytically to the lower half complex plane through its branch cut, calculating both the dispersion relation and the spectral weights (quasiparticle residues) of the branch. In the case of BCS superconductors, so called because the effect of the ion lattice is replaced by a short-range electron-electron interaction, we also include the Coulomb interaction and we restrict ourselves to the weak coupling limit $\Delta/\mu\to 0^+$ ($\Delta$ is the order parameter, $\mu $ the chemical potential) and to wavenumbers $q=O(1/\xi)$ where $\xi$ is the size of a pair; when the complex energy $z_q$ is expressed in units of $\Delta$ and $q$ in units of $1/\xi$, the branch follows a universal law insensitive to the Coulomb interaction. In the case of cold atoms in the BEC-BCS crossover, only a contact interaction remains, but the coupling strength $\Delta/\mu$ can take arbitrary values, and we study the branch at any wave number. At weak coupling, we predict three scales, that already mentioned $q\approx 1/\xi$, that $q\approx(\Delta/\mu)^{-1/3}/\xi$ where the real part of the dispersion relation has a minimum and that $q\approx(\mu/\Delta)/\xi\approx k_{\rm F}$ ($k_{\rm F}$ is the Fermi wave number) where the branch reaches the edge of its existence domain. Near the point where the chemical potential vanishes on the BCS side, $\mu/\Delta\to 0^+$, where $\xi\approx k_{\rm F}$, we find two scales $q\approx(\mu/\Delta)^{1/2}/\xi$ and $q\approx 1/\xi$. In all cases, the branch has a limit $2\Delta$ and a quadratic start at $q=0$. These results were obtained for $\mu>0$, where the eigenenergy equation admits at least two branching points $\epsilon_a(q)$ and $\epsilon_b(q)$ on the positive real axis, and for an analytic continuation through the interval $[\epsilon_a(q),\epsilon_b(q)] $. We find new continuum branches by performing the analytic continuation through $[\epsilon_b(q),+\infty[$ or even, for $q$ low enough, where there is a third real positive branching point $\epsilon_c(q)$, through $[\epsilon_b(q),\epsilon_c(q)]$ and $[\epsilon_c(q),+\infty[$. On the BEC side $\mu 0$, some of these new branches have a low-wavenumber exotic hypoacoustic $z_q\approx q^{3/2}$ or hyperacoustic $z_q\approx q^{4/5}$ behavior. For $\mu<0$, we find a hyperacoustic branch and a nonhypoacoustic branch, with a limit $2\Delta$ and a purely real quadratic start at $q=0$ for $\Delta/|\mu|<0,222$.
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pair breaking Collective branch in bcs superconductors and superfluid fermi gases
Physical Review Letters, 2019Co-Authors: Hadrien Kurkjian, J Tempere, S N Klimin, Yvan CastinAbstract:We demonstrate the existence of a Collective Excitation branch in the pair-breaking continuum of superfluid Fermi gases and BCS superconductors. At zero temperature, we analytically continue the equation on the Collective mode energy in Anderson's Random Phase Approximation or Gaussian fluctuations through its branch cut associated with the continuum, and obtain the full complex dispersion relation, including in the strong coupling regime. The branch exists as long as the chemical potential μ is positive and the wave number below sqrt[2mμ]/ℏ (with m the fermion mass). In the long wavelength limit, the branch varies quadratically with the wave number, with a complex effective mass that we compute analytically for an arbitrary interaction strength.
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concavity of the Collective Excitation branch of a fermi gas in the bec bcs crossover
Physical Review A, 2016Co-Authors: Hadrien Kurkjian, Yvan Castin, Alice SinatraAbstract:We study the concavity of the dispersion relation $q\mapsto \omega_{\mathbf{q}}$ of the bosonic Excitations of a three-dimensional spin-$1/2$ Fermi gas in the Random Phase Approximation (RPA). In the limit of small wave numbers $q$ we obtain analytically the spectrum up to order $5$ in $q$. In the neighborhood of $q=0$, a change in concavity between the convex BEC limit and the concave BCS limit takes place at $\Delta/\mu\simeq0.869$ [$1/(k_F a)\simeq-0.144$], where $a$ is the scattering length between opposite spin fermions, $k_F$ is the Fermi wave number and $\Delta$ the gap according to BCS theory, and $\mu$ is the chemical potential. At that point the branch is concave due to a negative fifth-order term. Our results are supplemented by a numerical study which shows the evolution of the border between the zone of the $(q,\Delta)$ plane where $q\mapsto \omega_{\mathbf{q}}$ is concave and the zone where it is convex.
Neil V. Corzo - One of the best experts on this subject based on the ideXlab platform.
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waveguide coupled single Collective Excitation of atomic arrays
arXiv: Quantum Physics, 2019Co-Authors: Neil V. Corzo, Jérémy Raskop, Aveek Chandra, Baptiste Gouraud, A. S. Sheremet, Julien LauratAbstract:Considerable efforts have been recently devoted to combining ultracold atoms and nanophotonic devices to obtain not only better scalability and figures of merit than in free-space implementations, but also new paradigms for atom-photon interactions. Dielectric waveguides offer a promising platform for such integration because they enable tight transverse confinement of the propagating light, strong photon-atom coupling in single-pass configurations and potentially long-range atom-atom interactions mediated by the guided photons. However, the preparation of non-classical quantum states in such atom-waveguide interfaces has not yet been realized. Here, by using arrays of individual caesium atoms trapped along an optical nanofibre, we observe a single Collective atomic Excitation coupled to a nanoscale waveguide. The stored Collective entangled state can be efficiently read out with an external laser pulse, leading to on-demand emission of a single photon into the guided mode. We characterize the emitted single photon via the suppression of the two-photon component and confirm the single character of the atomic Excitation, which can be retrieved with an efficiency of about 25%. Our results demonstrate a capability that is essential for the emerging field of waveguide quantum electrodynamics, with applications to quantum networking, quantum nonlinear optics and quantum many-body physics.
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Waveguide-coupled single Collective Excitation of atomic arrays
Nature, 2019Co-Authors: Neil V. Corzo, Jérémy Raskop, Aveek Chandra, Baptiste Gouraud, A. S. Sheremet, Julien LauratAbstract:Considerable efforts have been recently devoted to combining ultracold atoms and nanophotonic devices^ 1 – 4 to obtain not only better scalability and figures of merit than in free-space implementations, but also new paradigms for atom–photon interactions^ 5 . Dielectric waveguides offer a promising platform for such integration because they enable tight transverse confinement of the propagating light, strong photon–atom coupling in single-pass configurations and potentially long-range atom–atom interactions mediated by the guided photons. However, the preparation of non-classical quantum states in such atom–waveguide interfaces has not yet been realized. Here, by using arrays of individual caesium atoms trapped along an optical nanofibre^ 6 , 7 , we observe a single Collective atomic Excitation^ 8 , 9 coupled to a nanoscale waveguide. The stored Collective entangled state can be efficiently read out with an external laser pulse, leading to on-demand emission of a single photon into the guided mode. We characterize the emitted single photon via the suppression of the two-photon component and confirm the single character of the atomic Excitation, which can be retrieved with an efficiency of about 25%. Our results demonstrate a capability that is essential for the emerging field of waveguide quantum electrodynamics, with applications to quantum networking, quantum nonlinear optics and quantum many-body physics^ 10 , 11 .Waveguide quantum electrodynamics is used to couple a single Collective Excitation of an atomic array to a nanoscale waveguide; the Excitation is stored and later read out, generating guided single photons on demand.