The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Yvan Castin - One of the best experts on this subject based on the ideXlab platform.
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The interaction-sensitive states of a trapped two-component Ideal Fermi Gas and application to the virial expansion of the unitary Fermi Gas
Journal of Physics A: Mathematical and Theoretical, 2016Co-Authors: Shimpei Endo, Yvan CastinAbstract:We consider a two-component Ideal Fermi Gas in an isotropic harmonic potential. Some eigenstates have a wavefunction that vanishes when two distinguishable Fermions are at the same location, and would be unaffected by s-wave contact interactions between the two components. We determine the other, interaction-sensitive eigenstates, using a Faddeev ansatz. This problem is nontrivial, due to degeneracies and to the existence of unphysical Faddeev solutions. As an application we present a new conjecture for the fourth-order cluster or virial coefficient of the unitary Fermi Gas, in good agreement with the numerical results of Blume and coworkers.
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the interaction sensitive states of a trapped two component Ideal Fermi Gas
arXiv: Quantum Gases, 2015Co-Authors: Shimpei Endo, Yvan CastinAbstract:We consider a two-component Ideal Fermi Gas in an isotropic harmonic potential. Some eigenstates have a wavefunction that vanishes when two distinguishable Fermions are at the same location, and would be unaffected by s-wave contact interactions between the two components. We determine the other, interaction-sensitive eigenstates, using a Faddeev ansatz. This problem is non trivial, due to degeneracies and to the existence of unphysical Faddeev solutions. We present some applications to the fourth-order cluster or virial coefficient of the unitary Fermi Gas.
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Self-energy of an impurity in an Ideal Fermi Gas to second order in the interaction strength
Physical Review A, 2014Co-Authors: Christian Trefzger, Yvan CastinAbstract:We study in three dimensions the problem of a spatially homogeneous zero-temperature Ideal Fermi Gas of spin-polarized particles of mass $m$ perturbed by the presence of a single distinguishable impurity of mass $M$. The interaction between the impurity and the Fermions involves only the partial $s$-wave through the scattering length $a$, and has negligible range $b$ compared to the inverse Fermi wave number $1/\kf$ of the Gas. Through the interactions with the Fermi Gas the impurity gives birth to a quasi-particle, which will be here a Fermi polaron (or more precisely a {\sl monomeron}). We consider the general case of an impurity moving with wave vector $\KK\neq\OO$: Then the quasi-particle acquires a finite lifetime in its initial momentum channel because it can radiate particle-hole pairs in the Fermi sea. A description of the system using a variational approach, based on a finite number of particle-hole excitations of the Fermi sea, then becomes inappropriate around $\KK=\mathbf{0}$. We rely thus upon perturbation theory, where the small and negative parameter $\kf a\to0^-$ excludes any branches other than the monomeronic one in the ground state (as e.g.\ the dimeronic one), and allows us a systematic study of the system. We calculate the impurity self-energy $\Sigma^{(2)}(\KK,\omega)$ up to second order included in $a$. Remarkably, we obtain an analytical explicit expression for $\Sigma^{(2)}(\KK,\omega)$ allowing us to study its derivatives in the plane $(K,\omega)$. These present interesting singularities, which in general appear in the third order derivatives $\partial^3 \Sigma^{(2)}(\KK,\omega)$. In the special case of equal masses, $M=m$, singularities appear already in the physically more accessible second order derivatives $\partial^2 \Sigma^{(2)}(\KK,\omega)$; using a self-consistent heuristic approach based on $\Sigma^{(2)}$ we then regularise the divergence of the second order derivative $\partial_K^2 \Delta E(\KK)$ of the complex energy of the quasi-particle found in reference [C. Trefzger, Y. Castin, Europhys. Lett. {\bf 104}, 50005 (2013)] at $K=\kf$, and we predict an interesting scaling law in the neighborhood of $K=\kf$. As a by product of our theory we have access to all moments of the momentum of the particle-hole pair emitted by the impurity while damping its motion in the Fermi sea, at the level of Fermi's golden rule.
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The self-energy of an impurity in an Ideal Fermi Gas to second order in the interaction strength
Physical Review A, 2014Co-Authors: Christian Trefzger, Yvan CastinAbstract:We study in three dimensions the problem of a spatially homogeneous zero-temperature Ideal Fermi Gas of spin-polarized particles of mass $m$ perturbed by the presence of a single distinguishable impurity of mass $M$. The interaction between the impurity and the Fermions involves only the partial $s$-wave through the scattering length $a$, and has negligible range $b$ compared to the inverse Fermi wave number $1/\kf$ of the Gas. Through the interactions with the Fermi Gas the impurity gives birth to a quasi-particle, which will be here a Fermi polaron (or more precisely a {\sl monomeron}). We consider the general case of an impurity moving with wave vector $\KK\neq\OO$: Then the quasi-particle acquires a finite lifetime in its initial momentum channel because it can radiate particle-hole pairs in the Fermi sea. A description of the system using a variational approach, based on a finite number of particle-hole excitations of the Fermi sea, then becomes inappropriate around $\KK=\mathbf{0}$. We rely thus upon perturbation theory, where the small and negative parameter $\kf a\to0^-$ excludes any branches other than the monomeronic one in the ground state (as e.g.\ the dimeronic one), and allows us a systematic study of the system. We calculate the impurity self-energy $\Sigma^{(2)}(\KK,\omega)$ up to second order included in $a$. Remarkably, we obtain an analytical explicit expression for $\Sigma^{(2)}(\KK,\omega)$ allowing us to study its derivatives in the plane $(K,\omega)$. These present interesting singularities, which in general appear in the third order derivatives $\partial^3 \Sigma^{(2)}(\KK,\omega)$. In the special case of equal masses, $M=m$, singularities appear already in the physically more accessible second order derivatives $\partial^2 \Sigma^{(2)}(\KK,\omega)$; using a self-consistent heuristic approach based on $\Sigma^{(2)}$ we then regularise the divergence of the second order derivative $\partial_K^2 \Delta E(\KK)$ of the complex energy of the quasi-particle found in reference [C. Trefzger, Y. Castin, Europhys. Lett. {\bf 104}, 50005 (2013)] at $K=\kf$, and we predict an interesting scaling law in the neighborhood of $K=\kf$. As a by product of our theory we have access to all moments of the momentum of the particle-hole pair emitted by the impurity while damping its motion in the Fermi sea, at the level of Fermi's golden rule.
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Basic theory tools for degenerate Fermi Gases
2007Co-Authors: Yvan CastinAbstract:This is an introductory lecture to the theory of degenerate Fermi Gases, in the context of present experiments on atomic Fermi Gases. In part one, some properties of the Ideal Fermi Gas are presented, including a discussion of the fluctuations of the number of Fermions in a given spatial zone in 1D, 2D and 3D. In part two, two-body aspects of the interaction potential are discussed and several possible models for the interaction are analyzed, including the two-channel model for the Feshbach resonance. In part three, basic predictions of zero temperature BCS theory are presented, including a derivation of superfluid hydrodynamic equations from time dependent BCS theory.
Jincan Chen - One of the best experts on this subject based on the ideXlab platform.
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Isobaric expansion coefficient and isothermal compressibility for a finite-size Ideal Fermi Gas system
Physics Letters A, 2014Co-Authors: Guozhen Su, Liwei Chen, Jincan ChenAbstract:Abstract Due to quantum size effects (QSEs), the isobaric thermal expansion coefficient and isothermal compressibility well defined for macroscopic systems are invalid for finite-size systems. The two parameters are redefined and calculated for a finite-size Ideal Fermi Gas confined in a rectangular container. It is found that the isobaric thermal expansion coefficient and isothermal compressibility are generally anisotropic, i.e., they are generally different in different directions. Moreover, it is found the thermal expansion coefficient may be negative in some directions under the condition that the pressures in all directions are kept constant.
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Isobaric expansion coefficient and isothermal compressibility for a finite-size Ideal Fermi Gas system
Physics Letters A, 2014Co-Authors: Guozhen Su, Liwei Chen, Jincan ChenAbstract:Abstract Due to quantum size effects (QSEs), the isobaric thermal expansion coefficient and isothermal compressibility well defined for macroscopic systems are invalid for finite-size systems. The two parameters are redefined and calculated for a finite-size Ideal Fermi Gas confined in a rectangular container. It is found that the isobaric thermal expansion coefficient and isothermal compressibility are generally anisotropic, i.e., they are generally different in different directions. Moreover, it is found the thermal expansion coefficient may be negative in some directions under the condition that the pressures in all directions are kept constant.
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Parametric optimum analysis of an irreversible Ericsson cryogenic refrigeration cycle working with an Ideal Fermi Gas
Pramana, 2008Co-Authors: Yingru Zhao, Jincan ChenAbstract:An irreversible model of an Ericsson cryogenic refrigeration cycle working with an Ideal Fermi Gas is established, which is composed of two isothermal and two isobaric processes. The influence of both the quantum degeneracy and the finite-rate heat transfer between the working fluid and the heat reservoirs on the performance of the cycle is investigated, based on the theory of statistical mechanics and thermodynamic properties of an Ideal Fermi Gas. The inherent regeneration losses of the cycle are analyzed. Expressions for several important performance parameters such as the coefficient of performance, cooling rate and power input are derived. By using numerical solutions, the cooling rate of the cycle is optimized for a given power input. The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal regions of the coefficient of performance and power input are determined. Especially, the optimal performance of the cycle in the strong and weak Gas degeneracy cases and the high temperature limit is discussed in detail. The analytic expressions of some optimized parameters are derived. Some optimum criteria are given. The distinctions and connections between the Ericsson refrigeration cycles working with the Fermi and classical Gases are revealed.
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thermostatistic properties of a q deformed Ideal Fermi Gas with a general energy spectrum
Journal of Physics A, 2007Co-Authors: Shukuan Cai, Jincan ChenAbstract:The thermostatistic problems of a q-deformed Ideal Fermi Gas in any dimensional space and with a general energy spectrum are studied, based on the q-deformed Fermi?Dirac distribution. The effects of the deformation parameter q on the properties of the system are revealed. It is shown that q-deformation results in some novel characteristics different from those of an ordinary system. Besides, it is found that the effects of the q-deformation on the properties of the Fermi systems are very different for different dimensional spaces and different energy spectrums.
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The performance characteristics of an irreversible regenerative quantum refrigeration cycle
Physica Scripta, 2005Co-Authors: Yue Zhang, Bihong Lin, Jincan ChenAbstract:An irreversible regenerative model of the Brayton refrigeration cycle working with an Ideal Fermi Gas, which is simply called the quantum refrigeration cycle, is established. Expressions for several important performance parameters, such as the coefficient of performance, work input, refrigeration load and regeneration heat, are derived, based on the equation of state of an Ideal Fermi Gas. The influence of quantum degeneracy of the Gas, regeneration and irreversibility on the performance of the quantum refrigeration cycle is analysed comprehensively. The general performance characteristics of the cycle are revealed. Moreover, two special cases are discussed and compared in detail. Consequently, the importance of regeneration in the cryogenic refrigeration is expounded from theory. Finally, the performance of the Brayton refrigeration cycle at high temperatures is directly deduced.
Luca Pezze - One of the best experts on this subject based on the ideXlab platform.
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Dipole Oscillations of a Fermi Gas in a Disordered Trap: Damping and Localization
EPL - Europhysics Letters, 2009Co-Authors: Luca Pezze, Ben Hambrecht, Laurent Sanchez-palenciaAbstract:We study the dipole oscillations of an Ideal Fermi Gas in a disordered trap. We show that even weak disorder induces strong damping of the oscillations and we identify a metal-insulator crossover: For very weak disorder, we find under-damping and show that it results from weak random perturbations of the energy spectrum. For increasing disorder, we show that the Fermi Gas crosses over to a strongly insulating regime characterized by over-damping resulting from the proliferation of localized states.
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insulating behavior of a trapped Ideal Fermi Gas
Physical Review Letters, 2004Co-Authors: Luca Pezze, Lev P Pitaevskii, Augusto Smerzi, S Stringari, G Modugno, E De Mirandes, F Ferlaino, Herwig Ott, G RoatiAbstract:We investigate theoretically and experimentally the center-of-mass motion of an Ideal Fermi Gas in a combined periodic and harmonic potential. We find a crossover from a conducting to an insulating regime as the Fermi energy moves from the first Bloch band into the band gap of the lattice. The conducting regime is characterized by an oscillation of the cloud about the potential minimum, while in the insulating case the center of mass remains on one side of the potential.
Wolfgang Ketterle - One of the best experts on this subject based on the ideXlab platform.
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pauli paramagnetism of an Ideal Fermi Gas
Physical Review A, 2013Co-Authors: Tout T Wang, Timur M Rvachov, Jaehoon Choi, Wolfgang KetterleAbstract:We show how to use trapped ultracold atoms to measure the magnetic susceptibility of a two-component Fermi Gas. The method is illustrated for a non-interacting Gas of $^6$Li, using the tunability of interactions around a wide Feshbach resonances. The susceptibility versus effective magnetic field is directly obtained from the inhomogeneous density profile of the trapped atomic cloud. The wings of the cloud realize the high field limit where the polarization approaches 100%, which is not accessible for an electron Gas.
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suppression of density fluctuations in a quantum degenerate Fermi Gas
Physical Review Letters, 2010Co-Authors: Christian Sanner, Aviv Keshet, Ralf Gommers, Yongil Shin, Wujie Huang, Wolfgang KetterleAbstract:We study density profiles of an Ideal Fermi Gas and observe Pauli suppression of density fluctuations (atom shot noise) for cold clouds deep in the quantum degenerate regime. Strong suppression is observed for probe volumes containing more than 10 000 atoms. Measuring the level of suppression provides sensitive thermometry at low temperatures. After this method of sensitive noise measurements has been validated with an Ideal Fermi Gas, it can now be applied to characterize phase transitions in strongly correlated many-body systems.
Li Chao - One of the best experts on this subject based on the ideXlab platform.
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Joule–Thomson Coefficient for Strongly Interacting Unitary Fermi Gas
Communications in Theoretical Physics, 2010Co-Authors: Chen Mo-sheng, Li ChaoAbstract:The Joule–Thomson effect reflects the interaction among constituent particles of macroscopic system. For classical Ideal Gas, the corresponding Joule–Thomson coefficient is vanishing while it is non-zero for Ideal quantum Gas due to the quantum degeneracy. In recent years, much attention is paid to the unitary Fermi Gas with infinite two-body scattering length. According to universal analysis, the thermodynamical law of unitary Fermi Gas is similar to that of non-interacting Ideal Gas, which can be explored by the virial theorem P = 2E/3V. Based on previous works, we further study the unitary Fermi Gas properties. The effective chemical potential is introduced to characterize the nonlinear levels crossing effects in a strongly interacting medium. The changing behavior of the rescaled Joule–Thomson coefficient according to temperature manifests a quite different behavior from that for Ideal Fermi Gas.
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joule thomson coefficient for strongly interacting unitary Fermi Gas
Communications in Theoretical Physics, 2010Co-Authors: Liao Kai, Chen Jisheng, Li ChaoAbstract:The Joule–Thomson effect reflects the interaction among constituent particles of macroscopic system. For classical Ideal Gas, the corresponding Joule–Thomson coefficient is vanishing while it is non-zero for Ideal quantum Gas due to the quantum degeneracy. In recent years, much attention is paid to the unitary Fermi Gas with infinite two-body scattering length. According to universal analysis, the thermodynamical law of unitary Fermi Gas is similar to that of non-interacting Ideal Gas, which can be explored by the virial theorem P = 2E/3V. Based on previous works, we further study the unitary Fermi Gas properties. The effective chemical potential is introduced to characterize the nonlinear levels crossing effects in a strongly interacting medium. The changing behavior of the rescaled Joule–Thomson coefficient according to temperature manifests a quite different behavior from that for Ideal Fermi Gas.
