We develop a consistent formalism in order to explore the effects of density and spin fluctuation... more We develop a consistent formalism in order to explore the effects of density and spin fluctuations on the quasi-particle properties and on the pairing critical temperature of a trapped Fermi gas on the attractive side of a Feshbach resonance. We first analyze the quasi-particle properties of a gas due to interactions far from resonance (effective mass and lifetime, quasi-particle strength and effective interaction) for the two cases of a spherically symmetric harmonic trap and of a spherically symmetric infinite potential well. We then explore the effect of each of these quantities on Tc and point out the important role played by the discrete level structure. PACS numbers: 03.75.Ss, 21.10.-k, 21.60.Jz Quasi-particle properties of trapped Fermi gases 2
Viene presentato in questo articolo un lavoro nato dalla collaborazione del gruppo di Teoria dell... more Viene presentato in questo articolo un lavoro nato dalla collaborazione del gruppo di Teoria della Struttura Nucleare del Dipartimento di Fisica dell Università di Milano e del Centro di Ricerca e Sviluppo sulla Condensazione di Bose-Einstein dell INFM (Trento). L ...
Viene presentato in questo articolo il lavoro del gruppo di teoria della struttura nucleare dell&... more Viene presentato in questo articolo il lavoro del gruppo di teoria della struttura nucleare dell'Università di Milano riguardante la descrizione dello stato superfluido della materia nella inner crust di una stella di neutroni. Keywords: Stelle di neutroni, ...
Oscillations of mainly surface character (S = 0 modes) give rise, in atomic nuclei, to an attract... more Oscillations of mainly surface character (S = 0 modes) give rise, in atomic nuclei, to an attractive (induced) pairing interaction, while spin (S = 1) modes of mainly volume character generate a repulsive interaction, the net effect being an attraction which accounts for a sizeable fraction of the experimental pairing gap. Suppressing the particle-vibration coupling mediated by the proton degrees of freedom, i.e., mimicking neutron matter, the total surface plus spin-induced pairing interaction becomes repulsive.
The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Journal of Physics G: Nuclear and Particle Physics, 2005
The effective pairing interaction induced by the exchange of phonons between pairs of nucleons mo... more The effective pairing interaction induced by the exchange of phonons between pairs of nucleons moving in time-reversal states close to the Fermi energy in deformed nuclei modifies in a sizeable manner the superfluid properties of these systems, accounting for about half of the pairing gap.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2005
We develop a consistent formalism in order to explore the effects of density and spin fluctuation... more We develop a consistent formalism in order to explore the effects of density and spin fluctuations on the quasi-particle properties and on the pairing critical temperature of a trapped Fermi gas on the attractive side of a Feshbach resonance. We first analyze the quasi-particle properties of a gas due to interactions far from resonance (effective mass and lifetime, quasi-particle strength and effective interaction) for the two cases of a spherically symmetric harmonic trap and of a spherically symmetric infinite potential well. We then explore the effect of each of these quantities on T c and point out the important role played by the discrete level structure.
We calculate, for the first time, the state-dependent pairing gap of a finite nucleus (120 Sn) di... more We calculate, for the first time, the state-dependent pairing gap of a finite nucleus (120 Sn) diagonalizing the bare nucleon-nucleon potential (Argonne v14) in a Hartree-Fock basis (with effective k−mass m k ≈ 0.7 m), within the framework of the BCS approximation including scattering states up to 800 MeV above the Fermi energy to achieve convergence. The resulting gap accounts for about half of the experimental gap. We find that a consistent description of the low-energy nuclear spectrum requires, aside from the bare nucleon-nucleon interaction, not only the dressing of singleparticle motion through the coupling to the nuclear surface, to give the right density of levels close to the Fermi energy (and thus an effective mass m * ≈ m), but also the renormalization of collective vibrational modes through vertex and self-energy processes, processes which are also found to play an essential role in the pairing channel, leading to a long range, state dependent component of the pairing interaction. The combined effect of the bare nucleon-nucleon potential and of the induced pairing interaction arising from the exchange of low-lying surface vibrations between nucleons moving in time reversal states close to the Fermi energy accounts for the experimental gap.
The coupling of single-particle motion and of vibrations in 11 4 Be produces dressed neutrons whi... more The coupling of single-particle motion and of vibrations in 11 4 Be produces dressed neutrons which spend only a fraction of the time in pure single-particle states, and which weighting differently from the bare neutrons, lead to parity inversion. The interaction of the two least bound neutrons in the ground state of 12 4 Be mediated by the v14 Argonne nucleon-nucleon potential and by the exchange of the phonon cloud, give rise to a strongly correlated state, where the neutrons spend more than half of the time in (s 2 +d 2)-configurations, resulting in a breaking of the N = 8 shell closure.
The coupling of single-particle motion and of vibrations in 11 4 Be produces dressed neutrons whi... more The coupling of single-particle motion and of vibrations in 11 4 Be produces dressed neutrons which spend only a fraction of the time in pure single-particle states, and which weighting differently from the bare neutrons, lead to parity inversion. The interaction of the two least bound neutrons in the ground state of 12 4 Be mediated by the v14 Argonne nucleon-nucleon potential and by the exchange of the phonon cloud, give rise to a strongly correlated state, where the neutrons spend more than half of the time in (s 2 +d 2)-configurations, resulting in a breaking of the N = 8 shell closure.
We develop a consistent formalism in order to explore the effects of density and spin fluctuation... more We develop a consistent formalism in order to explore the effects of density and spin fluctuations on the quasi-particle properties and on the pairing critical temperature of a trapped Fermi gas on the attractive side of a Feshbach resonance. We first analyze the quasi-particle properties of a gas due to interactions far from resonance (effective mass and lifetime, quasi-particle strength and effective interaction) for the two cases of a spherically symmetric harmonic trap and of a spherically symmetric infinite potential well. We then explore the effect of each of these quantities on Tc and point out the important role played by the discrete level structure. PACS numbers: 03.75.Ss, 21.10.-k, 21.60.Jz Quasi-particle properties of trapped Fermi gases 2
Viene presentato in questo articolo un lavoro nato dalla collaborazione del gruppo di Teoria dell... more Viene presentato in questo articolo un lavoro nato dalla collaborazione del gruppo di Teoria della Struttura Nucleare del Dipartimento di Fisica dell Università di Milano e del Centro di Ricerca e Sviluppo sulla Condensazione di Bose-Einstein dell INFM (Trento). L ...
Viene presentato in questo articolo il lavoro del gruppo di teoria della struttura nucleare dell&... more Viene presentato in questo articolo il lavoro del gruppo di teoria della struttura nucleare dell'Università di Milano riguardante la descrizione dello stato superfluido della materia nella inner crust di una stella di neutroni. Keywords: Stelle di neutroni, ...
Oscillations of mainly surface character (S = 0 modes) give rise, in atomic nuclei, to an attract... more Oscillations of mainly surface character (S = 0 modes) give rise, in atomic nuclei, to an attractive (induced) pairing interaction, while spin (S = 1) modes of mainly volume character generate a repulsive interaction, the net effect being an attraction which accounts for a sizeable fraction of the experimental pairing gap. Suppressing the particle-vibration coupling mediated by the proton degrees of freedom, i.e., mimicking neutron matter, the total surface plus spin-induced pairing interaction becomes repulsive.
The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Journal of Physics G: Nuclear and Particle Physics, 2005
The effective pairing interaction induced by the exchange of phonons between pairs of nucleons mo... more The effective pairing interaction induced by the exchange of phonons between pairs of nucleons moving in time-reversal states close to the Fermi energy in deformed nuclei modifies in a sizeable manner the superfluid properties of these systems, accounting for about half of the pairing gap.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2005
We develop a consistent formalism in order to explore the effects of density and spin fluctuation... more We develop a consistent formalism in order to explore the effects of density and spin fluctuations on the quasi-particle properties and on the pairing critical temperature of a trapped Fermi gas on the attractive side of a Feshbach resonance. We first analyze the quasi-particle properties of a gas due to interactions far from resonance (effective mass and lifetime, quasi-particle strength and effective interaction) for the two cases of a spherically symmetric harmonic trap and of a spherically symmetric infinite potential well. We then explore the effect of each of these quantities on T c and point out the important role played by the discrete level structure.
We calculate, for the first time, the state-dependent pairing gap of a finite nucleus (120 Sn) di... more We calculate, for the first time, the state-dependent pairing gap of a finite nucleus (120 Sn) diagonalizing the bare nucleon-nucleon potential (Argonne v14) in a Hartree-Fock basis (with effective k−mass m k ≈ 0.7 m), within the framework of the BCS approximation including scattering states up to 800 MeV above the Fermi energy to achieve convergence. The resulting gap accounts for about half of the experimental gap. We find that a consistent description of the low-energy nuclear spectrum requires, aside from the bare nucleon-nucleon interaction, not only the dressing of singleparticle motion through the coupling to the nuclear surface, to give the right density of levels close to the Fermi energy (and thus an effective mass m * ≈ m), but also the renormalization of collective vibrational modes through vertex and self-energy processes, processes which are also found to play an essential role in the pairing channel, leading to a long range, state dependent component of the pairing interaction. The combined effect of the bare nucleon-nucleon potential and of the induced pairing interaction arising from the exchange of low-lying surface vibrations between nucleons moving in time reversal states close to the Fermi energy accounts for the experimental gap.
The coupling of single-particle motion and of vibrations in 11 4 Be produces dressed neutrons whi... more The coupling of single-particle motion and of vibrations in 11 4 Be produces dressed neutrons which spend only a fraction of the time in pure single-particle states, and which weighting differently from the bare neutrons, lead to parity inversion. The interaction of the two least bound neutrons in the ground state of 12 4 Be mediated by the v14 Argonne nucleon-nucleon potential and by the exchange of the phonon cloud, give rise to a strongly correlated state, where the neutrons spend more than half of the time in (s 2 +d 2)-configurations, resulting in a breaking of the N = 8 shell closure.
The coupling of single-particle motion and of vibrations in 11 4 Be produces dressed neutrons whi... more The coupling of single-particle motion and of vibrations in 11 4 Be produces dressed neutrons which spend only a fraction of the time in pure single-particle states, and which weighting differently from the bare neutrons, lead to parity inversion. The interaction of the two least bound neutrons in the ground state of 12 4 Be mediated by the v14 Argonne nucleon-nucleon potential and by the exchange of the phonon cloud, give rise to a strongly correlated state, where the neutrons spend more than half of the time in (s 2 +d 2)-configurations, resulting in a breaking of the N = 8 shell closure.
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