Gabriele Ferrari - Academia.edu (original) (raw)

Uploads

Papers by Gabriele Ferrari

Science (New York, N.Y.), Jan 9, 2015

Optics Express, 2007

Diode lasers enable one to continuously cover the 730 to 1100 nm range as well as the 370 to 550 ... more Diode lasers enable one to continuously cover the 730 to 1100 nm range as well as the 370 to 550 nm range by frequency doubling, but a large part of the electro-magnetic spectrum spanning from green to red remains accessible only through expensive and unpractical optically pumped dye lasers. Here we devise a method to multiply the frequency of optical waves by a factor 3/2 with a conversion that is phase-coherent and highly efficient. Together with harmonic generation, it will enable one to cover the visible spectrum with semiconductor lasers, opening new avenues in important fields such as laser spectroscopy and optical metrology.

Optics letters, 1999

The output of two grating-stabilized external-cavity diode lasers was injected into a semiconduct... more The output of two grating-stabilized external-cavity diode lasers was injected into a semiconductor tapered amplif ier in a master oscillator-power amplif ier (MOPA) configuration. At a wavelength of 671 nm this configuration produced 210 mW of power in a diffraction-limited mode with two frequency components of narrow linewidth. The frequency difference delta was varied from 20 MHz to 12 GHz, while the power ratio of the two components was freely adjustable. For delta < 2 GHz additional frequency sidebands appear in the output of the MOPA. This configuration is a f lexible and simple high-power cw laser source for light with multiple narrow-linewidth frequency components.

Physical Review Letters, 1998

We have measured the rate of inelastic collisions in a cloud of doubly polarized ground-state ces... more We have measured the rate of inelastic collisions in a cloud of doubly polarized ground-state cesium atoms (F m F 4) confined in a magnetic trap for temperatures T between 8 and 70 mK. We find a two-body rate coefficient varying as T 20.63 . At 8mK it reaches 4 3 10 212 cm 3 s 21 which is 3 orders of magnitude larger than predicted, ruling out a Bose-Einstein condensation of Cs in this internal state.

Physical Review A, 2009

We report about the realization of a quantum device for force sensing at micrometric scale. We tr... more We report about the realization of a quantum device for force sensing at micrometric scale. We trap an ultracold 88 Sr atomic cloud with a 1-D optical lattice, then we place the atomic sample close to a test surface using the same optical lattice as an elevator. We demonstrate precise positioning of the sample at the µm scale. By observing the Bloch oscillations of atoms into the 1-D optical standing wave, we are able to measure the total force on the atoms along the lattice axis, with a spatial resolution of few microns. We also demonstrate a technique for transverse displacement of the atoms, allowing to perform measurements near either transparent or reflective test surfaces. In order to reduce the minimum distance from the surface, we compress the longitudinal size of the atomic sample by means of an optical tweezer. Such system is suited for studies of atom-surface interaction at short distance, such as measurement of Casimir force and search for possible non-Newtonian gravity effects.

Physical Review A, 1999

We confine 4 × 10 8 fermionic 6 Li atoms simultaneously with 9 × 10 9 bosonic 7 Li atoms in a mag... more We confine 4 × 10 8 fermionic 6 Li atoms simultaneously with 9 × 10 9 bosonic 7 Li atoms in a magneto-optical trap based on an all-semiconductor laser system. We optimize the two-isotope sample for sympathetic evaporative cooling. This is an essential step towards the production of a quantum-degenerate gas of fermionic lithium atoms.

The European Physical Journal D, 2001

We describe the excitation spectrum of a two-component neutral Fermi gas in the superfluid phase ... more We describe the excitation spectrum of a two-component neutral Fermi gas in the superfluid phase at finite temperature by deriving a suitable Random-Phase approximation with the technique of functional derivatives. The obtained spectrum for the homogeneous gas at small wavevectors contains the Bogoliubov-Anderson phonon and is essentially different from the spectrum predicted by the static Bogoliubov theory, which instead shows an unphysically large response. We adapt the results for the homogeneous system to obtain the dynamic structure factor of a harmonically confined superfluid and we identify in the spectrum a unique feature of the superfluid phase.

Review of Scientific Instruments, 2013

We present a compact source of cold sodium atoms suitable for the production of quantum degenerat... more We present a compact source of cold sodium atoms suitable for the production of quantum degenerate gases and versatile for a multi-species experiment. The magnetic field produced by permanent magnets allows to simultaneously realize a Zeeman slower and a two-dimensional magneto-optical trap (MOT) within an order of magnitude smaller length than standard sodium sources. We achieve an atomic flux exceeding 4 × 10(9) atoms/s loaded in a MOT, with a most probable longitudinal velocity of 20 m/s, and a brightness larger than 2.5 × 10(12) atoms/s/sr. This atomic source allows us to produce pure Bose-Einstein condensates with more than 10(7) atoms and a background pressure limited lifetime of 5 min.

Physical Review Letters, 2014

We observe solitonic vortices in an atomic Bose-Einstein condensate after free expansion. Clear s... more We observe solitonic vortices in an atomic Bose-Einstein condensate after free expansion. Clear signatures of the nature of such defects are the twisted planar density depletion around the vortex line, observed in absorption images, and the double dislocation in the interference pattern obtained through homodyne techniques. Both methods allow us to determine the sign of the quantized circulation. Experimental observations agree with numerical simulations. These solitonic vortices are the decay product of grey solitons spontaneously created after a rapid quench across the BEC transition in a cigar-shaped harmonic trap and are shown to have a very long lifetime. PACS numbers: 03.75.Lm, 67.85.De

Physics Procedia, 2011

Considerable efforts have been made and are still being made to verify the validity of the princi... more Considerable efforts have been made and are still being made to verify the validity of the principle of the equivalence of gravitational and inertial mass, one of the cornerstones of the classical theory of general relativity. Specific attempts at quantummechanical formulations of gravity allow for non-Newtonian contributions, which might lead to a difference in the gravitational force on matter and antimatter. While it is widely expected that the gravitational interaction is independent of the composition of bodies, this has only been tested for matter systems, but never yet for antimatter systems. By combining techniques from different fields, and relying on recent developments in the production of Positronium and ongoing work to laser-excite Positronium to Rydberg states, such a test with neutral antimatter has become feasible. The primary goal of the AEGIS experiment being built at the Antiproton Decelerator at CERN is to carry out the first direct measurement of the Earth`s gravitational acceleration on antihydrogen by means of a classical Moiré deflectometer.

Science, 2002

We report the production of matter-wave solitons in an ultra-cold 7 Li gas. The effective interac... more We report the production of matter-wave solitons in an ultra-cold 7 Li gas. The effective interaction between atoms in a Bose-Einstein condensate is tuned with a Feshbach resonance from repulsive to attractive before release in a one-dimensional optical waveguide. Propagation of the soliton without dispersion over a macroscopic distance of 1.1 mm is observed. A simple theoretical model explains the stability region of the soliton. These matter-wave solitons open fascinating possibilities for future applications in coherent atom optics, atom interferometry and atom transport.

Review of Scientific Instruments, 2013

We present a compact source of cold sodium atoms suitable for the production of quantum degenerat... more We present a compact source of cold sodium atoms suitable for the production of quantum degenerate gases and versatile for a multi-species experiment. The magnetic field produced by permanent magnets allows to simultaneously realize a Zeeman slower and a two-dimensional magneto-optical trap (MOT) within an order of magnitude smaller length than standard sodium sources. We achieve an atomic flux exceeding 4 × 10(9) atoms/s loaded in a MOT, with a most probable longitudinal velocity of 20 m/s, and a brightness larger than 2.5 × 10(12) atoms/s/sr. This atomic source allows us to produce pure Bose-Einstein condensates with more than 10(7) atoms and a background pressure limited lifetime of 5 min.

Physical Review Letters, 2008

Atomic wavepackets loaded into a phase-modulated vertical optical-lattice potential exhibit a coh... more Atomic wavepackets loaded into a phase-modulated vertical optical-lattice potential exhibit a coherent delocalization dynamics arising from intraband transitions among Wannier-Stark levels. Wannier-Stark intraband transitions are here observed by monitoring the in situ wavepacket extent. By varying the modulation frequency, we find resonances at integer multiples of the Bloch frequency. The resonances show a Fourier-limited width for interrogation times up to 2 seconds. This can also be used to determine the gravity acceleration with ppm resolution.

Physical Review Letters, 2006

We report on the observation of Bloch oscillations on the unprecedented time scale of several sec... more We report on the observation of Bloch oscillations on the unprecedented time scale of several seconds. The experiment is carried out with ultra-cold bosonic strontium-88 loaded into a vertical optical standing wave. The negligible atom-atom elastic cross section and the absence of spin makes 88 Sr an almost ideal Bose gas insensitive to typical mechanisms of decoherence due to thermalization and to external stray fields. The small size enables precision measurements of forces at micrometer scale. This is a challenge in physics for studies of surfaces, Casimir effects, and searches for deviations from Newtonian gravity predicted by theories beyond the standard model.

Physical Review Letters, 2002

We determine the inter-species s-wave triplet scattering length a3 for all K-Rb isotopic mixtures... more We determine the inter-species s-wave triplet scattering length a3 for all K-Rb isotopic mixtures by measuring the elastic cross-section for collisions between 41 K and 87 Rb in different temperature regimes. The positive value a3 = +163 +57 −12 a0 ensures the stability of binary 41 K-87 Rb Bose-Einstein condensates. For the fermion-boson mixture 40 K-87 Rb we obtain a large and negative scattering length which implies an efficient sympathetic cooling of the fermionic species down to the degenerate regime.

Physical Review Letters, 2003

We report the direct frequency measurement of the visible 5s 2 1 S0-5s 5p 3 P1 intercombination l... more We report the direct frequency measurement of the visible 5s 2 1 S0-5s 5p 3 P1 intercombination line of strontium that is considered a possible candidate for a future optical frequency standard. The frequency of a cavity-stabilized laser is locked to the saturated fluorescence in a thermal Sr atomic beam and is measured with an optical-frequency comb-generator referenced to the SI second through a GPS signal. The 88 Sr transition is measured to be at 434 829 121 311 (10) kHz. We measure also the 88 Sr-86 Sr isotope shift to be 163 817.4 (0.2) kHz.

Physical Review Letters, 2001

We report the observation of co-existing Bose-Einstein condensate and Fermi gas in a magnetic tra... more We report the observation of co-existing Bose-Einstein condensate and Fermi gas in a magnetic trap. With a very small fraction of thermal atoms, the 7 Li condensate is quasi-pure and in thermal contact with a 6 Li Fermi gas. The lowest common temperature is 0.28 µK ≃ 0.2(1) TC = 0.2(1) TF where TC is the BEC critical temperature and TF the Fermi temperature. Behaving as an ideal gas in the radial trap dimension, the condensate is one-dimensional.

Science (New York, N.Y.), Jan 9, 2015

Optics Express, 2007

Diode lasers enable one to continuously cover the 730 to 1100 nm range as well as the 370 to 550 ... more Diode lasers enable one to continuously cover the 730 to 1100 nm range as well as the 370 to 550 nm range by frequency doubling, but a large part of the electro-magnetic spectrum spanning from green to red remains accessible only through expensive and unpractical optically pumped dye lasers. Here we devise a method to multiply the frequency of optical waves by a factor 3/2 with a conversion that is phase-coherent and highly efficient. Together with harmonic generation, it will enable one to cover the visible spectrum with semiconductor lasers, opening new avenues in important fields such as laser spectroscopy and optical metrology.

Optics letters, 1999

The output of two grating-stabilized external-cavity diode lasers was injected into a semiconduct... more The output of two grating-stabilized external-cavity diode lasers was injected into a semiconductor tapered amplif ier in a master oscillator-power amplif ier (MOPA) configuration. At a wavelength of 671 nm this configuration produced 210 mW of power in a diffraction-limited mode with two frequency components of narrow linewidth. The frequency difference delta was varied from 20 MHz to 12 GHz, while the power ratio of the two components was freely adjustable. For delta < 2 GHz additional frequency sidebands appear in the output of the MOPA. This configuration is a f lexible and simple high-power cw laser source for light with multiple narrow-linewidth frequency components.

Physical Review Letters, 1998

We have measured the rate of inelastic collisions in a cloud of doubly polarized ground-state ces... more We have measured the rate of inelastic collisions in a cloud of doubly polarized ground-state cesium atoms (F m F 4) confined in a magnetic trap for temperatures T between 8 and 70 mK. We find a two-body rate coefficient varying as T 20.63 . At 8mK it reaches 4 3 10 212 cm 3 s 21 which is 3 orders of magnitude larger than predicted, ruling out a Bose-Einstein condensation of Cs in this internal state.

Physical Review A, 2009

We report about the realization of a quantum device for force sensing at micrometric scale. We tr... more We report about the realization of a quantum device for force sensing at micrometric scale. We trap an ultracold 88 Sr atomic cloud with a 1-D optical lattice, then we place the atomic sample close to a test surface using the same optical lattice as an elevator. We demonstrate precise positioning of the sample at the µm scale. By observing the Bloch oscillations of atoms into the 1-D optical standing wave, we are able to measure the total force on the atoms along the lattice axis, with a spatial resolution of few microns. We also demonstrate a technique for transverse displacement of the atoms, allowing to perform measurements near either transparent or reflective test surfaces. In order to reduce the minimum distance from the surface, we compress the longitudinal size of the atomic sample by means of an optical tweezer. Such system is suited for studies of atom-surface interaction at short distance, such as measurement of Casimir force and search for possible non-Newtonian gravity effects.

Physical Review A, 1999

We confine 4 × 10 8 fermionic 6 Li atoms simultaneously with 9 × 10 9 bosonic 7 Li atoms in a mag... more We confine 4 × 10 8 fermionic 6 Li atoms simultaneously with 9 × 10 9 bosonic 7 Li atoms in a magneto-optical trap based on an all-semiconductor laser system. We optimize the two-isotope sample for sympathetic evaporative cooling. This is an essential step towards the production of a quantum-degenerate gas of fermionic lithium atoms.

The European Physical Journal D, 2001

We describe the excitation spectrum of a two-component neutral Fermi gas in the superfluid phase ... more We describe the excitation spectrum of a two-component neutral Fermi gas in the superfluid phase at finite temperature by deriving a suitable Random-Phase approximation with the technique of functional derivatives. The obtained spectrum for the homogeneous gas at small wavevectors contains the Bogoliubov-Anderson phonon and is essentially different from the spectrum predicted by the static Bogoliubov theory, which instead shows an unphysically large response. We adapt the results for the homogeneous system to obtain the dynamic structure factor of a harmonically confined superfluid and we identify in the spectrum a unique feature of the superfluid phase.

Review of Scientific Instruments, 2013

We present a compact source of cold sodium atoms suitable for the production of quantum degenerat... more We present a compact source of cold sodium atoms suitable for the production of quantum degenerate gases and versatile for a multi-species experiment. The magnetic field produced by permanent magnets allows to simultaneously realize a Zeeman slower and a two-dimensional magneto-optical trap (MOT) within an order of magnitude smaller length than standard sodium sources. We achieve an atomic flux exceeding 4 × 10(9) atoms/s loaded in a MOT, with a most probable longitudinal velocity of 20 m/s, and a brightness larger than 2.5 × 10(12) atoms/s/sr. This atomic source allows us to produce pure Bose-Einstein condensates with more than 10(7) atoms and a background pressure limited lifetime of 5 min.

Physical Review Letters, 2014

We observe solitonic vortices in an atomic Bose-Einstein condensate after free expansion. Clear s... more We observe solitonic vortices in an atomic Bose-Einstein condensate after free expansion. Clear signatures of the nature of such defects are the twisted planar density depletion around the vortex line, observed in absorption images, and the double dislocation in the interference pattern obtained through homodyne techniques. Both methods allow us to determine the sign of the quantized circulation. Experimental observations agree with numerical simulations. These solitonic vortices are the decay product of grey solitons spontaneously created after a rapid quench across the BEC transition in a cigar-shaped harmonic trap and are shown to have a very long lifetime. PACS numbers: 03.75.Lm, 67.85.De

Physics Procedia, 2011

Considerable efforts have been made and are still being made to verify the validity of the princi... more Considerable efforts have been made and are still being made to verify the validity of the principle of the equivalence of gravitational and inertial mass, one of the cornerstones of the classical theory of general relativity. Specific attempts at quantummechanical formulations of gravity allow for non-Newtonian contributions, which might lead to a difference in the gravitational force on matter and antimatter. While it is widely expected that the gravitational interaction is independent of the composition of bodies, this has only been tested for matter systems, but never yet for antimatter systems. By combining techniques from different fields, and relying on recent developments in the production of Positronium and ongoing work to laser-excite Positronium to Rydberg states, such a test with neutral antimatter has become feasible. The primary goal of the AEGIS experiment being built at the Antiproton Decelerator at CERN is to carry out the first direct measurement of the Earth`s gravitational acceleration on antihydrogen by means of a classical Moiré deflectometer.

Science, 2002

We report the production of matter-wave solitons in an ultra-cold 7 Li gas. The effective interac... more We report the production of matter-wave solitons in an ultra-cold 7 Li gas. The effective interaction between atoms in a Bose-Einstein condensate is tuned with a Feshbach resonance from repulsive to attractive before release in a one-dimensional optical waveguide. Propagation of the soliton without dispersion over a macroscopic distance of 1.1 mm is observed. A simple theoretical model explains the stability region of the soliton. These matter-wave solitons open fascinating possibilities for future applications in coherent atom optics, atom interferometry and atom transport.

Review of Scientific Instruments, 2013

We present a compact source of cold sodium atoms suitable for the production of quantum degenerat... more We present a compact source of cold sodium atoms suitable for the production of quantum degenerate gases and versatile for a multi-species experiment. The magnetic field produced by permanent magnets allows to simultaneously realize a Zeeman slower and a two-dimensional magneto-optical trap (MOT) within an order of magnitude smaller length than standard sodium sources. We achieve an atomic flux exceeding 4 × 10(9) atoms/s loaded in a MOT, with a most probable longitudinal velocity of 20 m/s, and a brightness larger than 2.5 × 10(12) atoms/s/sr. This atomic source allows us to produce pure Bose-Einstein condensates with more than 10(7) atoms and a background pressure limited lifetime of 5 min.

Physical Review Letters, 2008

Atomic wavepackets loaded into a phase-modulated vertical optical-lattice potential exhibit a coh... more Atomic wavepackets loaded into a phase-modulated vertical optical-lattice potential exhibit a coherent delocalization dynamics arising from intraband transitions among Wannier-Stark levels. Wannier-Stark intraband transitions are here observed by monitoring the in situ wavepacket extent. By varying the modulation frequency, we find resonances at integer multiples of the Bloch frequency. The resonances show a Fourier-limited width for interrogation times up to 2 seconds. This can also be used to determine the gravity acceleration with ppm resolution.

Physical Review Letters, 2006

We report on the observation of Bloch oscillations on the unprecedented time scale of several sec... more We report on the observation of Bloch oscillations on the unprecedented time scale of several seconds. The experiment is carried out with ultra-cold bosonic strontium-88 loaded into a vertical optical standing wave. The negligible atom-atom elastic cross section and the absence of spin makes 88 Sr an almost ideal Bose gas insensitive to typical mechanisms of decoherence due to thermalization and to external stray fields. The small size enables precision measurements of forces at micrometer scale. This is a challenge in physics for studies of surfaces, Casimir effects, and searches for deviations from Newtonian gravity predicted by theories beyond the standard model.

Physical Review Letters, 2002

We determine the inter-species s-wave triplet scattering length a3 for all K-Rb isotopic mixtures... more We determine the inter-species s-wave triplet scattering length a3 for all K-Rb isotopic mixtures by measuring the elastic cross-section for collisions between 41 K and 87 Rb in different temperature regimes. The positive value a3 = +163 +57 −12 a0 ensures the stability of binary 41 K-87 Rb Bose-Einstein condensates. For the fermion-boson mixture 40 K-87 Rb we obtain a large and negative scattering length which implies an efficient sympathetic cooling of the fermionic species down to the degenerate regime.

Physical Review Letters, 2003

We report the direct frequency measurement of the visible 5s 2 1 S0-5s 5p 3 P1 intercombination l... more We report the direct frequency measurement of the visible 5s 2 1 S0-5s 5p 3 P1 intercombination line of strontium that is considered a possible candidate for a future optical frequency standard. The frequency of a cavity-stabilized laser is locked to the saturated fluorescence in a thermal Sr atomic beam and is measured with an optical-frequency comb-generator referenced to the SI second through a GPS signal. The 88 Sr transition is measured to be at 434 829 121 311 (10) kHz. We measure also the 88 Sr-86 Sr isotope shift to be 163 817.4 (0.2) kHz.

Physical Review Letters, 2001

We report the observation of co-existing Bose-Einstein condensate and Fermi gas in a magnetic tra... more We report the observation of co-existing Bose-Einstein condensate and Fermi gas in a magnetic trap. With a very small fraction of thermal atoms, the 7 Li condensate is quasi-pure and in thermal contact with a 6 Li Fermi gas. The lowest common temperature is 0.28 µK ≃ 0.2(1) TC = 0.2(1) TF where TC is the BEC critical temperature and TF the Fermi temperature. Behaving as an ideal gas in the radial trap dimension, the condensate is one-dimensional.