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Papers by Bess Fang
Physical Review Letters, 2016
Analyzing the noise in the momentum profiles of single realizations of one-dimensional Bose gases... more Analyzing the noise in the momentum profiles of single realizations of one-dimensional Bose gases, we present the experimental measurement of the full momentum-space density correlations δnpδn p , which are related to the two-body momentum correlation function. Our data span the weakly interacting region of the phase diagram, going from the the ideal Bose gas regime to the quasicondensate regime. We show experimentally that the bunching phenomenon, which manifests itself as super-Poissonian local fluctuations in momentum space, is present in all regimes. The quasicondensate regime is however characterized by the presence of negative correlations between different momenta, in contrast to Bogolyubov theory for Bose condensates, predicting positive correlations between opposite momenta. Our data are in good agreement with ab-initio calculations.
We measure the position-and momentum-space breathing dynamics of trapped one-dimensional Bose gas... more We measure the position-and momentum-space breathing dynamics of trapped one-dimensional Bose gases at finite temperature. The profile in real space reveals sinusoidal width oscillations whose frequency varies continuously through the quasicondensate to ideal Bose gas crossover. A comparison with theoretical models taking temperature into account is provided. In momentum space, we report the first observation of a frequency doubling in the quasicondensate regime, corresponding to a selfreflection mechanism due to the repulsive interactions. Its disappearance through the crossover is mapped out experimentally, giving insights to the dynamics of the breathing evolution.
The European Physical Journal D, 2015
We describe an experimental apparatus capable of achieving a high loading rate of strontium atoms... more We describe an experimental apparatus capable of achieving a high loading rate of strontium atoms in a magneto-optical trap operating in a high vacuum environment. A key innovation of this setup is a two dimensional magneto-optical trap deflector located after a Zeeman slower. We find a loading rate of 6 × 10 9 s −1 whereas the lifetime of the magnetically trapped atoms in the 3 P2 state is 54 s.
Physical Review Letters, 2014
Physical Review A, 2009
We consider a strongly interacting one-dimensional (1D) Bose-Fermi mixture confined in a harmonic... more We consider a strongly interacting one-dimensional (1D) Bose-Fermi mixture confined in a harmonic trap. It consists of a Tonks-Girardeau (TG) gas (1D Bose gas with repulsive hard-core interactions) and of a non-interacting Fermi gas (1D spin-aligned Fermi gas), both species interacting through hard-core repulsive interactions. Using a generalized Bose-Fermi mapping, we determine the one-body density matrices, exact particle density profiles, momentum distributions and behaviour of the mixture under 1D expansion when opening the trap. In real space, bosons and fermions do not display any phase separation: the respective density profiles extend over the same region and they both present a number of peaks equal to the total number of particles in the trap. In momentum space the bosonic component has the typical narrow TG profile, while the fermionic component shows a broad distribution with fermionic oscillations at small momenta. Due to the large bosonfermion repulsive interactions, both the bosonic and the fermionic momentum distributions decay as Cp −4 at large momenta, like in the case of a pure bosonic TG gas. The coefficient C is related to the two-body density matrix and to the bosonic concentration in the mixture. When opening the trap, both momentum distributions "fermionize" under expansion and turn into that of a Fermi gas with a particle number equal to the total number of particles in the mixture. PACS numbers: 05.30.-d,67.85.-d,67.85.Pq
Physical Review A, 2011
We present the exact solution for the many-body wavefunction of a one-dimensional mixture of boso... more We present the exact solution for the many-body wavefunction of a one-dimensional mixture of bosons and spin-polarized fermions with equal masses and infinitely strong repulsive interactions under external confinement. Such a model displays a large degeneracy of the ground state. Using a generalized Bose-Fermi mapping we find the solution for the whole set of ground-state wavefunctions of the degenerate manifold and we characterize them according to group-symmetry considerations. We find that the density profile and the momentum distribution depends on the symmetry of the solution. By combining the wavefunctions of the degenerate manifold with suitable symmetry and guided by the strong-coupling form of the Bethe-Ansatz solution for the homogeneous system we propose an analytic expression for the many-body wavefunction of the inhomogeneous system which well describes the ground state at finite, large and equal interactions strengths, as validated by numerical simulations.
Physical Review Letters, 2016
Analyzing the noise in the momentum profiles of single realizations of one-dimensional Bose gases... more Analyzing the noise in the momentum profiles of single realizations of one-dimensional Bose gases, we present the experimental measurement of the full momentum-space density correlations δnpδn p , which are related to the two-body momentum correlation function. Our data span the weakly interacting region of the phase diagram, going from the the ideal Bose gas regime to the quasicondensate regime. We show experimentally that the bunching phenomenon, which manifests itself as super-Poissonian local fluctuations in momentum space, is present in all regimes. The quasicondensate regime is however characterized by the presence of negative correlations between different momenta, in contrast to Bogolyubov theory for Bose condensates, predicting positive correlations between opposite momenta. Our data are in good agreement with ab-initio calculations.
We measure the position-and momentum-space breathing dynamics of trapped one-dimensional Bose gas... more We measure the position-and momentum-space breathing dynamics of trapped one-dimensional Bose gases at finite temperature. The profile in real space reveals sinusoidal width oscillations whose frequency varies continuously through the quasicondensate to ideal Bose gas crossover. A comparison with theoretical models taking temperature into account is provided. In momentum space, we report the first observation of a frequency doubling in the quasicondensate regime, corresponding to a selfreflection mechanism due to the repulsive interactions. Its disappearance through the crossover is mapped out experimentally, giving insights to the dynamics of the breathing evolution.
The European Physical Journal D, 2015
We describe an experimental apparatus capable of achieving a high loading rate of strontium atoms... more We describe an experimental apparatus capable of achieving a high loading rate of strontium atoms in a magneto-optical trap operating in a high vacuum environment. A key innovation of this setup is a two dimensional magneto-optical trap deflector located after a Zeeman slower. We find a loading rate of 6 × 10 9 s −1 whereas the lifetime of the magnetically trapped atoms in the 3 P2 state is 54 s.
Physical Review Letters, 2014
Physical Review A, 2009
We consider a strongly interacting one-dimensional (1D) Bose-Fermi mixture confined in a harmonic... more We consider a strongly interacting one-dimensional (1D) Bose-Fermi mixture confined in a harmonic trap. It consists of a Tonks-Girardeau (TG) gas (1D Bose gas with repulsive hard-core interactions) and of a non-interacting Fermi gas (1D spin-aligned Fermi gas), both species interacting through hard-core repulsive interactions. Using a generalized Bose-Fermi mapping, we determine the one-body density matrices, exact particle density profiles, momentum distributions and behaviour of the mixture under 1D expansion when opening the trap. In real space, bosons and fermions do not display any phase separation: the respective density profiles extend over the same region and they both present a number of peaks equal to the total number of particles in the trap. In momentum space the bosonic component has the typical narrow TG profile, while the fermionic component shows a broad distribution with fermionic oscillations at small momenta. Due to the large bosonfermion repulsive interactions, both the bosonic and the fermionic momentum distributions decay as Cp −4 at large momenta, like in the case of a pure bosonic TG gas. The coefficient C is related to the two-body density matrix and to the bosonic concentration in the mixture. When opening the trap, both momentum distributions "fermionize" under expansion and turn into that of a Fermi gas with a particle number equal to the total number of particles in the mixture. PACS numbers: 05.30.-d,67.85.-d,67.85.Pq
Physical Review A, 2011
We present the exact solution for the many-body wavefunction of a one-dimensional mixture of boso... more We present the exact solution for the many-body wavefunction of a one-dimensional mixture of bosons and spin-polarized fermions with equal masses and infinitely strong repulsive interactions under external confinement. Such a model displays a large degeneracy of the ground state. Using a generalized Bose-Fermi mapping we find the solution for the whole set of ground-state wavefunctions of the degenerate manifold and we characterize them according to group-symmetry considerations. We find that the density profile and the momentum distribution depends on the symmetry of the solution. By combining the wavefunctions of the degenerate manifold with suitable symmetry and guided by the strong-coupling form of the Bethe-Ansatz solution for the homogeneous system we propose an analytic expression for the many-body wavefunction of the inhomogeneous system which well describes the ground state at finite, large and equal interactions strengths, as validated by numerical simulations.