Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1909.12141 · Physical Review A

In situ momentum-distribution measurement of a quantum degenerate Fermi gas using Raman spectroscopy

Constantine Shkedrov, Gal Ness, Yanay Florshaim, Yoav Sagi

Published Jan 10, 2020• 8 citations
arXivHTMLPDF

Abstract

The ability to directly measure the momentum distribution of quantum gases is both unique to these systems and pivotal in extracting many other important observables. Here we use Raman transitions to measure the momentum distribution of a weakly interacting Fermi gas in a harmonic trap. For narrow atomic dispersions, momentum and energy conservation imply a linear relation between the two-photon detuning and the atomic momentum. We detect the number of atoms transferred by the Raman beams using sensitive fluorescence detection in a magneto-optical trap. We apply this technique to a degenerate weakly interacting Fermi gas at different temperatures. The measured momentum distributions match theoretical curves over two decades, and the extracted temperatures are in very good agreement with the ones obtained from a conventional time-of-flight technique. The main advantages of our measurement scheme are that it can be spatially selective and directly probe a trapped gas, it can be completed in a relatively short time, and due to its high sensitivity, it can be used with very small clouds.

DOI
10.1103/physreva.101.013609

Related papers

Probing ultracold Fermi atoms with a single ion

Yu. B. Sherkunov, B. A. Muzykantskiǐ, N. d’Ambrumenil +1 more

We show that the recently proposed ionic microscope setup [Kollath et al., Phys. Rev. A 76, 063602 (2007)] could be adapted to measure the local single-particle energy distribution of a degenerate Fermi gas in situ with the resolution on the nanometer scale. We study an ion held in a Paul trap in an atomic Fermi gas and compute the two-photon Raman photo-association rate of the ion and an atom. We show that, as a function of the detunings between the frequencies of the two incident lasers and energies in the atom-ion system, the photoassociation rate directly measures the single-particle energy distribution in the Fermi gas around the ion. We describe an experiment to measure the photoassociation rate of a trapped ion and argue that, as the position of the ion can be scanned through the Fermi gas, this experiment directly probes the local energy and spin-state distribution of the Fermi gas.

arXiv:0802.3158•Physical Review A•Feb 4, 2009•24 citations

Spin-orbit coupling in Bose-Einstein condensate and degenerate Fermi gases

Pengjun Wang, Jing Zhang

We review our recent experimental realization and investigation of a spin-orbit (SO) coupled Bose-Einstein condensate (BEC) and quantum degenerate Fermi gas. By using two counter-propagating Raman lasers and controlling the different frequency of two Raman lasers to engineer the atom-light interaction, we first study the SO coupling in BEC. Then we study SO coupling in Fermi gas. We observe the spin dephasing in spin dynamics and momentum distribution asymmetry of the equilibrium state as hallmarks of SO coupling in a Fermi gas. To clearly reveal the property of SO coupling Fermi gas, we also study the momentum-resolved radio-frequency spectroscopy which characterizes the energy-momentum dispersion and spin composition of the quantum states. We observe the change of fermion surfaces in different helicity branches with different atomic density, which indicates that a Lifshitz transition of the Fermi surface topology change can be found by further cooling the system. At last, we study the momentum-resolved Raman spectroscopy of an ultracold Fermi gas.

Frontiers of Physics•Oct 1, 2014•10 citations

Gap and screening in Raman scattering of a Bose condensed gas

Patrick Navez, Kai Bongs

We propose different spectroscopic methods to explore the nature of the thermal excitations of a trapped Bose condensed gas: 1) a four photon process to probe the uniform region in the trap center: 2) a stimulated Raman process in order to analyze the influence of a momentum transfer in the resulting scattered atom momentum distribution. We apply these methods to address specifically the energy spectrum and the scattering amplitude of these excitations in a transition between two hyperfine levels of the gas atoms. In particular, we exemplify the potential offered by these proposed techniques by contrasting the spectrum expected from the non-conserving Bogoliubov approximation, valid for weak depletion, to the spectrum of the finite-temperature extensions like the conserving generalized random phase approximation (GRPA). Both predict the existence of the Bogoliubov collective excitations but the GRPA approximation distinguishes them from the single-atom excitations with a gapped and parabolic dispersion relation and accounts for the dynamical screening of any external perturbation applied to the gas. We present two feasible experiments, one concerns the observation of the gap associated to this second branch of excitations and the other deals with this screening effect.

arXiv:0903.1009•Europhysics Letters (EPL)•Dec 1, 2009•13 citations

Momentum-resolved Raman spectroscopy of bound molecules in ultracold Fermi gas

Zhengkun Fu, Pengjun Wang, Lianghui Huang +2 more

The binding energy of Feshbach molecules from a two-component Fermi gas of ${}^{40}$K atoms has been experimentally measured with the momentum-resolved Raman spectroscopy. Comparing with the radio-frequency spectroscopy, in the present experiment the signal of unpaired (free atoms) and the bound molecules can be directly observed and the binding energy can be simultaneously determined in a single running experiment. The energy-momentum dispersion spectra of the ultracold Fermi gas in the BEC side are also measured and reconstructed. The present experimental technology of the momentum-resolved Raman spectroscopy can be easily extended to perform spatially momentum-resolved Raman spectroscopy and to obtain the response spectra of a homogeneous system in the local density approximation.

arXiv:1208.4718•Physical Review A•Sep 7, 2012•9 citations

Thermometry of a deeply degenerate Fermi gas with a Bose-Einstein condensate

Rianne S. Lous, Isabella Fritsche, Michael Jag +2 more

We measure the temperature of a deeply degenerate Fermi gas, by using a weakly interacting sample of heavier bosonic atoms as a probe. This thermometry method relies on the thermalization between the two species and on the determination of the condensate fraction of the bosons. In our experimental implementation, a small sample of $^{41}\mathrm{K}$ atoms serves as the thermometer for a $^{6}\mathrm{Li}$ Fermi sea. We investigate the evaporative cooling of a $^{6}\mathrm{Li}$ spin mixture in a single-beam optical dipole trap and observe how the condensate fraction of the thermometry atoms depends on the final trap depth. From the condensate fraction, the temperature can be readily extracted. We show that the lowest temperature of 5.9(5)% of the Fermi temperature is obtained, when the decreasing trap depth closely approaches the Fermi energy. To understand the systematic effects that may influence the results, we carefully investigate the role of the number of bosons and the thermalization dynamics between the two species. Our thermometry approach provides a conceptually simple, accurate, and general way to measure the temperature of deeply degenerate Fermi gases. Since the method is independent of the specific interaction conditions within the Fermi gas, it applies to both weakly and strongly interacting Fermi gases.

arXiv:1702.02772•Physical Review A•May 23, 2017•39 citations

High-Sensitivity rf Spectroscopy of a Strongly Interacting Fermi Gas

Constantine Shkedrov, Yanay Florshaim, Gal Ness +2 more

rf spectroscopy is one of the most powerful probing techniques in the field of ultracold gases. We report on a novel rf spectroscopy scheme with which we can detect very weak signals of only a few atoms. Using this method, we extended the experimentally accessible photon-energies range by an order of magnitude compared to previous studies. We directly verify a universal property of fermions with short-range interactions which is a power-law scaling of the rf spectrum tail all the way up to the interaction scale. We also determine, with high precision, the trap average contact parameter for different interaction strength. Finally, we employ our technique to precisely measure the binding energy of Feshbach molecules in an extended range of magnetic fields. These data are used to extract a new calibration of the Feshbach resonance between the two lowest energy levels of ^{40}K.

arXiv:1803.01770•Physical Review Letters•Aug 30, 2018•26 citations
The ability to directly measure the momentum distribution of quantum gases is both unique to these systems and pivotal in extracting many other important observables. Here we use Raman transitions to measure the momentum distribution of a weakly interacting Fermi gas in a harmonic trap. For narrow atomic dispersions, momentum and energy conservation imply a linear relation between the two-photon detuning and the atomic momentum. We detect the number of atoms transferred by the Raman beams using sensitive fluorescence detection in a magneto-optical trap. We apply this technique to a degenerate weakly interacting Fermi gas at different temperatures. The measured momentum distributions match theoretical curves over two decades, and the extracted temperatures are in very good agreement with the ones obtained from a conventional time-of-flight technique. The main advantages of our measurement scheme are that it can be spatially selective and directly probe a trapped gas, it can be completed in a relatively short time, and due to its high sensitivity, it can be used with very small clouds.
We show that the recently proposed ionic microscope setup [Kollath et al., Phys. Rev. A 76, 063602 (2007)] could be adapted to measure the local single-particle energy distribution of a degenerate Fermi gas in situ with the resolution on the nanometer scale. We study an ion held in a Paul trap in an atomic Fermi gas and compute the two-photon Raman photo-association rate of the ion and an atom. We show that, as a function of the detunings between the frequencies of the two incident lasers and energies in the atom-ion system, the photoassociation rate directly measures the single-particle energy distribution in the Fermi gas around the ion. We describe an experiment to measure the photoassociation rate of a trapped ion and argue that, as the position of the ion can be scanned through the Fermi gas, this experiment directly probes the local energy and spin-state distribution of the Fermi gas.
We review our recent experimental realization and investigation of a spin-orbit (SO) coupled Bose-Einstein condensate (BEC) and quantum degenerate Fermi gas. By using two counter-propagating Raman lasers and controlling the different frequency of two Raman lasers to engineer the atom-light interaction, we first study the SO coupling in BEC. Then we study SO coupling in Fermi gas. We observe the spin dephasing in spin dynamics and momentum distribution asymmetry of the equilibrium state as hallmarks of SO coupling in a Fermi gas. To clearly reveal the property of SO coupling Fermi gas, we also study the momentum-resolved radio-frequency spectroscopy which characterizes the energy-momentum dispersion and spin composition of the quantum states. We observe the change of fermion surfaces in different helicity branches with different atomic density, which indicates that a Lifshitz transition of the Fermi surface topology change can be found by further cooling the system. At last, we study the momentum-resolved Raman spectroscopy of an ultracold Fermi gas.
We propose different spectroscopic methods to explore the nature of the thermal excitations of a trapped Bose condensed gas: 1) a four photon process to probe the uniform region in the trap center: 2) a stimulated Raman process in order to analyze the influence of a momentum transfer in the resulting scattered atom momentum distribution. We apply these methods to address specifically the energy spectrum and the scattering amplitude of these excitations in a transition between two hyperfine levels of the gas atoms. In particular, we exemplify the potential offered by these proposed techniques by contrasting the spectrum expected from the non-conserving Bogoliubov approximation, valid for weak depletion, to the spectrum of the finite-temperature extensions like the conserving generalized random phase approximation (GRPA). Both predict the existence of the Bogoliubov collective excitations but the GRPA approximation distinguishes them from the single-atom excitations with a gapped and parabolic dispersion relation and accounts for the dynamical screening of any external perturbation applied to the gas. We present two feasible experiments, one concerns the observation of the gap associated to this second branch of excitations and the other deals with this screening effect.
The binding energy of Feshbach molecules from a two-component Fermi gas of 40{}^{40}40K atoms has been experimentally measured with the momentum-resolved Raman spectroscopy. Comparing with the radio-frequency spectroscopy, in the present experiment the signal of unpaired (free atoms) and the bound molecules can be directly observed and the binding energy can be simultaneously determined in a single running experiment. The energy-momentum dispersion spectra of the ultracold Fermi gas in the BEC side are also measured and reconstructed. The present experimental technology of the momentum-resolved Raman spectroscopy can be easily extended to perform spatially momentum-resolved Raman spectroscopy and to obtain the response spectra of a homogeneous system in the local density approximation.
We measure the temperature of a deeply degenerate Fermi gas, by using a weakly interacting sample of heavier bosonic atoms as a probe. This thermometry method relies on the thermalization between the two species and on the determination of the condensate fraction of the bosons. In our experimental implementation, a small sample of 41K^{41}\mathrm{K}41K atoms serves as the thermometer for a 6Li^{6}\mathrm{Li}6Li Fermi sea. We investigate the evaporative cooling of a 6Li^{6}\mathrm{Li}6Li spin mixture in a single-beam optical dipole trap and observe how the condensate fraction of the thermometry atoms depends on the final trap depth. From the condensate fraction, the temperature can be readily extracted. We show that the lowest temperature of 5.9(5)% of the Fermi temperature is obtained, when the decreasing trap depth closely approaches the Fermi energy. To understand the systematic effects that may influence the results, we carefully investigate the role of the number of bosons and the thermalization dynamics between the two species. Our thermometry approach provides a conceptually simple, accurate, and general way to measure the temperature of deeply degenerate Fermi gases. Since the method is independent of the specific interaction conditions within the Fermi gas, it applies to both weakly and strongly interacting Fermi gases.
rf spectroscopy is one of the most powerful probing techniques in the field of ultracold gases. We report on a novel rf spectroscopy scheme with which we can detect very weak signals of only a few atoms. Using this method, we extended the experimentally accessible photon-energies range by an order of magnitude compared to previous studies. We directly verify a universal property of fermions with short-range interactions which is a power-law scaling of the rf spectrum tail all the way up to the interaction scale. We also determine, with high precision, the trap average contact parameter for different interaction strength. Finally, we employ our technique to precisely measure the binding energy of Feshbach molecules in an extended range of magnetic fields. These data are used to extract a new calibration of the Feshbach resonance between the two lowest energy levels of ^{40}K.