Compressibility of an ultracold Fermi gas with repulsive interactions

Lee, Ye-Ryoung; Heo, Myoung-Sun; Choi, Jaehoon; Wang, Tout T.; Christensen, Caleb A.; Rvachov, Timur M.; Ketterle, Wolfgang

doi:10.1103/physreva.85.063615

Cited by 49 publications

(38 citation statements)

References 42 publications

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“…However, the experimental measurement of the compressibility is more difficult than the density profiles. Nevertheless, progress in measuring the compressibility of an ultracold Fermi gas has recently been made [25].…”

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confidence: 99%

Quantum criticality of spin-1 bosons in a one-dimensional harmonic trap

et al. 2012

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We investigate universal thermodynamics and quantum criticality of spin-1 bosons with strongly repulsive density-density and antiferromagnetic spin-exchange interactions in a one-dimensional harmonic trap. From the equation of state, we find that a partially-polarized core is surrounded by two wings composed of either spin-singlet pairs or a fully spin-aligned Tonks-Girardeau gas depending on the polarization. We describe how the scaling behaviour of density profiles can reveal the universal nature of quantum criticality and map out the quantum phase diagram. We further show that at quantum criticality the dynamical critical exponent z = 2 and correlation length exponent ν = 1/2. This reveals a subtle resemblance to the physics of the spin-1/2 attractive Fermi gas.PACS numbers: 03.75. Ss, 03.75.Hh, 02.30.Ik, 05.30.Fk Alkali bosons with hyperfine spins in an optical trap provide exciting opportunities to simulate a variety of macroscopic quantum phenomena. In the spinor gas, the spin-dipolar collisions significantly change the spin states producing rich Zeeman effects. In particular, spinor Bose gases with density-density interaction and antiferromagnetic spin-exchange interaction [1, 2] exhibit various phases of strongly correlated quantum liquids and are thus particularly valuable to study quantum magnetism and criticality. The experimental study of quantum criticality and universal scaling behaviour has recently been initiated in low-dimensional cold atomic matter [3,4]. These advances build on theoretical schemes for mapping out quantum criticality in cold atom systems [5][6][7]. In this framework, exactly solved models of cold atoms, exhibiting quantum phase transitions, provide a rigorous way to investigate quantum criticality [8].One-dimensional (1D) spinor Bose gases with shortrange delta-function interaction and antiferromagnetic spin-exchange interaction are particularly interesting due to the existence of various phases of quantum liquids associated with exact Bethe ansatz solutions [9][10][11][12]. The antiferromagnetic interaction leads to an effective attraction in the spin-singlet channel that gives rise to a quasicondensate of singlet bosonic pairs when the external field is less than a lower critical field at zero temperature. In this phase, the low energy physics can be characterized by a spin-charge separation theory of the U (1) Tomonaga-Luttinger liquid (TLL) describing the charge sector and a O(3) non-linear sigma model describing the spin sector [10]. However, if the external field exceeds an upper critical field, we have a solely ferromagnetic quasi-condensate of unpaired bosons with spins aligned along the external field. For an intermediate magnetic field, the spin-singlet pairs and spin-aligned bosons form a two-component TLL with a magnetization, see Fig. 1.Quantum critical phenomena in the spin-1 Bose gas associated with phase transitions at zero temperature can 2 ) = 0.05. The lines R1 and R2 denote the phase boundaries of vanishing density of singlet-pairs and vanishing density o...

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Quantum criticality of spin-1 bosons in a one-dimensional harmonic trap

et al. 2012

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“…By contrast, in the "upper branch" of a Feshbach resonance, the system's wavefunction consists of scattering states such that we can neglect these bound pairs and their corresponding binding energies [23]. Motivated by a series of recent experiments conducted in this (metastable) upper branch state [24][25][26], static and dynamic properties of Fermi gases have been theoretically studied [27][28][29][30][31]. To further explore the thermodynamics of the upper branch, we set δ 0 = −π/2 (i.e.…”

Section: A Self-consistent Theory For Universal Thermodynamicsmentioning

confidence: 99%

“…We note that when η = 1.0, the chemical potentials are equal and Eq. (26) reduces to its population balanced form as depicted in FIG. 4.…”

Section: Population Imbalanced Fermions At Unitaritymentioning

confidence: 99%

Thermodynamic properties of universal Fermi gases

Weiler

Silva

2013

Phys. Rev. A

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We develop a simple, mean-field-like theory for the normal phase of a unitary Fermi gas by deriving a self-consistent equation for its self-energy via a momentum-dependent coupling constant for both attractive and repulsive universal fermions. For attractive universal fermions in the lower branch of a Feshbach resonance, we use zero-temperature Monte Carlo results as a starting point for one-step iteration in order to derive an analytical expression for the momentum-dependent self-energy. For repulsive universal fermions in the upper branch of a Feshbach resonance, we iteratively calculate the momentum-dependent self-energy via our self-consistent equation. Lastly, for the case of population imbalance, we propose an ansatz for higher order virial expansion coefficents. Overall, we find that our theory is in good agreement with currently available, high temperature experimental data.

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“…We present here experimental work studying repulsive interactions and pair formation in Fermi gases [5][6][7]. We show that for small scattering length recombination into pairs is slow, and one can study the properties of the atomic system in equilibrium.…”

Section: Introductionmentioning

confidence: 97%

Ultracold fermions with repulsive interactions

Ketterle

2013

EPJ Web of Conferences

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Abstract. An ultracold Fermi gas with repulsive interaction has been studied. For weak interactions, the atomic gas is metastable, and the interactions were characterized by obtaining the isothermal compressibility from atomic density profiles. For stronger interactions (k F a ≈ 1), rapid conversion into Feshbach molecules is observed. When the conversion rate becomes comparable to the Fermi energy divided by , the atomic gas cannot reach equilibrium without forming pairs. This precludes the predicted transition to a ferromagnetic state (Stoner transition). The absence of spin fluctuations proves that the gas stays paramagnetic. In free space, a Fermi gas with strong short-range repulsion does not exist because of the rapid coupling to molecular states.

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Compressibility of an ultracold Fermi gas with repulsive interactions

Cited by 49 publications

References 42 publications

Quantum criticality of spin-1 bosons in a one-dimensional harmonic trap

Quantum criticality of spin-1 bosons in a one-dimensional harmonic trap

Thermodynamic properties of universal Fermi gases

Ultracold fermions with repulsive interactions

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