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:2103.02418 · Physical Review Research

Optical spin conductivity in ultracold quantum gases

Yuta Sekino, Hiroyuki Tajima, Shun Uchino

Published Oct 10, 2022• 6 citations
arXivHTMLPDF

Abstract

We show that the optical spin conductivity, which is a small ac response of a bulk spin current and elusive in condensed matter systems, can be measured in ultracold atoms. We demonstrate that this conductivity contains rich information on quantum states by analyzing experimentally achievable systems such as a spin-$\frac{1}{2}$ superfluid Fermi gas, a spin-1 Bose-Einstein condensate, and a Tomonaga-Luttinger liquid. The obtained conductivity spectra, which are absent in the Drude conductivity, reflect quasiparticle excitations and non-Fermi-liquid properties. Accessible physical quantities include the superfluid gap and the contact for the superfluid Fermi gas, gapped and gapless spin excitations as well as quantum depletion for the Bose-Einstein condensate, and the spin part of the Tomonaga-Luttinger liquid parameter elusive in cold-atom experiments. Unlike its mass transport counterpart, the spin conductivity serves as a probe applicable to clean atomic gases without disorder or lattice potentials. Our formalism can be generalized to various systems such as spin-orbit-coupled and nonequilibrium systems.

DOI
10.1103/physrevresearch.4.043014

Related papers

Optical Spin Transport in Ultracold Quantum Gases.

Yuta Sekino, Hiroyuki Tajima, Shun Uchino

Measurement of frequency-resolved spin transport is a subject of much interest in condensed matter physics. Here we show that the optical spin conductivity being a small AC response of a spin current can be measured with existing methods in ultracold atom experiments. We point out that once interatomic interactions are turned on, the optical spin conductivity becomes nontrivial even in clean ultracold atomic gases and thereby can be a probe of generic quantum states of matter. This is a sharp contrast to the optical mass conductivity which becomes trivial in typical cold-atom systems without disorder and lattice potential. For systems with arbitrary spin degrees of freedom, we construct a general formalism of the optical spin conductivity and derive the $f$-sum rule. To demonstrate the availability of the optical spin conductivity, our formalism is applied to a spin-1/2 Fermi superfluid and a spin-1 Bose-Einstein condensate. It turns out that both superfluids show nontrivial responses that cannot be captured with the Drude conductivity. The application of our proposed method to generic ultracold atomic gases with spin degrees of freedom is feasible.

•Mar 3, 2021•0 citations

Optical spin transport theory of spin- 12 topological Fermi superfluids

Hiroyuki Tajima, Yuta Sekino, Shun Uchino

We theoretically investigate optical (frequency-dependent) bulk spin transport properties in a spin-$\frac{1}{2}$ topological Fermi superfluid. We specifically consider a one-dimensional system with an interspin $p$-wave interaction, which can be realized in ultracold-atom experiments. Developing the BCS-Leggett theory to describe the BCS to Bose-Einstein condensate (BEC) evolution and the ${\mathbb{Z}}_{2}$ topological phase transition in this system, we show how the spin transport reflects these many-body aspects. We find that the optical spin conductivity, which is a small AC response of a spin current, shows the spin-gapped spectrum in the wide parameter region and the gap closes at the ${\mathbb{Z}}_{2}$ topological phase transition point. Moreover, the validity of the low-energy effective model of the Majorana zero mode is discussed along the BCS-BEC evolution in connection with the scale invariance at $p$-wave unitarity.

arXiv:2109.14505•Physical review. B./Physical review. B•Feb 16, 2022•7 citations

Conductivity of Alternating Spin Currents in Ultracold Atomic Gases

Yuta Sekino, Hiroyuki Tajima, Shun Uchino

We study the response of an AC spin current in cold atomic systems.We propose how to measure the corresponding response function called the optical spin conductivity, which is difficult to measure in solid-state systems, by the current technique in cold atom experiment.To show the availability of the spin conductivity, we theoretically examine the spin conductivity in several cold atomic gases and find that the spectra include a lot of many-body information of the systems.

International Conference on Low Temperature Physics (LT)•May 22, 2023•0 citations

Probing and Manipulating Ultracold Fermi Superfluids

Lei Jiang

Ultracold Fermi gas is an exciting field benefiting from atomic physics, optical physics and condensed matter physics. It covers many aspects of quantum mechanics. Here I introduce some of my work during my graduate study. We proposed an optical spectroscopic method based on electromagnetically-induced transparency (EIT) as a generic probing tool that provides valuable insights into the nature of Fermi paring in ultracold Fermi gases of two hyperfine states. This technique has the capability of allowing spectroscopic response to be determined in a nearly non-destructive manner and the whole spectrum may be obtained by scanning the probe laser frequency faster than the lifetime of the sample without re-preparing the atomic sample repeatedly. Both quasiparticle picture and pseudogap picture are constructed to facilitate the physical explanation of the pairing signature in the EIT spectra. Motivated by the prospect of realizing a Fermi gas of 40 K atoms with a synthetic non-Abelian gauge field, we investigated theoretically BEC-HCS crossover physics in the presence of a Rashba spin-orbit coupling in a system of two-component Fermi gas with and without a Zeeman field that breaks the population balance. A new bound state (Rashba pair) emerges because of the spin-orbit interaction. We studied the properties of Rashba pairs using a standard pair fluctuation theory. As the two-fold spin degeneracy is lifted by spin-orbit interaction, bound pairs with mixed singlet and triplet pairings (referred to as rashbons) emerge, leading to an anisotropic superfluid. We discussed in detail the experimental signatures for observing the condensation of Rashba pairs by calculating various physical observables which characterize the properties of the system and can be measured in experiment. The role of impurities as experimental probes in the detection of quantum material properties is well appreciated. Here we studied the effect of a single classical impurity in trapped ultracold Fermi superfluids. Although a non-magnetic impurity does not change macroscopic properties of s-wave Fermi superfluids, depending on its shape and strength, a magnetic impurity can induce single or multiple mid-gap bound states. The multiple mid-gap states could coincide with the development of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase within the superfluid. As an analog of the Scanning Tunneling Microscope, we proposed a modified radio frequency spectroscopic method to measure the focal density of states which can be employed to detect these states and other quantum phases of cold atoms. A key result of our self consistent Bogoliubov-de Gennes calculations is that a magnetic impurity can controllably induce an FFLO state at currently accessible experimental parameters.

•Jan 1, 2011•0 citations

Superfluidity in ultracold atomic Fermi gases

Martin W. Zwierlein

Abstract This chapter reviews experimental studies of fermionic superfluidity in ultracold atomic gases. Scattering properties of ultracold atoms and Feshbach resonances are introduced. The basic theoretical framework is presented based on the Leggett ansatz that provides intuition into many of the observed phenomena. The various experimental observations related to fermion pair condensation and superfluidity are described. The thermodynamic measurements of strongly interacting Fermi gases are considered. Experiments on superfluidity in the presence of population imbalance are reviewed. These studies have led to the observation of the Clogston–Chandrasekhar (or Pauli) limit of fermionic superfluidity and to the identification of a novel attractive Fermi liquid of polaronic quasiparticles. Novel Fermi systems, such as Fermi gases in lower dimensions, optical lattices, dipolar Fermi gases, and spin–orbit coupled Fermi gases, are also touched on briefly.

•Nov 27, 2014•17 citations

Disordered ultracold atomic gases in optical lattices: A case study of Fermi-Bose mixtures

V. Ahufinger, Laurent Sanchez-Palencia, Adrian Kantian +2 more

We present a review of properties of ultracold atomic Fermi-Bose mixtures in inhomogeneous and random optical lattices. In the strong interacting limit and at very low temperatures, fermions form, together with bosons or bosonic holes, composite fermions. Composite fermions behave as a spinless interacting Fermi gas, and in the presence of local disorder they interact via random couplings and feel effective random local potential. This opens a wide variety of possibilities of realizing various kinds of ultracold quantum disordered systems. In this paper we review these possibilities, discuss the accessible quantum disordered phases, and methods for their detection. The discussed quantum phases include Fermi glasses, quantum spin glasses, ``dirty'' superfluids, disordered metallic phases, and phases involving quantum percolation.

arXiv:cond-mat/0508042•Physical Review A•Dec 21, 2005•68 citations
We show that the optical spin conductivity, which is a small ac response of a bulk spin current and elusive in condensed matter systems, can be measured in ultracold atoms. We demonstrate that this conductivity contains rich information on quantum states by analyzing experimentally achievable systems such as a spin-12\frac{1}{2}21​ superfluid Fermi gas, a spin-1 Bose-Einstein condensate, and a Tomonaga-Luttinger liquid. The obtained conductivity spectra, which are absent in the Drude conductivity, reflect quasiparticle excitations and non-Fermi-liquid properties. Accessible physical quantities include the superfluid gap and the contact for the superfluid Fermi gas, gapped and gapless spin excitations as well as quantum depletion for the Bose-Einstein condensate, and the spin part of the Tomonaga-Luttinger liquid parameter elusive in cold-atom experiments. Unlike its mass transport counterpart, the spin conductivity serves as a probe applicable to clean atomic gases without disorder or lattice potentials. Our formalism can be generalized to various systems such as spin-orbit-coupled and nonequilibrium systems.
Measurement of frequency-resolved spin transport is a subject of much interest in condensed matter physics. Here we show that the optical spin conductivity being a small AC response of a spin current can be measured with existing methods in ultracold atom experiments. We point out that once interatomic interactions are turned on, the optical spin conductivity becomes nontrivial even in clean ultracold atomic gases and thereby can be a probe of generic quantum states of matter. This is a sharp contrast to the optical mass conductivity which becomes trivial in typical cold-atom systems without disorder and lattice potential. For systems with arbitrary spin degrees of freedom, we construct a general formalism of the optical spin conductivity and derive the fff-sum rule. To demonstrate the availability of the optical spin conductivity, our formalism is applied to a spin-1/2 Fermi superfluid and a spin-1 Bose-Einstein condensate. It turns out that both superfluids show nontrivial responses that cannot be captured with the Drude conductivity. The application of our proposed method to generic ultracold atomic gases with spin degrees of freedom is feasible.
We theoretically investigate optical (frequency-dependent) bulk spin transport properties in a spin-12\frac{1}{2}21​ topological Fermi superfluid. We specifically consider a one-dimensional system with an interspin ppp-wave interaction, which can be realized in ultracold-atom experiments. Developing the BCS-Leggett theory to describe the BCS to Bose-Einstein condensate (BEC) evolution and the Z2{\mathbb{Z}}_{2}Z2​ topological phase transition in this system, we show how the spin transport reflects these many-body aspects. We find that the optical spin conductivity, which is a small AC response of a spin current, shows the spin-gapped spectrum in the wide parameter region and the gap closes at the Z2{\mathbb{Z}}_{2}Z2​ topological phase transition point. Moreover, the validity of the low-energy effective model of the Majorana zero mode is discussed along the BCS-BEC evolution in connection with the scale invariance at ppp-wave unitarity.
Ultracold Fermi gas is an exciting field benefiting from atomic physics, optical physics and condensed matter physics. It covers many aspects of quantum mechanics. Here I introduce some of my work during my graduate study. We proposed an optical spectroscopic method based on electromagnetically-induced transparency (EIT) as a generic probing tool that provides valuable insights into the nature of Fermi paring in ultracold Fermi gases of two hyperfine states. This technique has the capability of allowing spectroscopic response to be determined in a nearly non-destructive manner and the whole spectrum may be obtained by scanning the probe laser frequency faster than the lifetime of the sample without re-preparing the atomic sample repeatedly. Both quasiparticle picture and pseudogap picture are constructed to facilitate the physical explanation of the pairing signature in the EIT spectra. Motivated by the prospect of realizing a Fermi gas of 40 K atoms with a synthetic non-Abelian gauge field, we investigated theoretically BEC-HCS crossover physics in the presence of a Rashba spin-orbit coupling in a system of two-component Fermi gas with and without a Zeeman field that breaks the population balance. A new bound state (Rashba pair) emerges because of the spin-orbit interaction. We studied the properties of Rashba pairs using a standard pair fluctuation theory. As the two-fold spin degeneracy is lifted by spin-orbit interaction, bound pairs with mixed singlet and triplet pairings (referred to as rashbons) emerge, leading to an anisotropic superfluid. We discussed in detail the experimental signatures for observing the condensation of Rashba pairs by calculating various physical observables which characterize the properties of the system and can be measured in experiment. The role of impurities as experimental probes in the detection of quantum material properties is well appreciated. Here we studied the effect of a single classical impurity in trapped ultracold Fermi superfluids. Although a non-magnetic impurity does not change macroscopic properties of s-wave Fermi superfluids, depending on its shape and strength, a magnetic impurity can induce single or multiple mid-gap bound states. The multiple mid-gap states could coincide with the development of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase within the superfluid. As an analog of the Scanning Tunneling Microscope, we proposed a modified radio frequency spectroscopic method to measure the focal density of states which can be employed to detect these states and other quantum phases of cold atoms. A key result of our self consistent Bogoliubov-de Gennes calculations is that a magnetic impurity can controllably induce an FFLO state at currently accessible experimental parameters.
Abstract This chapter reviews experimental studies of fermionic superfluidity in ultracold atomic gases. Scattering properties of ultracold atoms and Feshbach resonances are introduced. The basic theoretical framework is presented based on the Leggett ansatz that provides intuition into many of the observed phenomena. The various experimental observations related to fermion pair condensation and superfluidity are described. The thermodynamic measurements of strongly interacting Fermi gases are considered. Experiments on superfluidity in the presence of population imbalance are reviewed. These studies have led to the observation of the Clogston–Chandrasekhar (or Pauli) limit of fermionic superfluidity and to the identification of a novel attractive Fermi liquid of polaronic quasiparticles. Novel Fermi systems, such as Fermi gases in lower dimensions, optical lattices, dipolar Fermi gases, and spin–orbit coupled Fermi gases, are also touched on briefly.
We present a review of properties of ultracold atomic Fermi-Bose mixtures in inhomogeneous and random optical lattices. In the strong interacting limit and at very low temperatures, fermions form, together with bosons or bosonic holes, composite fermions. Composite fermions behave as a spinless interacting Fermi gas, and in the presence of local disorder they interact via random couplings and feel effective random local potential. This opens a wide variety of possibilities of realizing various kinds of ultracold quantum disordered systems. In this paper we review these possibilities, discuss the accessible quantum disordered phases, and methods for their detection. The discussed quantum phases include Fermi glasses, quantum spin glasses, ``dirty'' superfluids, disordered metallic phases, and phases involving quantum percolation.