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:cond-mat/0605616

Pi-Josephson Junction and Spontaneous Superflow in Rings from Ultracold Fermionic Atomic Gases

Miodrag L. Kulić

Published May 25, 2006• 0 citations
arXivHTMLPDF

Abstract

The BCS-like pairing in ultracold fermionic atomic ($UCFAG$) gases is studied in the model of "isotopic-spin" pairing proposed in 1991 \cite% {Ku-Hof-SSC}. This model assumes a mismatch ($δ$) in chemical potentials of pairing fermionic atoms. It is shown that a $π$-Josephson junction can be realized in $UCFAG$ systems, where the left and right banks $% S$ are the $UCFAG$ superfluids. The weak link $M$ consists from the normal $% UCFAG$ with the finite mismatch $δ$. If the $π$-junction is a part of a closed ring the superfluid mass-current flows spontaneously in the ring, i.e., the time-reversal symmetry is broken spontaneously. This is realized if the radius of the ring $R$ is larger than the critical one $% R_{c} $. All these effects exist also in the case when $δ\gg Δ$, where $Δ$ is the superfluid gap, but with the reduced thickness of the weak link. It is also discussed, that if junctions $SM_{1}M_{2}S$ and trilayers $% M_{1}SM_{2}$ from $UCFAG$ are realizable this renders a possibility for a novel electronics - \textit{hypertronics}.

DOI
10.48550/arxiv.cond-mat/0605616

Related papers

Pi-Josephson Junction and Spontaneous Superflow in Rings from Ultracold Fermionic Atomic Gases

Miodrag L. Kulić

he BCS-like pairing in ultracold fermionic atomic ($UCFAG$) gases is studied in the model of "isotopic-spin" pairing proposed in 1991 \cite% {Ku-Hof-SSC}. This model assumes a mismatch ($δ$) in chemical potentials of pairing fermionic atoms. It is shown that a $π$-Josephson junction can be realized in $UCFAG$ systems, where the left and right banks $% S$ are the $UCFAG$ superfluids. The weak link $M$ consists from the normal $% UCFAG$ with the finite mismatch $δ$. If the $π$-junction is a part of a closed ring the superfluid mass-current flows spontaneously in the ring, i.e., the time-reversal symmetry is broken spontaneously. This is realized if the radius of the ring $R$ is larger than the critical one $% R_{c} $. All these effects exist also in the case when $δ\gg Δ$, where $Δ$ is the superfluid gap, but with the reduced thickness of the weak link. It is also discussed, that if junctions $SM_{1}M_{2}S$ and trilayers $% M_{1}SM_{2}$ from $UCFAG$ are realizable this renders a possibility for a novel electronics - \textit{hypertronics}.

arXiv:cond-mat/0605604•May 24, 2006•0 citations

π –superconducting quantum interference device from ultracold fermionic atomic gases

Miodrag L. Kulić

Ultracold fermionic atomic gas with Bardeen-Cooper-Schrieffer pairing between hyperfine states is studied. It is shown that a $\ensuremath{\pi}$-Josephson contact [superfluid--normal-gas--superfluid $(S∕N∕S)$] can be realized in systems where the left and right banks $S$ are superfluids and the weak link $N$ is a normal gas with the finite mismatch in chemical potentials ${\ensuremath{\delta}}_{{\ensuremath{\mu}}_{N}}\ensuremath{\ne}0$. If such a $\ensuremath{\pi}$-junction is part of a closed superfluid ring the superfluid mass-current flows spontaneously---the ultracold atomic $\ensuremath{\pi}$--superconducting quantum interference device ($\ensuremath{\pi}$-SQUID). This situation is realized if the radius of the ring $R$ is larger than the critical one ${R}_{c}$. The same effect will be realized also for ${\ensuremath{\delta}}_{{\ensuremath{\mu}}_{N}}⪢\ensuremath{\Delta}$, where $\ensuremath{\Delta}$ is the superfluid gap in S. The sensitivity of the $\ensuremath{\pi}$-SQUID to inertial effects is discussed in the case of rotational motion.

Physical Review A•Nov 28, 2007•7 citations

Persistent Currents in Rings of Ultracold Fermionic Atoms

Yanping Cai, Daniel Allman, Parth Sabharwal +1 more

We have produced persistent currents of ultracold fermionic atoms trapped in a ring, with lifetimes greater than 10 sec in the strongly interacting regime. These currents remain stable well into the BCS regime at sufficiently low temperature. We drive a circulating BCS superfluid into the normal phase and back by changing the interaction strength and find that the probability for quantized superflow to reappear is remarkably insensitive to the time spent in the normal phase and the minimum interaction strength. After ruling out spontaneous current formation for our experimental conditions, we argue that the reappearance of superflow is due to weak damping of normal currents in this limit. These results establish that ultracold fermionic atoms with tunable interactions can be used to create matter-wave circuits similar to those previously created with weakly interacting bosonic atoms.

arXiv:2104.02218•Physical Review Letters•Apr 12, 2022•70 citations

π junction and spontaneous current state in a superfluid Fermi gas

Takashi Kashimura, Shunji Tsuchiya, Yoji Ohashi

We discuss an idea to realize a spontaneous current in a superfluid Fermi gas. When a polarized Fermi superfluid (${N}_{\ensuremath{\uparrow}}>{N}_{\ensuremath{\downarrow}}$, where ${N}_{\ensuremath{\sigma}}$ is the number of atoms in the hyperfine state described by pseudospin $\ensuremath{\sigma}=\ensuremath{\uparrow},\ensuremath{\downarrow}$) is loaded onto a ring-shaped trap with a weak potential barrier, some excess atoms ($\ensuremath{\Delta}N={N}_{\ensuremath{\uparrow}}\ensuremath{-}{N}_{\ensuremath{\downarrow}}$) are localized around the barrier. As shown in our previous paper [T. Kashimura, S. Tsuchiya, and Y. Ohashi, Phys. Rev. A 82, 033617 (2010)], this polarized potential barrier works as a $\ensuremath{\pi}$ junction in the sense that the superfluid order parameter changes its sign across the barrier. Because of this, the phase of the superfluid order parameter outside the junction is shown to be twisted by $\ensuremath{\pi}$ along the ring, which naturally leads to a circulating supercurrent. While the ordinary supercurrent state is obtained as a metastable state, this spontaneous current state is shown to be more stable than the case with no current. Our results indicate that localized excess atoms would be useful for the manipulation of the superfluid order parameter in cold Fermi gases.

arXiv:1105.4023•Physical Review A•Jul 20, 2011•4 citations

Superfluidity and pairing phenomena in ultracold atomic Fermi gases in one-dimensional optical lattices. I. Balanced case

Jibiao Wang, Leifeng Zhang, Yi Yu +2 more

The superfluidity and pairing phenomena in ultracold atomic Fermi gases have been of great interest in recent years, with multiple tunable parameters. Here we study the BCS-BEC crossover behavior of balanced two-component Fermi gases in a one-dimensional optical lattice, which is distinct from the simple three-dimensional (3D) continuum and a fully 3D lattice often found in a condensed matter system. We use a pairing fluctuation theory which includes self-consistent feedback effects at finite temperatures and find widespread pseudogap phenomena beyond the BCS regime. As a consequence of the lattice periodicity, the superfluid transition temperature ${T}_{\mathrm{c}}$ decreases with pairing strength in the BEC regime, where it approaches asymptotically ${T}_{\mathrm{c}}=\ensuremath{\pi}an/2m$, with $a$ being the $s$-wave scattering length, and $n$ ($m$) the fermion density (mass). In addition, the quasi-two dimensionality leads to fast-growing (absolute value of the) fermionic chemical potential $\ensuremath{\mu}$ and pairing gap $\mathrm{\ensuremath{\Delta}}$, which depends exponentially on the ratio $d/a$. Importantly, ${T}_{\mathrm{c}}$ at unitarity increases with the lattice constant $d$ and hopping integral $t$. The effect of the van Hove singularity on ${T}_{\mathrm{c}}$ is identified. The superfluid density exhibits ${T}^{3/2}$ power laws at low $T$, away from the extreme BCS limit. These predictions can be tested in future experiments.

arXiv:2001.00545•Physical Review A•May 11, 2020•6 citations

Symmetry Breaking in Interacting Ring-Shaped Superflows of Bose–Einstein Condensates

Artem Oliinyk, I. V. Yatsuta, Boris A. Malomed +1 more

We demonstrate that the evolution of superflows in interacting persistent currents of ultracold gases is strongly affected by symmetry breaking of the quantum vortex dynamics. We study counter-propagating superflows in a system of two parallel rings in regimes of weak (a Josephson junction with tunneling through the barrier) and strong (rings merging across a reduced barrier) interactions. For the weakly interacting toroidal Bose–Einstein condensates, formation of rotational fluxons (Josephson vortices) is associated with spontaneous breaking of the rotational symmetry of the tunneling superflows. The influence of a controllable symmetry breaking on the final state of the merging counter-propagating superflows is investigated in the framework of a weakly dissipative mean-field model. It is demonstrated that the population imbalance between the merging flows and the breaking of the underlying rotational symmetry can drive the double-ring system to final states with different angular momenta.

arXiv:1909.08116•Symmetry•Oct 19, 2019•17 citations
The BCS-like pairing in ultracold fermionic atomic (UCFAGUCFAGUCFAG) gases is studied in the model of "isotopic-spin" pairing proposed in 1991 \cite% {Ku-Hof-SSC}. This model assumes a mismatch (δδδ) in chemical potentials of pairing fermionic atoms. It is shown that a πππ-Josephson junction can be realized in UCFAGUCFAGUCFAG systems, where the left and right banks % S are the UCFAGUCFAGUCFAG superfluids. The weak link MMM consists from the normal % UCFAG with the finite mismatch δδδ. If the πππ-junction is a part of a closed ring the superfluid mass-current flows spontaneously in the ring, i.e., the time-reversal symmetry is broken spontaneously. This is realized if the radius of the ring RRR is larger than the critical one % R_{c} . All these effects exist also in the case when δ≫Δδ\gg Δδ≫Δ, where ΔΔΔ is the superfluid gap, but with the reduced thickness of the weak link. It is also discussed, that if junctions SM1M2SSM_{1}M_{2}SSM1​M2​S and trilayers % M_{1}SM_{2} from UCFAGUCFAGUCFAG are realizable this renders a possibility for a novel electronics - \textit{hypertronics}.
he BCS-like pairing in ultracold fermionic atomic (UCFAGUCFAGUCFAG) gases is studied in the model of "isotopic-spin" pairing proposed in 1991 \cite% {Ku-Hof-SSC}. This model assumes a mismatch (δδδ) in chemical potentials of pairing fermionic atoms. It is shown that a πππ-Josephson junction can be realized in UCFAGUCFAGUCFAG systems, where the left and right banks % S are the UCFAGUCFAGUCFAG superfluids. The weak link MMM consists from the normal % UCFAG with the finite mismatch δδδ. If the πππ-junction is a part of a closed ring the superfluid mass-current flows spontaneously in the ring, i.e., the time-reversal symmetry is broken spontaneously. This is realized if the radius of the ring RRR is larger than the critical one $% R_{c} $. All these effects exist also in the case when δ≫Δδ\gg Δδ≫Δ, where ΔΔΔ is the superfluid gap, but with the reduced thickness of the weak link. It is also discussed, that if junctions SM1M2SSM_{1}M_{2}SSM1​M2​S and trilayers % M_{1}SM_{2} from UCFAGUCFAGUCFAG are realizable this renders a possibility for a novel electronics - \textit{hypertronics}.
Ultracold fermionic atomic gas with Bardeen-Cooper-Schrieffer pairing between hyperfine states is studied. It is shown that a $\ensuremath{\pi}$-Josephson contact [superfluid--normal-gas--superfluid (S∕N∕S)(S∕N∕S)(S∕N∕S)] can be realized in systems where the left and right banks SSS are superfluids and the weak link NNN is a normal gas with the finite mismatch in chemical potentials ${\ensuremath{\delta}}_{{\ensuremath{\mu}}_{N}}\ensuremath{\ne}0$. If such a $\ensuremath{\pi}$-junction is part of a closed superfluid ring the superfluid mass-current flows spontaneously---the ultracold atomic $\ensuremath{\pi}$--superconducting quantum interference device ($\ensuremath{\pi}$-SQUID). This situation is realized if the radius of the ring RRR is larger than the critical one Rc{R}_{c}Rc​. The same effect will be realized also for ${\ensuremath{\delta}}_{{\ensuremath{\mu}}_{N}}⪢\ensuremath{\Delta}$, where $\ensuremath{\Delta}$ is the superfluid gap in S. The sensitivity of the $\ensuremath{\pi}$-SQUID to inertial effects is discussed in the case of rotational motion.
We have produced persistent currents of ultracold fermionic atoms trapped in a ring, with lifetimes greater than 10 sec in the strongly interacting regime. These currents remain stable well into the BCS regime at sufficiently low temperature. We drive a circulating BCS superfluid into the normal phase and back by changing the interaction strength and find that the probability for quantized superflow to reappear is remarkably insensitive to the time spent in the normal phase and the minimum interaction strength. After ruling out spontaneous current formation for our experimental conditions, we argue that the reappearance of superflow is due to weak damping of normal currents in this limit. These results establish that ultracold fermionic atoms with tunable interactions can be used to create matter-wave circuits similar to those previously created with weakly interacting bosonic atoms.
We discuss an idea to realize a spontaneous current in a superfluid Fermi gas. When a polarized Fermi superfluid (${N}_{\ensuremath{\uparrow}}>{N}_{\ensuremath{\downarrow}}$, where ${N}_{\ensuremath{\sigma}}$ is the number of atoms in the hyperfine state described by pseudospin $\ensuremath{\sigma}=\ensuremath{\uparrow},\ensuremath{\downarrow}$) is loaded onto a ring-shaped trap with a weak potential barrier, some excess atoms ($\ensuremath{\Delta}N={N}_{\ensuremath{\uparrow}}\ensuremath{-}{N}_{\ensuremath{\downarrow}}$) are localized around the barrier. As shown in our previous paper [T. Kashimura, S. Tsuchiya, and Y. Ohashi, Phys. Rev. A 82, 033617 (2010)], this polarized potential barrier works as a $\ensuremath{\pi}$ junction in the sense that the superfluid order parameter changes its sign across the barrier. Because of this, the phase of the superfluid order parameter outside the junction is shown to be twisted by $\ensuremath{\pi}$ along the ring, which naturally leads to a circulating supercurrent. While the ordinary supercurrent state is obtained as a metastable state, this spontaneous current state is shown to be more stable than the case with no current. Our results indicate that localized excess atoms would be useful for the manipulation of the superfluid order parameter in cold Fermi gases.
The superfluidity and pairing phenomena in ultracold atomic Fermi gases have been of great interest in recent years, with multiple tunable parameters. Here we study the BCS-BEC crossover behavior of balanced two-component Fermi gases in a one-dimensional optical lattice, which is distinct from the simple three-dimensional (3D) continuum and a fully 3D lattice often found in a condensed matter system. We use a pairing fluctuation theory which includes self-consistent feedback effects at finite temperatures and find widespread pseudogap phenomena beyond the BCS regime. As a consequence of the lattice periodicity, the superfluid transition temperature Tc{T}_{\mathrm{c}}Tc​ decreases with pairing strength in the BEC regime, where it approaches asymptotically ${T}_{\mathrm{c}}=\ensuremath{\pi}an/2m$, with aaa being the sss-wave scattering length, and nnn (mmm) the fermion density (mass). In addition, the quasi-two dimensionality leads to fast-growing (absolute value of the) fermionic chemical potential $\ensuremath{\mu}$ and pairing gap $\mathrm{\ensuremath{\Delta}}$, which depends exponentially on the ratio d/ad/ad/a. Importantly, Tc{T}_{\mathrm{c}}Tc​ at unitarity increases with the lattice constant ddd and hopping integral ttt. The effect of the van Hove singularity on Tc{T}_{\mathrm{c}}Tc​ is identified. The superfluid density exhibits T3/2{T}^{3/2}T3/2 power laws at low TTT, away from the extreme BCS limit. These predictions can be tested in future experiments.
We demonstrate that the evolution of superflows in interacting persistent currents of ultracold gases is strongly affected by symmetry breaking of the quantum vortex dynamics. We study counter-propagating superflows in a system of two parallel rings in regimes of weak (a Josephson junction with tunneling through the barrier) and strong (rings merging across a reduced barrier) interactions. For the weakly interacting toroidal Bose–Einstein condensates, formation of rotational fluxons (Josephson vortices) is associated with spontaneous breaking of the rotational symmetry of the tunneling superflows. The influence of a controllable symmetry breaking on the final state of the merging counter-propagating superflows is investigated in the framework of a weakly dissipative mean-field model. It is demonstrated that the population imbalance between the merging flows and the breaking of the underlying rotational symmetry can drive the double-ring system to final states with different angular momenta.