arXiv subjects

Shao-Jian Jiang

Publications and source records attributed to Shao-Jian Jiang.

11 recordsLinked to original sources

arXiv2023

Three-Dimensional Low-Density Fermions in Planckian Limit: Entropy and Dynamics

In this Letter, we explore dynamics in a three-dimensional strongly interacting liquid. In quantum liquids discussed below, thermodynamic properties such as pressure and thermal energies are fully characterized by $s(T)$, the entropy density of the liquid (that is also directly proportional to the hydrodynamic viscosity). We obtain a universal fermion spectral function $A(ω, {\bf k})$ that is distinctly specified by $\hbar / T$, a Planckian time scale. These phenomena can emerge in strongly interacting many-body states with a finite fermion density $ρ$ at temperatures $T^*$ where the chemical potential of fermions $μ(ρ, T=T^*)$ approaches zero and can be thought as many-body simulations of certain aspects of Planckian dynamics.

cond-mat.str-el↗

arXiv2023

Long-lived universal resonant Bose gases

Quantum simulations based on near-resonance Bose gases are limited by their short lifetimes due to severe atom losses. In addition to this, the recently predicted thermodynamical instability adds another constraint on accessing the resonant Bose gases. In this article, we offer a potential solution by proposing long-lived resonant Bose gases in both two and three dimensions, where the conventional few-body losses are strongly suppressed. We show that the thermodynamical properties as well as the lifetimes of these strongly interacting systems are universal, and independent of short-range physics.

cond-mat.quant-gas↗

arXiv2020

Relativistic Borromean States

In this work the existence of Borromean states has been discussed for bosonic and fermionic cases in both the relativistic and non-relativistic limits from the 3-momentum shell renormalization. With the linear bosonic model we checked the existence of Efimov-like states in the bosonic system. In both limits a geometric series of singularities are found in the 3-boson interaction vertex, while the energy ratio is reduced by around 70\% in the relativistic limit because of the anti-particle contribution. Motivated by the quark-diquark model in heavy baryon studies, we have carefully examined the p-wave quark-diquark interaction and found an isolated Borromean pole at finite energy scale. This may indicate a special baryonic state of light quarks in high energy quark matters. In other cases trivial results are obtained as expected. In relativistic limit, for both bosonic and fermionic cases, potential Borromean states are independent of the mass, which means the results would be valid even in zero-mass limit as well.

hep-ph↗

arXiv2020

Tricritical physics in two-dimensional $p$-wave superfluids

We study effects of quantum fluctuations on two-dimensional $p+ip$ superfluids near resonance. In the standard paradigm, phase transitions between superfluids and zero density vacuum are continuous. When strong quantum fluctuations near resonance are taken into account, the line of continuous phase transitions terminates at two multicritical points near resonance, between which the transitions are expected to be first-order ones. The size of the window where first-order phase transitions occur is shown to be substantial when the coupling is strong. Near first-order transitions, superfluids self-contract due to phase separations between superfluids and vacuum.

cond-mat.quant-gas↗

arXiv2019

Cusps near Topological Phase Transitions: Signatures of Majorana fermions and interactions with fluctuations

In this article, we study non-analyticities or cusps near a topological phase transition driven by changes of global topologies rather than by the formation of conventional (local) order. The particular phase transitions between topologically ordered superfluids and non-topological superfluids studied in this article are always accompanied by the emergence or disappearance of Majorana boundary modes, while at the critical point these boundary modes are liberated and evolve into the bulk. Proliferation of massless Majorana fermions at the transition leaves unique thermodynamic signatures. For a very broad class of isotropic superfluids or superconductors (with or without time reversal symmetry), the resultant transitions in $d$ spatial dimensions will be of $(d+1)$th order. The $(d+1)$th order derivatives of the grand potential are either discontinuous in even dimensions or logarithmically divergent in odd dimensions. Bulk quantities such as compressibility can develop a cusp along with the change of topology of the superfluids. We compute quantitatively the cusp structures and further investigate the effect of interactions induced by massive fluctuation fields. These cusps are direct manifestations of Majorana fermions and their interactions, and can be potentially considered as an alternative approach for detecting these puzzling particles.

cond-mat.str-el↗

arXiv2019

Achieving continuously tunable critical exponents for long-range spin systems simulated with trapped ions

Quantum phase transitions are usually classified into discrete universality classes that typically only depend on symmetries and spatial dimensionalities. In this Letter, we demonstrate an opportunity to continuously vary the critical exponents or universalities by tuning experimental parameters in a given physical system. Particularly, we show that critical exponents in long-range spin systems simulated in ion traps can be easily tuned with laser detuning. We suggest that such experiments also effectively simulate some aspects of critical phenomena in conventional spin systems but in artificial non-integer spatial dimensions.

quant-ph↗

arXiv2018

Two-dimensional Fermi gases near a p-wave resonance: effect of quantum fluctuations

We study the stability of p-wave superfluidity against quantum fluctuations in two-dimensional Fermi gases near a p-wave Feshbach resonance . An analysis is carried out in the limit when the interchannel coupling is strong. By investigating the effective potential for the pairing field via the standard loop expansion, we show that a homogeneous p-wave pairing state becomes unstable when two-loop quantum fluctuations are taken into account. This is in contrast to the previously predicted $p + ip$ supefluid in the weak-coupling limit [V. Gurarie et al., Phys. Rev. Lett. 94, 230403 (2005)]. It implies a possible onset of instability at certain intermediate interchannel coupling strength. Alternatively, the instability can also be driven by lowering the particle density. We also discuss the validity of our analysis.

cond-mat.quant-gas↗

arXiv2016

Scale Invariant Dynamics and Universal Quantum Beats in Bose Gases

We study the signature of scale invariance in the far-from-equilibrium quantum dynamics of two dimensional Bose gases. We show that the density profile displays a scale invariant logarithmic singularity near the center. In addition, the density oscillates due to quantum beats with universal structures. Namely, the frequencies of the beats can be connected with one another by a universal discrete scale transformation induced by the scale invariance. The experimental applicability of these results is then discussed.

cond-mat.quant-gas↗

arXiv2015

Stability and Anomalous Compressibility of Bose Gases Near Resonance: The scale-dependent interactions and thermal effects

The stability of Bose gases near resonance has been a puzzling problem in recent years. In this Letter, we demonstrate that in addition to generating thermal pressure, thermal atoms enhance the repulsiveness of the scale-dependent interactions between condensed atoms due to renormalization effect and further stabilize the Bose gases. Consequently, we find that, as a precursor of instability, the compressibility develops an anomalous structure as a function of scattering length and is drastically reduced compared with the mean-field value. Furthermore, the density profile of a Bose gas in a harmonic trap is found to develop a flat top near the center. This is due to the anomalous behavior of compressibility and can be a potential smoking gun for probing such an effect.

cond-mat.quant-gas↗

arXiv2014

Universal Bose Gases Near Resonance: A Rigorous Solution

We obtain a rigorous solution of universal Bose gases near resonance and offer an answer to one of the long-standing challenges of quantum gases at large scattering lengths, where the standard dilute theory breaks down. The solution was obtained by using an $ε$ expansion near four spatial dimension. In dimension $d = 4 - ε$, the chemical potential of Bose gases near resonances is shown to approach the universal value $ε^{(2/(4-ε))} ε_F \sqrt{2/3} (1 + 0.474 ε- i 1.217 ε+ ...)$, where $ε_F$ is the Fermi energy defined for a Fermi gas of density $n$, and the condensation fraction is equal to $2/3 (1 + 0.0877 ε+ ...)$. We also discuss the implications on ultra-cold gases in physical dimensions.

cond-mat.quant-gas↗

arXiv2011

Imbalanced ultracold Fermi gas in the weakly repulsive regime: Renormalization group approach for p-wave superfluidity

We theoretically study a possible new pairing mechanism for a two-dimensional population imbalanced Fermi gas with short-range repulsive interactions which can be realized on the upper branch of a Feshbach resonance. We use a well-controlled renormalization group approach, which allows an unbiased study of the instabilities of imbalanced Fermi liquid without assumption of a broken symmetry and gives a numerical calculation of the transition temperature from microscopic parameters. Our results show a leading superfluid instability in the p-wave channel for the majority species. The corresponding mechanism is that there are effective attractive interactions for the majority species, induced by the particle-hole susceptibility of the minority species, where the mismatch of the Fermi surfaces of the two species plays an important role. We also propose an experimental protocol for detecting the p-wave superfluidity and discuss the corresponding experimental signatures.

cond-mat.quant-gas↗