Degenerate Gas Research Articles

The Chandrasekhar limit: a simplified approach

This article outlines a simplified approach to approximating the Chandrasekhar limit for white dwarf stars at a level appropriate for advanced high school students, beginning undergraduate students, and high school teachers. Using a combination of introductory quantum mechanics and Einstein’s theory of special relativity, the electron degeneracy pressure is calculated in the non-relativistic and ultra-relativistic limits. By combining the electron degeneracy energy with the gravitational energy for a constant density star, an approximation to the Chandrasekhar mass is derived.

The Design, Realization, and Validation of the Scheme for Quantum Degenerate Research in Microgravity

In microgravity, atoms can be prepared to a lower temperature and manipulated with a longer time. The Cold Atom Physics Research Rack (CAPR) in Chinese Space Station, which aims to prepare quantum degenerate gas for deep cooling and quantum simulation in microgravity, has been designed, realized, and validated. We built an integrated CAPR, consisting of a physical system, an all-fiber 780nm laser system and a low phase noise 1064nm fiber laser system, and an electrical driving and controlling system. With the CAPR, a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">87</sup> Rb quantum degenerate gas with 1.2ⅹ10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> atoms and a temperature below 30nK was achieved on ground. In this article, we also show the robustness of the rack, based on the experimental results before and after the simulation of the vibration and impact during the launch.

Long-lived fermionic Feshbach molecules with tunable p -wave interactions

Ultracold fermionic Feshbach molecules are promising candidates for exploring quantum matter with strong $p$-wave interactions, however, their lifetimes were measured to be short. Here, we characterize the $p$-wave collisions of ultracold fermionic $^{23}\mathrm{Na}^{40}\mathrm{K}$ Feshbach molecules for different scattering lengths and temperatures. By increasing the binding energy of the molecules, the two-body loss coefficient reduces by three orders of magnitude leading to a second-long lifetime, 20 times longer than that of ground-state molecules. We exploit the scaling of elastic and inelastic collisions with the scattering length and temperature to identify a regime where the elastic collisions dominate over the inelastic ones allowing the molecular sample to thermalize. Our work provides a benchmark for four-body calculations of molecular collisions and is essential for producing a degenerate Fermi gas of Feshbach molecules.

Late-forming primordial black holes: Beyond the CMB era

The intermediate mass black hole range, ${10}^{2}\ensuremath{\lesssim}{M}_{\mathrm{BH}}/{M}_{\ensuremath{\bigodot}}\ensuremath{\lesssim}{10}^{5}$, has long offered enticing possibilities for primordial black holes (PBHs), with populations in this range postulated to be responsible for some of the black hole binary merger detected events as well as the existence of supermassive black holes embedded at galactic centers. However, a prominent bound derived from PBH accretion during recombination severely restricts the mass fraction of intermediate mass PBHs. We address this problem by proposing a formation scenario in which ``primordial'' black holes form late in our cosmological history, beyond the cosmic microwave background era, and bypassing this bound. During this crucial epoch, our population of compact objects exist as thermal balls supported by thermal pressure, which eventually cool to Fermi balls supported by degeneracy pressure and finally collapse to PBHs. Our mechanism is a viable production method for both the mass gap LIGO-VIRGO-KAGRA detections and the James Webb Space Telescope observation of an early time $z&gt;10$ supermassive black hole. Furthermore, we present the remarkable possibility of PBH formation after the present era, which we term future PBH. Such a population would evade most, if not all, bounds on the PBH mass spectrum in the literature and open up previously unthought-of possibilities. Light future PBHs could form below the Hawking evaporation threshold and convert the bulk of the matter in the Universe into radiation.

Black Hole Spectra from Vaz's Quantum Gravitational Collapse

AbstractIn 2014, in a famous paper Hawking strongly criticized the firewall paradox by claiming that it violates the equivalence principle and breaks the CPT invariance of quantum gravity. He proposed that the final result of the gravitational collapse should not be an event horizon, but an apparent horizon instead. On the other hand, Hawking did not give a mechanism for how this could work. In the same year, Vaz endorsed Hawking's proposal in a quantum gravitational model of dust collapse by winning the Second Prize in the 2014 Gravity Research Foundation Essay Competition. He indeed showed that continued collapse to a singularity can only be obtained if one combines two independent and entire solutions of the Wheeler‐DeWitt equation. Vaz's interpretation of the paradox was in terms of simply forbidding such a combination. This leads naturally to matter condensing on the apparent horizon during quantum collapse. In that way, an entirely new framework for black holes (BHs) has emerged. The approach of Vaz was also consistent with Einstein's idea in 1939 of the localization of the collapsing particles within a thin spherical shell. In this work we derive the BH mass and energy spectra via a Schrodinger‐like approach, by further supporting Vaz's conclusions that instead of a spacetime singularity covered by an event horizon, the final result of the gravitational collapse is an essentially quantum object, an extremely compact “dark star”. This “gravitational atom” is held up not by any degeneracy pressure but by quantum gravity in the same way that ordinary atoms are sustained by quantum mechanics. Finally, by evoking the generalized uncertainty principle, the maximum value of the density of Vaz's shell will be estimated.

Self-binding of one-dimensional fermionic mixtures with zero-range interspecies attraction

For sufficiently large mass ratios the attractive exchange force caused by a single light atom interacting with a few heavy identical fermions can overcome their Fermi degeneracy pressure and bind them into an N+1N+1 cluster. Here, by using a mean-field approach valid for large NN, we find that N+1N+1 clusters can attract each other and form a self-bound charge density wave, the properties of which we fully characterize. Our work shows that there are no fundamental obstacles for having self-bound states in fermionic mixtures with zero-range interactions.

Effect of spin polarization on electron acceleration in magnetized quantum plasma by a surface plasma wave.

The effect of spin-up and spin-down exchange interaction on electron acceleration by a surface plasma wave (SPW) propagating in magnetized quantum plasma has been studied. The SPW was excited over the metal-vacuum interface with maximum amplitude at the interface. The effective dielectric constant was evaluated, considering the effects of quantum Bohm potential, degenerate Fermi pressure, and electron spin. The externally applied magnetic field perturbed the densities of the oppositely spinning electrons, which resulted in spin polarization. The dispersion relation and energy exchange mechanism for the electron acceleration was built, incorporating the effects of spin polarization in the wave-plasma interaction. The energy gain was found to increase with the spin polarization.

Mitigating heating of degenerate fermions in a ring-dimple atomic trap

We report on the impact of the extended geometry of a ring-dimple trap on particle-loss heating of a degenerate Fermi gas. When the Fermi level is slightly greater than the depth of the dimple and a broad, low-density ``halo'' is present, the overall heating rate is reduced relative to the case of a bare ring. We find that the experimentally measured heating rates for the overfilled dimple are in good agreement with a model of the hole-induced heating caused by background-gas collisions. This suppression of the heating rate can be helpful for experimental studies of fermionic superfluids in the weak pairing limit, where achieving and maintaining low temperatures over long timescales are essential.

Kinetic Theory Study of Pressure and Equation of State in a Strongly Degenerate Fermi Gas

Starting from the Fermi-Dirac distribution fuunction, Kinetic Theory prescriptions are applied to express number density and pressure as integrals, which are then solved for nonvanishing temperature. The results are then combined to arrive at an equation of state, given in closed form, yielding pressure as a function of number density.

Thermodynamics of decoherence

We investigate the non-equilibrium thermodynamics of pure decoherence. In a pure decoherence process, the system Hamiltonian is a constant of motion and there is no direct energy exchange between the system and its surroundings. Nevertheless, the environment’s energy is not generally conserved and in this work we show that this leads to non-trivial heat dissipation as a result of decoherence alone. This heat has some very distinctive properties: it obeys an integral fluctuation relation and can be interpreted in terms of the entropy production associated with populations in the energy eigenbasis of the initial state. We show that the heat distribution for a pure decoherence process is different from the distribution of work done by the initial system–bath interaction quench. Instead, it corresponds to a mixture of work distributions of cyclical processes, each conditioned on a state of the open system. Inspired by recent experiments on impurities in ultracold gases, we demonstrate our general results by studying the heat generated by the decoherence of a qubit immersed within a degenerate Fermi gas in the lowest band of a species-selective optical lattice.

Electrical conductivity of strongly magnetized dense quark matter - possibility of quantum Hall effect

We have pointed out the possibilities of quantum Hall effect (QHE) and Shubnikov-de Haas (SdH) oscillation in the transportation of strongly magnetized degenerate quark matter- expected inside the highly dense compact star, such as the neutron star. The anisotropic pattern of electrical conductivity and resistivity tensor is explored in classical to quantum cases by considering the Landau quantization of quarks in the presence of a finite magnetic field. With increasing magnetic field, classical to quantum transitions are realized through enhanced (reduced) resistivity (conductivity) with QHE/SdH type oscillatory patterns. Estimating QCD relaxation time for degenerate quark matter from Ref. [57], eB≈(1−4)mπ2 can be considered a strong magnetic field for massless and degenerate quark matter with quark chemical potential μ≈0.2−0.4 GeV. We discovered exotic quantum magnetic oscillating patterns associated with the QHE and SdH phenomena within the mentioned regimes.

Tunable Transparency and Group Delay in Cavity Optomechanical Systems with Degenerate Fermi Gas

We theoretically investigate the optical response and the propagation of an external probe field in a Fabry–Perot cavity, which consists of a mechanical mode of trapped, ultracold, fermionic atoms inside and simultaneously driven by an optical laser field. We investigate the electromagnetically-induced transparency due to coupling of the optical cavity field with the collective density excitations of the ultracold fermionic atoms via radiation pressure force. Moreover, we discuss the variations in the phase and group delay of the transmitted probe field with respect to effective cavity detuning as well as pumping power. It is observed that the transmitted field is lagging in this fermionic cavity optomechanical system. Our study shall provide a method to control the propagation as well as the speed of the transmitted probe field in this kind of fermionic, ultracold, atom-based, optomechanical cavity system, which might have potential applications in optical communications, signal processing and quantum information processing.

Precision measurement of atom-dimer interaction in a uniform planar Bose gas

Cold quantum gases, when acted upon by electromagnetic fields, can give rise to samples where isolated atoms coexist with dimers or trimers, which raises the question of the interactions between these various constituents. Here we perform microwave photoassociation in a degenerate gas of Rb87 atoms to create weakly bound dimers in their electronic ground level. We determine the complete energy diagram of one hyperfine manifold of the least-bound level, which we accurately reproduce with a simple model. Then, from the density-induced shift of the photoassociation line, we measure the atom-dimer scattering length for two weakly bound states of the molecular potential.Received 14 November 2022Accepted 12 January 2023DOI:https://doi.org/10.1103/PhysRevResearch.5.L012020Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBose-Einstein condensatesCold and ultracold moleculesCold atoms & matter wavesInteratomic & molecular potentialsPhotoassociationUltracold collisionsVan der Waals interactionAtomic, Molecular & Optical

Quasi-one-dimensional equation for a tube-shaped dilute Fermi gas

In this paper we consider a degenerate Fermi gas strongly confined in the transverse direction by a singular potential. By using an appropriate factorized ansatz from the three-dimensional mean-field model (i.e., a nonlinear Schrödinger equation) and using a variational approximation, we derive a one-dimensional (1D) effective equation that correctly describes the behavior of the particle distribution in the longitudinal direction. Systematic simulations are performed in view to confirm the robustness of the effective equation in describing the axial behavior of the tube-shaped Fermi gas in the attractive and repulsive regimes. Furthermore, from a dynamic point of view, we have analyzed the periodic oscillations of the wave function by abruptly increasing the depth of the harmonic axial potential, where we find that the 1D effective equation derived here is the best approximation to describe this oscillatory behavior.

Multidimensional spectroscopy of heavy impurities in ultracold fermions

We investigate the system of a heavy impurity immersed in a degenerate Fermi gas, where the impurity's internal degree of freedom (pseudospin) is manipulated by a series of radio-frequency (RF) pulses at several different times. Applying the functional determinant approach, we carry out an essentially exact calculation of the Ramsey-interference-type responses to the RF pulses. These responses can be regarded as multidimensional (MD) spectroscopy of the system in the time domain. Similar to their one-dimensional counterpart studied by Knap et al. [M. Knap et al., Phys. Rev. X 2, 041020 (2012)], these responses are universal functions. A Fourier transformation of the time intervals gives the MD spectroscopy in the frequency domain, providing insightful information on the many-body correlation and relaxation via the cross peaks, e.g., the off-diagonal peaks in a two-dimensional spectrum. These features are inaccessible for the conventional, one-dimensional absorption spectrum. Our scheme provides a different method to investigate many-body nonequilibrium physics beyond the linear response regime with accessible tools in cold atoms.

Nonlinear electron-acoustic structures in two-temperature relativistic degenerate plasmas

Fully nonlinear electron-acoustic (EA) structures are studied in the presence of relativistic degeneracy pressure attributing to electron species in a degenerate plasma. The plasma is taken as a collisionless and unmagnetized, containing mobile cool electrons, inertialess hot electrons and static ions. The fluid equations for such a plasma are incorporated and solved together by using the charge-neutrality hypothesis and diagonalization matrix technique obtaining the characteristic wave equations in the form of inviscid Burgers’ equations. Negative solitary structures are found in the form of potential profiles, which can be developed into nonstationary shocklets, greatly affected by the weak and strong relativistic degenerate densities. The structures are not only modified by the temporal evolution but also by thermal correction parameter. Moreover, the application of Taylor expansion to the eigenvalue may lead to the derivation of nonlinear phase and shock speeds, depending significantly on the electrostatic potential and other plasma parameters. The present findings are important to understand solitary and shocklet structures in dense plasmas, where both cool and hot electrons are regarded as the relativistic and degenerate species.

Risk Factor Hypertension Prediction Model

According to the 2020 Ministry of Health reports, the public health sector is facing an acute shortage of logistical resources and qualified competent human resources, as evidenced by the doctor-to-hospital ratio in relation to population [1]. Aside from these structural and cyclical issues, the above ratios are even lower in rural areas with low incomes. Underdevelopment is a major impediment to establishing a normal public health situation, though the Burundian government is working hard to ensure that it is at an acceptable level. Furthermore, some Burundian traditions, customs, and practices are undermining efforts to build an international-standard public health facility. Indeed, the mental state of a people (tradition, culture, and practices) has a significant impact on the fluctuation of risk factors in public health. It is determined by the socioeconomic development and sociocultural behavior of the population. This demonstrates that hypertension is a public health concern in Burundi. Unfortunately, the vast majority of people are completely unaware of the risks that high blood pressure poses to public health. High blood pressure, on the other hand, has always been a key physiological measure in medical examinations, serving as one of the most important biological markers in clinical evaluation. As a result, cardiovascular diseases caused by high blood pressure have a significant impact on mortality worldwide, particularly in Burundi. Predicting high blood pressure based on risk factors can help to reduce complications associated with this disease, which is known as a silent killer. The digital era provides a variety of tools for studying, analyzing, managing, and monitoring the risk factors that contribute to and degenerate high blood pressure. The primary goal of this work is to create a decision-making tool based on the outcomes of high blood pressure epidemic and/or pandemic predictions from sanitarian districts. The current paper work employs a prediction support tool created using linear regression methods from machine learning, one of the fields of artificial intelligence. It is especially useful for optimizing the cost function. The latter allows the predicted values to be determined and defined using the gradient descent algorithm.

Theology and thermodynamics of life and mind in the scientific legacy of Nikolay Ivanovich Kobozev

Nikolay Ivanovich Kobozev (1903–1974), Professor of Moscow State University, famous Russian physico-chemist, specialist in the field of thermodynamics. In his works devoted to thermodynamics of information and thinking, he emphasized the incompatibility between the entropy law for molecular structures, including molecular machinery of the mind, and the law of identity for thinking. In order to compensate for the molecular entropy, the mind should receive a negative entropy or antientropy, which is defined on the basis of the extended concept of thermodynamic probability. The latter is defined as a number of procedures (algorithms) that can be used to produce a physico-chemical system from its elementary components. For non-algorithmic systems, the entropy is negative. In order to model processing and production of information, N. I. Kobozev postulated the existence in a brain of a strongly degenerate Fermi gas of superlight Ψ-particles (psychons), thus being one of the first scientists who emphasized the importance of quantum processes for the physics of mind. In all its levels, life contains an antientropic component, which distinguishes it from the non-living matter. According to Kobozev, ‘human mind cannot be the result of evolutionary transformation of information function into thinking. The latter must be given to us, and not acquired in the course of evolution’. Since the source of information is the God Himself, the N. I. Kobozev’s works correspond to the theocentric scientific worldview and they can well be considered as theological construction in natural sciences.

Dark matter fermions: from linear to non-linear structure formation

The transition from linear to non-linear structure formation in cosmology is here studied from the point of view of the thermodynamics of self-gravitating fermions. We start by reviewing the principle of maximum entropy production through which such a fermionic system can relax towards spherical equilibrium states able to explain the dark matter (DM) in galaxies. We then analyze the stability, lifetime and morphology of the above configurations, and show that the most general DM profile develops a compact core governed by degeneracy pressure, which is surrounded by an extended halo. For DM particles which are in the range of $\mathcal{O}$(10--100) keV, we apply this theory to the case of the Milky Way, and show that the compact DM-core explains the dynamics of all the best resolved S-cluster stars orbiting SgrA *, without the need of assuming a central black hole (BH). Further consequences of this theory regarding open issues in cosmology are outlined, including the problem of formation of supermassive BHs in the early Universe.

Observational constraints on maximum mass limit and physical properties of anisotropic strange star models by gravitational decoupling in Einstein–Gauss–Bonnet gravity

ABSTRACT In this work, we are guided by the gravitational wave events GW 170817 and GW 190814 together with observations of neutron stars PSR J1614-2230, PSR J1903+6620, and LMC X-4 to model compact objects within the framework of Einstein–Gauss–Bonnet (EGB) gravity. In addition, we employ the extended gravitational decoupling (EGD) method to explore the impact of anisotropy by varying the decoupling parameter. We model strange quark stars in which the interior stellar fluid obeys the MIT Bag equation of state which represents a degenerated Fermi gas comprising of up, down, and strange quarks. In order to close the system of field equations describing the seed solution, we employ the Buchdahl ansatz for one of the metric functions. The θ sector is solved under the bifurcation: $\epsilon =\theta ^0_0$ and $P_r=\theta ^1_1$ leading to two new families of solutions. In order to test the physical viability of the models, we vary the EGB parameter (α) or the decoupling constant (β) to achieve the observed masses and radii of compact objects. Our models are able to account for low-mass stars for a range of β values while α is fixed. The present models mimic the secondary component of the GW 190814 with a mass range of 2.5–2.67 M⊙ and radii typically of the order of 11.76$^{+0.14}_{-0.19}$ km for large values of the EGB parameter and the decoupling constant. The energy exchange between fluids inside the stellar object is sensitive to model parameters which lead to stable configurations.