Science China Physics, Mechanics & Astronomy最新文献

A group of massive galaxies at redshifts of z ≳ 7 have been recently detected by the James Webb Space Telescope (JWST), which were unexpected to form at such an early time within the standard Big Bang cosmology. In this work, we propose that this puzzle can be explained by the presence of some primordial black holes (PBHs) with a mass of ∼ 1000M_⊙. These PBHs act as seeds for early galaxy formation with masses of ∼ 10⁸–10¹⁰M_⊙ at high redshift, hence accounting for the JWST observations. We use a hierarchical Bayesian inference framework to constrain the PBH mass distribution models, and find that the Lognormal model with the M_c ∼ 750M_⊙ is preferred over other hypotheses. These rapidly growing BHs are expected to have strong radiation and may appear as high-redshift compact objects, similar to those recently discovered by JWST. Although we focused on PBHs in this work, the bound on the initial mass of the seed black holes remains robust even if they were formed through astrophysical channels.

Precision measurement of magnetic fields is a crucial issue in both fundamental scientific research and practical sensing technology. The sensitive detection of a vector magnetic field poses a significant challenge in quantum magnetometry, particularly in estimating a vector DC magnetic field with high precision. Here, we propose a comprehensive protocol for quantum vector DC magnetometry, utilizing selective phase accumulation in both non-entangled and entangled quantum probes. Building upon the principles of Ramsey interferometry, our protocol enables the selective accumulation of phase for a specific magnetic field component by incorporating a meticulously designed pulse sequence. In the individual measurement scheme, we employ three individual quantum interferometries to independently estimate each of the three magnetic field components. Alternatively, in the simultaneous measurement scheme, the application of a pulse sequence along different directions enables the simultaneous estimation of all three magnetic field components using only one quantum interferometry. Notably, by employing an entangled state (such as the Greenberger-Horne-Zeilinger state) as the input state, the measurement precisions of all three components may reach the Heisenberg limit. This study not only establishes a general protocol for measuring vector magnetic fields using quantum probes, but also presents a viable pathway for achieving entanglement-enhanced multi-parameter estimation.

Cavity magnomechanics, exhibiting remarkable experimental tunability, rich magnonic nonlinearities, and compatibility with various quantum systems, has witnessed considerable advances in recent years. However, the potential benefits of using cavity magnomechanical (CMM) systems in further improving the performance of quantum-enhanced sensing for weak forces remain largely unexplored. Here we show that, by squeezing the magnons, the performance of a quantum CMM sensor can be significantly enhanced beyond the standard quantum limit (SQL). We find that, for comparable parameters, two orders of magnitude enhancement in the force sensitivity can be achieved in comparison with the case without magnon squeezing. Moreover, we obtain the optimal parameter regimes of homodyne angle for minimizing the added quantum noise. Our findings provide a promising approach for highly tunable and compatible quantum force sensing using hybrid CMM devices, with potential applications ranging from quantum precision measurements to quantum information processing.

The scaling relation of central massive black holes (MBHs) and their host galaxies is well-studied for supermassive BHs (SMBHs, M_BH ≥ 10⁶M_⊙). However, this relation has large uncertainties in the mass range of the intermediate-mass BHs (IMBHs, M_BH ∼ 10³–10⁶M_⊙). Since Green pea (GP) galaxies are luminous compact dwarf galaxies, which may be likely to host less massive SMBHs or even IMBHs, we systematically search for MBHs in a large sample of 2190 GP galaxies at z < 0.4, selected from LAMOST and SDSS spectroscopic surveys. Here, we report a newly discovered sample of 59 MBH candidates with broad Hα lines. This sample has a median stellar mass of 10^8.83±0.11M_⊙ and hosts MBHs with single-epoch virial masses ranging from M_BH ∼ 10^4.7 to 10^8.5M_⊙ (median 10^5.85±0.64M_⊙). Among the 59 MBH candidates, 36 have black hole masses M_BH ≤ 10⁶M_⊙ (IMBH candidates), one of which even has M_BH ≲ 10⁵M_⊙. We find that the M_BH-M_* relation of our MBH sample is consistent with the M_BH-M_bulge relation for SMBHs, while is above the M_BH-M_* relation for MBHs in dwarf galaxies in the same mass range. Furthermore, we show that 25 MBH candidates, including 4 IMBH candidates, have additional evidence of black hole activities, assessed through various methods such as the broad-line width, BPT diagram, mid-infrared color, X-ray luminosity, and radio emission. Our studies show that it is very promising to find IMBHs in GP galaxies, and the BH sample so obtained enables us to probe the connection between the MBHs and compact dwarf galaxies in the low-redshift Universe.

In an endeavor to establish a connection between the mean velocity profile in compressible wall-bounded turbulence and its incompressible analogue, a refined version of the Trettel and Larsson’s (TL) transformation is systematically derived and rigorously assessed across diverse flow scenarios. Incorporating the recently proposed intrinsic compressibility effects and modeling the multi-layer structure of mixing lengths, the proposed transformation demonstrates exceptional performance in collapsing 57 canonical flow cases, including cooled channel and pipe flows, channel flows with pseudo heat sources, as well as adiabatic and diabatic boundary layer flows. Furthermore, the transformation seamlessly extends to low Reynolds number cooled channel and pipe flows, achieving a level of accuracy unparalleled by other transformations in the current state-of-the-art.

Quantum systems are exceedingly difficult to engineer because they are sensitive to various types of noises. In particular, time-dependent noises are frequently encountered in experiments but how to overcome them remains a challenging problem. In this work, we propose a flexible robust control technique to resist time-dependent noises based on inverse geometric optimization working in the filter-function formalism. The basic idea is to parameterize the control filter function geometrically and minimize its overlap with the noise spectral density. This then effectively reduces the noise susceptibility of the controlled system evolution. We show that the proposed method can produce high-quality robust pulses for realizing desired quantum evolutions under realistic noise models. Also, we demonstrate this method in examples including dynamical decoupling and quantum sensing protocols to enhance their performances.

We present a study of electrical and thermal transport in Weyl semimetal WTe₂ down to 0.3 K. The Wiedemann-Franz law holds below 2 K and a downward deviation starts above. The deviation is more pronounced in cleaner samples, as expected in the hydrodynamic picture of electronic transport, where a fraction of electron-electron collisions conserve momentum. Phonons are the dominant heat carriers and their mean-free-path does not display a Knudsen minimum. This is presumably a consequence of weak anharmonicity, as indicated by the temperature dependence of the specific heat. Frequent momentum exchange between phonons and electrons leads to quantum oscillations of the phononic thermal conductivity. Bloch-Grüneisen picture of electron-phonon scattering breaks down at low temperature when Umklapp ph-ph collisions cease to be a sink for electronic flow of momentum. Comparison with semi-metallic Sb shows that normal ph-ph collisions are amplified by anharmonicity. In both semimetals, at cryogenic temperature, e-ph collisions degrade the phononic flow of energy but not the electronic flow of momentum.

Recently, much attention has been focused on the false vacuum islands that are flooded by an expanding ocean of true-vacuum bubbles slightly later than most of the other parts of the world. These delayed decay regions will accumulate locally larger vacuum energy density by staying in the false vacuum longer than those already transited into the true vacuum. A false vacuum island with thus acquired density contrast of a super-horizon size will evolve locally from radiation dominance to vacuum dominance, creating a local baby Universe that can be regarded effectively as a local closed Universe. If such density contrasts of super-horizon sizes can ever grow large enough to exceed the threshold of gravitational collapse, primordial black holes will form similar to those collapsing curvature perturbations on super-horizon scales induced by small-scale enhancements during inflation. If not, such density contrasts can still induce curvature perturbations potentially observable today. In this paper, we revisit and elaborate on the generations of primordial black holes and curvature perturbations from delayed-decayed false vacuum islands during asynchronous first-order phase transitions with fitting formulas convenient for future model-independent studies.

Rare-earth chalcogenide compounds ARECh₂ (A = alkali or monovalent metal, RE = rare earth, Ch = O, S, Se, Te) are a large family of quantum spin liquid (QSL) candidate materials. NaYbS₂ is a representative member of the family. Several key issues on NaYbS₂, particularly how to determine the highly anisotropic spin Hamiltonian and describe the magnetism at finite temperatures and the ground state, remain to be addressed. In this paper, we conducted an in-depth and comprehensive study on the magnetism of NaYbS₂ from finite temperatures to the ground state. Firstly, we successfully detected three crystalline electric field (CEF) excitation energy levels using low-temperature Raman scattering technique. Combining them with the CEF theory and magnetization data, we worked out the CEF parameters, CEF energy levels, and CEF wavefunctions. We further determined a characteristic temperature of ∼40 K, above which the magnetism is dominated by CEF excitations while below which the spin-exchange interactions play a main role. The characteristic temperature has been confirmed by the temperature-dependent electron spin resonance (ESR) linewidth. Low-temperature ESR experiments on the dilute magnetic doped crystal of NaYb_0.1Lu_0.9S₂ further helped us to determine the accurate g-factor. Next, we quantitatively obtained the spin-exchange interactions in the spin Hamiltonian by consistently simulating the magnetization and specific heat data. Finally, the above studies allow us to explore the ground state magnetism of NaYbS₂ by using the density matrix renormalization group. We combined numerical calculations and experimental results to demonstrate that the ground state of NaYbS₂ is a Dirac-like QSL.