Blind search for 21-cm absorption systems using a new generation of Chinese radio telescopes

Neutral hydrogen clouds are known to exist in the Universe, however their spatial distributions and physical properties are poorly understood. Such missing information can be studied by the new generation of Chinese radio telescopes through a blind search of 21-cm absorption systems. We forecast the capabilities of surveys of 21-cm absorption systems by two representative radio telescopes in China - the Five-hundred-meter Aperture Spherical radio Telescope （FAST） and Tianlai 21-cm cosmology experiment （Tianlai）. Facilitated by either the high sensitivity （FAST） or wide field of view （Tianlai） of these telescopes, more than a thousand 21-cm absorption systems can be discovered in a few years, representing orders of magnitude improvement over the cumulative discoveries in the past half a century.

An Intermediate-field Fast Radio Burst Model and the Quasi-periodic Oscillation

Quasi-periodic oscillation(QPO)signals are discovered in some fast radio bursts(FRBs)such as FRB 20191221A,as well as in the X-ray burst associated with the galactic FRB from SGR 1935+2154.We revisit the intermediatefield FRB model where the radio waves are generated as fast-magnetosonic waves through magnetic reconnection near the light cylinder.The current sheet in the magnetar wind is compressed by a low frequency pulse emitted from the inner magnetosphere to trigger magnetic reconnection.By incorporating the wave dynamics of the magnetosphere,we demonstrate how the FRB frequency,the single pulse width,and luminosity are determined by the period,magnetic field,QPO frequency and quake energetics of the magnetar.We find that this model can naturally and self-consistently interpret the X-ray/radio event from SGR 1935+2154 and the QPO in FRB20191221A.It can also explain the observed wide energy range of repeating FRBs in a narrow bandwidth.

Planar matrices and arrays of Feynman diagrams:poles for higher k

Planar arrays of tree diagrams were introduced as a generalization of Feynman diagrams that enable the computation of biadjoint amplitudes m_(n)(^(k))for k>2.In this follow-up work,we investigate the poles of m_(n)(^(k))from the perspective of such arrays.For general k,we characterize the underlying polytope as a Flag Complex and propose a computation of the amplitude-based solely on the knowledge of the poles,whose number is drastically less than the number of the full arrays.As an example,we first provide all the poles for the cases(k,n)=(3,7),(3,8),(3,9),(3,10),(4,8)and(4,9)in terms of their planar arrays of degenerate Feynman diagrams.We then implement simple compatibility criteria together with an addition operation between arrays and recover the full collections/arrays for such cases.Along the way,we implement hard and soft kinematical limits,which provide a map between the poles in kinematic space and their combinatoric arrays.We use the operation to give a proof of a previously conjectured combinatorial duality for arrays in(k,n)and(n-k,n).We also outline the relation to boundary maps of the hypersimplex Δ_(k,n) and rays in the tropical Grassmannian Tr(k,n).

A Lattice Non-Perturbative Definition of an SO(10) Chiral Gauge Theory and Its Induced Standard Model

The standard model is a chiral gauge theory where the gauge fields couple to the right-hand and the left-hand fermions differently.The standard model is defined perturbatively and describes all elementary particles(except gravitons)very well.However,for a long time,we do not know if we can have a non-perturbative definition of the standard model as a Hamiltonian quantum mechanical theory.Here we propose a way to give a modified standard model(with 48 two-component Weyl fermions)a non-perturbative definition by embedding the modified standard model into an SO(10)chiral gauge theory.We show that the SO(10)chiral gauge theory can be put on a lattice(a 3D spatial lattice with a continuous time)if we allow fermions to interact.Such a non-perturbatively defined standard model is a Hamiltonian quantum theory with a finite-dimensional Hilbert space for a finite space volume.More generally,using the defining connection between gauge anomalies and the symmetry-protected topological orders,one can show that any truly anomaly-free chiral gauge theory can be non-perturbatively defined by putting it on a lattice in the same dimension.

Cosmological neutrino simulations at extreme scale

Constraining neutrino mass remains an elusive challenge in modern physics.Precision measurements are expected from several upcoming cosmological probes of large-scale structure.Achieving this goal relies on an equal level of precision from theoretical predictions of neutrino clustering.Numerical simulations of the non-linear evolution of cold dark matter and neutrinos play a pivotal role in this process.We incorporate neutrinos into the cosmological N-body code CUBEP3M and discuss the challenges associated with pushing to the extreme scales demanded by the neutrino problem.We highlight code optimizations made to exploit modern high performance computing architectures and present a novel method of data compression that reduces the phase-space particle footprint from 24 bytes in single precision to roughly 9 bytes.We scale the neutrino problem to the Tianhe-2 supercomputer and provide details of our production run,named Tian Nu,which uses 86%of the machine(13 824 compute nodes).With a total of 2.97 trillion particles,Tian Nu is currently the world’s largest cosmological N-body simulation and improves upon previous neutrino simulations by two orders of magnitude in scale.We finish with a discussion of the unanticipated computational challenges that were encountered during the Tian Nu runtime.

Planar matrices and arrays of Feynman diagrams

Recently,planar collections of Feynman diagrams were proposed by Borges and one of the authors as the natural generalization of Feynman diagrams for the computation of k=3 biadjoint amplitudes.Planar collections are one-dimensional arrays of metric trees satisfying an induced planarity and compatibility condition.In this work,we introduce planar matrices of Feynman diagrams as the objects that compute k=4 biadjoint amplitudes.These are symmetric matrices of metric trees satisfying compatibility conditions.We introduce two notions of combinatorial bootstrap techniques for finding collections from Feynman diagrams and matrices from collections.As applications of the first,we find all 693,13612 and 346710 collections for(k,n)=(3,7),(3,8)and(3,9),respectively.As applications of the second kind,we find all90608 and 30659424 planar matrices that compute(k,n)=(4,8)and(4,9)biadjoint amplitudes,respectively.As an example of the evaluation of matrices of Feynman diagrams,we present the complete form of the(4,8)and(4,9)biadjoint amplitudes.We also start a study of higher-dimensional arrays of Feynman diagrams,including the combinatorial version of the duality between(k,n)and(n-k,n)objects.

Optimal photonic indistinguishability tests in multimode networks

Particle indistinguishability is at the heart of quantum statistics that regulates fundamental phenomena such as the electronic band structure of solids, Bose-Einstein condensation and superconductivity.Moreover, it is necessary in practical applications such as linear optical quantum computation and simulation, in particular for Boson Sampling devices.It is thus crucial to develop tools to certify genuine multiphoton interference between multiple sources.Our approach employs the total variation distance to find those transformations that minimize the error probability in discriminating the behaviors of distinguishable and indistinguishable photons.In particular, we show that so-called Sylvester interferometers are near-optimal for this task.By using Bayesian tests and inference, we numerically show that Sylvester transformations largely outperform most Haar-random unitaries in terms of sample size required.Furthermore, we experimentally demonstrate the efficacy of the transformation using an efficient 3 D integrated circuits in the single-and multiple-source cases.We then discuss the extension of this approach to a larger number of photons and modes.These results open the way to the application of Sylvester interferometers for optimal assessment of multiphoton interference experiments.

Experimental preparation of topologically ordered states via adiabatic evolution

Topological orders are a class of exotic states of matter characterized by patterns of long-range entanglement. Certain topologically ordered systems are proposed as potential realization of fault-tolerant quantum computation. Topological orders can arise in two-dimensional spin-lattice models. In this paper, we engineer a time-dependent Hamiltonian to prepare a topologically ordered state through adiabatic evolution. The other sectors in the degenerate ground-state space of the model are obtained by applying nontrivial operations corresponding to closed string operators. Each sector is highly entangled, as shown from the completely reconstructed density matrices. This paves the way towards exploring the properties of topological orders and the application of topological orders in topological quantum memory.

Photon sphere and phase transition of ddimensional(d≥5) charged Gauss–Bonnet AdS black holes

Motivated by recent work,nonmonotonic behaviors of photon sphere radius can be used to reflect black hole phase transition for Reissner–Nordstr?m–AdS(RN–AdS)black holes,we study the case of five-dimensional charged Gauss–Bonnet–AdS black holes in the reduced parameter space.We find that the nonmonotonic behaviors of photon sphere radius still exist.Using the coexistence line calculated from P–V plane,we capture the photon sphere radius of saturated small and large black holes(the boundary of the coexistence phase),then illustrate the reduced coexistence region.The results show that,reduced coexistence region decreases with charge Q but increases with Gauss–Bonnet coefficientα.When the charge vanishes,reduced coexistence region does not vary with Gauss–Bonnet coefficientαany more.In this case,the Gauss–Bonnet coefficientαplays the same role as the charge of five-dimensional RN–AdS black holes.Also,the situation of higher dimension is studied in the end.

Joint product numerical range and geometry of reduced density matrices

The reduced density matrices of a many-body quantum system form a convex set, whose three-dimensional projection Θ is convex in R3. The boundary ?Θ of Θ may exhibit nontrivial geometry, in particular ruled surfaces. Two physical mechanisms are known for the origins of ruled surfaces: symmetry breaking and gapless. In this work, we study the emergence of ruled surfaces for systems with local Hamiltonians in infinite spatial dimension, where the reduced density matrices are known to be separable as a consequence of the quantum de Finetti's theorem. This allows us to identify the reduced density matrix geometry with joint product numerical range Π of the Hamiltonian interaction terms. We focus on the case where the interaction terms have certain structures, such that a ruled surface emerges naturally when taking a convex hull of Π. We show that, a ruled surface on ?Θsitting in Π has a gapless origin, otherwise it has a symmetry breaking origin. As an example, we demonstrate that a famous ruled surface, known as the oloid, is a possible shape of Θ, with two boundary pieces of symmetry breaking origin separated by two gapless lines.

Physical origins of ruled surfaces on the reduced density matrices geometry

The reduced density matrices(RDMs) of many-body quantum states form a convex set. The boundary of low dimensional projections of this convex set may exhibit nontrivial geometry such as ruled surfaces. In this paper, we study the physical origins of these ruled surfaces for bosonic systems. The emergence of ruled surfaces was recently proposed as signatures of symmetrybreaking phase. We show that, apart from being signatures of symmetry-breaking, ruled surfaces can also be the consequence of gapless quantum systems by demonstrating an explicit example in terms of a two-mode Ising model. Our analysis was largely simplified by the quantum de Finetti's theorem—in the limit of large system size, these RDMs are the convex set of all the symmetric separable states. To distinguish ruled surfaces originated from gapless systems from those caused by symmetrybreaking, we propose to use the finite size scaling method for the corresponding geometry. This method is then applied to the two-mode XY model, successfully identifying a ruled surface as the consequence of gapless systems.