We demonstrate particle clustering on macroscopic scales in a coupled nonequilibrium system where two species of particles are advected by a fluctuating landscape and modify the landscape in the process. The phase diagram generated by varying the particle-landscape coupling, valid for all particle density and in both one and two dimensions, shows novel nonequilibrium phases. While particle species are completely phase separated, the landscape develops macroscopically ordered regions coexisting with a disordered region, resulting in coarsening and steady state dynamics on time scales which grow algebraically with size, not seen earlier in systems with pure domains.PACS numbers: 64.75.Gh, 68.43.Jk Particle clustering is important in many natural physical and biological phenomena, for instance, the formation of sediments [1] and protein clustering on a biological membrane [2]. Evidently, it is important to understand processes that cause clustering in different physical contexts, and how these processes influence the properties of the cluster and the time taken to form it. Often, large-scale clustering is driven by interactions with an external medium which itself has correlations in space and time [3][4][5]. An important physical effect in such systems is the back-influence of the particles on the medium. This interaction can aid clustering, or destroy it. If a cluster does form, it may be compact and robust, or a dynamic object that undergoes constant reorganization. The formation time may grow exponentially with the size, or as a power law. Given this wealth of possibilities, it is important to look for an understanding, within simple models, of the circumstances under which different sorts of macroscopically clustered states occur.In this letter, we derive the phase diagram of a simple model system as we vary the interaction between the environment and particles. In the process, we unmask a novel non-equilibrium phase of particles with compact clustering and rich and rapid dynamics coexisting with a macroscopically organized landscape. The model has partial overlap with the lattice gas model of Lahiri and Ramaswamy (LR) for sedimenting colloidal crystals [6,7], but the new phases manifest themselves outside the LR regime. Our results hold in both one and two dimensions.The model consists of two sets of particles moving stochastically in a fluctuating potential energy landscape. Particles try to minimize their energy by (a) moving along the local potential gradient of the landscape and (b) modifying the landscape around them in such a way as to lower the energy further. The model is generic but we discuss it in the language of particles confined to move on a fluctuating surface in the presence of gravity, where the particles can locally distort the surface shape to further lower the energy (see Fig. 1). One of the particle species is considered lighter and the other is heavier; we use the name LH (Light-heavy) model to describe the system. Process (b) affects the landscape dynamics quite differently in parts...

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We consider a minimal model to describe the quantum phases of ultracold dipolar bosons in two-dimensional (2D) square optical lattices. The model is a variation of the extended Bose-Hubbard model and apt to study the quantum phases arising from the variation in the tilt angle θ of the dipolar bosons. At low tilt angles 0 • θ 25 • , the ground state of the system are phases with checkerboard order, which could be either checkerboard supersolid or checkerboard density wave. For high tilt angles 55 • θ 35 • , phases with striped order of supersolid or density wave are preferred. In the intermediate domain 25 • θ 35 • an emulsion or SF phase intervenes the transition between the checkerboard and striped phases. The attractive interaction dominates for θ 55 • , which renders the system unstable and there is a density collapse. For our studies we use Gutzwiller mean-field theory to obtain the quantum phases and the phase boundaries. In addition, we calculate the phase boundaries between an incompressible and a compressible phase of the system by considering second order perturbation analysis of the mean-field theory. The analytical results, where applicable, are in excellent agreement with the numerical results.

Bacteria are far more intelligent than we can think of. They adopt different survival strategies to make their life comfortable. Researches on bacterial communication to date suggest that bacteria can communicate with each other using chemical signaling molecules as well as using ion channel mediated electrical signaling. Though in past few decades the scopes of chemical signaling have been investigated extensively, those of electrical signaling have received less attention. In this article, we present a novel perspective on time-sharing behavior, which maintains the biofilm growth under reduced nutrient supply between two distant biofilms through electrical signaling based on the experimental evidence reported by Liu et al., in 2017. In addition, following the recent work by Humphries et al. Cell 168(1):200-209, in 2017, we highlight the consequences of long range electrical signaling within biofilm communities through spatially propagating waves of potassium. Furthermore, we address the possibility of two-way cellular communication between artificial and natural cells through chemical signaling being inspired by recent experimental observation (Lentini et al. 2017) where the efficiency of artificial cells in imitating the natural cells is estimated through cellular Turing test. These three spectacular observations lead us to envisage and devise new classical and quantum views of these complex biochemical networks that have never been realized previously.

Quantum Hall (QH) states of two dimensional (2D) single layer optical lattices are examined using Bose-Hubbard model (BHM) in presence of artificial gauge field. We study the QH states of both the homogeneous and inhomogeneous systems. For the homogeneous case we use cluster Gutzwiller mean-field (CGMF) theory with cluster sizes ranging from 2 × 2 to 5 × 5. We, then, consider the inhomogeneous case, which is relevant to experimental realization. In this case, we use CGMF and exact diagonalization (ED). The ED studies are using lattice sizes ranging from 3 × 3 to 4 × 12. Our results show that the geometries of the QH states are sensitive to the magnetic flux α and cluster sizes. For homogeneous system, among various combinations of 1/5 α 1/2 and filling factor ν, only the QH state of α = 1/4 with ν = 1/2, 1, 3/2 and 2 occur as ground states. For other combinations, the competing superfluid (SF) state is the ground state and QH state is metastable. For BHM with envelope potential, all the QH states observed in homogeneous system exist for box potentials, but none for the harmonic potential. The QH states also persist for very shallow Gaussian envelope potential. As a possible experimental signature we study the two-point correlations of the QH and SF states.

Biofilms are the compact association of micro organisms and the communication processes in these biofilms are always a wonder. Electrical and chemical signaling mechanism are the key to understand the bacterial communication network. Quorum sensing so far has been able to explain the coordinated motion of bacteria through its chemical signaling mechanism. Bacteria residing within biofilm communities are trivial to communicate. But the recent observation in 2017 by Humphries et al. has revealed that the ion channels enabled electrical signaling mechanism can be as powerful as to attract the distant cells i.e., this signaling mechanism are capable of holding a long range behavior. As a result long range cross species communication in the bacterial world have been possible. This substantial outcome has brought this field into a new paradigm to investigate the complex co-existence of biofilm communities and distant cells with a possible scope of application in synthetic biology. In this present article, we briefly describe this new signaling mechanism and how it gives rise to a long range communication ability in bacterial communities.

We examine the effects of an artificial gauge field and finite temperature in a two-dimensional disordered Bose-Hubbard model. The disorder considered is diagonal and quenched in nature. A signature of disorder in the Bose-Hubbard model is the Bose glass phase. Our work shows that the introduction of an artificial gauge field enhances the domain of the Bose glass phase in the phase diagram. Most importantly, the size of the domain can be tuned with the strength of the artificial gauge field. The introduction of the finite temperature effects is essential to relate theoretical results with the experimental realizations. For our studies we use the single site and cluster Gutzwiller mean-field theories. The results from the latter are more reliable as it better describes the correlation effects. Our results show that the Bose glass phase has a larger domain with the latter method.arXiv:1807.00269v2 [cond-mat.quant-gas]

We develop a variational theory for a dipolar condensate in an elongated (cigar shaped) confinement potential. Our formulation provides an effective one-dimensional extended meanfield theory for the ground state and its collective excitations. We apply our theory to investigate the properties of rotons in the system comparing the variational treatment to a full numerical solution. We consider the effect of quantum fluctuations on the scattering length at which the roton excitation softens to zero energy.