41 research outputs found
Changeover from the discontinuous to continuous phase transitions in dissipative spin system with collective decay
We investigate the steady-state phase transitions in an all-to-all
transverse-field Ising model subjected to an environment. The considered model
is composed of two ingredient Hamiltonians. The orientation of the external
field, which is perpendicular to the spin interaction, can be tuned to be along
either -direction or -direction in each ingredient Hamiltonian while the
dissipations always tend to flip the spins down to the -direction. By means
of mean-field approximation, we find that the quasi continuous steady-state
phase transition is presented as a consequence of the merging of two branches
of steady-state solutions. The emergence of bistability is confirmed by
analyzing the steady-state behaviors of a set of finite-size systems which is
also revealed by the Liouvillian spectrum.Comment: 9 pages, 6 figure
Steady-state phase diagram of a driven QED-cavity array with cross-Kerr nonlinearities
We study the properties of an array of QED-cavities coupled by nonlinear
elements in the presence of photon leakage and driven by a coherent source. The
main effect of the nonlinear couplings is to provide an effective cross-Kerr
interaction between nearest-neighbor cavities. Additionally, correlated photon
hopping between neighboring cavities arises. We provide a detailed mean-field
analysis of the steady-state phase diagram as a function of the system
parameters, the leakage, and the external driving, and show the emergence of a
number of different quantum phases. A photon crystal associated to a spatial
modulation of the photon blockade appears. The steady state can also display
oscillating behavior and bistability. In some regions the crystalline ordering
may coexist with the oscillating behavior. Furthermore we study the effect of
short-range quantum fluctuations by employing a cluster mean-field analysis.
Focusing on the corrections to the photon crystal boundaries, we show that,
apart for some quantitative differences, the cluster mean field supports the
findings of the simple single-site analysis. In the last part of the paper we
concentrate on the possibility to build up the class of arrays introduced here,
by means of superconducting circuits of existing technology. We consider a
realistic choice of the parameters for this specific implementation and discuss
some properties of the steady-state phase diagram.Comment: 11 pages, 12 figure
Photon solid phases in driven arrays of nonlinearly coupled cavities
We introduce and study the properties of an array of QED cavities coupled by
nonlinear elements, in the presence of photon leakage and driven by a coherent
source. The nonlinear couplings lead to photon hopping and to nearest-neighbor
Kerr terms. By tuning the system parameters, the steady state of the array can
exhibit a photon crystal associated with a periodic modulation of the photon
blockade. In some cases, the crystalline ordering may coexist with phase
synchronization. The class of cavity arrays we consider can be built with
superconducting circuits of existing technology.Comment: 8 pages, 8 figures. Published versio
Quantum non-stationary phenomena of spin systems in collision models
We investigate the non-stationary phenomenon in a tripartite spin-1/2 system
in the collision model (CM) framework. After introducing the dissipation
through the system-environment collision for both Markovian and non-Markovian
cases, we find the emergence of long-time oscillation in the dynamics of the
system and the synchronization among subsystems. We connect the CM description
and the quantum master equation in the continuous time limit and explain the
existence of the stable oscillation by means of Liouvillian spectrum analysis.
The time-dependence of the thermal property and the correlations are
investigated, in particular we discuss the possibility of violation of the
Landauer's principle in non-Markovian dynamics. In addition, we find that the
imperfection of collective dissipation can be compensated by the randomness of
the interaction sequence in our CM.Comment: 13 pages, 8 figures, accepted versio
Linked cluster expansions for open quantum systems on a lattice
We propose a generalization of the linked-cluster expansions to study
driven-dissipative quantum lattice models, directly accessing the thermodynamic
limit of the system. Our method leads to the evaluation of the desired
extensive property onto small connected clusters of a given size and topology.
We first test this approach on the isotropic spin-1/2 Hamiltonian in two
dimensions, where each spin is coupled to an independent environment that
induces incoherent spin flips. Then we apply it to the study of an anisotropic
model displaying a dissipative phase transition from a magnetically ordered to
a disordered phase. By means of a Pad\'e analysis on the series expansions for
the average magnetization, we provide a viable route to locate the phase
transition and to extrapolate the critical exponent for the magnetic
susceptibility.Comment: 10 pages, 5 figure
Dissipation induced quantum synchronization in few-body spin systems
We explore the synchronization phenomenon in quantum few-body spin system
with the non-local dissipation by quantum trajectory approach. We find that
even without external drive, the system can achieve spontaneous synchronization
due to the interaction of non-local dissipation, and the time-dependent
non-stationarity oscillations can be confirmed through the purely imaginary
eigenvalues of the Liouvillian. We theoretically analyze the dissipative
dynamics of the system and consider the measure to quantify synchronization
through the stochastic quantum trajectories. In each quantum trajectory, it is
also possible for the system to ignore dissipative process and build up
oscillations in the long-time evolution. We finally investigate the robustness
of the oscillations to perturbations, and determine the so-call the largest
Lyapunov exponent to confirm the stability of oscillations.Comment: 8 pages, 5 figure
All-optical non-Markovian stroboscopic quantum simulator
An all-optical scheme for simulating non-Markovian evolution of a quantum
system is proposed. It uses only linear optics elements and by controlling the
system parameters allows one to control the presence or absence of information
backflow from the environment. A sufficient and necessary condition for the
non-Markovianity of our channel based on Gaussian inputs is proved. Various
criteria for detecting non-Markovianity are also investigated by checking the
dynamical evolution of the channel.Comment: 7 figures. Typos are corrected and new reference is adde
Soil Organic Carbon Content and Microbial Functional Diversity Were Lower in Monospecific Chinese Hickory Stands than in Natural Chinese Hickory–Broad-Leaved Mixed Forests
To assess the effects of long-term intensive management on soil carbon cycle and microbial functional diversity, we sampled soil in Chinese hickory (Carya cathayensis Sarg.) stands managed intensively for 5, 10, 15, and 20 years, and in reference Chinese hickory–broad-leaved mixed forest (NMF) stands. We analyzed soil total organic carbon (TOC), microbial biomass carbon (MBC), and water-soluble organic carbon (WSOC) contents, applied 13C-nuclear magnetic resonance analysis for structural analysis, and determined microbial carbon source usage. TOC, MBC, and WSOC contents and the MBC to TOC ratios were lower in the intensively managed stands than in the NMF stands. The organic carbon pool in the stands managed intensively for twenty years was more stable, indicating that the easily degraded compounds had been decomposed. Diversity and evenness in carbon source usage by the microbial communities were lower in the stands managed intensively for 15 and 20 years. Based on carbon source usage, the longer the management time, the less similar the samples from the monospecific Chinese hickory stands were with the NMF samples, indicating that the microbial community compositions became more different with increased management time. The results call for changes in the management of the hickory stands to increase the soil carbon content and restore microbial diversity