Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDynamics and thermodynamics in spinor quantum gases
85
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We discuss magnetism in spinor quantum gases theoretically and experimentally with emphasis on temporal dynamics of the spinor order parameter in the presence of an external magnetic field. In a simple coupled Gross-Pitaevskii picture we observe a dramatic suppression of spin dynamics due to quadratic Zeeman dephasing. In view of an inhomogeneous density profile of the trapped condensate we present evidence of spatial variations of spin dynamics. In addition we study spinor quantum gases as a model system for thermodynamics of Bose-Einstein condensation. As a particular example we present measurements on condensate magnetisation due to the interaction with a thermal bath.
rate research
Read More
In ultracold gases many experiments use atom imaging as a basic observable. The resulting image is averaged over a number of realizations and mostly only this average is used. Only recently the noise has been measured to extract physical information. In the present paper we investigate the quantum noise arising in these gases at zero temperature. We restrict ourselves to the homogeneous situation and study the fluctuations in particle number found within a given volume in the gas, and more specifically inside a sphere of radius $R$. We show that zero-temperature fluctuations are not extensive and the leading term scales with sphere radius $R$ as $R^2ln R$ (or $ln R$) in three- (or one-) dimensional systems. We calculate systematically the next term beyond this leading order. We consider first the generic case of a compressible superfluid. Then we investigate the whole Bose-Einstein-condensation (BEC)-BCS crossover crossover, and in particular the limiting cases of the weakly interacting Bose gas and of the free Fermi gas.
Two-dimensional quantum loop gases are elementary examples of topological ground states with Abelian or non-Abelian anyonic excitations. While Abelian loop gases appear as ground states of local, gapped Hamiltonians such as the toric code, we show that gapped non-Abelian loop gases require non-local interactions (or non-trivial inner products). Perturbing a local, gapless Hamiltonian with an anticipated ``non-Abelian ground-state wavefunction immediately drives the system into the Abelian phase, as can be seen by measuring the Hausdorff dimension of loops. Local quantum critical behavior is found in a loop gas in which all equal-time correlations of local operators decay exponentially.
We study single crystals of Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$ under magnetic field and stress applied along their [001] direction. We find that many of the features that the emergent gauge field of spin ice confers to the macroscopic magnetic properties are preserved in spite of the finite temperature. The magnetisation vs. field shows an upward convexity within a broad range of fields, while the static and dynamic susceptibilities present a peculiar peak. Following this feature for both compounds, we determine a single experimental transition curve: that for the Kasteleyn transition in three dimensions, proposed more than a decade ago. Additionally, we observe that compression up to $-0.8%$ along [001] does not significantly change the thermodynamics. However, the dynamical response of Ho$_2$Ti$_2$O$_7$ is quite sensitive to changes introduced in the ${rm Ho}^{3+}$ environment. Uniaxial compression can thus open up experimental access to equilibrium properties of spin ice at low temperatures.
Driven lattice gases as the ASEP are useful tools for the modeling of various stochastic transport processes carried out by self-driven particles, such as molecular motors or vehicles in road traffic. Often these processes take place in one-dimensional systems offering several tracks to the particles, and in many cases the particles are able to change track with a given rate. In this work we consider the case of strong coupling where the hopping rate along the tracks and the exchange rates are of the same order, and show how a phenomenological approach based on a domain wall theory can describe the dynamics of the system. In particular, the domain walls on the different tracks form pairs, whose dynamics dominate the behavior of the system.
Using the recently constructed covariant Ito-Langevin dynamics, we develop a covariant theory of non-equilibrium thermodynamics that is applicable to small systems with multiplicative noises and with slow variables forming curved manifolds. Assuming instantaneous detailed balance, we derive expressions for work, heat, entropy production, and free energy both at ensemble level, as well as at the level of individual dynamic trajectory. We also relate time-reversal asymmetry to entropy production, and derive its consequences such as fluctuation theorem and work relation. The theory is based on Ito-calculus, is fully covariant under time-independent nonlinear transformation of variables, and is applicable to systems strongly coupled to environments.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
