Relaxation under conditions of strong interaction

Mio Murao, Fumiaki Shibata

Mikhail V. Petrenko, Anton K. Vershovskii

Hydrogen-like alkali atoms with a single valence electron are the most common objects in quantum optics and, at the same time, serve as essential tools of the field. Under conditions of optical pumping, strong spin-exchange and ultra-weak magnetic field (spin-exchange relaxation free mode, SERF), ensembles of such atoms in the gas phase can demonstrate not only the absence of spin-exchange relaxation, but also nonlinear collective effects. We present experimental evidence that the alignment, i.e. the quadrupole momentum, can not only be preserved under SERF conditions, but also coexist and interact with the orientation, i.e. the dipole momentum. We also show that this interaction leads to bistability: a small change in conditions can cause the medium to transition to a different steady state, an effect characterized by hysteresis. The combination of properties of this effect opens up a wide range of applications as optical keys or memory elements with a storage time of hundreds of seconds in tasks of quantum information and cryptography.

Adithya Kandhadai, Antony Valentini

Malcolm L. Stitch

The theoretical power output of a ruby laser is examined under certain idealized operating conditions, and it is found that there are two principal regions of operation. These are the regions of strong oscillation characterized by the condition pτ2/A»hν13/σ13 and the region of saturation in which pτ3/A»hν13/σ13. Here p/A is the ``pumping'' illumination within the absorption band of ruby, τ2 is a charactersitic relaxation time of fluorescence in ruby, τ3 is a characteristic thermal relaxation time from the excited U band, ν13 is the pumping frequency, and σ13 is the cross section for interaction between pumping radiation and Cr3+ ions in ruby. Efficiency of operation is examined under two limiting conditions.

Sumita Datta

The Mpemba effect, broadly understood as the counterintuitive phenomenon in which a system initially farther from equilibrium relaxes faster than a system closer to equilibrium, has been widely studied in classical stochastic systems and, more recently, in quantum settings. However, its manifestation is strongly dependent on the choice of observable and the dynamical constraints of the system. In this work, we investigate the emergence of a Mpemba-type effect in the density redistribution dynamics of a strongly interacting one-dimensional Bose gas in the Tonks-Girardeau regime undergoing a sudden box expansion from length L_0 to L. By defining a physically motivated distance function based on the difference of densities between spatial regions, we provide evidence that -the relaxation dynamics of the ground and excited symmetry sectors exhibit a clear crossing in time, indicating a reversal in relaxation ordering. We emphasize that the Mpemba effect is not a universal law but rather an observable-dependent phenomenon that arises under specific dynamical conditions. In particular, we show that the interplay between initial state structure, integrability, and spatial redistribution leads to distinct relaxation pathways that enable the effect. Our results clarify common misconceptions linking the Mpemba effect to Newton's law of cooling and highlight the conditions under which such anomalous relaxation behavior can emerge in integrable quantum systems.

И. В. Александров