Thermalization of isolated quantum many-body system and entanglement

Thermalization of an isolated quantum system has been a non-trivial problem since the early days of quantum mechanics. In generic isolated systems, non-equilibrium dynamics is expected to result in thermalization, indicating the emergence of statistical mechanics from quantum dynamics. However, what feature of many-body quantum system facilitates quantum thermalization is still not well understood. Here we revisit this problem and show that introduction of entanglement in the system gives rise to thermalization, and it takes place at the level of individual eigenstate. We also show that the expectation value in the energy eigenstate of each subsystem is close to the canonical average.Comment: Suggestions welcom

Using thermodynamics to identify quantum subsystems

There are many ways to decompose the Hilbert space ℋ of a composite quantum system into tensor product subspaces. Different subsystem decompositions generally imply different interaction Hamiltonians V, and therefore different expectation values for subsystem observables. This means that the uniqueness of physical predictions is not guaranteed, despite the uniqueness of the total Hamiltonian H and the total Hilbert space ℋ. Here we use Clausius’ version of the second law of thermodynamics (CSL) and standard identifications of thermodynamic quantities to identify possible subsystem decompositions. It is shown that agreement with the CSL is obtained, whenever the total Hamiltonian and the subsystem-dependent interaction Hamiltonian commute (i.e. [H,V]=0). Not imposing this constraint can result in the transfer of heat from a cooler to a hotter subsystem, in conflict with thermodynamics. We also investigate the status of the CSL with respect to non-standard definitions of thermodynamic quantities and quantum subsystems

Cavity-mediated collective laser-cooling of a non-interacting atomic gas inside an asymmetric trap to very low temperatures

In this paper, we identify a many-particle phonon expectation value ζ with the ability to induce collective dynamics in a non-interacting atomic gas inside an optical cavity. We then propose to utilise this expectation value to enhance the laser cooling of many atoms through a cyclic two-stage process which consists of cooling and displacement stages. During cooling stages, short laser pulses are applied. These use ζ as a resource and decrease the vibrational energy of the atomic gas by a fixed amount. Subsequent displacement stages use the asymmetry of the trapping potential to replenish the many-particle phonon expectation value ζ.. Alternating both stages of the cooling process is shown to transfer the atomic gas to a final temperature which vanishes in the infinitely-many particle limit

Application of radio frequency based digital thermometer for real-time monitoring of dairy cattle rectal temperature

Aim: Dairy cattle health monitoring program becomes vital for detecting the febrile conditions to prevent the outbreak of the animal diseases as well as ensuring the fitness of the animals that are directly affecting the health of the consumers. The aim of this study was to validate real-time rectal temperature (RT) data of radio frequency based digital (RFD) thermometer with RT data of mercury bulb (MB) thermometer in dairy cattle. Materials and Methods: Two experiments were conducted. In experiment I, six female Jersey crossbred cattle with a mean (±standard error of the mean) body weight of 534.83±13.90 kg at the age of 12±0.52 years were used to record RT for 2 h on empty stomach and 2 h after feeding at 0, 30, 60, 90, and 120 min using a RFD thermometer as well as a MB thermometer. In experiment II, six female Jersey crossbred cattle were further used to record RT for 2 h before exercise and 2 h after exercise at 0, 30, 60, 90, and 120 min. Two-way repeated measures analysis of variance with post hoc comparisons by Bonferroni test was done. Results: Real-time RT data recorded by RFD thermometer as well as MB thermometer did not differ (p>0.05) before and after feeding/exercise. An increase (p<0.05) in RT after feeding/exercise in experimental crossbred cattle was recorded by both RFD thermometer and MB thermometer. Conclusion: The results obtained in the present study suggest that the body temperature recordings from RFD thermometer would be acceptable and thus RFD thermometer could work well for monitoring real-time RT in cattle