Relaxation in a double potential well

Ilaria Cacciari, Paolo Moretti

Christopher Feuillade, C. Böttcher

Boguslaw Stec, Czesław Jędrzejek

Jayson G. Cosme

We numerically investigate the relaxation dynamics in an isolated quantum system of interacting bosons trapped in a double-well potential after an integrability breaking quench. Using the statistics of the spectrum, we identify the postquench Hamiltonian as nonchaotic and close to integrability over a wide range of interaction parameters. We demonstrate that the system exhibits thermalization in the context of the eigenstate thermalization hypothesis (ETH). We also explore the possibility of an initial state to delocalize with respect to the eigenstates of the postquench Hamiltonian even for energies away from the middle of the spectrum. We observe distinct regimes of equilibration process depending on the initial energy. For low energies, the system rapidly relaxes in a single step to a thermal state. As the energy increases towards the middle of the spectrum, the relaxation dynamics exhibits prethermalization and the lifetime of the metastable states grows. Time evolution of the occupation numbers and the von Neumann entropy in the mode-partitioned system underpins the analyses of the relaxation dynamics.

Wei Li Wu, Jing-Dong Bao

M. Podt, A.J. Mieog, B. G.A. Rolink +2 more

A digital double relaxation oscillation (DROS) superconducting quantum interference device (SQUID) has the potential for a very large dynamic range and a slew rate that is orders of magnitude larger than that of conventional SQUID systems. This is, for example, advantageous when using the SQUID in an unshielded environment. An important characteristic of the digital DROS is that the feedback flux is quantized since this flux is supplied by a superconducting up-down counter. Together with the clock frequency, the quantization unit of the feedback flux determines the maximum slew rate. In an optimized design, the quantization unit is adapted to the broadband flux noise of the DROS, so that the slew rate is maximized without compromising the sensitivity. Simulations on our optimized digital DROS showed proper operation for slew rates up to 5×10 6 Φ 0 s -1 . The relaxation oscillations generated at a frequency of 100 MHz deliver an on-chip clock signal, so that no external clock is required. Slew rates up to 10 8 Φ 0 s -1 can be achieved by increasing the relaxation oscillation frequency to a few GHz. This means that sub-µm 2 Josephson junctions with high critical current densities are required. The first experiments using low- T c ramp-type Josephson junctions are presented in this paper.