Bosonization and doubling

Konstantinos G. Lagoudakis

One of the most striking manifestations of the quantum collective behavior of matter is the Josephson effect: it allows for a classically forbidden current to flow without dissipation [125]. Traditional Josephson junctions are built by means of superconductors separated by thin non-conducting oxide barriers and they have drawn an intense interest for their striking phenomenology. A bosonic analog is the so-called Bosonic Josephson junction (BJJ) where two macroscopic populations of bosons are trapped in a double well geometry. Bose-Einstein condensation of dilute atomic gases has allowed for the demonstration of BJJs by trapping two condensates in double wells [126],[127].

Philip Phillips

Fujisawa, T., Wilfred G. van der Wiel, Leo P. Kouwenhoven +2 more

Coupling a quantum system to a bosonic environment always give rise to inelastic processes, which reduce the coherency of the system. We measure energy-dependent rates for inelastic tunneling processes in a fully controllable two-level system of a double quantum dot. The emission and absorption rates are well reproduced by Einstein's coefficients, which relate to the spontaneous emission rate. The inelastic tunneling rate can be comparable to the elastic tunneling rate if the boson occupation number becomes large. In the specific semiconductor double dot, the energy dependence of the inelastic rate suggests that acoustic phonons are coupled to the double dot piezoelectrically.

Yitzhak Frishman, Jacob Sonnenschein B

Hou Zhi-lan

Double-parameter variational approach in combination with the spin-boson model to study the macroscopic quantum effect of molecules magnet is emploied, further investigated the ground state energy of spin-boson model and the phase boundary of two-level system from delocalized to localized phases by numerical calculation. The computational results show that the double-parameter variational approach can deduce lower ground state energy than two types of single-parameter variational approaches, which indicates the superiority of the double-parameter variational approach. Calculations also show that different variational approach can result in different ground state energy and phase boundary. The further discussions are focused on the results of the double parameters variational approach, and a brief comparison with two types of single-parameter variational approaches is also presented.