Stable quantum interference enabled by coexisting detuned and resonant STIRAPs

Inspired by a recent experiment[Phys.Rev.Lett.122253201(2019)]that an unprecedented quantum interference was observed in the way of stimulated Raman adiabatic passage(STIRAP)due to the coexisting resonant-and detuned-STIRAPs,we comprehensively study this effect.Our results uncover the scheme robustness towards any external-field fluctuations coming from laser intensity noise and imperfect resonance condition,as well as the persistence of high-contrast interference pattern even when more nearby excited levels are involved.We verify that an auxiliary dynamical phase accumulated in hold time caused by the presence of the quasi-dark state in detuned-STIRAP can sensitively manipulate the visibility and frequency of the interference pattern,representing a new hallmark to measure the hyperfine energy accurately.The robust stability of the scheme comes from the intrinsic superiority embedded in the STIRAP mechanism that preserves the coherence of population transfer,which promises a remarkable performance of quantum interference in a practical implementation.

Tunable thermoelectric properties in bended graphene nanoribbons

The ballistic thermoelectric properties in bended graphene nanoribbons（GNRs） are systematically investigated by using atomistic simulation of electron and phonon transport. We find that the electron resonant tunneling effect occurs in the metallic–semiconducting linked ZZ-GNRs（the bended GNRs with zigzag edge leads）. The electron-wave quantum interference effect occurs in the metallic–metallic linked AA-GNRs（the bended GNRs with armchair edge leads）.These different physical mechanisms lead to the large Seebeck coefficient S and high electron conductance in bended ZZGNRs/AA-GNRs. Combined with the reduced lattice thermal conduction, the significant enhancement of the figure of merit ZT is predicted. Moreover, we find that the ZTmax（the maximum peak of ZT） is sensitive to the structural parameters. It can be conveniently tuned by changing the interbend length of bended GNRs. The magnitude of ZT ranges from the 0.15 to 0.72. Geometry-controlled ballistic thermoelectric effect offers an effective way to design thermoelectric devices such as thermocouples based on graphene.

Macroscopic Quantum Tunneling and Coherence of the Néel Vector in Small Antiferromagnets

The tunneling behavior of the Néel vector out of metastable easy directions or between degenerate easy directions is studied for a small single\|domain antiferromagnetic particle at low temperature. The quantum tunneling rates for these processes are evaluated for two examples of macroscopic quantum tunneling and one example of macroscopic quantum coherence. The calculations are performed by using the two sublattice model and the instanton method in the spin coherent state path integral. Quantum interference or the spin parity effect is also discussed for each case.