Many-body Tunneling and Nonequilibrium Dynamics of Doublons in Strongly Correlated Quantum Dots

Many-body tunneling and nonequilibrium dynamics in double quantum dots with capacitive coupling

Double quantum dots (DQDs) systems may be the minimal setups for realization of QD-based qubits and quantum computation. Pauli spin blockade (PSB) and a kind of novel many-body tunneling (MBT) are identified to play important roles in these systems, and dominate the quantum tunneling at moderate and weak interdot coupling t, respectively. On the other hand, inter-dot Coulomb interaction U' and related inter-dot Coulomb blockade (IDCB) is inevitable in DQDs. However, what would happen on the effect of U' in DQDs has not been touched, in particular for PSB and MBT. Here, we study the tunneling processes and transport properties with various U' in series-coupled DQDs, and find MBT process is rather robust against U' within U'/U < 0.1, where U is the intra-dot Coulomb interaction. Meanwhile, the linearity relationship between the carrier doublon number and MBT current remains valid. These findings enrich the understanding of the many-body tunneling in the DQDs and may shed light on the manipulation of the QD-based qubits.

Ferromagnetic Phase in Nonequilibrium Quantum Dots

By nonperturbatively solving the nonequilibrium Anderson two-impurity model with the hierarchical equations of motion approach, we report a robust ferromagnetic (FM) phase in series-coupled double quantum dots, which can suppress the antiferromagnetic (AFM) phase and dominate the phase diagram at finite bias and detuning energy in the strongly correlated limit. The FM exchange interaction origins from the passive parallel spin arrangement caused by the Pauli exclusion principle during the electrons transport. At very low temperature, the Kondo screening of the magnetic moment in the FM phase induces some nonequilibrium Kondo effects in magnetic susceptibility, spectral functions and current. In the weakly correlated limit, the AFM phase is found still stable, therefore, a magnetic-field-free internal control of spin states can be expected through the continuous FM–AFM phase transition.

Manipulation of Pauli spin blockade in double quantum dot systems

Pauli spin blockade (PSB) is a significant physical effect in double quantum dot (DQD) systems. In this paper, we start from the fundamental quantum model of the DQD with the electron-electron interaction being considered and then systematically study the PSB effect in DQD by using a recently developed nonperturbative method, the hierarchical equations of motion approach. By checking the current-voltage and nonequilibrium spectral function features, the physical picture of the PSB is explicitly elucidated. Then, various kinds of manipulation of PSBs are discussed, including gate voltage, exchange interaction, and electron spin resonance. Three main characteristics beyond low-order perturbation theory are demonstrated in detail as follows: (1) the finite leakage current in the strongly correlated limit; (2) the enhancement and lifting of PSB by exchange interaction; and (3) the ON-and-OFF switch of PSB by real-time modulation.