Dynamical second-order noise sweetspots in resonantly driven spin qubits

Quantum dot-based quantum computation employs extensively the exchange interaction between nearby electronic spins in order to manipulate and couple different qubits. The exchange interaction, however, couples the qubit states to charge noise, which reduces the fidelity of the quantum gates that employ it. The effect of charge noise can be mitigated by working at noise sweetspots in which the sensitivity to charge variations is reduced. In this work we study the response to charge noise of a double quantum dot based qubit in the presence of ac gates, with arbitrary driving amplitudes, applied either to the dot levels or to the tunneling barrier. Tuning with an ac driving allows to manipulate the sign and strength of the exchange interaction as well as its coupling to environmental electric noise. Moreover, we show the possibility of inducing a second-order sweetspot in the resonant spin-triplet qubit in which the dephasing time is significantly increased.

Stabilizing nanolasers via polarization lifetime tuning

We investigate the emission dynamics of mutually coupled nanolasers and predict ways to optimize their stability, i.e., maximize their locking range. We find that tuning the cavity lifetime to the same order of magnitude as the dephasing time of the microscopic polarization yields optimal operation conditions, which allow for wider tuning ranges than usually observed in conventional semiconductor lasers. The lasers are modeled by Maxwell–Bloch type class-C equations. For our analysis, we analytically determine the steady state solutions, analyze the symmetries of the system and numerically characterize the emission dynamics via the underlying bifurcation structure. The polarization lifetime is found to be a crucial parameter, which impacts the observed dynamics in the parameter space spanned by frequency detuning, coupling strength and coupling phase.

Stabilizing Nanolasers via Polarization Lifetime Tuning

We investigate the emission dynamics of mutually coupled nanolasers and predict ways to optimize their stability i.e. maximize their locking range. We find that tuning the cavity lifetime to the same order of magnitude as the dephasing time of the microscopic polarization yields optimal operation conditions which allow for wider tuning ranges than usually observed in conventional semiconductor lasers. The lasers are modeled by a Maxwell-Bloch type class-C laser model. For our analysis we analytically determine the steady state solutions, analyze the symmetries of the system and numerically characterize the emission dynamics via the underlying bifurcation structure. The polarization lifetime is found to be a crucial parameter which impacts the observed dynamics in the parameter space spanned by frequency detuning, coupling strength and coupling phase.

Exciton Dephasing in Tungsten Diselenide Atomic Layer

An intrinsic exciton dephasing is the coherence loss of exciton dipole oscillation, while the total exciton dephasing originates from coherence loss due to exciton–exciton interaction and excitonphonon coupling. In this article, the total exciton dephasing time of tungsten diselenide (WSe2) atomic layers was analyzed as functions of excitation intensity with exciton–exciton coupling strength and temperature with exciton–phonon coupling strength. It was hypothesized that the total exciton dephasing time is shortened as the exciton–exciton interaction and the exciton–phonon coupling are increased. The coherence loss analysis revealed that the exciton dephasing time of WSe2 atomic layers is due to mainly the temperature rather than the excitation intensity.