Strong-Field Nonsequential Double Ionization of Ar and Ne

We investigate the nonsequential double ionization (NSDI) of Ar and Ne based on quantitative rescattering theory (QRS). According to QRS theory, each elementary NSDI process can be calculated by multiplying the returning electron wave packet with appropriate differential electron-ion scattering cross sections. We include (e, 2e) and electron-impact excitation cross sections of Ar+ to obtain the correlated electron momentum spectra for the NSDI of Ar by few-cycle pulses to check the dependence of NSDI on the carrier-envelope phase. The results are compared to the ion momentum spectra from the recent experiment of Johnson [Phys. Rev. APLRAAN1050-294710.1103/ PhysRevA.83.013412 83, 013412 (2011)]. Calculations have also been performed for Ar at another intensity to illustrate the intensity dependence of NSDI and to compare with the earlier data of Feuerstein [Phys. Rev. Lett.PRLTAO0031-900710. 1103/PhysRevLett.87.043003 87, 043003 (2001)] and for Ne to illustrate the target dependence. We also address the presence of resonant capture processes in electron-ion collisions in the NSDI spectra

Dynamics of Vortices and Charges in Two Dimensional Arrays of Small Josephson Junctions

This thesis is based on experimental work on two dimensional (2D) Josephson junction arrays. The junctions are small (~ 0.004~0.04 \ub5m2) so that the charging energy E~ e2/2C associated with the junction capacitance C is large. In this case, charging effect becomes important and leads to a zero-current state called Coulomb blockade of Cooper pair tunneling. This zero-current state is complementary to the zero- voltage state seen in the Josephson effect. Emphasis in this work is placed on the competition between the Josephson effect and the charging effect; A competition which results in a rich behavior of both the current-voltage (IV) characteristics and the temperature dependence of zero bias resistance RO(T). This thesis explores fundamental properties in this new field and the experimental results probe the vortex dynamics, the charge dynamics and the region where they overlap. The arrays are characterized by two parameters, x ~ EJ/EC and .alpha.N ~ RQ/RN,where EJ ~ (.DELTA.O/2)(RQ/RN) is the Josephson coupling energy, RN is the junction normal state resitance. RQ ~ 6.45 k.OMEGA. is the quantum resistance, .DELTA.0 is the superconducting gap. In a region where x>=0.8 and .alpha.N >=0.5, the characteristics of the arrays can be described by the motion of vortices. The R0(T) at high temperatures display a Kosterlitz-Thouless vortex pair-unbinding transition. Below the transition temperature, we observe a thermal activation behavior, R0 ~ exp(Eb/kBT), where the effective barrier height, Eb, is proportional to EJ and is magnetic field dependent. At low temperatures, quantum fluctuations dominate and the resistance flattens off, becoming temperature independent. The flattening-off resistance is lower for arrays with large x and for arrays of larger size. The effective damping resistance which characterizes the flux-flow motion is found to be close to RN. In the region where x>=0.27 and .alpha.N >=0.26, the transport properties are described by the motion of charges. The RO(T) behavior follows a simple Arrhenius form, RO ~exp(Ea/kBT), where the activation energy Ea is 1/4Ec in the normal state, and is between 1/4Ec and 1/4Ec + .DELTA.0 in the superconducting state. When in the normal state, the resistance at low temperatures (

Tunable photonic heat transport in a quantum heat valve

Quantum thermodynamics is emerging both as a topic of fundamental research and as a means to understand and potentially improve the performance of quantum devices1–10. A prominent platform for achieving the necessary manipulation of quantum states is superconducting circuit quantum electrodynamics (QED)11. In this platform, thermalization of a quantum system12–15 can be achieved by interfacing the circuit QED subsystem with a thermal reservoir of appropriate Hilbert dimensionality. Here we study heat transport through an assembly consisting of a superconducting qubit16 capacitively coupled between two nominally identical coplanar waveguide resonators, each equipped with a heat reservoir in the form of a normal-metal mesoscopic resistor termination. We report the observation of tunable photonic heat transport through the resonator–qubit–resonator assembly, showing that the reservoir-to-reservoir heat flux depends on the interplay between the qubit–resonator and the resonator–reservoir couplings, yielding qualitatively dissimilar results in different coupling regimes. Our quantum heat valve is relevant for the realization of quantum heat engines17 and refrigerators, which can be obtained, for example, by exploiting the time-domain dynamics and coherence of driven superconducting qubits18,19. This effort would ultimately bridge the gap between the fields of quantum information and thermodynamics of mesoscopic systems.Peer reviewe