46 research outputs found
Determination of the Carrier-Envelope Phase of Few-Cycle Laser Pulses with Terahertz-Emission Spectroscopy
The availability of few-cycle optical pulses opens a window to physical
phenomena occurring on the attosecond time scale. In order to take full
advantage of such pulses, it is crucial to measure and stabilise their
carrier-envelope (CE) phase, i.e., the phase difference between the carrier
wave and the envelope function. We introduce a novel approach to determine the
CE phase by down-conversion of the laser light to the terahertz (THz) frequency
range via plasma generation in ambient air, an isotropic medium where optical
rectification (down-conversion) in the forward direction is only possible if
the inversion symmetry is broken by electrical or optical means. We show that
few-cycle pulses directly produce a spatial charge asymmetry in the plasma. The
asymmetry, associated with THz emission, depends on the CE phase, which allows
for a determination of the phase by measurement of the amplitude and polarity
of the THz pulse
Simulation Methodology for Electron Transfer in CMOS Quantum Dots
The construction of quantum computer simulators requires advanced software
which can capture the most significant characteristics of the quantum behavior
and quantum states of qubits in such systems. Additionally, one needs to
provide valid models for the description of the interface between classical
circuitry and quantum core hardware. In this study, we model electron transport
in semiconductor qubits based on an advanced CMOS technology. Starting from 3D
simulations, we demonstrate an order reduction and the steps necessary to
obtain ordinary differential equations on probability amplitudes in a
multi-particle system. We compare numerical and semi-analytical techniques
concluding this paper by examining two case studies: the electron transfer
through multiple quantum dots and the construction of a Hadamard gate simulated
using a numerical method to solve the time-dependent Schrodinger equation and
the tight-binding formalism for a time-dependent Hamiltonian
Attosecond Dynamics of Molecular Electronic Ring Currents
Ultrafast charge migration is of fundamental importance to photoinduced chemical reactions. However, exploring such a quantum dynamical process requires demanding spatial and temporal resolutions. We show how electronic coherence dynamics induced in molecules by a circularly polarized UV pulse can be tracked by using a time-delayed circularly polarized attosecond X-ray pulse. The X-ray probe spectra retrieve an image at different time delays, encoding instantaneous pump-induced circular charge migration information on an attosecond time scale. A time-dependent ultrafast electronic coherence associated with the periodical circular ring currents shows a strong dependence on the helicity of the UV pulse, which may provide a direct approach to access and control the electronic quantum coherence dynamics in photophysical and photochemical reactions in real time
Identifying Strong-Field Effects in Indirect Photofragmentation Reactions
Exploring molecular breakup processes induced by light-matter interactions has both fundamental and practical implications. However, it remains a challenge to elucidate the underlying reaction mechanism in the strong field regime, where the potentials of the reactant are modified dramatically. Here we perform a theoretical analysis combined with a time-dependent wavepacket calculation to show how a strong ultrafast laser field affects the photofragment products. As an example, we examine the photochemical reaction of breaking up the molecule NaI into the neutral atoms Na and I, which due to inherent nonadiabatic couplings are indirectly formed in a stepwise fashion via the reaction intermediate NaI∗. By analyzing the angular dependencies of fragment distributions, we are able to identify the reaction intermediate NaI∗ from the weak to the strong field-induced nonadiabatic regimes. Furthermore, the energy levels of NaI∗ can be extracted from the quantum interference patterns of the transient photofragment momentum distribution
Identifying Strong-Field Effects in Indirect Photofragmentation Reactions
Exploring molecular breakup processes induced by light-matter interactions has both fundamental and practical implications. However, it remains a challenge to elucidate the underlying reaction mechanism in the strong field regime, where the potentials of the reactant are modified dramatically. Here we perform a theoretical analysis combined with a time-dependent wavepacket calculation to show how a strong ultrafast laser field affects the photofragment products. As an example, we examine the photochemical reaction of breaking up the molecule NaI into the neutral atoms Na and I, which due to inherent nonadiabatic couplings are indirectly formed in a stepwise fashion via the reaction intermediate NaI∗. By analyzing the angular dependencies of fragment distributions, we are able to identify the reaction intermediate NaI∗ from the weak to the strong field-induced nonadiabatic regimes. Furthermore, the energy levels of NaI∗ can be extracted from the quantum interference patterns of the transient photofragment momentum distribution