Samuel Bengtsson

Spectral phase measurement of a Fano resonance using tunable attosecond pulses.

Electron dynamics induced by resonant absorption of light is of fundamental importance in nature and has been the subject of countless studies in many scientific areas. Above the ionization threshold of atomic or molecular systems, the presence of discrete states leads to autoionization, which is an interference between two quantum paths: direct ionization and excitation of the discrete state coupled to the continuum. Traditionally studied with synchrotron radiation, the probability for autoionization exhibits a universal Fano intensity profile as a function of excitation energy. However, without additional phase information, the full temporal dynamics cannot be recovered. Here we use tunable attosecond pulses combined with weak infrared radiation in an interferometric setup to measure not only the intensity but also the phase variation of the photoionization amplitude across an autoionization resonance in argon. The phase variation can be used as a fingerprint of the interactions between the discrete state and the ionization continua, indicating a new route towards monitoring electron correlations in time.

Gating attosecond pulses in a noncollinear geometry

The efficient generation of isolated attosecond pulses (IAPs), giving access to ultrafast electron dynamics in various systems, is a key challenge in attosecond science. IAPs can be produced by confining the extreme ultraviolet emission generated by an intense laser pulse to a single field half-cycle or, as shown recently, by employing angular streaking methods. Here, we experimentally demonstrate the angular streaking of attosecond pulse trains in a noncollinear geometry, leading to the emission of angularly separated IAPs. The noncollinear geometry simplifies the separation of the fundamental laser field and the generated pulses, making this scheme promising for intracavity attosecond pulse generation, thus opening new possibilities for high-repetition-rate attosecond sources.

Space–time control of free induction decay in the extreme ultraviolet

The spatial phase and direction of extreme-ultraviolet light are controlled by an all-optical modulator based on argon gas. It works by using an infrared pulse to control the spatial and spectral phase of the free induction decay in the gas system.

High-fidelity readout scheme for rare-earth solid-state quantum computing

We propose and analyze a high-fidelity readout scheme for a single-instance approach to quantum computing in rare-earth-ion-doped crystals. The scheme is based on using different elements as qubit and readout ions, where the readout ions are doped into the material at a much lower concentration than the qubit ions. It is shown that by allowing the qubit ion sitting closest to a readout ion to act as a readout buffer, the readout error can be reduced by more than an order of magnitude. The scheme is shown to be robust against certain experimental variations, such as varying detection efficiencies, and we use the scheme to predict the attainable quantum fidelity of a controlled NOT (CNOT) gate in these solid-state systems. In addition, we discuss the potential scalability of the protocol to larger qubit systems. The results are based on parameters which we believe are experimentally feasible with current technology and which can be simultaneously realized. (Less)

Phase Measurement of a Fano Resonance Using Tunable Attosecond Pulses

We study photoionization of argon atoms close to the 3s(2)3p(6) -> 3s(1)3p(6)4p Fano resonance using an attosecond pulse train and a weak infrared probe field. An interferometric technique combined with tunable attosecond pulses allows us to determine the phase of the photoionization amplitude as a function of photon energy. We interpret the experimental results using an analytical two-photon model based on the Fano formalism and obtain quantitative agreement.

Sources and Diagnostics for Attosecond Science

We present a novel scheme to generate trains of angularly separated single attosecond pulses by driving high-order harmonic generation with two identical, but temporally delayed, laser pulses, which are noncollinearly overlapped in the generation medium.

Photoionization time delay measurement close to a Fano resonance using tunable attosecond pulses

We investigate the influence of a Fano resonance on the delays for electron emission in two-photon, near-resonant ionization of argon. The delays were measured using an interferometric method that employed an attosecond pulse train.