A nonlinear interferometry scheme is described theoretically to induce and resolve electron wavefunction beating on time scales shorter than the optical cycle of the time-delayed pump and probe pulses.By employing two moderately intense few-cycle laser fields with a stable carrier-envelope phase, a large range of the entire electronic level structure of a quantum system can be retrieved.In contrast to single-photon excitation schemes, the retrieved electronic states include levels that are both dipole-and non-dipole-accessible from the ground electronic state.The results show that strong-field interferometry can reveal both high-resolution and broad-band spectral information at the same time with important consequences for quantum-beat spectroscopy on attosecond or even shorter time scales.
A nonlinear interferometry scheme is described theoretically to induce and resolve electron wavefunction beating on time scales shorter than the optical cycle of the time-delayed pump and probe pulses.By employing two moderately intense few-cycle laser fields with a stable carrier-envelope phase, a large range of the entire electronic level structure of a quantum system can be retrieved.In contrast to single-photon excitation schemes, the retrieved electronic states include levels that are both dipole-and non-dipole-accessible from the ground electronic state.The results show that strong-field interferometry can reveal both high-resolution and broad-band spectral information at the same time with important consequences for quantum-beat spectroscopy on attosecond or even shorter time scales.
A nonlinear interferometry scheme is described theoretically to induce and resolve electron wavefunction beating on time scales shorter than the optical cycle of the time-delayed pump and probe pulses. By employing two moderately intense few-cycle laser fields with a stable carrier-envelope phase, a large range of the entire electronic level structure of a quantum system can be retrieved. In contrast to single-photon excitation schemes, the retrieved electronic states include levels that are both dipole- and non-dipole-accessible from the ground electronic state. The results show that strong-field interferometry can reveal both high-resolution and broad-band spectral information at the same time with important consequences for quantum-beat spectroscopy on attosecond time scales.
The reconstruction of the full temporal dipole response of a strongly driven time-dependent system from a single absorption spectrum is demonstrated, only requiring that a sufficiently short pulse is employed to initialize the coherent excitation of the system. We apply this finding to the time-domain observation of Rabi cycling between doubly excited atomic states in the few-femtosecond regime. This allows us to pinpoint the breakdown of few-level quantum dynamics at the critical laser intensity near 2 TW/cm^{2} in doubly excited helium. The present approach unlocks single-shot real-time-resolved signal reconstruction across timescales down to attoseconds for nonequilibrium states of matter. In contrast to conventional pump-probe schemes, there is no need for scanning time delays in order to access real-time information. The potential future applications of this technique range from testing fundamental quantum dynamics in strong fields to measuring and controlling ultrafast chemical and biological reaction processes when applied to traditional transient-absorption spectroscopy.
Until recently, attosecond optical spectroscopy and quantum optics evolved along non-overlapping directions. In attosecond science, attosecond pulses have been regarded as classical waves, applied to probe electron dynamics on their natural time scale. Here, we transfer fundamental concepts of quantum optics into attosecond physics, enabling control of both the properties of the XUV attosecond pulses and the quantum fluctuations of matter on attosecond time scales. By combining bright squeezed vacuum (BSV) with a strong laser field to drive high-harmonic generation, we transfer the quantum properties of the BSV onto the resulting XUV attosecond pulses. Applying advanced attosecond interferometry, we reconstruct the quantum state of the XUV high harmonics and their associated attosecond pulses with attosecond precision. Finally, we resolve the squeezing of the electron's wavepacket during one of the most fundamental strong-field phenomena - field induced tunneling. The ability to measure and control quantum correlations in both electrons and XUV attosecond pulses establishes a foundation for attosecond quantum electrodynamics, manipulating the quantum state of electrons and photons with sub-cycle precision.
Within this work, electron dynamics in atoms are experimentally and numerically investigated on their natural attosecond time scales. To access these dynamics, ultrashort and moderately-intense few-cycle laser pulses are superposed with attosecond pulsed radiation in the extreme-ultraviolet spectral region. Both these sources are combined in a new experimental vacuum setup which was designed and built up from scratch, also in order to generate the attosecond pulses. Novel experimental schemes are developed which involve the temporal and spectral interferometric utilization of both ultrashort light sources and include the multidimensional spectroscopy employing different dynamical parameters. These are the intensity and the carrier-envelope phase of the laser pulses, as well as their temporal delay with respect to the attosecond pulses. Scientifically, the observation and control of the quantum-motion of bound electrons, as well as the laser-driven quasi-classical motion of free electrons was a key goal of this work. In particular, a bound two-electron wave packet in helium on attosecond time scales was experimentally observed for the first time. This was realized by combining unprecedented high temporal and spectral resolution. In addition, a new coupling mechanism of several doubly-excited states to an effective single-electron continuum is identified and analyzed. Both these two-electron states as well as single-electron states are interferometrically investigated with access to the phase of their quantum-mechanical wave function. This allows the observation and control of the quantum dynamics of two correlated electrons in atoms on the attosecond time scale which was demonstrated within the scope of this work.
Causality implies that by measuring an absorption spectrum, the time-dependent linear response function can be retrieved. Recent experiments suggest a link between the shape of spectral lines observed in absorption spectroscopy with the amplitude and phase of the systems response function. This has even been observed in the presence of strong, nonlinear interactions, which promote the observed system out of equilibrium, making it explicitly time dependent. Thus far, however, only the special case of a sudden modification of the response function was understood analytically, leaving the general case of the dynamical response to arbitrary interactions open to interpretation. Here, we demonstrate that even for the case of a strongly driven, time-dependent system, one can reconstruct the full temporal response information from a single spectrum if a sufficiently short signal is used to trigger the absorption process. This finding is directly applied to a time-domain observation of Rabi cycling between doubly-excited atomic states in the few-femtosecond regime. This general approach unlocks single-shot real-time-resolved signal reconstruction across time scales down to attoseconds for non-equilibrium states of matter. In contrast to available pump-probe schemes, there is no need for scanning time delays in order to access real-time information. The scientific applications of this technique range from testing fundamental quantum dynamics, to measuring and controlling ultrafast, chemical and biological reaction processes.
The generation and control of extreme ultraviolet (XUV) radiation by high harmonic generation (HHG) have advanced ultrafast science, providing direct insights into electron dynamics on their natural time scale. Attosecond science has established the capability to resolve ultrafast quantum phenomena in matter by characterizing and controlling the classical properties of the high harmonics. Recent theoretical proposals have introduced novel schemes for generating and manipulating XUV HHG with distinct quantum features, paving the way to attosecond quantum optics. In this work, we transfer fundamental concepts in quantum optics into attosecond science. By driving the HHG process with a combination of an infrared bright squeezed vacuum (BSV, a non-classical state of light), and a strong coherent field, we imprint the quantum correlations of the input BSV onto both the ultrafast electron wavefunction and the harmonics' field. Performing in-situ HHG interferometry provides an insight into the underlying sub-cycle dynamics, revealing squeezing in the statistical properties of one of the most fundamental strong-field phenomena -- field induced tunneling. Our measurement allows the reconstruction of the quantum state of the harmonics through homodyne-like tomography, resolving correlated fluctuations in the harmonic field that mirror those of the input BSV. By controlling the delay between the two driving fields, we manipulate the photon statistics of the emitted attosecond pulses with sub-cycle accuracy. The ability to measure and control quantum correlations in both electrons and XUV attosecond pulses establishes a foundation for attosecond electrodynamics, manipulating the quantum state of electrons and photons with sub-cycle precision.