Ultracold-atom quantum simulator for attosecond science

Abstract

A quantum simulator based on ultracold optically trapped atoms for simulating the physics of atoms and molecules in ultrashort intense laser fields is introduced. The slowing down by about 13 orders of magnitude allows to watch in slow motion the tunneling and recollision processes that form the heart of attosecond science. The extreme flexibility of the simulator promises a deeper understanding of strong-field physics, especially for many-body systems beyond the reach of classical computers. The quantum simulator can experimentally straightforwardly be realized and is shown to recover the ionization characteristics of atoms in the different regimes of laser-matter interaction.In his renowned lecture, "Simulating physics with computers" [1] Richard P. Feynman suggested the use of quantum simulators, i.e. precisely controllable quantum systems, to simulate other quantum systems that cannot be described theoretically due to their exponentially growing Hilbert space. For instance, the Mott-insulator to superfluid phase transition in condensed-matter systems [2] was predicted [3] to be observable with ultracold atoms in an optical lattice and then successfully demonstrated [4,5]. Also the Higgs mechanism [6], high temperature superconductivity [7], or Zitterbewegung [8] (to name just a few) were successfully investigated by quantum simulation. Moreover, the quantum simulation of electrons in crystalline solids exposed to laser fields [9] has been proposed. Strong-field physics has contributed considerably to the understanding of the light-matter interaction. The progress leading to pulses on the attosecond timescale [11] has even raised visions of real-time imaging of molecular processes [12] and orbital tomography [13]. Yet, attosecond many-body physics is challenging. An exact investigation on classical computers beyond the single-active-electron approximation becomes prohibitively complex for many-electron systems. In fact, the numerical treatment of two-electron systems like He or H 2 is today still state of the art [14][15][16][17]. Thus, simplified models are widely used for interpreting modern experiments. These models are controversial and their validation is difficult for several reasons. First, the used light pulses are bound to the specifications of the laser. The wavelength range of lasers is limited, mostly Ti:sapphire lasers are used. The pulse shapes are restricted and can often only be reproduced and determined up to a considerable uncertainty. The intensity and timescale of laser pulses are already pushed to a limit where further improvements require major technical or even principle developments with new limitations, like free-electron lasers. Second, atoms, ions, and molecules are complicated many-body systems. Their internal structure cannot be simply manipulated. For example, a variation of the number of electrons or protons underlies constraints due to electroneutrality. Third, although the correlation of electronic and nuclear motion is known to influence the ionization behavior [18,19], in mo...

Time-dependent restricted-active-space self-consistent-field theory for bosonic many-body systems

“…It is nowadays experimentally possible to design and control systems with a specific number of atoms [4][5][6] trapped in various potential shapes [7,8] and dimensions [9], with tunable inter-particle interactions [10,11], and to provide a controllable transition from a few-to a many-particle system. Such a detailed control of cold atom systems has opened the possibility to simulate various physical systems [12] from solid-state physics [13] to black-holes analogs [14] through matterlight interaction [15] and electrons dynamics in molecules [16].…”

Quantum Emulation of Extreme Non‐Equilibrium Phenomena with Trapped Atoms

“…], and dynamical phenomena from quantum quenches to dynamical suppression of tunneling to integrability [, e.g.]. In the non‐equilibrium context, the difference in energy scales leads to a rescaling of time: the processes underlying ultrafast phenomena like tunnel ionization occur over milliseconds rather than attoseconds, and are thus in a sense observable in ultra‐slow‐motion . This greatly simplifies experimental access to the dynamics.…”

Quantum simulation of ultrafast dynamics using trapped ultracold atoms

“…The study of ultrafast-equivalent electronic and vibrational dynamics is a natural but largely unexplored application of cold-atom quantum simulation techniques [1][2][3][4][5]. Quantum simulation experiments often rely on an analogy between trapped neutral atoms and electrons in matter [6][7][8].…”

“…Collective excitations in Bose condensates were a major focus of early experimental and theoretical research [21][22][23][24][25][26], and the analogy between degenerate trapped gases and individual atoms was noted at that time [1,27,28]. Ultrafast probes have recently been used to study many-body dynamics in Rydberg atoms [29], and recent theoretical proposals have suggested the use of cold atoms to simulate ultrafast dynamics in atoms [2,5], molecules [4], and solids [3].…”