Ivan A. Burenkov

Ionization of atoms and molecules by a few-cycle laser pulse and interference effects in the rescattering process

We investigate the diffraction pictures arising due to strong-field ionization of a molecule in an ultrashort laser pulse and further field-induced recollision of the ionized electron with the parent molecular ion by direct numerical solution of the non-stationary Schrödinger equation. In molecules the angular distributions of the re-scattered electron are shown to differ dramatically from the simple usually used double-slit diffraction picture. The reason for this consists in the interference between scattered and non-scattered parts of the electron wave packet in the continuum. The found interference effect is demonstrated to play an important role in the formation of angular and momentum distribution both for molecules and atoms.

Ionization and stabilization of an atom in a quantum electromagnetic field

The dynamics of a model atomic system interacting with a quantum electromagnetic field has been investigated. The effect of statistics and average number of photons in a quantum state of the field on the ionization and stabilization of the atomic subsystem has been studied. The formation of a state with the maximum entanglement between the atomic and field subsystems in the case of interaction with a single-photon field has been demonstrated.

Quantum receiver for large alphabet communication

Quantum mechanics allows measurements that surpass the fundamental sensitivity limits of classical methods. To benefit from the quantum advantage in a practical setting, the receiver should use communication channels resources optimally; this can be done employing large communication alphabets. Here we show the fundamental sensitivity potential of a quantum receiver for coherent communication with frequency shift keying. We introduce an adaptive quantum protocol for this receiver, show that its sensitivity outperforms other receivers for alphabet sizes above 4 and scales favorably, whereas quantum receivers explored to date suffer from degraded sensitivity with the alphabet size. In addition, we show that the quantum measurement advantage allows the much better use of the frequency space in comparison to classical frequency keying protocols and orthogonal frequency division multiplexing.

Molecular dynamics driven by ultrashort laser pulses: Interference effects due to rescattering

A time-dependent Schrödinger equation is integrated numerically to investigate the dynamics of a model molecular system driven by a high-intensity ultrashort laser pulse. Two-dimensional photoelectron momentum distributions are analyzed. Highly nonmonotonic electron angular distributions are obtained that cannot be explained by diffraction in the double-well potential of a molecular ion. The nonmonotonicity is also demonstrated for atomic ionization and is attributed to the interference that occurs between components of an electron wave packet after its rescattering from the parent ion. An analytical model explaining the observed effects is developed.

Coherent quantum frequency bridge: phase preserving, nearly noiseless parametric frequency converter

We characterize an efficient and nearly-noiseless parametric frequency upconverter. The ultra-low noise regime is reached by the wide spectral separation between the input and pump frequencies and the low pump frequency relative to the input photons. The background of only ≈100 photons per hour is demonstrated. We demonstrate phase preservation in a frequency upconversion process at the single-photon level. We summarize our efforts to measure this ultra-low noise level, and discuss both single-photon avalanche photodiode measurements and a photon-counting transition edge sensor (TES) measurements. To reach the required accuracy, we supplemented our TES with a dark count reduction algorithm. The preservation of the coherence was demonstrated by simultaneously upconverting the input of each arm of a Mach-Zehnder interferometer through high interference fringe contrast. We observe fringe visibilities of ≥0.97 with faint coherent input.

Quantum frequency bridge: high-accuracy characterization of a nearly-noiseless parametric frequency converter

We demonstrate an efficient and inherently ultra-low noise frequency conversion via a parametric sum frequency generation. Due to the wide separation between the input and pump frequencies and the low pump frequency relative to the input photons, the upconversion results in only ≈100 background photons per hour. To measure such a low rate, we introduced a dark count reduction algorithm for an optical transition edge sensor.

Scalable, chip-based optically-controlled gates for quantum information processing

Here we present a simple and robust method to build on-the-fly configurable quantum gates based on a photonic exchange between quantum nodes. The idea is based on a high reflectivity of Bragg grating structures near resonant wavelengths. The control is exerted by applying an external strongly off-resonant or even a static electromagnetic field and taking advantage of the Kerr effect. When the nonlinear phase shift is strong enough, the Bragg mirror disappears, thereby allowing a transmission of a wave packet from one node to another. An example of a protocol for quantum logic gates that relies on this framework is offered.

Quantum information processing with chip-based optically-controlled gates

We show that basic quantum gates can be realized with simple two-level quantum nodes connected through actively, optically controlled waveguides. This allows to simplify nodes and drastically reduce nonlinearities required for quantum gates, while improving scalability and versatility.

Ionization and entanglement of two interacting Rydberg atoms in a strong laser field

Dynamics of ionization and entanglement of two Rydberg atoms interacting with each other and with external strong laser field is investigated. The phenomenon of interference stabilization of the bipartite atomic system is established in a strong field limit. The production of highly-entangled state of the studied atoms is shown to be realized. The possibility to control the evolution and time-dependent entanglement of the examined multilevel q-dit system is demonstrated.

Strong field effects in the system of two interacting Rydberg atoms

The ionization dynamics of two interacting Rydberg atoms in a strong laser field has been investigated. Each atom has been described in the “two discrete levels + continuum” model. Quasienergy states in this system, which describe field-dressed atoms, have been studied. It has been shown that one of the quasienergy states corresponds to the formation of an atomic state stable against ionization, which leads to the interference stabilization regime first observed in the case of individual atoms in [M. V. Fedorov and A. M. Movsesian, J. Phys. B 21, L155 (1988)]. Methods for creating entangled states in this system have been proposed and the dynamics of entanglement in the process of interaction with the laser field has been analyzed.