Three-player polaritons: nonadiabatic fingerprints in an entangled atom-molecule-photon system

A quantum system composed of a molecule and an atomic ensemble, confined in a microscopic cavity, is investigated theoretically. The indirect coupling between atoms and the molecule, realized by their interaction with the cavity radiation mode, leads to a coherent mixing of atomic and molecular states, and at strong enough cavity field strengths hybrid atom-molecule-photon polaritons are formed. It is shown for the Na$_2$ molecule that by changing the cavity wavelength and the atomic transition frequency, the potential energy landscape of the polaritonic states and the corresponding spectrum could be changed significantly. Moreover, an unforeseen intensity borrowing effect, which can be seen as a strong nonadiabatic fingerprint, is identified in the atomic transition peak, originating from the contamination of the atomic excited state with excited molecular rovibronic states

Ultrafast dynamics in the vicinity of quantum light-induced conical intersections

Nonadiabatic effects appear due to avoided crossings or conical intersections that are either intrinsic properties in field-free space or induced by a classical laser field in a molecule. It was demonstrated that avoided crossings in diatomics can also be created in an optical cavity. Here, the quantized radiation field mixes the nuclear and electronic degrees of freedom creating hybrid field-matter states called polaritons. In the present theoretical study we go further and create conical intersections in diatomics by means of a radiation field in the framework of cavity quantum electrodynamics (QED). By treating all degrees of freedom, that is the rotational, vibrational, electronic and photonic degrees of freedom on an equal footing we can control the nonadiabatic quantum light-induced dynamics by means of conical intersections. First, the pronounced difference between the the quantum light-induced avoided crossing and the conical intersection with respect to the nonadiabatic dynamics of the molecule is demonstrated. Second, we discuss the similarities and differences between the classical and the quantum field description of the light for the studied scenario

Quantum Control with Quantum Light of Molecular Nonadiabaticity

Coherent control experiments in molecules are often done with shaped laser fields. The electric field is described classically and control over the time evolution of the system is achieved by shaping the laser pulses in the time or frequency domain. Moving on from a classical to a quantum description of the light field allows to engineer the quantum state of light to steer chemical processes. The quantum field description of the photon mode allows to manipulate the light-matter interaction directly in phase-space. In this paper we will demonstrate the basic principle of coherent control with quantum light on the avoided crossing in lithium fluoride. Using a quantum description of light together with the nonadiabatic couplings and vibronic degrees of freedoms opens up new perspective on quantum control. We show the deviations from control with purely classical light field and how back-action of the light field becomes important in a few photon regime

Robust field-dressed spectra of diatomics in an optical lattice

The absorption spectra of the cold Na2 molecule dressed by a linearly polarized standing laser wave is investigated. In the studied scenario the rotational motion of the molecules is frozen while the vibrational and translational degrees of freedom are accounted for as dynamical variables. In such a situation a light-induced conical intersection (LICI) can be formed. To measure the spectra a weak field is used whose propagation direction is perpendicular to the direction of the dressing field but has identical polarization direction. Although LICIs are present in our model, the simulations demonstrate a very robust absorption spectrum, which is insensitive to the intensity and the wavelength of the dressing field and which does not reflect clear signatures of light-induced nonadiabatic phenomena related to the strong mixing between the electronic, vibration and translational motions. However, by widening artificially the very narrow translational energy level gaps, the fingerprint of the LICI appears to some extent in the spectrum

SŰRŰSÉG FUNKCIONÁL ÉS SŰRŰSÉGMÁTRIX ELMÉLETEK = DENSITY FUNCTIONAL AND DENSITY MATRIX THEORIES

Napjainkban az elektronszerkezet-számítások többnyire a sűrűségfunkcionál elmélet Kohn-Sham-egyenleteinek megoldásával történnek. Ennek az az oka, hogy nem ismerjük a kinetikus energiafunkcionált (mint a sűrűség funkcionálját). A kinetikus energiát a pályak funkcionáljaként ismerjük csak. Általában annyi Kohn-Sham-egyenletet kell megoldani, ahány elektron van a vizsgált rendszerben. A kinetikus energiafunkcionál ismeretében viszont elegendő mindig csak egyetlen egyenletet, az ú.n. Euler-egyenletet megoldani akárhány elektron is van jelen. Egy ilyen pálya-független módszer lehetővé teszi igen nagy rendszerek tárgyalását is. Ezért van nagy jelentőségük az ilyen irányú kutatásoknak. A pályázat legfontosabb eredménye, hogy sikerült jelentős előrehaladást elérni a kinetikus energia több mint 80 éve megoldatlan problémájában: A Nagy-March differenciális viriáltétel sokaságra történő általánosításából elsőrendű differenciálegyenletet vezettünk le a sokaság kinetikus energia funkcionálderiváltjára gömbszimmetrikus rendszerekre. Az egyenlet megoldásának egy speciális esete megadja az eredeti kinetikus energiát. Ez az eredeti probléma egzakt megoldását jelenti, de csak gömbszimmetrikus esetben. További fontos eredmények: egzakt tételeket, relációkat vezettünk le a sűrűségmátrix funkcionál elméletben. Összefüggést találtunk, a Fisher-informáciÓ, a Rényi-információ és a kinetikus energia között. | Nowadays, electron structure calculations are mainly done by the solution of the Kohn-Sham equations of the density functional theory. The reason is that the kinetic energy functional (as a functional of the density) is unknown. The kinetic energy is known only as a functional of the orbitals. One has to solve as many Kohn-Sham equations as the number of electrons. In the knowledge of the kinetic energy functional, one always has to solve a single equation, the so called Euler equation independently of the number of electrons in the system. Such an orbital-free method makes it possible to treat very large systems. That is why studies in this direction are very important. An important progress has been achieved in the problem of kinetic energy unsolved more than 80 years. The differential virial theorem of Nagy and March is generalized for ensembles. A first-order differential equation for the functional derivative of the ensemble non-interacting kinetic energy functional has been derived. A special case of the solution of this equation gives the original non-interacting kinetic energy. This provides the exact solution of the original problem but only for spherically symmetric case. Further important results: exact theorems and relations have been derived in the density matrix functional theory. Relations have been obtained between the Fisher information, the Rényi information and the kinetic energy

On the preservation of coherence in the electronic wavepacket of a neutral and rigid polyatomic molecule

We present various types of reduced models including five vibrational modes and three electronic states for the pyrazine molecule in order to investigate the lifetime of electronic coherence in a rigid and neutral system. Using an ultrafast optical pumping in the ground state (1 1 A g ), we prepare a coherent superposition of two bright excited states, 1 1 B 2u and 1 1 B 1u , and reveal the effect of the nuclear motion on the preservation of the electronic coherence induced by the laser pulse. More specifically, two aspects are considered: the anharmonicity of the potential energy surfaces and the dependence of the transition dipole moments (TDMs) with respect to the nuclear coordinates. To this end, we define an ideal model by making three approximations: (i) only the five totally symmetric modes move, (ii) which correspond to uncoupled harmonic oscillators, and (iii) the TDMs from the ground electronic state to the two bright states are constant (Franck-Condon approximation). We then lift the second and third approximations by considering, first, the effect of anharmonicity, second, the effect of coordinate-dependence of the TDMs (first-order Herzberg- Teller contribution), third, both. Our detailed numerical study with quantum dynamics confirms long-term revivals of the electronic coherence even for the most realistic model