193 research outputs found
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 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
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