Banca de DEFESA: JUAN CARLOS CHAVES CAPELLA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : JUAN CARLOS CHAVES CAPELLA
DATE: 30/06/2023
TIME: 09:00
LOCAL: Através de Videoconferência: meet.google.com/oev-yizj-tvw
TITLE:

Modelling of quantum memories based on atomic external degrees of freedom

KEY WORDS:

quantum optics; quantum information; atomic physics; first-principles modelling;
quantum imaging.

PAGES: 95
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

In this work, we present some fundamental tools in the modelling of quantum networks. We
intend to develop theoretical tools such as the usage of the mixed variables density matrix
formalism to model from first principles atomic experiments where external degrees of freedom
play an important role, and entanglement quantification in atom-photon systems where
entanglement is present in the continuous variables of the system. Namely, we first perform
a detailed theoretical and experimental investigation of an atomic memory based on recoilinduced
resonance in cold cesium atoms. We consider the interaction of a nearly degenerated
pump and probe beams with an ensemble of two-level atoms. A full theoretical density matrix
calculation in the extended Hilbert space of the internal and external atomic degrees of
freedom allows us to obtain, from first principles, the transient and stationary responses determining
the probe transmission and the forward four-wave mixing spectra. These two signals
are generated together at the same order of perturbation with respect to the intensities of
pump and probe beams. Moreover, we have investigated the storage of optical information on
the spatial modes of light beams in the atomic external degrees of freedom, which provided
a simple interpretation for the previously-reported non-volatile character of this memory. The
retrieved signals after storage reveal the equivalent role of probe transmission and four-wave
mixing, as the two signals have similar amplitudes. Probe transmission and forward four-wavemixing
spectra were then experimentally measured for both continuous excitation and after
storage. The experimental observations are in good agreement with the developed theory and
open a new pathway for the reversible exchange of optical information with atomic systems.
Next, we review the Weisskopf-Wigner formalism for spontaneous emission considering the
spatial modes of light as well as external atomic degrees of freedom which we introduce in
the theory by modelling the atom as a wavepacket in momentum space with a given initial
uncertainty, and perform a purity calculation in order to quantify the entanglement encoded
in the momentum variables of the atom-photon system. Our purity calculations reveal two
high entanglement regimes depending on the initial atomic momentum uncertainty: the Recoil
entanglement regime (which arises in the small momentum uncertainty region), where recoil
effects dominate the mechanisms that originate entanglement and the Doppler entanglement
regime (in the large momentum uncertainty region) where homogeneous Doppler shifts in the
emitted photon’s frequency play the fundamental part in the build up of quantum correlations
in the system. Simplified expressions for the system’s wavefunction are found for each of the
entanglement regimes and physical considerations are made to explain their nature. Finally, we
briefly investigate the role of entanglement in the distinguishability of two physically different
quantum states that arise naturally from the theory, where we note that entanglement in the
system leads to a better resolution of the two quantum states.

COMMITTEE MEMBERS:
Externo à Instituição - BERTULIO DE LIMA BERNARDO - UFPB
Presidente - 2316177 - DANIEL FELINTO PIRES BARBOSA
Interno - 1654830 - FERNANDO ROBERTO DE LUNA PARISIO FILHO
Interna - 1132318 - SANDRA SAMPAIO VIANNA
Externo à Instituição - SEBASTIÃO JOSÉ NASCIMENTO DE PÁDUA - UFMG