arXiv subjects

Mihaela Vatasescu

Publications and source records attributed to Mihaela Vatasescu.

6 recordsLinked to original sources

arXiv2020

Comment on "Quantum Fisher information flow and non-Markovian processes of open systems"

In [Phys. Rev. A 82, 042103 (2010)], the authors showed that "for a class of the non-Markovian master equations in time-local forms", the quantum Fisher information (QFI) flow can be decomposed into additive subflows corresponding to different dissipative channels. However, the paper does not specify the class of non-Markovian time-local master equations for which their analytic decomposition of the QFI flow is valid. Here we show that several suppositions have to be made in order to reach the central result of Ref. \cite{luwsun10}, which appears to be valid for a narrow class of density operators $ρ(θ;t)$ and quantum Fisher information $\mathcal{F}(θ;t)$, and under strict conditions on the time-local master equation. More precisely, the decomposition of the QFI flow obtained in Ref. \cite{luwsun10} is valid under two conditions not mentioned in the paper: (i) $\frac{d}{dt} \left( \frac{\partial ρ}{\partial θ} \right)=$ $\frac{\partial}{\partial θ} \left( \frac{d ρ}{dt} \right)$; (ii) $\frac{\partial H}{\partial θ}=0$, $\frac{\partial γ_i}{\partial θ}=0$, $\frac{\partial A_i}{\partial θ}=0$, meaning that the Hamiltonian $H(t)$, the decay rates $γ_i(t)$, and the Lindblad operators $A_i(t)$ appearing in the non-Markovian time-local master equation have to not depend on the parameter $θ$ about which the quantum Fisher information is defined.

quant-ph↗

arXiv2018

Non-Markovian dynamics of the electronic subsystem in a laser-driven molecule: Characterization and connections with electronic-vibrational entanglement and electronic coherence

Non-Markovian quantum evolution of the electronic subsystem in a laser-driven molecule is characterized through the appearance of negative decoherence rates in the canonical form of the electronic master equation. For a driven molecular system described in a bipartite Hilbert space H=Hel x Hvib of dimension 2 x Nv, we derive the canonical form of the electronic master equation, deducing the canonical measures of non-Markovianity and the Bloch volume of accessible states. We find that one of the decoherence rates is always negative, accounting for the inherent non-Markovian character of the electronic evolution in the vibrational environment. Enhanced non-Markovian behavior, characterized by two negative decoherence rates, appears if there is a coupling between the electronic states g, e, such that the evolution of the electronic populations obeys d(PgPe)/dt > 0. Non-Markovianity of the electronic evolution is analyzed in relation to temporal behaviors of the electronic-vibrational entanglement and electronic coherence, showing that enhanced non-Markovian behavior accompanies entanglement increase. Taking as an example the coupling of two electronic states by a laser pulse in the Cs2 molecule, we analyze non-Markovian dynamics under laser pulses of various strengths, finding that the weaker pulse stimulates the bigger amount of non-Markovianity. We show that increase of the electronic-vibrational entanglement over a time interval is correlated to the growth of the total amount of non-Markovianity calculated over the same interval using canonical measures and connected with the increase of the Bloch volume. After the pulse, non-Markovian behavior is correlated to electronic coherence, such that vibrational motion in the electronic potentials which diminishes the nuclear overlap, implicitly increasing the linear entropy of entanglement, brings a memory character to dynamics.

quant-ph↗

arXiv2018

Measures of electronic-vibrational entanglement and quantum coherence in a molecular system

We characterize both entanglement and quantum coherence in a molecular system by connecting the linear entropy of electronic-nuclear entanglement with Wigner-Yanase skew information measuring vibronic coherence and local quantum uncertainty on electronic energy. Linear entropy of entanglement and quantifiers of quantum coherence are derived for a molecular system described in a bipartite Hilbert space H=Hel x Hvib of finite dimension Nel x Nv, and relations between them are established. For the specific case of the electronic-vibrational entanglement, we find the linear entropy of entanglement as having a more complex informational content than the von Neumann entropy. By keeping the information carried by the vibronic coherences in a molecule, linear entropy seizes vibrational motion in the electronic potentials as entanglement dynamics. We analyze entanglement oscillations in an isolated molecule, and show examples for the control of entanglement dynamics in a molecule through the creation of coherent vibrational wave packets in several electronic potentials by using chirped laser pulses.

quant-ph↗

arXiv2014

Entanglement between electronic and vibrational degrees of freedom in a laser-driven molecular system

We investigate the entanglement between electronic and vibrational degrees of freedom produced by a vibronic coupling in a molecular system described in the Born-Oppenheimer approximation. Entanglement in a pure state of the Hilbert space $\cal{H}$$=$$\cal{H}$$_{el}$$\bigotimes$$\cal{H}$$_{vib}$ is quantified using the von Neumann entropy of the reduced density matrix and the reduced linear entropy. Expressions for these entanglement measures are derived for the $2 \times N_v$ and $3 \times N_v$ cases of the bipartite entanglement, where 2 and 3 are the dimensions of the electronic Hilbert space $\cal{H}$$_{el}$, and $N_v$ is the dimension of $\cal{H}$$_{vib}$. We study the entanglement dynamics for two electronic states coupled by a laser pulse (a $2 \times N_v$ case), taking as an example a coupling between the $a^3Σ_{u}^{+} (6s,6s)$ and $1_g(6s,6p_{3/2})$ states of the Cs$_2$ molecule. The reduced linear entropy expression obtained for the $3 \times N_v$ case is used to follow the entanglement evolution in a scheme proposed for the control of the vibronic dynamics in a Cs$_2$ cold molecule, implying the $a^3Σ_{u}^{+}(6s,6s)$, $0_g^-(6s,6p_{3/2})$, and $0_g^-(6s,5d)$ electronic states, which are coupled by a non-adiabatic radial coupling and a sequence of chirped laser pulses.

quant-ph↗

arXiv2006

Efficient formation of strongly bound ultracold cesium molecules by photoassociation with tunneling

We calculate the rates of formation and detection of ultracold Cs_2 molecules obtained from the photoassociation of ultracold atoms through the double-well 0g- (6S1/2 + 6P3/2) state. We concentrate on two features previously observed experimentally and attributed to tunneling between the two wells [Vatasescu et al 2000 Phys. Rev. A 61 044701]. We show that the molecules obtained are in strongly bound levels (v''=5,6) of the metastable a3Sigma_u+ (6S1/2 + 6S1/2) ground electronic state.

physics.atom-ph↗

arXiv2004

Optimizing the photoassociation of cold atoms by use of chirped laser pulses

Photoassociation of ultracold atoms induced by chirped picosecond pulses is analyzed in a non-perturbative treatment by following the wavepackets dynamics on the ground and excited surfaces. The initial state is described by a Boltzmann distribution of continuum scattering states. The chosen example is photoassociation of cesium atoms at temperature T=54 $μK$ from the $a^3 Σ_u^+(6s,6s)$ continuum to bound levels in the external well of the $0_g^-(6s+6p_{3/2})$ potential. We study how the modification of the pulse characteristics (carrier frequency, duration, linear chirp rate and intensity) can enhance the number of photoassociated molecules and suggest ways of optimizing the production of stable molecules.

physics.atm-clus↗