6,391 research outputs found
Entropy and entanglement in a bipartite quasi-Hermitian system and its Hermitian counterparts
We consider a quantum oscillator coupled to a bath of other oscillators.
The total system evolves with a quasi-Hermitian Hamiltonian. Associated to it
is a family of Hermitian systems, parameterized by a unitary map . Our main
goal is to find the influence of on the entropy and the entanglement in the
Hermitian systems. We calculate explicitly the reduced density matrix of the
single oscillator for all Hermitian systems and show that, regardless of ,
their von Neumann entropy oscillates with a common period which is twice that
of the non-Hermitian system. We show that generically, the oscillator and the
bath are entangled for almost all times. While the amount of entanglement
depends on the choice of , it is independent of when averaged over a
period. These results describe some universality in the physical properties of
all Hermitian systems associated to a given non-Hermitian one
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Time-dependence in non-Hermitian quantum systems
In this thesis we present a coherent and consistent framework for explicit time-dependence in non-Hermitian quantum mechanics. The area of non-Hermitian quantum mechanics has been growing rapidly over the past twenty years [2]. This has been driven by the fact that PT -symmetric non-Hermitian systems exhibit real energy eigenvalues and unitary time evolution [1, 3, 4].
Historically, the introduction of time into the world of non-Hermitian quantum mechanics has been a conceptually difficult problem to address [5, 6], as it requires the Hamiltonian to become unobservable. However, we solve this issue with the introduction of a new observable energy operator [7]. We explain why its instigation is a necessary and natural progression in this setting.
For the first time, the introduction of time has allowed us to make sense of the parameter regime in which the PT -symmetry is spontaneously broken. Ordinarily, in the time-independent setting, the energy eigenvalues become complex and the wave functions are asymptotically unbounded. However, we demonstrate that in the time-independent setting this broken symmetry can be mended and analysis on the spontaneously broken PT regime is indeed possible. We provide many examples of this mending on a wide range of different systems, beginning with a 2 x 2 matrix model [8] and extending to higher dimensional matrix models [9] and coupled harmonic oscillator systems with infinite Hilbert space [10, 11]. Furthermore, we use the framework to perform analysis on time-dependent quasi-exactly solvable models [12].
The ability to make sense of the spontaneously broken PT regime has revealed a vast array of new and exotic effects. We present the "eternal life" of entropy [13] in this thesis. Ordinarily, for entangled quantum systems coupled to the environments, the entropy decays rapidly to zero. However, in the spontaneously broken regime, we find the entropy decays asymptotically to a non-zero value.
Finally, we create an elegant framework for Darboux and Darboux/Crum transformations for time-dependent non-Hermitian Hamiltonians [14]. This combines the area of non-Hermitian quantum mechanics with non linear differential equations and solitons
Quantum chimera states
We study a theoretical model of closed quasi-hermitian chain of spins which
exhibits quantum analogues of chimera states, i.e. long life classical states
for which a part of an oscillator chain presents an ordered dynamics whereas
another part presents a disordered chaotic dynamics. For the quantum analogue,
the chimera behavior deals with the entanglement between the spins of the
chain. We discuss the entanglement properties, quantum chaos, quantum disorder
and semi-classical similarity of our quantum chimera system. The quantum
chimera concept is novel and induces new perspectives concerning the
entanglement of multipartite systems
Non-Hermitian quantum dynamics and entanglement of coupled nonlinear resonators
We consider a generalization of recently proposed non-Hermitian model for
resonant cavities coupled by a chiral mirror by taking into account number
non-conservation and nonlinear interactions. We analyze non-Hermitian quantum
dynamics of populations and entanglement of the cavity modes. We find that an
interplay of initial coherence and non-Hermitian coupling leads to a
counterintuitive population transfer. While an initially coherent cavity mode
is depleted, the other empty cavity can be populated more or less than the
initially filled one. Moreover, presence of nonlinearity yields population
collapse and revival as well as bipartite entanglement of the cavity modes. In
addition to coupled cavities, we point out that similar models can be found in
symmetric Bose-Hubbard dimers of Bose-Einstein condensates or in
coupled soliton-plasmon waveguides. We specifically illustrate quantum dynamics
of populations and entanglement in a heuristic model that we propose for a
soliton-plasmon system with soliton amplitude dependent asymmetric interaction.
Degree of asymmetry, nonlinearity and coherence are examined to control plasmon
excitations and soliton-plasmon entanglement. Relations to
symmetric lasers and Jahn-Teller systems are pointed out
Dissipative quantum theory: Implications for quantum entanglement
Three inter-related topics are discussed here. One, the Lindblad dynamics of
quantum dissipative systems; two, quantum entanglement in composite systems and
its quantification based on the Tsallis entropy; and three, robustness of
entanglement under dissipation. After a brief review of the Lindblad theory of
quantum dissipative systems and the idea of quantum entanglement in composite
quantum systems illustrated by describing the three particle systems, the
behavior of entanglement under the influence of dissipative processes is
discussed. These issues are of importance in the discussion of quantum
nanometric systems of current research.Comment: 12 pages, 1 Tabl
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