arXiv subjects

B. Virgin Jenisha

Publications and source records attributed to B. Virgin Jenisha.

4 recordsLinked to original sources

arXiv2020

Study of the spin kitten states in a strongly coupled spin-oscillator system

Utilizing an adiabatic approximation method a bipartite qudit-oscillator Hamiltonian is explicitly studied for low spin values in both strong and ultrastrong coupling regimes. The quasiprobability densities on the hybrid factorized phase space are introduced. Integrating over a sector of the composite phase space, the quasiprobability distributions of the complementary subsystem are recovered. In the strong coupling regime the qudit entropy displays a pattern of quasiperiodic collapses and revivals, where the locally minimum nonzero configurations appearing at rational fractions of the revival time correspond to the spin kitten states. Starting with a bipartite factorizable initial state the evolution to the nonclassical transitory spin kitten states are displayed via the diagonal spin PQ-representation. The formation of transient spin kitten states is further substantiated by constructing the spin tomogram that employs the positive definite probability distributions embodying the diagonal elements of the corresponding density matrix in an arbitrarily rotated frame. As another manifestation of nonclassicality the emergence of the spin squeezed states during the bipartite evolution is observed. In the ultrastrong coupling domain a large number of interaction dependent modes and their harmonics are generated. The consequent randomization of the phases eliminates the quasiperiodicity of the system which is now driven towards a stabilization of the entropy accompanied with stochastic fluctuations around its stabilized value. Both in the strong and ultrastrong coupling realms antibunching of the photoemission events are realized particularly for the small spin values.

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arXiv2016

Deconstruction and differentiation of squeezed kitten states in a qubit-oscillator system

We study the evolution of the hybrid entangled squeezed states of the qubit-oscillator system in the strong coupling domain. Following the adiabatic approximation we obtain the reduced density matrices of the qubit and the oscillator degrees of freedom. The oscillator reduced density matrix is utilized to calculate the quasiprobability distributions such as the Sudarshan-Glauber diagonal P -representation, the Wigner W -distribution, and the nonnegative Husimi Q-function. The negativity associated with the W -distribution acts as a measure of the nonclassicality of the state. The existence of the multiple time scales induced by the interaction introduces certain features in the bipartite system. In the strong coupling regime the transient evolution to low entropy configurations reveals brief emergence of nearly pure kitten states that may be regarded as superposition of uniformly separated distinguishable squeezed coherent states. However, the quantum fluctuations with a short time period engender bifurcation and subsequent rejoining of these peaks in the phase space. The abovementioned doubling of the number of peaks increases the entropy to its near maximal value. Nonetheless, these states characterized by high entropy values, are endowed with a large negativity of the W -distribution that points towards their non-Gaussian behavior. This may be ascertained by the significantly large Hilbert-Schmidt distance between the oscillator state and an ensemble of most general statistical mixture of squeezed Gaussian states possessing nearly identical second order quadrature moments as that of the oscillator.

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arXiv2015

Quasi-Bell states in a strongly coupled qubit-oscillator system and their delocalization in the phase space

We study the evolution of bipartite entangled quasi-Bell states in a strongly coupled qubit-oscillator system in the presence of a static bias, and extend it to the ultra-strong coupling regime. Using the adiabatic approximation the reduced density matrix of the qubit is obtained for the strong coupling domain in closed form that involves linear combinations of the Jacobi theta functions. The reduced density matrix of the oscillator yields the phase space Husimi Q-distribution. In the strong coupling regime the $Q$-function evolves to uniformly separated macroscopically distinct Gaussian peaks representing `kitten' states at certain specified times that depend on multiple time scales present in the interacting system. For the ultra-strong coupling realm the delocalization in the phase space of the oscillator is studied by using the Wehrl entropy and the complexity of the quantum state. For a small phase space amplitude the entangled quasi-Bell state develops, during its time evolution, squeezing property and nonclassicality of the photon statistics which are measured by the quadrature variance and the Mandel parameter, respectively.

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arXiv2015

Evolution of nonclassicality of the quasi-Bell states for a strongly coupled qubit-oscillator system

Starting with the quasi-Bell states of the qubit-oscillator system, we obtain time evolution of the density matrix under the adiabatic approximation. The composite density matrix leads to, via partial tracing of the qubit degree of freedom, the reduced density matrix of the oscillator that is utilized to obtain the quasi-probability distributions such as Glauber-Sudarshan P function, Wigner W function and Husimi Q function. The negativity of the Wigner function acts as a measure of the nonclassicality of the state. The negativity becomes particularly relevant in understanding a comparison between the Wigner entropy with the Wehrl entropy, which are based on the W function and Q function, respectively.

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