Search results for " DECOHERENCE"
showing 10 items of 165 documents
Decoherence from dipolar interspin interactions in molecular spin qubits
2019
The realization of spin-based logical gates crucially depends on magnetically coupled spin qubits. Thus, understanding decoherence when spin qubits are in close proximity will become a roadblock to overcome. Herein, we propose a method free of fitting parameters to evaluate the qubit phase memory time ${T}_{m}$ in samples with high electron spin concentrations. The method is based on a model aimed to estimate magnetic nuclear decoherence [P. C. E. Stamp and I. S. Tupitsyn, Phys. Rev. B 69, 014401 (2004)]. It is applied to a ground-spin $J=8$ magnetic molecule 1 displaying atomic clock transitions, namely ${{[\mathrm{H}{\mathrm{o}}^{\mathrm{III}}{({\mathrm{W}}_{5}{\mathrm{O}}_{18})}_{2}]}^{9…
Cavity QED with a trapped ion in a leaky cavity
2002
The dynamics of the interaction of a quantized cavity field and the vibronic degrees of freedom of a trapped ion is studied under realistic conditions by including cavity losses, spontaneous electronic transitions, and atomic nonlinearities. As long as spontaneous electronic transitions are negligible, analytical results are derived for describing the interaction of the trapped ion and the damped cavity field in the secular approximation. Under more general conditions, when the secular approximation breaks down and spontaneous emission effects become important, the dynamics of the system is studied by quantum-trajectory methods. As an example we demonstrate that, by exploiting the nonlinear…
Field-free molecular orientation of1Σand2Πmolecules at high temperature
2012
We analyze the control of field-free molecular orientation at high temperature by use of a two-color laser bipulse strategy proposed in Zhang et al. [Phys. Rev. A 83, 043410 (2011)]. A general study shows that there exist two types of linear molecules for which a different mechanism has to be used. For molecules with a large hyperpolarizability, a monochromatic laser pre-pulse is applied before the two-color laser pulse at a time close to the rotational period ${T}_{r}$, while for molecules with a small hyperpolarizability, the optimal delay is found close to ${T}_{r}/4$ or $3{T}_{r}/4$. We extend this analysis to the case of a ${}^{2}\phantom{\rule{-0.16em}{0ex}}\ensuremath{\Pi}$ molecule …
SIMPRE1.2: Considering the hyperfine and quadrupolar couplings and the nuclear spin bath decoherence
2016
SIMPRE is a fortran77code which uses an effective electrostatic model of point charges to predict the magnetic behavior of rare-earth-based mononuclear complexes. In this manuscript, we present SIMPRE1.2, which now takes into account two further phenomena.Firstly, SIMPRE now considers the hyperfine and quadrupolar interactions within the rare-earth ion, resulting in a more complete and realistic set of energy levels and wave functions. Secondly,and in order to widen SIMPRE’s predictive capabilities regarding potential molecular spin qubits, it now includes a routine that calculates an upper-bound estimate of the decoherence time considering only the dipolar coupling between the electron spi…
Optimal control of a three-level quantum system by laser fields plus von Neumann measurements
2008
International audience; We investigate the control of a three-level quantum system by laser fields assisted by von Neumann measurements. We consider a system which is not completely controllable by unitary evolution but which becomes controllable if particular measurements are used. The optimal control is defined from a cost functional which takes into account the measurements. The cost corresponds either to the minimization of the duration of the control or to the minimization of the energy of the laser field. Using the Pontryagin maximum principle, we determine the optimal control which steers the system from a given initial state toward a desired target state. This allows one to determin…
Master equations for two qubits coupled via a nonlinear mode
2013
A microscopic master equation describing the dynamics of two qubits coupled via a nonlinear mediator is constructed supposing that the two qubits, as well as the nonlinear mode, interact, each with its own independent bosonic bath. Generally speaking the master equation derived in this way represents a more appropriate tool for studying the dynamics of open quantum systems. Indeed we show that it is more complex than the phenomenological master equation, constructed simply adding ad hoc dissipative terms.
Coherent quantum evolution via reservoir driven holonomies.
2006
We show that in the limit of a strongly interacting environment a system initially prepared in a decoherence-free subspace (DFS) coherently evolves in time, adiabatically following the changes of the DFS. If the reservoir cyclicly evolves in time, the DFS states acquire a holonomy.
Wave Packet Decoherence in Momentum Space
2004
We consider the development of decoherence between the momentum components of a wave packet of a non relativistic charged particle interacting linearly with the electromagnetic field in equilibrium at temperature T. By adopting from the beginning the electric dipole approximation the Hamiltonian assumes a form analogous to the one used in the context of quantum computing for an ensemble of two level systems. We obtain the characteristic vacuum and thermal decoherence times and we show that decoherence between different momenta is due to the onset of a correlation between each momentum component and the associated transverse photons that are also responsible of mass renormalization.
Bilayer graphene lattice-layer entanglement in the presence of non-Markovian phase noise
2018
The evolution of single particle excitations of bilayer graphene under effects of non-Markovian noise is described with focus on the decoherence process of lattice-layer (LL) maximally entangled states. Once that the noiseless dynamics of an arbitrary initial state is identified by the correspondence between the tight-binding Hamiltonian for the AB-stacked bilayer graphene and the Dirac equation -- which includes pseudovector- and tensor-like field interactions -- the noisy environment is described as random fluctuations on bias voltage and mass terms. The inclusion of noisy dynamics reproduces the Ornstein-Uhlenbeck processes: a non-Markovian noise model with a well-defined Markovian limit…
Nondissipative Decoherence and Entanglement in the Dynamics of a Trapped Ion
2006
We study the robustness of the entanglement between the 2D vibrational motion and two ground state hyperfine levels of a trapped ion with respect to the presence of non-dissipative sources of decoherence.