Search results for "Quantum Decoherence"
showing 10 items of 159 documents
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.
Exploiting Clock Transitions for the chemical design of resilient molecular spin qubits
2021
Molecular spin qubits are chemical nanoobjects with promising applications that are so far hampered by the rapid loss of quantum information, a process known as decoherence. A strategy to improve this situation involves employing so-called Clock Transitions (CTs), which arise at anticrossings between spin energy levels. At CTs, the spin states are protected from magnetic noise and present an enhanced quantum coherence. Unfortunately, these optimal points are intrinsically hard to control since their transition energy cannot be tuned by an external magnetic field; moreover, their resilience towards geometric distortions has not yet been analyzed. Here we employ a python-based computational t…
Decoherence effects in the Stern-Gerlach experiment using matrix Wigner functions
2016
We analyze the Stern-Gerlach experiment in phase space with the help of the matrix Wigner function, which includes the spin degree of freedom. Such analysis allows for an intuitive visualization of the quantum dynamics of the device. We include the interaction with the environment, as described by the Caldeira-Leggett model. The diagonal terms of the matrix provide us with information about the two components of the state that arise from interaction with the magnetic field gradient. In particular, from the marginals of these components, we obtain an analytical formula for the position and momentum probability distributions in the presence of decoherence that shows a diffusive behavior for l…
Coherence and organisation in lanthanoid complexes: from single ion magnets to spin qubits
2016
Molecular magnetism is reaching a degree of development that will allow for the rational design of sophisticated systems. Among these, here we will focus on those that display single-molecule magnetic behaviour, i.e. classical memories, and on magnetic molecules that can be used as molecular spin qubits, the irreducible components of any quantum technology. Compared with candidates developed from physics, a major advantage of molecular spin qubits stems from the power of chemistry for the tailored and inexpensive synthesis of new systems for their experimental study; in particular, the so-called lanthanoid-based single-ion magnets, which have for a long time been one of the hottest topics i…
Unified view of correlations using the square-norm distance
2012
The distance between a quantum state and its closest state not having a certain property has been used to quantify the amount of correlations corresponding to that property. This approach allows a unified view of the various kinds of correlations present in a quantum system. In particular, using relative entropy as a distance measure, total correlations can be meaningfully separated into a quantum part and a classical part thanks to an additive relation involving only the distances between states. Here we investigate a unified view of correlations using as a distance measure the square norm, which has already been used to define the so-called geometric quantum discord. We thus also consider…