619 research outputs found
Complex chaos in conditional qubit dynamics and purification protocols
Selection of an ensemble of equally prepared quantum systems, based on
measurements on it, is a basic step in quantum state purification. For an
ensemble of single qubits, iterative application of selective dynamics has been
shown to lead to complex chaos, which is a novel form of quantum chaos with
true sensitivity to the initial conditions. The Julia set of initial valuse
with no convergence shows a complicated structre on the complex plane. The
shape of the Julia set varies with the parameter of the dynamics. We present
here results for the two qubit case demonstrating how a purification process
can be destroyed with chaotic oscillations
Complex chaos in the conditional dynamics of qubits
We analyze the consequences of iterative measurement-induced nonlinearity on
the dynamical behavior of qubits. We present a one-qubit scheme where the
equation governing the time evolution is a complex-valued nonlinear map with
one complex parameter. In contrast to the usual notion of quantum chaos,
exponential sensitivity to the initial state occurs here. We calculate
analytically the Lyapunov exponent based on the overlap of quantum states, and
find that it is positive. We present a few illustrative examples of the
emerging dynamics.Comment: 4 pages, 3 figure
Antisymmetric multi-partite quantum states and their applications
Entanglement is a powerful resource for processing quantum information. In
this context pure, maximally entangled states have received considerable
attention. In the case of bipartite qubit-systems the four orthonormal
Bell-states are of this type. One of these Bell states, the singlet Bell-state,
has the additional property of being antisymmetric with respect to particle
exchange. In this contribution we discuss possible generalizations of this
antisymmetric Bell-state to cases with more than two particles and with
single-particle Hilbert spaces involving more than two dimensions. We review
basic properties of these totally antisymmetric states. Among possible
applications of this class of states we analyze a new quantum key sharing
protocol and methods for comparing quantum states
Analysis and minimization of bending losses in discrete quantum networks
We study theoretically the transfer of quantum information along bends in
two-dimensional discrete lattices. Our analysis shows that the fidelity of the
transfer decreases considerably, as a result of interactions in the
neighbourhood of the bend. It is also demonstrated that such losses can be
controlled efficiently by the inclusion of a defect. The present results are of
relevance to various physical implementations of quantum networks, where
geometric imperfections with finite spatial extent may arise as a result of
bending, residual stress, etc
Quantum walk with a four-dimensional coin
We examine the physical implementation of a discrete time quantum walk with a four-dimensional coin. Our quantum walker is a photon moving repeatedly through a time delay loop, with time being our position space. The quantum coin is implemented using the internal states of the photon: the polarization and two of the orbital angular momentum states. We demonstrate how to implement this physically and what components would be needed. We then illustrate some of the results that could be obtained by performing the experiment
Directional correlations in quantum walks with two particles
Quantum walks on a line with a single particle possess a classical analogue. Involving more walkers opens up the possibility of studying collective quantum effects, such as many-particle correlations. In this context, entangled initial states and the indistinguishability of the particles play a role. We consider the directional correlations between two particles performing a quantum walk on a line. For non-interacting particles, we find analytic asymptotic expressions and give the limits of directional correlations. We show that by introducing delta-interaction between the particles, one can exceed the limits for non-interacting particles
Communication in quantum networks of logical bus topology
Perfect state transfer (PST) is discussed in the context of passive quantum
networks with logical bus topology, where many logical nodes communicate using
the same shared media, without any external control. The conditions under
which, a number of point-to-point PST links may serve as building blocks for
the design of such multi-node networks are investigated. The implications of
our results are discussed in the context of various Hamiltonians that act on
the entire network, and are capable of providing PST between the logical nodes
of a prescribed set in a deterministic manner.Comment: 9 pages, 1 figur
- …