7,723 research outputs found
Tunneling, self-trapping and manipulation of higher modes of a BEC in a double well
We consider an atomic Bose-Einstein condensate trapped in a symmetric
one-dimensional double well potential in the four-mode approximation and show
that the semiclassical dynamics of the two ground state modes can be strongly
influenced by a macroscopic occupation of the two excited modes. In particular,
the addition of the two excited modes already unveils features related to the
effect of dissipation on the condensate. In general, we find a rich dynamics
that includes Rabi oscillations, a mixed Josephson-Rabi regime, self-trapping,
chaotic behavior, and the existence of fixed points. We investigate how the
dynamics of the atoms in the excited modes can be manipulated by controlling
the atomic populations of the ground states.Comment: 12 pages, 5 figure
Protecting subspaces by acting on the outside
Many quantum control tasks aim at manipulating the state of a quantum
mechanical system within a finite subspace of states. However, couplings to the
outside are often inevitable. Here we discuss strategies which keep the system
in the controlled subspace by applying strong interactions onto the outside.
This is done by drawing analogies to simple toy models and to the quantum Zeno
effect. Special attention is paid to the constructive use of dissipation in the
protection of subspaces.Comment: 16 pages, 10 figure
Approximate joint measurement of qubit observables through an Arthur-Kelly type model
We consider joint measurement of two and three unsharp qubit observables
through an Arthur-Kelly type joint measurement model for qubits. We investigate
the effect of initial state of the detectors on the unsharpness of the
measurement as well as the post-measurement state of the system. Particular
emphasis is given on a physical understanding of the POVM to PVM transition in
the model and entanglement between system and detectors.Two approaches for
characterizing the unsharpness of the measurement and the resulting measurement
uncertainty relations are considered.The corresponding measures of unsharpness
are connected for the case where both the measurements are equally unsharp. The
connection between the POVM elements and symmetries of the underlying
Hamiltonian of the measurement interaction is made explicit and used to perform
joint measurement in arbitrary directions. Finally in the case of three
observables we derive a necessary condition for the approximate joint
measurement and use it show the relative freedom available when the observables
are non-orthogonal.Comment: 22 pages; Late
Heisenberg's uncertainty principle for simultaneous measurement of positive-operator-valued measures
A limitation on simultaneous measurement of two arbitrary positive operator
valued measures is discussed. In general, simultaneous measurement of two
noncommutative observables is only approximately possible. Following Werner's
formulation, we introduce a distance between observables to quantify an
accuracy of measurement. We derive an inequality that relates the achievable
accuracy with noncommutativity between two observables. As a byproduct a
necessary condition for two positive operator valued measures to be
simultaneously measurable is obtained.Comment: 7 pages, 1 figure. To appear in Phys. Rev.
Cold Power Tests of the sc 325 MHz CH-Cavity
At the Institute for Applied Physics (IAP), Frankfurt University, a superconducting 325 MHz CH-Cavity has been designed, built and first tests have successfully been performed. The cavity is determined for a 11.4 AMeV, 10 mA ion beam at the GSI UNILAC. Consisting of 7 gaps this resonator is envisaged to deliver a gradient of 5 MV/m. Novel features of this structure are a compact design, low peak fields, improved surface processing and power coupling. Furthermore a tuner system based on bellow tuners driven by a stepping motor and a piezo actuator and attached inside the resonator will control the frequency. In this contribution measurements executed at 4 K and 2 K at the cryo lab in Frankfurt will be presented
Simultaneous measurement of two non-commuting quantum variables: Solution of a dynamical model
The possibility of performing simultaneous measurements in quantum mechanics
is investigated in the context of the Curie-Weiss model for a projective
measurement. Concretely, we consider a spin- system simultaneously
interacting with two magnets, which act as measuring apparatuses of two
different spin components. We work out the dynamics of this process and
determine the final state of the measuring apparatuses, from which we can find
the probabilities of the four possible outcomes of the measurements. The
measurement is found to be non-ideal, as (i) the joint statistics do not
coincide with the one obtained by separately measuring each spin component, and
(ii) the density matrix of the spin does not collapse in either of the measured
observables. However, we give an operational interpretation of the process as a
generalised quantum measurement, and show that it is fully informative: The
expected value of the measured spin components can be found with arbitrary
precision for sufficiently many runs of the experiment.Comment: 24 pages, 9 figures; close to published versio
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