98 research outputs found
A device for feasible fidelity, purity, Hilbert-Schmidt distance and entanglement witness measurements
A generic model of measurement device which is able to directly measure
commonly used quantum-state characteristics such as fidelity, overlap, purity
and Hilbert-Schmidt distance for two general uncorrelated mixed states is
proposed. In addition, for two correlated mixed states, the measurement
realizes an entanglement witness for Werner's separability criterion. To
determine these observables, the estimation only one parameter - the visibility
of interference, is needed. The implementations in cavity QED, trapped ion and
electromagnetically induced transparency experiments are discussed.Comment: 6 pages, 3 figure
Decoherence in trapped ions due to polarization of the residual background gas
We investigate the mechanism of damping and heating of trapped ions
associated with the polarization of the residual background gas induced by the
oscillating ions themselves. Reasoning by analogy with the physics of surface
electrons in liquid helium, we demonstrate that the decay of Rabi oscillations
observed in experiments on 9Be+ can be attributed to the polarization phenomena
investigated here. The measured sensitivity of the damping of Rabi oscillations
with respect to the vibrational quantum number of a trapped ion is also
predicted in our polarization model.Comment: 26 pdf pages with 5 figures, http://www.df.ufscar.br/~quantum
Measurements on trapped laser-cooled ions using quantum computations
We show that a series of quantum computations involving an isolated N-quantum-bit ion register can be used to make an approximate quantum nondemolition measurement of the number state distribution of a collective vibrational mode. A unitary transformation is applied to the Fourier transformed state of the ion register to copy the vibrational statistics to the electronic mode, and the number state distribution is then measured in the electronic number state basis using the quantum jumps technique
Quantum entanglement and information processing via excitons in optically-driven quantum dots
We show how optically-driven coupled quantum dots can be used to prepare
maximally entangled Bell and Greenberger-Horne-Zeilinger states. Manipulation
of the strength and duration of the selective light-pulses needed for producing
these highly entangled states provides us with crucial elements for the
processing of solid-state based quantum information. Theoretical predictions
suggest that several hundred single quantum bit rotations and Controlled-Not
gates could be performed before decoherence of the excitonic states takes
place.Comment: 3 separate PostScript Figures + 7 pages. Typos corrected. Minor
changes added. This updated version is to appear in PR
Toward scalable quantum computation with cavity QED systems
We propose a scheme for quantum computing using high-Q cavities in which the
qubits are represented by single cavity modes restricted in the space spanned
by the two lowest Fock states. We show that single qubit operations and
universal multiple qubit gates can be implemented using atoms sequentially
crossing the cavities.Comment: 14 pages, 8 figure
Single Spin Measurement using Single Electron Transistors to Probe Two Electron Systems
We present a method for measuring single spins embedded in a solid by probing
two electron systems with a single electron transistor (SET). Restrictions
imposed by the Pauli Principle on allowed two electron states mean that the
spin state of such systems has a profound impact on the orbital states
(positions) of the electrons, a parameter which SET's are extremely well suited
to measure. We focus on a particular system capable of being fabricated with
current technology: a Te double donor in Si adjacent to a Si/SiO2 interface and
lying directly beneath the SET island electrode, and we outline a measurement
strategy capable of resolving single electron and nuclear spins in this system.
We discuss the limitations of the measurement imposed by spin scattering
arising from fluctuations emanating from the SET and from lattice phonons. We
conclude that measurement of single spins, a necessary requirement for several
proposed quantum computer architectures, is feasible in Si using this strategy.Comment: 22 Pages, 8 Figures; revised version contains updated references and
small textual changes. Submitted to Phys. Rev.
Generation of arbitrary two dimensional motional state of a trapped ion
We present a scheme to generate an arbitrary two-dimensional quantum state of
motion of a trapped ion. This proposal is based on a sequence of laser pulses,
which are tuned appropriately to control transitions on the sidebands of two
modes of vibration. Not more than laser pulses are needed to
generate a pure state with upper phonon number and in the and
direction respectively.Comment: to appear in PR
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