6,709 research outputs found
Quantum bit detector
We propose and analyze an experimental scheme of quantum nondemolition
detection of monophotonic and vacuum states in a superconductive toroidal
cavity by means of Rydberg atoms.Comment: 4 pages, 3 figure
Realization of a photonic CNOT gate sufficient for quantum computation
We report the first experimental demonstration of a quantum controlled-NOT
gate for different photons, which is classically feed-forwardable. In the
experiment, we achieved this goal with the use only of linear optics, an
entangled ancillary pair of photons and post-selection. The techniques
developed in our experiment will be of significant importance for quantum
information processing with linear optics.Comment: 4 pages 4 figures, sumbitted to PR
Full characterization of a three-photon GHZ state using quantum state tomography
We have performed the first experimental tomographic reconstruction of a
three-photon polarization state. Quantum state tomography is a powerful tool
for fully describing the density matrix of a quantum system. We measured 64
three-photon polarization correlations and used a "maximum-likelihood"
reconstruction method to reconstruct the GHZ state. The entanglement class has
been characterized using an entanglement witness operator and the maximum
predicted values for the Mermin inequality was extracted.Comment: 3 pages, 3 figure
Sequential Generation of Matrix-Product States in Cavity QED
We study the sequential generation of entangled photonic and atomic
multi-qubit states in the realm of cavity QED. We extend the work of C. Schoen
et al. [Phys. Rev. Lett. 95, 110503 (2005)], where it was shown that all states
generated in a sequential manner can be classified efficiently in terms of
matrix-product states. In particular, we consider two scenarios: photonic
multi-qubit states sequentially generated at the cavity output of a
single-photon source and atomic multi-qubit states generated by their
sequential interaction with the same cavity mode.Comment: 11 page
Experimental violation of a cluster state Bell inequality
Cluster states are a new type of multiqubit entangled states with
entanglement properties exceptionally well suited for quantum computation. In
the present work, we experimentally demonstrate that correlations in a
four-qubit linear cluster state cannot be described by local realism. This
exploration is based on a recently derived Bell-type inequality [V. Scarani et
al., Phys. Rev A 71, 042325 (2005)] which is tailored, by using a combination
of three- and four-particle correlations, to be maximally violated by cluster
states but not violated at all by GHZ states. We observe a cluster state Bell
parameter of , which is more than 7 standard deviations larger
than the threshold of 2 imposed by local realism.Comment: 4 pages, 2 figure
High fidelity transport of trapped-ion qubits through an X-junction trap array
We report reliable transport of 9Be+ ions through a 2-D trap array that
includes a separate loading/reservoir zone and an "X-junction". During
transport the ion's kinetic energy in its local well increases by only a few
motional quanta and internal-state coherences are preserved. We also examine
two sources of energy gain during transport: a particular radio-frequency (RF)
noise heating mechanism and digital sampling noise. Such studies are important
to achieve scaling in a trapped-ion quantum information processor.Comment: 4 pages, 3 figures Updated to reduce manuscript to four pages. Some
non-essential information was removed, including some waveform information
and more detailed information on the tra
Single microwave photon detection in the micromaser
High efficiency single photon detection is an interesting problem for many
areas of physics, including low temperature measurement, quantum information
science and particle physics. For optical photons, there are many examples of
devices capable of detecting single photons with high efficiency. However
reliable single photon detection of microwaves is very difficult, principally
due to their low energy. In this paper we present the theory of a cascade
amplifier operating in the microwave regime that has an optimal quantum
efficiency of 93%. The device uses a microwave photon to trigger the stimulated
emission of a sequence of atoms where the energy transition is readily
detectable. A detailed description of the detector's operation and some
discussion of the potential limitations of the detector are presented.Comment: 8 pages, 5 figure
- …