4,762 research outputs found
Photon-Number Squeezing in Circuit Quantum Electrodynamics
A superconducting single-electron transistor (SSET) coupled to an anharmonic
oscillator, e.g., a Josephson junction-L-C circuit, can drive the latter to a
nonequilibrium photon number state. By biasing the SSET in a regime where the
current is carried by a combination of inelastic quasiparticle tunneling and
coherent Cooper-pair tunneling (Josephson quasiparticle cycle), cooling of the
oscillator as well as a laser like enhancement of the photon number can be
achieved. Here we show, that the cut-off in the quasiparticle tunneling rate
due to the superconducting gap, in combination with the anharmonicity of the
oscillator, may create strongly squeezed photon number distributions. For low
dissipation in the oscillator nearly pure Fock states can be produced.Comment: 5 pages, 5 figure
Wireless distance estimation with low-power standard components in wireless sensor nodes
In the context of increasing use of moving wireless sensor nodes the interest
in localizing these nodes in their application environment is strongly rising.
For many applications, it is necessary to know the exact position of the nodes
in two- or three-dimensional space. Commonly used nodes use state-of-the-art
transceivers like the CC430 from Texas Instruments with integrated signal
strength measurement for this purpose. This has the disadvantage, that the
signal strength measurement is strongly dependent on the orientation of the
node through the antennas inhomogeneous radiation pattern as well as it has a
small accuracy on long ranges. Also, the nodes overall attenuation and output
power has to be calibrated and interference and multipath effects appear in
closed environments. Another possibility to trilaterate the position of a
sensor node is the time of flight measurement. This has the advantage, that the
position can also be estimated on long ranges, where signal strength methods
give only poor accuracy. In this paper we present an investigation of the
suitability of the state-of-the-art transceiver CC430 for a system based on
time of flight methods and give an overview of the optimal settings under
various circumstances for the in-field application. For this investigation, the
systematic and statistical errors in the time of flight measurements with the
CC430 have been investigated under a multitude of parameters. Our basic system
does not use any additional components but only the given standard hardware,
which can be found on the Texas Instruments evaluation board for a CC430. Thus,
it can be implemented on already existent sensor node networks by a simple
software upgrade.Comment: 8 pages, Proceedings of the 14th Mechatronics Forum International
Conference, Mechatronics 201
Preparation and manipulation of a fault-tolerant superconducting qubit
We describe a qubit encoded in continuous quantum variables of an rf
superconducting quantum interference device. Since the number of accessible
states in the system is infinite, we may protect its two-dimensional subspace
from small errors introduced by the interaction with the environment and during
manipulations. We show how to prepare the fault-tolerant state and manipulate
the system. The discussed operations suffice to perform quantum computation on
the encoded state, syndrome extraction, and quantum error correction. We also
comment on the physical sources of errors and possible imperfections while
manipulating the system.Comment: Typo corrected, title changed as suggested by the editors of Phys.
Rev. B, references adde
Compensation of anisotropy effects in the generation of two-photon light
We analyse a method to compensate for anisotropy effects in the spatial
distribution of parametric down-conversion (PDC) radiation in bulk crystals. In
this method, a single nonlinear crystal is replaced by two consecutive crystals
with opposite transverse walk-off directions. We implement a simple numerical
model to calculate the spatial distribution of intensity and correlations, as
well as the Schmidt mode structure, with an account for the anisotropy.
Experimental results are presented which prove the validity of both the model
and the method.Comment: 9 pages, 8 figure
A "fair sampling" perspective on an apparent violation of duality
In the event in which a quantum mechanical particle can pass from an initial
state to a final state along two possible paths, the duality principle states
that "the simultaneous observation of wave and particle behavior is
prohibited". [M. O. Scully, B.-G. Englert, and H. Walther. Nature, 351:111-116,
1991.] emphasized the importance of additional degrees of freedom in the
context of complementarity. In this paper, we show how the consequences of
duality change when allowing for biased sampling, that is, postselected
measurements on specific degrees of freedom of the environment of the two-path
state. Our work contributes to the explanation of previous experimental
apparent violations of duality [R. Menzel, D. Puhlmann, A. Heuer, and W. P.
Schleich. Proc. Natl. Acad. Sci., 109(24):9314-9319, 2012.] and opens up the
way for novel experimental tests of duality.Comment: 10 pages, 8 figure
Distillability via protocols respecting the positivity of partial transpose
We show that all quantum states that do not have a positive partial transpose
are distillable via channels, which preserve the positivity of the partial
transpose. The question whether NPT bound entanglement exist is therefore
closely related to the connection between the set of separable superoperators
and PPT-preserving maps.Comment: 3 pages, REVTeX, remark on complete positivity and reference adde
- …