46 research outputs found
Cloning Entangled Qubits to Scales One Can See
By amplifying photonic qubits it is possible to produce states that contain
enough photons to be seen with a human eye, potentially bringing quantum
effects to macroscopic scales [1]. In this paper we theoretically study quantum
states obtained by amplifying one side of an entangled photon pair with
different types of optical cloning machines for photonic qubits. We propose a
detection scheme that involves lossy threshold detectors (such as human eye) on
the amplified side and conventional photon detectors on the other side. We show
that correlations obtained with such coarse-grained measurements prove the
entanglement of the initial photon pair and do not prove the entanglement of
the amplified state. We emphasize the importance of the detection loophole in
Bell violation experiments by giving a simple preparation technique for
separable states that violate a Bell inequality without closing this loophole.
Finally we analyze the genuine entanglement of the amplified states and its
robustness to losses before, during and after amplification.Comment: 15 pages, 9 figure
Quantum Cloning for Absolute Radiometry
In the quantum regime information can be copied with only a finite fidelity.
This fidelity gradually increases to 1 as the system becomes classical. In this
article we show how this fact can be used to directly measure the amount of
radiated power. We demonstrate how these principles could be used to build a
practical primary standard
Experimental Realization of Polarization Qutrits from Non-Maximally Entangled States
Based on a recent proposal [Phys. Rev. A 71, 062337 (2005)], we have
experimentally realized two photon polarization qutrits by using non-maximally
entangled states and linear optical transformations. By this technique high
fidelity mutually unbiased qutrits are generated at a high brilliance level.Comment: RevTex, 8 pages, 6 figure
Realization and characterization of a 2-photon 4-qubit linear cluster state
We report on the experimental realization of a 4-qubit linear cluster state
via two photons entangled both in polarization and linear momentum. This state
was investigated by performing tomographic measurements and by evaluating an
entanglement witness. By use of this state we carried out a novel nonlocality
proof, the so-called ``stronger two observer all versus nothing'' test of
quantum nonlocality.Comment: 4 pages, 4 figure
32 Bin Near-Infrared Time-Multiplexing Detector with Attojoule Single-Shot Energy Resolution
We present two implementations of photon counting time-multiplexing detectors
for near-infrared wavelengths, based on Peltier cooled InGaAs/InP avalanche
photo diodes (APDs). A first implementation is motivated by practical
considerations using only commercially available components. It features 16
bins, pulse repetition rates of up to 22 kHz and a large range of applicable
pulse widths of up to 100 ns. A second implementation is based on rapid gating
detectors, permitting deadtimes below 10 ns. This allows one to realize a high
dynamic-range 32 bin detector, able to process pulse repetition rates of up to
6 MHz for pulse width of up to 200 ps. Analysis of the detector response at
16.5% detection efficiency, reveals a single-shot energy resolution on the
attojoule level.Comment: 7 pages, 7 figure
Waveguide-based OPO source of entangled photon pairs
In this paper we present a compact source of narrow-band energy-time
entangled photon pairs in the telecom regime based on a Ti-indiffused
Periodically Poled Lithium Niobate (PPLN) waveguide resonator, i.e. a waveguide
with end-face dielectric multi-layer mirrors. This is a monolithic doubly
resonant Optical Parametric Oscillator (OPO) far below threshold, which
generates photon pairs by Spontaneous Parametric Down Conversion (SPDC) at
around 1560nm with a 117MHz (0.91 pm)- bandwidth. A coherence time of 2.7 ns is
estimated by a time correlation measurement and a high quality of the entangled
states is confirmed by a Bell-type experiment. Since highly coherent
energy-time entangled photon pairs in the telecom regime are suitable for long
distance transmission and manipulation, this source is well suited to the
requirements of quantum communication.Comment: 13 page