176 research outputs found
Pulsed source of spectrally uncorrelated and indistinguishable photons at telecom wavelengths
We report on the generation of indistinguishable photon pairs at telecom
wavelengths based on a type-II parametric down conversion process in a
periodically poled potassium titanyl phosphate (PPKTP) crystal. The phase
matching, pump laser characteristics and coupling geometry are optimised to
obtain spectrally uncorrelated photons with high coupling efficiencies. Four
photons are generated by a counter- propagating pump in the same crystal and
anlysed via two photon interference experiments between photons from each pair
source as well as joint spectral and g^(2) measurements. We obtain a spectral
purity of 0.91 and coupling efficiencies around 90% for all four photons
without any filtering. These pure indistinguishable photon sources at telecom
wavelengths are perfectly adapted for quantum network demonstrations and other
multi-photon protocols
Intrinsically stable light source at telecom wavelengths
We present a highly stable light source at telecom wavelengths, based on a
short erbium doped fiber. The high stability arises from the high inversion of
the Er3+ion population. This source is developed to work as a stable reference
in radiometric applications and is useful in any application where high
stability and/or a large bandwidth are necessary. The achieved long-term
stability is 10 ppm
Quantum random number generation on a mobile phone
Quantum random number generators (QRNGs) can significantly improve the
security of cryptographic protocols, by ensuring that generated keys cannot be
predicted. However, the cost, size, and power requirements of current QRNGs has
prevented them from becoming widespread. In the meantime, the quality of the
cameras integrated in mobile telephones has improved significantly, so that now
they are sensitive to light at the few-photon level. We demonstrate how these
can be used to generate random numbers of a quantum origin
Absolute calibration of fiber-coupled single-photon detector
We show a setup for characterising the efficiency of a single-photon-detector
absolutely and with a precision better of 1%. Since the setup does not rely on
calibrated devices and can be implemented with standard-optic components, it
can be realised in any laboratory. Our approach is based on an
Erbium-Doped-Fiber-Amplifier (EDFA) radiometer as a primary measurement
standard for optical power, and on an ultra-stable source of spontaneous
emission. As a proof of principle, we characterise the efficiency of an
InGaAs/InP single-photon detector. We verified the correctness of the
characterisation with independent measurements. In particular, the measurement
of the optical power made with the EDFA radiometer has been compared to that of
the Swiss Federal Office of Metrology using a transfer power meter. Our
approach is suitable for frequent characterisations of high-efficient
single-photon detectors.Comment: 14 pages, 4 figure
Measuring absolute spectral radiance using an Erbium Doped Fibre Amplifier
We describe a method to measure the spectral radiance of a source in an
absolute way without the need of a reference. Here we give the necessary detail
to allow for the device to be reproduced from standard fiber-optic components.
The device is suited for fiber-optic applications at telecom wavelengths and
calibration of powermeters and spectrometers at light levels from 1nW to 1uW
Single-photon space-like antibunching
We use heralded single photons to perform an antibunching experiment in which
the clicks at the detectors are spacelike separated events. The idea of such
experiment dates back to the 5th Solvay conference, when it was proposed by
Einstein as an expression of his concerns about quantum theory
Perfectly secure steganography: hiding information in the quantum noise of a photograph
We show that the quantum nature of light can be used to hide a secret message
within a photograph. Using this physical principle we achieve
information-theoretic secure steganography, which had remained elusive until
now. The protocol is such that the digital picture in which the secret message
is embedded is perfectly undistinguishable from an ordinary photograph. This
implies that, on a fundamental level, it is impossible to discriminate a
private communication from an exchange of photographs.Comment: 5 pages, 3 figures + appendix : 5 pages, 6 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
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
High efficiency coupling of photon pairs in practice
Multi-photon and quantum communication experiments such as loophole-free Bell
tests and device independent quantum key distribution require entangled photon
sources which display high coupling efficiency. In this paper we put forward a
simple quantum theoretical model which allows the experimenter to design a
source with high pair coupling efficiency. In particular we apply this approach
to a situation where high coupling has not been previously obtained: we
demonstrate a symmetric coupling efficiency of more than 80% in a highly
frequency non-degenerate configuration. Furthermore, we demonstrate this
technique in a broad range of configurations, i.e. in continuous wave and
pulsed pump regimes, and for different nonlinear crystals
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