91 research outputs found
Measurement of Coupling PDC photon sources with single-mode and multimode optical fibers
We investigate the coupling efficiency of parametric downconversion light
(PDC) into single and multi-mode optical fibers as a function of the pump beam
diameter, crystal length and walk-off. We outline two different theoretical
models for the preparation and collection of either single-mode or multi-mode
PDC light (defined by, for instance, multi-mode fibers or apertures,
corresponding to bucket detection). Moreover, we define the mode-matching
collection efficiency, important for realizing a single-photon source based on
PDC output into a well-defined single spatial mode. We also define a multimode
collection efficiency that is useful for single-photon detector calibration
applications.Comment: 13 pages, 12 figure
A Molecule‐Based Single‐Photon Source Applied in Quantum Radiometry
Single photon sources (SPSs) based on quantum emitters hold promise in
quantum radiometry as metrology standard for photon fluxes at the low light
level. Ideally this requires control over the photon flux in a wide dynamic
range, sub-Poissonian photon statistics and narrow-band emission spectrum. In
this work, a monochromatic single-photon source based on an organic dye
molecule is presented, whose photon flux is traceably measured to be adjustable
between 144 000 and 1320 000 photons per second at a wavelength of (785.6 +/-
0.1) nm, corresponding to an optical radiant flux between 36.5 fW and 334 fW.
The high purity of the single-photon stream is verified, with a second-order
autocorrelation function at zero time delay below 0.1 throughout the whole
range. Featuring an appropriate combination of emission properties, the
molecular SPS shows here application in the calibration of a silicon
Single-Photon Avalanche Detector (SPAD) against a low-noise analog silicon
photodiode traceable to the primary standard for optical radiant flux (i.e. the
cryogenic radiometer). Due to the narrow bandwidth of the source, corrections
to the SPAD detection efficiency arising from the spectral power distribution
are negligible. With this major advantage, the developed device may finally
realize a low-photon-flux standard source for quantum radiometry
Experimental Test of an Event-Based Corpuscular Model Modification as an Alternative to Quantum Mechanics
We present the first experimental test that distinguishes between an
event-based corpuscular model (EBCM) [H. De Raedt et al.: J. Comput. Theor.
Nanosci. 8 (2011) 1052] of the interaction of photons with matter and quantum
mechanics. The test looks at the interference that results as a single photon
passes through a Mach-Zehnder interferometer [H. De Raedt et al.: J. Phys. Soc.
Jpn. 74 (2005) 16]. The experimental results, obtained with a low-noise
single-photon source [G. Brida et al.: Opt. Expr. 19 (2011) 1484], agree with
the predictions of standard quantum mechanics with a reduced of 0.98
and falsify the EBCM with a reduced of greater than 20
Experimental realization of Counterfactual Quantum Cryptography
In counterfactual QKD information is transfered, in a secure way, between
Alice and Bob even when no particle carrying the information is in fact
transmitted between them. In this letter we fully implement the scheme for
counterfactual QKD proposed in [T. Noh, \PRL \textbf{103}, 230501 (2009)],
demonstrating for the first time that information can be transmitted between
two parties without the transmission of a carrier
Optimal estimation of entanglement and discord in two-qubit states
Recently, the fast development of quantum technologies led to the need for
tools allowing the characterization of quantum resources. In particular, the
ability to estimate non-classical aspects, e.g. entanglement and quantum
discord, in two-qubit systems, is relevant to optimise the performance of
quantum information processes. Here we present an experiment in which the
amount of entanglement and discord are measured exploiting different
estimators. Among them, some will prove to be optimal, i.e., able to reach the
ultimate precision bound allowed by quantum mechanics. These estimation
techniques have been tested with a specific family of states ranging from
nearly pure Bell states to completely mixed states. This work represents a
significant step in the development of reliable metrological tools for quantum
technologies
Experimental quantum cryptography scheme based on orthogonal states
Since, in general, non-orthogonal states cannot be cloned, any eavesdropping
attempt in a Quantum Communication scheme using non-orthogonal states as
carriers of information introduces some errors in the transmission, leading to
the possibility of detecting the spy. Usually, orthogonal states are not used
in Quantum Cryptography schemes since they can be faithfully cloned without
altering the transmitted data. Nevertheless, L. Goldberg and L. Vaidman [\prl
75 (1995) 1239] proposed a protocol in which, even if the data exchange is
realized using two orthogonal states, any attempt to eavesdrop is detectable by
the legal users. In this scheme the orthogonal states are superpositions of two
localized wave packets travelling along separate channels. Here we present an
experiment realizing this scheme
Improved implementation of nonclassicality test for a single particle
Recently a test of nonclassicality for a single qubit was proposed [R. Alicki
and N. Van Ryn, J. Phys. A: Math. Theor. 41, 062001 (2008)]. We present an
optimized experimental realization of this test leading to a 46 standard
deviation violation of classicality. This factor of 5 improvement over our
previous result was achieved by moving from the infrared to the visible where
we can take advantage of higher efficiency and lower noise photon detectors.Comment: 4 pages, 1 figur
Quantifying backflash radiation to prevent zero-error attacks in quantum key distribution
Single-photon avalanche diodes (SPADs) are the most widespread commercial solution for single-photon counting in quantum
key distribution applications. However, the secondary photon emission that arises from the avalanche of charge carriers that
occurs during the detection of a photon may be exploited by an eavesdropper to gain information without inducing errors in the
transmission key. In this paper, we characterize such backflash light in gated InGaAs/InP SPADs and discuss its spectral and
temporal characterization for different detector models and different operating parameters. We qualitatively bound the maximum
information leakage due to backflash light and propose solutions for preventing such leakage
Quantifying backflash radiation to prevent zero-error attacks in quantum key distribution
Single-photon avalanche diodes (SPADs) are the most widespread commercial solution for single-photon counting in quantum key distribution applications. However, the secondary photon emission that arises from the avalanche of charge carriers that occurs during the detection of a photon may be exploited by an eavesdropper to gain information without inducing errors in the transmission key. In this paper, we characterize such backflash light in gated InGaAs/InP SPADs and discuss its spectral and temporal characterization for different detector models and different operating parameters. We qualitatively bound the maximum information leakage due to backflash light and propose solutions for preventing such leakage
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