119 research outputs found
Coexistence of continuous variable QKD with intense DWDM classical channels
We demonstrate experimentally the feasibility of continuous variable quantum
key distribution (CV-QKD) in dense-wavelength-division multiplexing networks
(DWDM), where QKD will typically have to coexist with several co- propagating
(forward or backward) C-band classical channels whose launch power is around
0dBm. We have conducted experimental tests of the coexistence of CV-QKD
multiplexed with an intense classical channel, for different input powers and
different DWDM wavelengths. Over a 25km fiber, a CV-QKD operated over the
1530.12nm channel can tolerate the noise arising from up to 11.5dBm classical
channel at 1550.12nm in forward direction (9.7dBm in backward). A positive key
rate (0.49kb/s) can be obtained at 75km with classical channel power of
respectively -3dBm and -9dBm in forward and backward. Based on these
measurements, we have also simulated the excess noise and optimized channel
allocation for the integration of CV-QKD in some access networks. We have, for
example, shown that CV-QKD could coexist with 5 pairs of channels (with nominal
input powers: 2dBm forward and 1dBm backward) over a 25km WDM-PON network. The
obtained results demonstrate the outstanding capacity of CV-QKD to coexist with
classical signals of realistic intensity in optical networks.Comment: 19 pages, 9 figures. Revised version, to appear in New Journal of
Physic
Controlling single diamond NV color center photoluminescence spectrum with a Fabry-Perot microcavity
We present both theoretical and experimental results on fluorescence of
single defect centers in diamond nanocrystals embedded in a planar dielectric
microcavity. From a theoretical point of view, we show that the overall
fluorescence collection efficiency using moderate numerical aperture microscope
objective can be enhanced by using a low quality factor microcavity. This could
be used in particular for low temperature applications where the numerical
aperture of collection microscope objectives is limited due to the experimental
constraints. We experimentally investigate the control of the fluorescence
spectrum of the emitted light from a single center. We show the simultaneous
narrowing of the room temperature broadband emission spectrum and the increase
of the fluorescence spectral density.Comment: 22 pages, 10 figure
Hybrid Quantum Cryptography from Communication Complexity
We introduce an explicit construction for a key distribution protocol in the
Quantum Computational Timelock (QCT) security model, where one assumes that
computationally secure encryption may only be broken after a time much longer
than the coherence time of available quantum memories.
Taking advantage of the QCT assumptions, we build a key distribution protocol
called HM-QCT from the Hidden Matching problem for which there exists an
exponential gap in one-way communication complexity between classical and
quantum strategies.
We establish that the security of HM-QCT against arbitrary i.i.d. attacks can
be reduced to the difficulty of solving the underlying Hidden Matching problem
with classical information. Legitimate users, on the other hand, can use
quantum communication, which gives them the possibility of sending multiple
copies of the same quantum state while retaining an information advantage. This
leads to an everlasting secure key distribution scheme over bosonic modes.
Such a level of security is unattainable with purely classical techniques.
Remarkably, the scheme remains secure with up to input photons for each channel use, extending
the functionalities and potentially outperforming QKD rates by several orders
of magnitudes.Comment: 25 pages, 5 figure
Optimal eavesdropping on QKD without quantum memory
We consider the security of the BB84, six-state and SARG04 quantum key
distribution protocols when the eavesdropper doesn't have access to a quantum
memory. In this case, Eve's most general strategy is to measure her ancilla
with an appropriate POVM designed to take advantage of the post-measurement
information that will be released during the sifting phase of the protocol.
After an optimization on all the parameters accessible to Eve, our method
provides us with new bounds for the security of six-state and SARG04 against a
memoryless adversary. In particular, for the six-state protocol we show that
the maximum QBER for which a secure key can be extracted is increased from
12.6% (for collective attacks) to 20.4% with the memoryless assumption.Comment: 7 pages, 3 figures. Analysis of six-state and SARG04 QKD protocols
adde
Multidimensional reconciliation for continuous-variable quantum key distribution
We propose a method for extracting an errorless secret key in a
continuous-variable quantum key distribution protocol, which is based on
Gaussian modulation of coherent states and homodyne detection. The crucial
feature is an eight-dimensional reconciliation method, based on the algebraic
properties of octonions. Since the protocol does not use any postselection, it
can be proven secure against arbitrary collective attacks, by using
well-established theorems on the optimality of Gaussian attacks. By using this
new coding scheme with an appropriate signal to noise ratio, the distance for
secure continuous-variable quantum key distribution can be significantly
extended.Comment: 8 pages, 3 figure
4-Sulfamoylanilinium nitrate
In the crystal structure of the title compound, C6H9N2O2S+·NO3
â, the cations and anions are connected by NâHâŻO hydrogen bonds into a three-dimensional network
Direct Measurement of the Photon Statistics of a Triggered Single Photon Source
We studied intensity fluctuations of a single photon source relying on the
pulsed excitation of the fluorescence of a single molecule at room temperature.
We directly measured the Mandel parameter Q(T) over 4 orders of magnitude of
observation timescale T, by recording every photocount. On timescale of a few
excitation periods, subpoissonian statistics is clearly observed and the
probablility of two-photons events is 10 times smaller than Poissonian pulses.
On longer times, blinking in the fluorescence, due to the molecular triplet
state, produces an excess of noise.Comment: 4 pages, 3 figures, 1 table submitted to Physical Review Letter
Experimental open air quantum key distribution with a single photon source
We present a full implementation of a quantum key distribution (QKD) system
with a single photon source, operating at night in open air. The single photon
source at the heart of the functional and reliable setup relies on the pulsed
excitation of a single nitrogen-vacancy color center in diamond nanocrystal. We
tested the effect of attenuation on the polarized encoded photons for inferring
longer distance performance of our system. For strong attenuation, the use of
pure single photon states gives measurable advantage over systems relying on
weak attenuated laser pulses. The results are in good agreement with
theoretical models developed to assess QKD security
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