47 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
Homodyne detector blinding attack in continuous-variable quantum key distribution
We propose an efficient strategy to attack a continuous-variable (CV) quantum key distribution (QKD) system, which we call homodyne detector blinding. This attack strategy takes advantage of a generic vulnerability of homodyne receivers: A bright light pulse sent on the signal port can lead to a saturation of the detector electronics. While detector saturation has already been proposed to attack CV QKD, the attack we study in this paper has the additional advantage of not requiring an eavesdropper to be phase locked with the homodyne receiver. We show that under certain conditions, an attacker can use a simple laser, incoherent with the homodyne receiver, to generate bright pulses and bias the excess noise to arbitrary small values, fully comprising CV QKD security. These results highlight the feasibility and the impact of the detector-blinding attack. We finally discuss how to design countermeasures in order to protect against this attack
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
Parallelizable Synthesis of Arbitrary Single-Qubit Gates with Linear Optics and Time-Frequency Encoding
We propose novel methods for the exact synthesis of single-qubit unitaries
with high success probability and gate fidelity, considering both time-bin and
frequency-bin encodings. The proposed schemes are experimentally implementable
with a spectral linear-optical quantum computation (S- LOQC) platform, composed
of electro-optic phase modulators and phase-only programmable filters (pulse
shapers). We assess the performances in terms of fidelity and probability of
the two simplest 3-components configurations for arbitrary gate generation in
both encodings and give an exact analytical solution for the synthesis of an
arbitrary single-qubit unitary in the time-bin encoding, using a single-tone
Radio Frequency (RF) driving of the EOMs. We further investigate the
parallelization of arbitrary single-qubit gates over multiple qubits with a
compact experimental setup, both for spectral and temporal encodings. We
systematically evaluate and discuss the impact of the RF bandwidth - that
conditions the number of tones driving the modulators - and of the choice of
encoding for different targeted gates. We moreover quantify the number of high
fidelity Hadamard gates that can be synthesized in parallel, with minimal and
increasing resources in terms of driving RF tones in a realistic system. Our
analysis positions spectral S-LOQC as a promising platform to conduct massively
parallel single qubit operations, with potential applications to quantum
metrology and quantum tomography.Comment: 21 pages, 6 figure