388 research outputs found
Three-intensity decoy state method for device independent quantum key distribution with basis dependent errors
We study the measurement device independent quantum key distribution (MDIQKD)
in practice with limited resource, when there are only 3 different states in
implementing the decoy-state method and when there are basis dependent coding
errors. We present general formulas for the decoy-state method for two-pulse
sources with 3 different states, which can be applied to the recently proposed
MDIQKD with imperfect single-photon source such as the coherent states or the
heralded states from the parametric down conversion. We point out that the
existing result for secure QKD with source coding errors does not always hold.
We find that very accurate source coding is not necessary. In particular, we
loosen the precision of existing result by several magnitude orders for secure
QKD.Comment: Published version with Eq.(17) corrected. We emphasize that our major
result (Eq.16) for the decoy-state part can be applied to generate a key rate
very close to the ideal case of using infinite different coherent states, as
was numerically demonstrated in Ref.[21]. Published in PRA, 2013, Ja
Randomness in post-selected events
Bell inequality violations can be used to certify private randomness for use
in cryptographic applications. In photonic Bell experiments, a large amount of
the data that is generated comes from no-detection events and presumably
contains little randomness. This raises the question as to whether randomness
can be extracted only from the smaller post-selected subset corresponding to
proper detection events, instead of from the entire set of data. This could in
principle be feasible without opening an analogue of the detection loophole as
long as the min-entropy of the post-selected data is evaluated by taking all
the information into account, including no-detection events. The possibility of
extracting randomness from a short string has a practical advantage, because it
reduces the computational time of the extraction.
Here, we investigate the above idea in a simple scenario, where the devices
and the adversary behave according to i.i.d. strategies. We show that indeed
almost all the randomness is present in the pair of outcomes for which at least
one detection happened. We further show that in some cases applying a
pre-processing on the data can capture features that an analysis based on
global frequencies only misses, thus resulting in the certification of more
randomness. We then briefly consider non-i.i.d strategies and provide an
explicit example of such a strategy that is more powerful than any i.i.d. one
even in the asymptotic limit of infinitely many measurement rounds, something
that was not reported before in the context of Bell inequalities.Comment: similar to published version, new section (III) on photonic
experiment
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