27,278 research outputs found
Entanglement-assisted quantum metrology
Entanglement-assisted quantum communication employs pre-shared entanglement
between sender and receiver as a resource. We apply the same framework to
quantum metrology, introducing shared entanglement between the preparation and
the measurement stage, namely using some entangled ancillary system that does
not interact with the system to be sampled. This is known to be useless in the
noiseless case, but was recently shown to be useful in the presence of noise.
Here we detail how and when it can be of use. For example, surprisingly it is
useful when randomly time sharing two channels where ancillas do not help
(depolarizing). We show that it is useful for all levels of noise for many
noise models and propose a simple experiment to test these results.Comment: 5 pages, 5 figure
Insider-proof encryption with applications for quantum key distribution
It has been pointed out that current protocols for device independent quantum
key distribution can leak key to the adversary when devices are used repeatedly
and that this issue has not been addressed. We introduce the notion of an
insider-proof channel. This allows us to propose a means by which devices with
memories could be reused from one run of a device independent quantum key
distribution protocol to the next while bounding the leakage to Eve, under the
assumption that one run of the protocol could be completed securely using
devices with memories.Comment: 20 pages, version 2: new presentation introducing the insider-proof
channel as a cryptographic elemen
Quantum key distribution based on private states: unconditional security over untrusted channels with zero quantum capacity
We prove unconditional security for a quantum key distribution (QKD) protocol
based on distilling pbits (twisted ebits) [quant-ph/0309110] from an arbitrary
untrusted state that is claimed to contain distillable key. Our main result is
that we can verify security using only public communication -- via parameter
estimation of the given untrusted state. The technique applies even to bound
entangled states, thus extending QKD to the regime where the available quantum
channel has zero quantum capacity. We also show how to convert our
purification-based QKD schemes to prepare-measure schemes.Comment: Final version for IEEE TI
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