14,499 research outputs found
Attacking quantum key distribution with single-photon two-qubit quantum logic
The Fuchs-Peres-Brandt (FPB) probe realizes the most powerful individual
attack on Bennett-Brassard 1984 quantum key distribution (BB84 QKD) by means of
a single controlled-NOT (CNOT) gate. This paper describes a complete physical
simulation of the FPB-probe attack on polarization-based BB84 QKD using a
deterministic CNOT constructed from single-photon two-qubit quantum logic.
Adding polarization-preserving quantum nondemolition measurements of photon
number to this configuration converts the physical simulation into a true
deterministic realization of the FPB attack.Comment: 8 pages, 9 figures; references added, 1 new figure, appendix
expanded; accepted for publication in Phys. Rev.
Inverse Landau-Zener-Stuckelberg problem for qubit-resonator systems
We consider theoretically a superconducting qubit - nanomechanical resonator
(NR) system, which was realized by LaHaye et al. [Nature 459, 960 (2009)].
First, we study the problem where the state of the strongly driven qubit is
probed through the frequency shift of the low-frequency NR. In the case where
the coupling is capacitive, the measured quantity can be related to the
so-called quantum capacitance. Our theoretical results agree with the
experimentally observed result that, under resonant driving, the frequency
shift repeatedly changes sign. We then formulate and solve the inverse
Landau-Zener-Stuckelberg problem, where we assume the driven qubit's state to
be known (i.e. measured by some other device) and aim to find the parameters of
the qubit's Hamiltonian. In particular, for our system the qubit's bias is
defined by the NR's displacement. This may provide a tool for monitoring of the
NR's position.Comment: 10 pages, 7 figure
Floodlight Quantum Key Distribution: A Practical Route to Gbps Secret-Key Rates
The channel loss incurred in long-distance transmission places a significant
burden on quantum key distribution (QKD) systems: they must defeat a passive
eavesdropper who detects all the light lost in the quantum channel and does so
without disturbing the light that reaches the intended destination. The current
QKD implementation with the highest long-distance secret-key rate meets this
challenge by transmitting no more than one photon per bit [Opt. Express 21,
24550-24565 (2013)]. As a result, it cannot achieve the Gbps secret-key rate
needed for one-time pad encryption of large data files unless an impractically
large amount of multiplexing is employed. We introduce floodlight QKD (FL-QKD),
which floods the quantum channel with a high number of photons per bit
distributed over a much greater number of optical modes. FL-QKD offers security
against the optimum frequency-domain collective attack by transmitting less
than one photon per mode and using photon-coincidence channel monitoring, and
it is completely immune to passive eavesdropping. More importantly, FL-QKD is
capable of a 2 Gbps secret-key rate over a 50 km fiber link, without any
multiplexing, using available equipment, i.e., no new technology need be
developed. FL-QKD achieves this extraordinary secret-key rate by virtue of its
unprecedented secret-key efficiency, in bits per channel use, which exceeds
those of state-of-the-art systems by two orders of magnitude.Comment: 18 pages, 5 figure
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