156 research outputs found
Deterministic Plug-and-Play for Quantum Communication
We present a scheme for secure deterministic quantum communication without
using entanglement, in a Plug-and-Play fashion. The protocol is completely
deterministic, both in the encoding procedure and in the control one, thus
doubling the communication rate with respect to other setups; moreover,
deterministic nature of transmission, apart from rendering unnecessary bases
revelation on the public channel, allows the realization of protocols like
`direct communication' and `quantum dialogue'. The encoding exploits the phase
degree of freedom of a photon, thus paving the way to an optical fiber
implementation, feasible with present day technology.Comment: 4 pages, 2 figures; one reference update
Robust Unconditionally Secure Quantum Key Distribution with Two Nonorthogonal and Uninformative States
We introduce a novel form of decoy-state technique to make the single-photon
Bennett 1992 protocol robust against losses and noise of a communication
channel. Two uninformative states are prepared by the transmitter in order to
prevent the unambiguous state discrimination attack and improve the phase-error
rate estimation. The presented method does not require strong reference pulses,
additional electronics or extra detectors for its implementation.Comment: 7 pages, 2 figure
Compensating the Noise of a Communication Channel via Asymmetric Encoding of Quantum Information
An asymmetric preparation of the quantum states sent through a noisy channel
can enable a new way to monitor and actively compensate the channel noise. The
paradigm of such an asymmetric treatment of quantum information is the Bennett
1992 protocol, in which the ratio between conclusive and inconclusive counts is
in direct connection with the channel noise. Using this protocol as a guiding
example, we show how to correct the phase drift of a communication channel
without using reference pulses, interruptions of the quantum transmission or
public data exchanges.Comment: 5 pages, 3 figure
Two qubits entanglement dynamics in a symmetry-broken environment
We study the temporal evolution of entanglement pertaining to two qubits
interacting with a thermal bath. In particular we consider the simplest
nontrivial spin bath models where symmetry breaking occurs and treat them by
mean field approximation. We analytically find decoherence free entangled
states as well as entangled states with an exponential decay of the quantum
correlation at finite temperature.Comment: 10 pages, 2 figure
Trigger-disabling Acquisition System for Quantum Key Distribution failsafe against Self-blinding
Modern single-photon detectors based on avalanche photodiodes offer
increasingly higher triggering speeds, thus fostering their use in several
fields, prominently in the recent area of Quantum Key Distribution. To reduce
the probability of an afterpulse, these detectors are usually equipped with a
circuitry that disables the trigger for a certain time after a positive
detection event, known as dead time. If the acquisition system connected to the
detector is not properly designed, efficiency issues arise when the triggering
rate is faster than the inverse of detector's dead-time. Moreover, when this
happens with two or more detectors used in coincidence, a security risk called
"self-blinding" can jeopardize the distribution of a secret quantum key. In
this paper we introduce a trigger-disabling circuitry based on an FPGA-driven
feedback loop, so to avoid the above-mentioned inconveniences. In the regime of
single-photon-attenuated light, the electronics dynamically accept a trigger
only after detectors' complete recovery from dead-time. This technique proves
useful to work with detectors at their maximum speed and to increase the
security of a quantum key distribution setup.Comment: 5 pages, 3 figures. Version 2 corrected and improve
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