112 research outputs found
Estimation of Output Channel Noise for Continuous Variable Quantum Key Distribution
Estimation of channel parameters is important for extending the range and
increasing the key rate of continuous variable quantum key distribution
protocols. We propose a new estimator for the channel noise parameter based on
the method of moments. The method of moments finds an estimator from the
moments of the output distribution of the protocol. This estimator has the
advantage of being able to use all of the states shared between Alice and Bob.
Other estimators are limited to a smaller publicly revealed subset of the
states. The proposed estimator has a lower variance for high loss channel than
what has previously been proposed. We show that the method of moments estimator
increases the key rate by up to an order of magnitude at the maximum
transmission of the protocol.Comment: 5 pages, 3 figure
Raw-data attacks in quantum cryptography with partial tomography
We consider a variant of the BB84 protocol for quantum cryptography, the
prototype of tomographically incomplete protocols, where the key is generated
by one-way communication rather than the usual two-way communication. Our
analysis, backed by numerical evidence, establishes thresholds for
eavesdropping attacks on the raw data and on the generated key at quantum bit
error rates of 10% and 6.15%, respectively. Both thresholds are lower than the
threshold for unconditional security in the standard BB84 protocol.Comment: 11 pages, 2 figure
A Security Study of Two Non-Tomographic Quantum Communication Protocols
Ph.DNUS-ANU JOINT PH
Joint measurement of multiple noncommuting parameters
Although quantum metrology allows us to make precision measurements beyond the standard quantum limit, it mostly works on the measurement of only one observable due to the Heisenberg uncertainty relation on the measurement precision of noncommuting observables for one system. In this paper, we study the schemes of joint measurement of multiple observables which do not commute with each other using the quantum entanglement between two systems. We focus on analyzing the performance of a SU(1,1) nonlinear interferometer on fulfilling the task of joint measurement. The results show that the information encoded in multiple noncommuting observables on an optical field can be simultaneously measured with a signal-to-noise ratio higher than the standard quantum limit, and the ultimate limit of each observable is still the Heisenberg limit. Moreover, we find a resource conservation rule for the joint measurement
Overarching framework between Gaussian quantum discord and Gaussian quantum illumination
We cast the problem of illuminating an object in a noisy environment into a
communication protocol. A probe is sent into the environment, and the presence
or absence of the object constitutes a signal encoded on the probe. The probe
is then measured to decode the signal. We calculate the Holevo information and
bounds to the accessible information between the encoded and received signal
with two different Gaussian probes---an Einstein-Podolsky-Rosen (EPR) state and
a coherent state. We also evaluate the Gaussian discord consumed during the
encoding process with the EPR probe. We find that the Holevo quantum advantage,
defined as the difference between the Holevo information obtained from the EPR
and coherent state probes, is approximately equal to the discord consumed.
These quantities become exact in the typical illumination regime of low object
reflectivity and low probe energy. Hence we show that discord is the resource
responsible for the quantum advantage in Gaussian quantum illumination.Comment: 12 pages, 8 figure
- …