13 research outputs found
Transformations between symmetric sets of quantum states
We investigate probabilistic transformations of quantum states from a
`source' set to a `target' set of states. Such transforms have many
applications. They can be used for tasks which include state-dependent cloning
or quantum state discrimination, and as interfaces between systems whose
information encodings are not related by a unitary transform, such as
continuous-variable systems and finite-dimensional systems. In a probabilistic
transform, information may be lost or leaked, and we explain the concepts of
leak and redundancy. Following this, we show how the analysis of probabilistic
transforms significantly simplifies for symmetric source and target sets of
states. In particular, we give a simple linear program which solves the task of
finding optimal transforms, and a method of characterizing the introduced leak
and redundancy in information-theoretic terms. Using the developed techniques,
we analyse a class of transforms which convert coherent states with information
encoded in their relative phase to symmetric qubit states. Each of these sets
of states on their own appears in many well studied quantum information
protocols. Finally, we suggest an asymptotic realization based on quantum
scissors.Comment: 10 pages; 5 figure
Ideal quantum protocols in the non-ideal physical world
The development of quantum protocols from conception to experimental realizations is one of
the main sources of the stimulating exchange between fundamental and experimental research
characteristic to quantum information processing. In this thesis we contribute to the development
of two recent quantum protocols, Universal Blind Quantum Computation (UBQC) and Quantum
Digital Signatures (QDS). UBQC allows a client to delegate a quantum computation to a more
powerful quantum server while keeping the input and computation private. We analyse the resilience
of the privacy of UBQC under imperfections. Then, we introduce approximate blindness
quantifying any compromise to privacy, and propose a protocol which enables arbitrary levels of
security despite imperfections. Subsequently, we investigate the adaptability of UBQC to alternative
implementations with practical advantages. QDS allow a party to send a message to other
parties which cannot be forged, modified or repudiated. We analyse the security properties of a
first proof-of-principle experiment of QDS, implemented in an optical system. We estimate the
security failure probabilities of our system as a function of protocol parameters, under all but the
most general types of attacks. Additionally, we develop new techniques for analysing transformations
between symmetric sets of states, utilized not only in the security proofs of QDS but in
other applications as well
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Combinatorial Optimization
This report summarizes the meeting on Combinatorial Optimization where new and promising developments in the field were discussed. Th
Finiteness of circulant weighing matrices of fixed weight
10.1016/j.jcta.2010.10.004Journal of Combinatorial Theory. Series A1183908-919JCBT