437 research outputs found
Symmetric Multiplets in Quantum Algebras
We consider a modified version of the coproduct for \U(\su_q(2)) and show
that in the limit when , there exists an essentially
non-cocommutative coproduct. We study the implications of this
non-cocommutativity for a system of two spin- particles. Here it is shown
that, unlike the usual case, this non-trivial coproduct allows for symmetric
and anti-symmetric states to be present in the multiplet. We surmise that our
analysis could be related to the ferromagnetic and antiferromagnetic cases of
the Heisenberg magnets.Comment: Needs subeqnarray.sty. To be published in Mod Phys Lett.
Direct estimation of functionals of density operators by local operations and classical communication
We present a method of direct estimation of important properties of a shared bipartite quantum state, within the "distant laboratories" paradigm, using only local operations and classical communication. We apply this procedure to spectrum estimation of shared states, and locally implementable structural physical approximations to incompletely positive maps. This procedure can also be applied to the estimation of channel capacity and measures of entanglement
Quantum cryptography based on qutrit Bell inequalities
We present a cryptographic protocol based upon entangled qutrit pairs. We analyze the scheme under a symmetric incoherent attack and plot the region for which the protocol is secure and compare this with the region of violations of certain Bell inequalities
Experimental Demonstration of Quantum State Multi-meter and One-qubit Fingerprinting in a Single Quantum Device
We experimentally demonstrate in NMR a quantum interferometric multi-meter
for extracting certain properties of unknown quantum states without resource to
quantum tomography. It can perform direct state determinations,
eigenvalue/eigenvector estimations, purity tests of a quantum system, as well
as the overlap of any two unknown quantum states. Using the same device, we
also demonstrate one-qubit quantum fingerprinting
A universal quantum estimator
Almost all computational tasks in the modem computer can be designed from basic building blocks. These building blocks provide a powerful and efficient language for describing algorithms. In quantum computers, the basic building blocks are the quantum gates. In this tutorial, we will look at quantum gates that act on one and two qubits and briefly discuss how these gates can be used in quantum networks
Kraus representation for density operator of arbitrary open qubit system
We show that the time evolution of density operator of open qubit system can
always be described in terms of the Kraus representation. A general scheme on
how to construct the Kraus operators for an open qubit system is proposed,
which can be generalized to open higher dimensional quantum systems.Comment: 5 pages, no figures. Some words are rephrase
Multi-Component Bell Inequality and its Violation for Continuous Variable Systems
Multi-component correlation functions are developed by utilizing d-outcome
measurements. Based on the multi-component correlation functions, we propose a
Bell inequality for bipartite d-dimensional systems. Violation of the Bell
inequality for continuous variable (CV) systems is investigated. The violation
of the original Einstein-Podolsky-Rosen state can exceed the Cirel'son bound,
the maximal violation is 2.96981. For finite value of squeezing parameter,
violation strength of CV states increases with dimension d. Numerical results
show that the violation strength of CV states with finite squeezing parameter
is stronger than that of original EPR state.Comment: 5 pages and 1 figure, rewritten version, accepted by Phys. Rev.
Operator-sum representation of time-dependent density operators and its applications
We show that any arbitrary time-dependent density operator of an open system
can always be described in terms of an operator-sum representation regardless
of its initial condition and the path of its evolution in the state space, and
we provide a general expression of Kraus operators for arbitrary time-dependent
density operator of an -dimensional system. Moreover, applications of our
result are illustrated through several examples.Comment: 4 pages, no figure, brief repor
- …