30 research outputs found
Exact Solutions of the Caldeira-Leggett Master Equation: A Factorization Theorem For Decoherence
Exact solutions of the Caldeira-Leggett Master equation for the reduced
density matrix for a free particle and for a harmonic oscillator system coupled
to a heat bath of oscillators are obtained for arbitrary initial conditions.
The solutions prove that the Fourier transform of the density matrix at time t
with respect to (x + x')/2, where x and x' are the initial and final
coordinates, factorizes exactly into a part depending linearly on the initial
density matrix and a part independent of it. The theorem yields the exact
initial state dependence of the density operator at time t and its eventual
diagonalization in the energy basis.Comment: 8 pages, late
Decoherence and the Quantum Zeno Effect
The experiment of Etano et al which demonstrated the quantum Zeno effect
(QZE) in an optical experiment was explained by Frerichs and Schenzle without
invoking the wave function collapse. In this report it is proposed that the
collapse does occur, and it can be explained by the `environment induced
decoherence' theory. The environment here consists of the completely quantized
field vacuum modes. The spontaneous emission life time of the atom sets a
fundamental limit on the requirement of `continuous measurements' for QZE. This
limit turns out to be related to the time-energy uncertainty relation discussed
by Ghirardi et al.Comment: Based on a poster presented at the "Workshop on Advanced Laser
Spectroscopy", I.I.T. Kanpur, India, 25-28 February 1995. RevTeX, one page,
two uunecoded post-script figures appended
A Simplified Hierarchical Dynamic Quantum Secret Sharing Protocol with Added Features
Generalizing the notion of dynamic quantum secret sharing (DQSS), a
simplified protocol for hierarchical dynamic quantum secret sharing (HDQSS) is
proposed and it is shown that the protocol can be implemented using any
existing protocol of quantum key distribution, quantum key agreement or secure
direct quantum communication. The security of this proposed protocol against
eavesdropping and collusion attacks is discussed with specific attention
towards the issues related to the composability of the subprotocols that
constitute the proposed protocol. The security and qubit efficiency of the
proposed protocol is also compared with that of other existing protocols of
DQSS. Further, it is shown that it is possible to design a semi-quantum
protocol of HDQSS and in principle, the protocols of HDQSS can be implemented
using any quantum state. It is also noted that the completely
orthogonal-state-based realization of HDQSS protocol is possible and that HDQSS
can be experimentally realized using a large number of alternative approaches.Comment: 9 pages, 1 figur
Comparing coherence measures for X states: Can quantum states be ordered based on quantum coherence?
Quantum coherence is an essential resource for quantum information processing
and various quantitative measures of it have been introduced. However, the
interconnections between these measures are not yet understood properly. Here,
using a large set of randomly prepared states and analytically obtained
expressions of various measures of coherence (e.g., relative entropy of
coherence, norm of coherence, coherence via skew information, and
first-order coherence), it is established that these measures of quantum
coherence cannot be used to perform ordering of a set of quantum states based
on the amount of coherence present in a state. Further, it is shown that for a
given value of quantum coherence measured by the relative entropy of coherence,
maximally nonlocal mixed states of type (which are characterized by maximal
violation of the CHSH inequality) have maximum quantum coherence as measured by
norm of coherence. In addition, the amount of coherence measured by
norm of coherence for a Werner state is found to be always less than that for a
maximally nonlocal mixed state even when they possess an equal amount of
coherence measured by the relative entropy of coherence. These resource theory
based measures of coherence are not observed to show any relation with the
first-order coherence, while its maximum (hidden coherence) is found to be more
connected to concurrence both being basis independent quantities. These
observations could be of use in obtaining a deeper understanding of the
interconnections between various measures of quantum coherence.Comment: Interconnections between various measures of quantum coherence is
investigated using state