906 research outputs found
A Quantum Observable for the Graph Isomorphism Problem
Suppose we are given two graphs on vertices. We define an observable in
the Hilbert space \Co[(S_n \wr S_2)^m] which returns the answer ``yes'' with
certainty if the graphs are isomorphic and ``no'' with probability at least
if the graphs are not isomorphic. We do not know if this observable
is efficiently implementable.Comment: 5 pages, no figure
Defeating classical bit commitments with a quantum computer
It has been recently shown by Mayers that no bit commitment scheme is secure
if the participants have unlimited computational power and technology. However
it was noticed that a secure protocol could be obtained by forcing the cheater
to perform a measurement. Similar situations had been encountered previously in
the design of Quantum Oblivious Transfer. The question is whether a classical
bit commitment could be used for this specific purpose. We demonstrate that,
surprisingly, classical unconditionally concealing bit commitments do not help.Comment: 13 pages. Supersedes quant-ph/971202
The Hidden Subgroup Problem and Eigenvalue Estimation on a Quantum Computer
A quantum computer can efficiently find the order of an element in a group,
factors of composite integers, discrete logarithms, stabilisers in Abelian
groups, and `hidden' or `unknown' subgroups of Abelian groups. It is already
known how to phrase the first four problems as the estimation of eigenvalues of
certain unitary operators. Here we show how the solution to the more general
Abelian `hidden subgroup problem' can also be described and analysed as such.
We then point out how certain instances of these problems can be solved with
only one control qubit, or `flying qubits', instead of entire registers of
control qubits.Comment: 16 pages, 3 figures, LaTeX2e, to appear in Proceedings of the 1st
NASA International Conference on Quantum Computing and Quantum Communication
(Springer-Verlag
A brief review on the impossibility of quantum bit commitment
The desire to obtain an unconditionally secure bit commitment protocol in
quantum cryptography was expressed for the first time thirteen years ago. Bit
commitment is sufficient in quantum cryptography to realize a variety of
applications with unconditional security. In 1993, a quantum bit commitment
protocol was proposed together with a security proof. However, a basic flaw in
the protocol was discovered by Mayers in 1995 and subsequently by Lo and Chau.
Later the result was generalized by Mayers who showed that unconditionally
secure bit commitment is impossible. A brief review on quantum bit commitment
which focuses on the general impossibility theorem and on recent attempts to
bypass this result is provided.Comment: 11 page
Long-Short-Range Message-Passing: A Physics-Informed Framework to Capture Non-Local Interaction for Scalable Molecular Dynamics Simulation
Computational simulation of chemical and biological systems using ab initio
molecular dynamics has been a challenge over decades. Researchers have
attempted to address the problem with machine learning and fragmentation-based
methods, however the two approaches fail to give a satisfactory description of
long-range and many-body interactions, respectively. Inspired by
fragmentation-based methods, we propose the Long-Short-Range Message-Passing
(LSR-MP) framework as a generalization of the existing equivariant graph neural
networks (EGNNs) with the intent to incorporate long-range interactions
efficiently and effectively. We apply the LSR-MP framework to the recently
proposed ViSNet and demonstrate the state-of-the-art results with up to
error reduction for molecules in MD22 and Chignolin datasets. Consistent
improvements to various EGNNs will also be discussed to illustrate the general
applicability and robustness of our LSR-MP framework
CHEERS: A tool for Correlated Hole-Electron Evolution from Real-time Simulations
We put forward a practical nonequilibrium Green's function (NEGF) scheme to
perform real-time evolutions of many-body interacting systems driven out of
equilibrium by external fields. CHEERS is a computational tool to solve the
NEGF equation of motion in the so called generalized Kadanoff-Baym ansatz and
it can be used for model systems as well as first-principles Hamiltonians.
Dynamical correlation (or memory) effects are added to the Hartree-Fock
dynamics through a many-body self-energy. Applications to time-dependent
quantum transport, time-resolved photoabsorption and other ultrafast phenomena
are discussed.Comment: 15 pages, 6 figures, to be published, J. Phys.: Condens. Matter
(2018
Computational Collapse of Quantum State with Application to Oblivious Transfer
Quantum 2-party cryptography differs from its classical counterpart in at least one important way: Given black-box access to a perfect commitment scheme there exists a secure 1-2 quantum oblivious transfer. This reduction proposed by Crépeau and Kilian was proved secure against any receiver by Yao, in the case where perfect commitments are used. However, quantum commitments would normally be based on computational assumptions. A natural question therefore arises: What happens to the security of the above reduction when computationally secure commitments are used instead of perfect ones? In this paper, we address the security of 1-2 QOT when computationally binding string commitments are available. In particular, we analyse the security of a primitive called Quantum Measurement Commitment when it is constructed from unconditionally concealing but computationally binding commitments. As measuring a quantum state induces an irreversible collapse, we describe a QMC as an instance of ``computational collapse of a quantum state''. In a QMC a state appears to be collapsed to a polynomial time observer who cannot extract full information about the state without breaking a computational assumption. We reduce the security of QMC to a weak binding criteria for the string commitment. We also show that secure QMCs implies QOT using a straightforward variant of the reduction above
What are the implications for global value chains when the market shifts from the north to the south?
Rapid growth in many low-income economies was fuelled by the insertion of producers into global value chains feeding into high-income northern markets. This paper charts the evolution of financial and economic crisis in the global economy and argues that the likely outcome will be sustained growth in the two very large Asian Driver economies of China and India and stagnation in the historically dominant northern economies. Given the nature of demand in low-income southern economies, it is likely to be reflected in sustained demand for commodities, with other southern economy producers in global value chains being forced into lower levels of value added. Standards are likely to be of considerably reduced significance in value chains feeding into China and India
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