432 research outputs found
Two-excitation routing via linear quantum channels
Routing quantum information among different nodes in a network is a
fundamental prerequisite for a quantum internet. While single-qubit routing has
been largely addressed, many-qubit routing protocols have not been intensively
investigated so far. Building on the many-excitation transfer protocol in
arXiv:1911.12211, we apply the perturbative transfer scheme to a two-excitation
routing protocol on a network where multiple two-receivers block are coupled to
a linear chain. We address both the case of switchable and permanent couplings
between the receivers and the chain. We find that the protocol allows for
efficient two-excitation routing on a fermionic network, although for a
spin- network only a limited region of the network is suitable for
high-quality routing.Comment: 12 pages, 7 figure
Coherent state transfer via highly mixed quantum spin chains
Spin chains have been proposed as quantum wires in many quantum information
processing architectures. Coherent transmission of quantum information over
short distances is enabled by their internal dynamics, which drives the
transport of single-spin excitations in perfectly polarized chains. Given the
practical challenge of preparing the chain in a pure state, we propose to use a
chain that is initially in the maximally mixed state. We compare the transport
properties of pure and mixed-state chains, finding similarities that enable the
experimental study of pure-state transfer by its simulation via mixed-state
chains, and demonstrate protocols for the perfect transfer of quantum
information in these chains. Remarkably, mixed-state chains allow the use of
Hamiltonians which do not preserve the total number of excitations, and which
are more readily obtainable from the naturally occurring magnetic dipolar
interaction. We propose experimental implementations using solid-state nuclear
magnetic resonance and defect centers in diamond.Comment: 9 page
Chaos and Complexity of quantum motion
The problem of characterizing complexity of quantum dynamics - in particular
of locally interacting chains of quantum particles - will be reviewed and
discussed from several different perspectives: (i) stability of motion against
external perturbations and decoherence, (ii) efficiency of quantum simulation
in terms of classical computation and entanglement production in operator
spaces, (iii) quantum transport, relaxation to equilibrium and quantum mixing,
and (iv) computation of quantum dynamical entropies. Discussions of all these
criteria will be confronted with the established criteria of integrability or
quantum chaos, and sometimes quite surprising conclusions are found. Some
conjectures and interesting open problems in ergodic theory of the quantum many
problem are suggested.Comment: 45 pages, 22 figures, final version, at press in J. Phys. A, special
issue on Quantum Informatio
Studies of quantum spin chain dynamics and their potential applications in quantum information
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Quantum Simulators: Architectures and Opportunities
Quantum simulators are a promising technology on the spectrum of quantum devices from specialized quantum experiments to universal quantum computers. These quantum devices utilize entanglement and many-particle behavior to explore and solve hard scientific, engineering, and computational problems. Rapid development over the last two decades has produced more than 300 quantum simulators in operation worldwide using a wide variety of experimental platforms. Recent advances in several physical architectures promise a golden age of quantum simulators ranging from highly optimized special purpose simulators to flexible programmable devices. These developments have enabled a convergence of ideas drawn from fundamental physics, computer science, and device engineering. They have strong potential to address problems of societal importance, ranging from understanding vital chemical processes, to enabling the design of new materials with enhanced performance, to solving complex computational problems. It is the position of the community, as represented by participants of the National Science Foundation workshop on “Programmable Quantum Simulators,” that investment in a national quantum simulator program is a high priority in order to accelerate the progress in this field and to result in the first practical applications of quantum machines. Such a program should address two areas of emphasis: (1) support for creating quantum simulator prototypes usable by the broader scientific community, complementary to the present universal quantum computer effort in industry; and (2) support for fundamental research carried out by a blend of multi-investigator, multidisciplinary collaborations with resources for quantum simulator software, hardware, and education.This document is a summary from a U.S. National Science Foundation supported workshop held on 16–17 September 2019 in Alexandria, VA. Attendees were charged to identify the scientific and community needs, opportunities, and significant challenges for quantum simulators over the next 2–5 years
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