248 research outputs found
Implementation of a Quantum Search Algorithm on a Nuclear Magnetic Resonance Quantum Computer
We demonstrate an implementation of a quantum search algorithm on a two qubit
NMR quantum computer based on cytosine.Comment: Six pages, three figure
Quantum computation by local measurement
Quantum computation is a novel way of information processing which allows,
for certain classes of problems, exponential speedups over classical
computation. Various models of quantum computation exist, such as the
adiabatic, circuit and measurement-based models. They have been proven
equivalent in their computational power, but operate very differently. As such,
they may be suitable for realization in different physical systems, and also
offer different perspectives on open questions such as the precise origin of
the quantum speedup. Here, we give an introduction to the one-way quantum
computer, a scheme of measurement-based quantum computation. In this model, the
computation is driven by local measurements on a carefully chosen, highly
entangled state. We discuss various aspects of this computational scheme, such
as the role of entanglement and quantum correlations. We also give examples for
ground states of simple Hamiltonians which enable universal quantum computation
by local measurements.Comment: 36 pages, single column, 6 figures, not published version (as
restricted by the journal), please refer to ARCMP for the final published
versio
Quantum Computing in Molecular Magnets
Shor and Grover demonstrated that a quantum computer can outperform any
classical computer in factoring numbers and in searching a database by
exploiting the parallelism of quantum mechanics. Whereas Shor's algorithm
requires both superposition and entanglement of a many-particle system, the
superposition of single-particle quantum states is sufficient for Grover's
algorithm. Recently, the latter has been successfully implemented using Rydberg
atoms. Here we propose an implementation of Grover's algorithm that uses
molecular magnets, which are solid-state systems with a large spin; their spin
eigenstates make them natural candidates for single-particle systems. We show
theoretically that molecular magnets can be used to build dense and efficient
memory devices based on the Grover algorithm. In particular, one single crystal
can serve as a storage unit of a dynamic random access memory device. Fast
electron spin resonance pulses can be used to decode and read out stored
numbers of up to 10^5, with access times as short as 10^{-10} seconds. We show
that our proposal should be feasible using the molecular magnets Fe8 and Mn12.Comment: 13 pages, 2 figures, PDF, version published in Nature, typos
correcte
Quantum Teleportation is a Universal Computational Primitive
We present a method to create a variety of interesting gates by teleporting
quantum bits through special entangled states. This allows, for instance, the
construction of a quantum computer based on just single qubit operations, Bell
measurements, and GHZ states. We also present straightforward constructions of
a wide variety of fault-tolerant quantum gates.Comment: 6 pages, REVTeX, 6 epsf figure
Quantum enhanced positioning and clock synchronization
A wide variety of positioning and ranging procedures are based on repeatedly
sending electromagnetic pulses through space and measuring their time of
arrival. This paper shows that quantum entanglement and squeezing can be
employed to overcome the classical power/bandwidth limits on these procedures,
enhancing their accuracy. Frequency entangled pulses could be used to construct
quantum positioning systems (QPS), to perform clock synchronization, or to do
ranging (quantum radar): all of these techniques exhibit a similar enhancement
compared with analogous protocols that use classical light. Quantum
entanglement and squeezing have been exploited in the context of
interferometry, frequency measurements, lithography, and algorithms. Here, the
problem of positioning a party (say Alice) with respect to a fixed array of
reference points will be analyzed.Comment: 4 pages, 2 figures. Accepted for publication by Natur
Bridging Elementary Landscapes and a Geometric Theory of Evolutionary Algorithms: First Steps
This is the author accepted manuscript. The final version is available from Springer via the DOI in this record.Paper to be presented at the Fifteenth International Conference on Parallel Problem Solving from Nature (PPSN XV), Coimbra, Portugal on 8-12 September.Based on a geometric theory of evolutionary algorithms, it was shown that all evolutionary algorithms equipped with a geometric crossover and no mutation operator do the same kind of convex search across representations, and that they are well matched with generalised forms of concave fitness landscapes for which they provably find the optimum in polynomial time. Analysing the landscape structure is essential to understand the relationship between problems and evolutionary algorithms. This paper continues such investigations by considering the following challenge: develop an analytical method to recognise that the fitness landscape for a given problem provably belongs to a class of concave fitness landscapes. Elementary landscapes theory provides analytic algebraic means to study the landscapes structure. This work begins linking both theories to better understand how such method could be devised using elementary landscapes. Examples on well known One Max, Leading Ones, Not-All-Equal Satisfiability and Weight Partitioning problems illustrate the fundamental concepts supporting this approach
Biophysics - Quantum path to photosynthesis
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62904/1/446740a.pd
Interfacing External Quantum Devices to a Universal Quantum Computer
We present a scheme to use external quantum devices using the universal quantum computer previously constructed. We thereby show how the universal quantum computer can utilize networked quantum information resources to carry out local computations. Such information may come from specialized quantum devices or even from remote universal quantum computers. We show how to accomplish this by devising universal quantum computer programs that implement well known oracle based quantum algorithms, namely the Deutsch, Deutsch-Jozsa, and the Grover algorithms using external black-box quantum oracle devices. In the process, we demonstrate a method to map existing quantum algorithms onto the universal quantum computer
Multimode quantum interference of photons in multiport integrated devices
We report the first demonstration of quantum interference in multimode
interference (MMI) devices and a new complete characterization technique that
can be applied to any photonic device that removes the need for phase stable
measurements. MMI devices provide a compact and robust realization of NxM
optical circuits, which will dramatically reduce the complexity and increase
the functionality of future generations of quantum photonic circuits
Operational Significance of Discord Consumption: Theory and Experiment
Coherent interactions that generate negligible entanglement can still exhibit
unique quantum behaviour. This observation has motivated a search beyond
entanglement for a complete description of all quantum correlations. Quantum
discord is a promising candidate. Here, we demonstrate that under certain
measurement constraints, discord between bipartite systems can be consumed to
encode information that can only be accessed by coherent quantum interactions.
The inability to access this information by any other means allows us to use
discord to directly quantify this `quantum advantage'. We experimentally encode
information within the discordant correlations of two separable Gaussian
states. The amount of extra information recovered by coherent interaction is
quantified and directly linked with the discord consumed during encoding. No
entanglement exists at any point of this experiment. Thus we introduce and
demonstrate an operational method to use discord as a physical resource.Comment: 10 pages, 3 figures, updated with Nature Physics Reference,
simplified proof in Appendi
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