Vol.5 No.7
November 1,
2005
Research Articles:
System design for largescale ion
trap quantum information processor (pp515537)
J. Kim, S. Pau, Z. Ma, H.R. McLellan,
J.V. Gates, A. Kornblit, R.E. Slusher, R.M. Jopson, I. Kang and
M. Dinu
We present a detailed system design and available
technology choices for building a large scale ($>$ 100 qubits) ion trap
quantum information processor (QIP). The system design is based on
technologies that are within reach today, and utilizes
singleinstructiononmultipledata (SIMD) principles to reuse
resources that cannot be duplicated easily. The system engineering
principles adopted highlight various design tradeoffs in the QIP design
and serve as a guideline to find design spaces for a much larger QIP.
Recasting Mermin's
multiplayer game into the framework of pseudotelepathy
(pp538550)
G. Brassard, A. Broadbent, and A. Tapp
Entanglement is perhaps the most nonclassical
manifestation of quantum \mbox{mechanics}. Among its many interesting
applications to information processing, it can be harnessed to \emph{reduce}
the amount of communication required to process a variety of
distributed computational tasks. Can it be used to eliminate
communication altogether? Even though it cannot serve to signal
information between remote parties, there are distributed tasks that can
be performed without any need for communication, provided the parties
share prior entanglement: this is the realm pseudotelepathy.
One of the earliest uses of multiparty entanglement was
presented by Mermin in 1990. Here we recast his idea in terms of
pseudotelepathy: we provide a new computerscientistfriendly analysis
of this game. We prove an upper bound on the best possible classical
strategy for attempting to play this game, as well as a novel, matching
lower bound. This leads us to considerations on how well imperfect
quantummechanical apparatus must perform in order to exhibit a
behaviour that would be classically impossible to explain. Our results
include improved bounds that could help vanquish the infamous detection
loophole.
A quantum cryptographic protocol with
detection of compromised server
(pp551560)
D. R. Kuhn
This paper
presents a serverbased hybrid cryptographic protocol, using quantum and
classical resources, to generate a key for authentication and optionally
for encryption in a network. A novel feature of the protocol is that it
can detect a compromised server. Additional advantages are that it
avoids the requirement for timestamps used in classical protocols,
guarantees that the trusted server cannot know the authentication key,
can provide resistance to multiple photon attacks, and can be used with
BB84 or other quantum key distribution protocols. Each resource shares a
previously distributed secret key with the trusted server, and resources
can communicate with the server using both classical and quantum
channels. Resources do not share secret keys with each other, so that
the key distribution problem for the network is reduced from
to .
Globally
controlled artificial semiconducting molecules as quantum computers
(pp561572)
J. Tribollet
Quantum computers are expected to be
considerably more efficient than classical computers for the execution
of some specific tasks. The difficulty in the practical implementation
of those computers is to build a microscopic quantum system that can be
controlled at a larger macroscopic scale. Here I show that vertical
lines of donor atoms embedded in an appropriate Zinc Oxide semiconductor
structure can constitute artificial molecules that are as many copy of
the same quantum computer. In this scalable architecture, each unit of
information is encoded onto the electronic spin of a donor. Contrary to
most existing practical proposals, here the logical operations only
require a global control of the spins by electromagnetic pulses.
Ensemble measurements simplify the readout. With appropriate improvement
of its growth and doping methods, Zinc Oxide could be a good
semiconductor for the next generation of computers.
A comparison of
decoherencefree subsystem/subspace for partially broken symmetry
(pp573582)
S. Siddiqui and J. GeaBanacloche
We study the performance of the 3qubit decoherencefree
subsystem and the 4qubit decoherencefree subspace in the presence of
partially correlated noise. We characterize their performance in terms
of the average and worstcase fidelity, as a function of the ratio of
the interqubit distance to the correlation length of the noise, and find
that, in general, more symmetric arrangements (triangles or squares)
lead to better performance. Overall, we find the 3qubit code to perform
better than the 4qubit code by about a factor of 2 in the average
infidelity. We observe that this is related to the greater robustness of
this code against uncorrelated (independent) errors.
Highly asymmetric
quantum cloning in arbitrary dimension
(pp583592)
J. Fiuravsek, R. Filip, and N.J. Cerf
We investigate the universal asymmetric cloning of states
in a Hilbert space of arbitrary dimension. We derive the class of
optimal and fully asymmetric $1\rightarrow 3$ cloners, which produce
three copies, each having a different fidelity. A simple parametric
expression for the maximum achievable cloning fidelity triplets is then
provided. As a sideproduct, we also prove the optimality of the $1\rightarrow
2$ asymmetric cloning machines that have been proposed in the
literature.
Quantum algorithms
for subset finding
(pp593604)
A.M. Childs and J.M. Eisenberg
Recently, Ambainis gave an $O(N^{2/3})$query
discretetime quantum walk algorithm for the element distinctness
problem, and more generally, an $O(N^{L/(L+1)})$query algorithm for
finding $L$ equal numbers. We review this algorithm and give a
simplified and tightened analysis of its query complexity using
techniques previously applied to the analysis of continuoustime quantum
walk. We also briefly discuss applications of the algorithm and pose two
open problems regarding continuoustime quantum walk and lower bounds.
Erratum:
On “Quantum and Classical Message
Identification via Quantum Channels”
(pp605606)
A. Winter
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