1,627 research outputs found
Using of small-scale quantum computers in cryptography with many-qubit entangled states
We propose a new cryptographic protocol. It is suggested to encode
information in ordinary binary form into many-qubit entangled states with the
help of a quantum computer. A state of qubits (realized, e.g., with photons) is
transmitted through a quantum channel to the addressee, who applies a quantum
computer tuned to realize the inverse unitary transformation decoding of the
message. Different ways of eavesdropping are considered, and an estimate of the
time needed for determining the secret unitary transformation is given. It is
shown that using even small quantum computers can serve as a basis for very
efficient cryptographic protocols. For a suggested cryptographic protocol, the
time scale on which communication can be considered secure is exponential in
the number of qubits in the entangled states and in the number of gates used to
construct the quantum network
Quantum complexities of ordered searching, sorting, and element distinctness
We consider the quantum complexities of the following three problems:
searching an ordered list, sorting an un-ordered list, and deciding whether the
numbers in a list are all distinct. Letting N be the number of elements in the
input list, we prove a lower bound of \frac{1}{\pi}(\ln(N)-1) accesses to the
list elements for ordered searching, a lower bound of \Omega(N\log{N}) binary
comparisons for sorting, and a lower bound of \Omega(\sqrt{N}\log{N}) binary
comparisons for element distinctness. The previously best known lower bounds
are {1/12}\log_2(N) - O(1) due to Ambainis, \Omega(N), and \Omega(\sqrt{N}),
respectively. Our proofs are based on a weighted all-pairs inner product
argument.
In addition to our lower bound results, we give a quantum algorithm for
ordered searching using roughly 0.631 \log_2(N) oracle accesses. Our algorithm
uses a quantum routine for traversing through a binary search tree faster than
classically, and it is of a nature very different from a faster algorithm due
to Farhi, Goldstone, Gutmann, and Sipser.Comment: This new version contains new results. To appear at ICALP '01. Some
of the results have previously been presented at QIP '01. This paper subsumes
the papers quant-ph/0009091 and quant-ph/000903
Quantum state transfer and entanglement distribution among distant nodes in a quantum network
We propose a scheme to utilize photons for ideal quantum transmission between
atoms located at spatially-separated nodes of a quantum network. The
transmission protocol employs special laser pulses which excite an atom inside
an optical cavity at the sending node so that its state is mapped into a
time-symmetric photon wavepacket that will enter a cavity at the receiving node
and be absorbed by an atom there with unit probability. Implementation of our
scheme would enable reliable transfer or sharing of entanglement among
spatially distant atoms.Comment: 4 pages, 3 postscript figure
Autonomous three-dimensional formation flight for a swarm of unmanned aerial vehicles
This paper investigates the development of a new guidance algorithm for a formation of unmanned aerial vehicles. Using the new approach of bifurcating potential fields, it is shown that a formation of unmanned aerial vehicles can be successfully controlled such that verifiable autonomous patterns are achieved, with a simple parameter switch allowing for transitions between patterns. The key contribution that this paper presents is in the development of a new bounded bifurcating potential field that avoids saturating the vehicle actuators, which is essential for real or safety-critical applications. To demonstrate this, a guidance and control method is developed, based on a six-degreeof-freedom linearized aircraft model, showing that, in simulation, three-dimensional formation flight for a swarm of unmanned aerial vehicles can be achieved
Geometry of the 3-Qubit State, Entanglement and Division Algebras
We present a generalization to 3-qubits of the standard Bloch sphere
representation for a single qubit and of the 7-dimensional sphere
representation for 2 qubits presented in Mosseri {\it et
al.}\cite{Mosseri2001}. The Hilbert space of the 3-qubit system is the
15-dimensional sphere , which allows for a natural (last) Hopf
fibration with as base and as fiber. A striking feature is, as in
the case of 1 and 2 qubits, that the map is entanglement sensitive, and the two
distinct ways of un-entangling 3 qubits are naturally related to the Hopf map.
We define a quantity that measures the degree of entanglement of the 3-qubit
state. Conjectures on the possibility to generalize the construction for higher
qubit states are also discussed.Comment: 12 pages, 2 figures, final versio
Quantum Cryptography Based on the Time--Energy Uncertainty Relation
A new cryptosystem based on the fundamental time--energy uncertainty relation
is proposed. Such a cryptosystem can be implemented with both correlated photon
pairs and single photon states.Comment: 5 pages, LaTex, no figure
Microcurrent stimulation in the treatment of dry and wet macular degeneration
Purpose: To determine the safety and efficacy of the application of transcutaneous (transpalpebral) microcurrent stimulation to slow progression of dry and wet macular degeneration or improve vision in dry and wet macular degeneration. Methods: Seventeen patients aged between 67 and 95 years with an average age of 83 years were selected to participate in the study over a period of 3 months in two eye care centers. There were 25 eyes with dry age-related macular degeneration (DAMD) and six eyes with wet age-related macular degeneration (WAMD). Frequency-specific microcurrent stimulation was applied in a transpalpebral manner, using two programmable dual channel microcurrent units delivering pulsed microcurrent at 150 ÎŒA for 35 minutes once a week. The frequency pairs selected were based on targeting tissues, which are typically affected by the disease combined with frequencies that target disease processes. Early Treatment Diabetic Retinopathy Study or Snellen visual acuity (VA) was measured before and after each treatment session. All treatment was administered in a clinical setting. Results: Significant increases were seen in VA in DAMD (P=0.012, Wilcoxon one-sample test), but in WAMD, improvements did not reach statistical significance (P=0.059). In DAMD eyes, twice as many patients showed increase in VA (52%) compared to those showing dete-rioration (26%), with improvements being often sizeable, whereas deteriorations were usually very slight. In WAMD eyes, five of six (83%) patients showed an increase and none showed deterioration. Conclusion: The substantial changes observed over this period, combined with continued improvement for patients who continued treatment once a month, are encouraging for future studies. The changes observed indicate the potential efficacy of microcurrent to delay degeneration and possibly improve age-related macular degeneration, both wet and dry. However, this study has no control arm, so results should be treated with caution. Randomized double-blind controlled studies are needed to determine long-term effects
Scaling Property of the global string in the radiation dominated universe
We investigate the evolution of the global string network in the radiation
dominated universe by use of numerical simulations in 3+1 dimensions. We find
that the global string network settles down to the scaling regime where the
energy density of global strings, , is given by with the string tension per unit length and the scaling parameter,
, irrespective of the cosmic time. We also find that the
loop distribution function can be fitted with that predicted by the so-called
one scale model. Concretely, the number density, , of the loop with
the length, , is given by
where and is related with the Nambu-Goldstone(NG)
boson radiation power from global strings, , as with
. Therefore, the loop production function also scales and
the typical scale of produced loops is nearly the horizon distance. Thus, the
evolution of the global string network in the radiation dominated universe can
be well described by the one scale model in contrast with that of the local
string network.Comment: 18 pages, 9 figures, to appear in Phys. Rev.
Affine Constellations Without Mutually Unbiased Counterparts
It has been conjectured that a complete set of mutually unbiased bases in a
space of dimension d exists if and only if there is an affine plane of order d.
We introduce affine constellations and compare their existence properties with
those of mutually unbiased constellations, mostly in dimension six. The
observed discrepancies make a deeper relation between the two existence
problems unlikely.Comment: 8 page
Acceptability, usability and performance of lateral flow immunoassay tests for SARS-CoV-2 antibodies: REACT-2 study of self-testing in non-healthcare key workers
Background Seroprevalence studies are essential to understand the epidemiology of SARS-CoV-2. Various technologies, including laboratory assays and point-of-care self-tests, are available for antibody testing. The interpretation of seroprevalence studies requires comparative data on the performance of antibody tests. Methods In June 2020, current and former members of the UK Police forces and Fire service performed a self-test lateral flow immunoassay (LFIA), had a nurse-performed LFIA and provided a venous blood sample for ELISA . We present the prevalence of antibodies to SARS-CoV-2; the acceptability and usability of self-test LFIAs; and determine the sensitivity and specificity of LFIAs compared to laboratory ELISA. Results In this cohort of 5189 current and former members of the Police service and 263 members of the Fire service, 7.4% (396/5,348; 95% CI, 6.7-8.1) were antibody positive. Seroprevalence was 8.9% (6.9-11.4) in those under 40 years, 11.5% (8.8-15.0) in those of non-white ethnicity and 7.8% (7.1-8.7) in those currently working. Self-test LFIA had an acceptability of 97.7% and a usability of 90.0%. There was substantial agreement between within-participant LFIA results (kappa 0.80; 0.77-0.83). The LFIAs had a similar performance: compared to ELISA, sensitivity was 82.1% (77.7-86.0) self-test and 76.4% (71.9-80.5) nurse-performed with specificity of 97.8% (97.3-98.2) and 98.5% (98.1-98.8) respectively. Conclusion A greater proportion of this non-healthcare key worker cohort showed evidence of previous infection with SARS-CoV-2 than the general population at 6.0% (5.8-6.1) following the first wave in England. The high acceptability and usability reported by participants and similar performance of self-test and nurse-performed LFIAs indicate that the self-test LFIA is fit for purpose for home-testing in occupational and community prevalence studies
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