2,065 research outputs found
Adiabatic quantum computation and quantum phase transitions
We analyze the ground state entanglement in a quantum adiabatic evolution
algorithm designed to solve the NP-complete Exact Cover problem. The entropy of
entanglement seems to obey linear and universal scaling at the point where the
mass gap becomes small, suggesting that the system passes near a quantum phase
transition. Such a large scaling of entanglement suggests that the effective
connectivity of the system diverges as the number of qubits goes to infinity
and that this algorithm cannot be efficiently simulated by classical means. On
the other hand, entanglement in Grover's algorithm is bounded by a constant.Comment: 5 pages, 4 figures, accepted for publication in PR
Approximate quantum counting on an NMR ensemble quantum computer
We demonstrate the implementation of a quantum algorithm for estimating the
number of matching items in a search operation using a two qubit nuclear
magnetic resonance (NMR) quantum computer.Comment: 4 pages LaTeX/RevTex including 4 figures (3 LaTeX, 1 PostScript).
Submitted to Physical Review Letter
Implementation of quantum search algorithm using classical Fourier optics
We report on an experiment on Grover's quantum search algorithm showing that
{\em classical waves} can search a -item database as efficiently as quantum
mechanics can. The transverse beam profile of a short laser pulse is processed
iteratively as the pulse bounces back and forth between two mirrors. We
directly observe the sought item being found in iterations, in
the form of a growing intensity peak on this profile. Although the lack of
quantum entanglement limits the {\em size} of our database, our results show
that entanglement is neither necessary for the algorithm itself, nor for its
efficiency.Comment: 4 pages, 3 figures; minor revisions plus extra referenc
Entanglement in the interaction between two quantum oscillator systems
The fundamental quantum dynamics of two interacting oscillator systems are
studied in two different scenarios. In one case, both oscillators are assumed
to be linear, whereas in the second case, one oscillator is linear and the
other is a non-linear, angular-momentum oscillator; the second case is, of
course, more complex in terms of energy transfer and dynamics. These two
scenarios have been the subject of much interest over the years, especially in
developing an understanding of modern concepts in quantum optics and quantum
electronics. In this work, however, these two scenarios are utilized to
consider and discuss the salient features of quantum behaviors resulting from
the interactive nature of the two oscillators, i.e., coherence, entanglement,
spontaneous emission, etc., and to apply a measure of entanglement in analyzing
the nature of the interacting systems. ... For the coupled linear and
angular-momentum oscillator system in the fully quantum-mechanical description,
we consider special examples of two, three, four-level angular momentum
systems, demonstrating the explicit appearances of entanglement. We also show
that this entanglement persists even as the coupled angular momentum oscillator
is taken to the limit of a large number of levels, a limit which would go over
to the classical picture for an uncoupled angular momentum oscillator
Vaginal bleeding in children: A retrospective audit at a tertiary paediatric gynaecology service
Aim: The aim of this study was to describe the clinical features and investigations of vaginal bleeding in prepubertal children.
Methods: We performed a retrospective case series of children under the age of 10 who presented with vaginal bleeding to our institution between 2018 and 2019.
Results: There were 32 cases identified during the timeframe, with a mean age of 5.5 years (standard deviation 3.2 years, range 5.5 days to 9.6 years). Vulvovaginitis was the most common diagnosis (n = 12, 37.5%), followed by precocious puberty (n = 5, 15.6%). Uncommon but serious causes were vaginal rhabdomyosarcoma (n = 1), and sexual abuse (one patient presenting with gonorrhoea and one with a non-accidental injury). Vaginoscopy was performed in nine patients (28.1%) for various reasons, and a vaginal foreign body was identified in two patients (6.3%). All the patients who had a serious cause of bleeding (neoplasm or sexual assault) or who required specific treatment (precocious puberty, lichen sclerosus, urethral prolapse) presented with red flags on history and/or examination: recurrent episodes of vaginal bleeding, heavy bleeding, associated general symptoms (poor feeding and growth), presence of thelarche, abdominal mass, associated profuse vaginal discharge and abnormal genital examination (skin changes, urethral prolapse or protruding mass from the vagina).
Conclusions: A thorough history-taking and clinical examination aiming at identifying red flags may help to discriminate between benign causes of vaginal bleeding, where no further investigations are indicated, and alternative diagnoses with a poor outcome and/or requiring specific treatment and additional investigations
The Majorization Arrow in Quantum Algorithm Design
We apply majorization theory to study the quantum algorithms known so far and
find that there is a majorization principle underlying the way they operate.
Grover's algorithm is a neat instance of this principle where majorization
works step by step until the optimal target state is found. Extensions of this
situation are also found in algorithms based in quantum adiabatic evolution and
the family of quantum phase-estimation algorithms, including Shor's algorithm.
We state that in quantum algorithms the time arrow is a majorization arrow.Comment: REVTEX4.b4 file, 4 color figures (typos corrected.
Universality of Entanglement and Quantum Computation Complexity
We study the universality of scaling of entanglement in Shor's factoring
algorithm and in adiabatic quantum algorithms across a quantum phase transition
for both the NP-complete Exact Cover problem as well as the Grover's problem.
The analytic result for Shor's algorithm shows a linear scaling of the entropy
in terms of the number of qubits, therefore difficulting the possibility of an
efficient classical simulation protocol. A similar result is obtained
numerically for the quantum adiabatic evolution Exact Cover algorithm, which
also shows universality of the quantum phase transition the system evolves
nearby. On the other hand, entanglement in Grover's adiabatic algorithm remains
a bounded quantity even at the critical point. A classification of scaling of
entanglement appears as a natural grading of the computational complexity of
simulating quantum phase transitions.Comment: 30 pages, 17 figures, accepted for publication in PR
Quantum phase retrieval of a Rydberg wave packet using a half-cycle pulse
A terahertz half-cycle pulse was used to retrieve information stored as
quantum phase in an -state Rydberg atom data register. The register was
prepared as a wave packet with one state phase-reversed from the others (the
"marked bit"). A half-cycle pulse then drove a significant portion of the
electron probability into the flipped state via multimode interference.Comment: accepted by PR
Quantum entanglement in the NMR implementation of the Deutsch-Jozsa algorithm
A scheme to execute an n-bit Deutsch-Jozsa (D-J) algorithm using n qubits has
been implemented for up to three qubits on an NMR quantum computer. For the one
and two bit Deutsch problem, the qubits do not get entangled, hence the NMR
implementation is achieved without using spin-spin interactions. It is for the
three bit case, that the manipulation of entangled states becomes essential.
The interactions through scalar J-couplings in NMR spin systems have been
exploited to implement entangling transformations required for the three bit
D-J algorithm.Comment: 4-pages in revtex with 5 eps figure included using psfi
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