1,653 research outputs found
Optimal focusing for maximal collection of entangled narrow-band photon pairs into single-mode fibers
We present a theoretical and experimental investigation of the emission
characteristics and the flux of photon pairs generated by spontaneous
parametric downconversion in quasi-phase matched bulk crystals for the use in
quantum communication sources. We show that, by careful design, one can attain
well defined modes close to the fundamental mode of optical fibers and obtain
high coupling efficiencies also for bulk crystals, these being more easily
aligned than crystal waveguides. We distinguish between singles coupling,
conditional coincidence, and pair coupling, and show how each of these
parameters can be maximized by varying the focusing of the pump mode and the
fiber-matched modes using standard optical elements. Specifically we analyze a
periodically poled KTP-crystal pumped by a 532 nm laser creating photon pairs
at 810 nm and 1550 nm. Numerical calculations lead to coupling efficiencies
above 94% at optimal focusing, which is found by the geometrical relation L/z_R
to be ~ 1 to 2 for the pump mode and ~ 2 to 3 for the fiber-modes, where L is
the crystal length and z_R is the Rayleigh-range of the mode-profile. These
results are independent on L. By showing that the single-mode bandwidth
decreases as 1/L, we can therefore design the source to produce and couple
narrow bandwidth photon pairs well into the fibers. Smaller bandwidth means
both less chromatic dispersion for long propagation distances in fibers, and
that telecom Bragg gratings can be utilized to compensate for broadened photon
packets--a vital problem for time-multiplexed qubits. Longer crystals also
yield an increase in fiber photon flux proportional to sqrt{L}, and so,
assuming correct focusing, we can only see advantages using long crystals.Comment: 19 pages, 15 figures, ReVTeX4, minor revisio
Using Authentic Literature to Enrich Young Children’s Literacy Experiences
This article focuses on the five components (phonemic awareness, phonics, fluency, vocabulary, and comprehension) needed to effectively teach children to read. Early childhood educators can teach these five skills through the use of authentic literature. To be classified as authentic literature, books and texts need to utilize “real life” writing that is written to engage the reader. Authentic narrative texts generally appeal to the reader and offers a theme and a moral to the story. The article explains the five components needed to teach children to read and offers some authentic texts, synopses, and lesson ideas specifically for each of the components. Although children may not be able to read the texts, the texts selected are at the child’s listen-ing comprehension level. In addition, the selected texts will aid early childhood educators and parents in infusing these skills for engaging implementation
Quantum interference by two temporally distinguishable pulses
We report a two-photon interference effect, in which the entangled photon
pairs are generated from two laser pulses well-separated in time. In a single
pump pulse case, interference effects did not occur in our experimental scheme.
However, by introducing a second pump pulse delayed in time, quantum
interference was then observed. The visibility of the interference fringes
shows dependence on the delay time between two laser pulses. The results are
explained in terms of indistinguishability of biphoton amplitudes which
originated from two temporally separated laser pulses.Comment: two-column, 4pages, submitted to PRA, minor change
Experimental storage of photonic polarization entanglement in a broadband loop-based quantum memory
We describe an experiment in which one member of a polarization-entangled
photon pair is stored in an active "loop and switch" type quantum memory
device, while the other propagates through a passive optical delay line. A
comparison of Bell's inequality tests performed before and after the storage is
used to investigate the ability of the memory to maintain entanglement, and
demonstrate a rudimentary entanglement distribution protocol. The entangled
photons are produced by a conventional Spontaneous Parametric Down Conversion
source with center wavelengths at 780 nm and bandwidths of 10 THz, while
the memory has an even wider operational bandwidth that is enabled by the
weakly dispersive nature of the Pockels effect used for
polarization-insensitive switching in the loop-based quantum memory platform.Comment: 6 pages, 4 figure
Implementation of a Toffoli Gate with Superconducting Circuits
The quantum Toffoli gate allows universal reversible classical computation.
It is also an important primitive in many quantum circuits and quantum error
correction schemes. Here we demonstrate the realization of a Toffoli gate with
three superconducting transmon qubits coupled to a microwave resonator. By
exploiting the third energy level of the transmon qubit, the number of
elementary gates needed for the implementation of the Toffoli gate, as well as
the total gate time can be reduced significantly in comparison to theoretical
proposals using two-level systems only. We characterize the performance of the
gate by full process tomography and Monte Carlo process certification. The gate
fidelity is found to be %.Comment: 4 pages, 5figure
Two-photon imaging and quantum holography
It has been claimed that ``the use of entangled photons in an imaging system
can exhibit effects that cannot be mimicked by any other two-photon source,
whatever strength of the correlations between the two photons'' [A. F.
Abouraddy, B. E. A. Saleh, A. V. Sergienko, and M. C. Teich, Phys. Rev. Lett.
87, 123602 (2001)]. While we believe that the cited statement is true, we show
that the method proposed in that paper, with ``bucket detection'' of one of the
photons, will give identical results for entangled states as for appropriately
prepared classically correlated states.Comment: 4 pages, 2 figures, REVTe
Role of entanglement in two-photon imaging
The use of entangled photons in an imaging system can exhibit effects that
cannot be mimicked by any other two-photon source, whatever the strength of the
correlations between the two photons. We consider a two-photon imaging system
in which one photon is used to probe a remote (transmissive or scattering)
object, while the other serves as a reference. We discuss the role of
entanglement versus correlation in such a setting, and demonstrate that
entanglement is a prerequisite for achieving distributed quantum imaging.Comment: 15 pages, 2 figure
Generating Entangled Two-Photon States with Coincident Frequencies
It is shown that parametric downconversion, with a short-duration pump pulse
and a long nonlinear crystal that is appropriately phase matched, can produce a
frequency-entangled biphoton state whose individual photons are coincident in
frequency. Quantum interference experiments which distinguish this state from
the familiar time-coincident biphoton state are described.Comment: Revised version (a typo was corrected) as published on PR
Tight Finite-Key Analysis for Quantum Cryptography
Despite enormous progress both in theoretical and experimental quantum
cryptography, the security of most current implementations of quantum key
distribution is still not established rigorously. One of the main problems is
that the security of the final key is highly dependent on the number, M, of
signals exchanged between the legitimate parties. While, in any practical
implementation, M is limited by the available resources, existing security
proofs are often only valid asymptotically for unrealistically large values of
M. Here, we demonstrate that this gap between theory and practice can be
overcome using a recently developed proof technique based on the uncertainty
relation for smooth entropies. Specifically, we consider a family of
Bennett-Brassard 1984 quantum key distribution protocols and show that security
against general attacks can be guaranteed already for moderate values of M.Comment: 11 pages, 2 figure
Quantum Imaging
We provide a brief overview of the newly born field of quantum imaging, and
discuss some concepts that lie at the root of this field.Comment: 8 pages, 19 figure
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