1,704 research outputs found
Long-Distance High-Fidelity Teleportation Using Singlet States
A quantum communication system is proposed that uses polarization-entangled
photons and trapped-atom quantum memories. This system is capable of
long-distance, high-fidelity teleportation, and long-duration quantum storage.Comment: 8 pages, 5 figure
The Inadequate Police Protection of Battered Wives: Can a city and its police be held liable under the equal protection clause?
The police strive to settle the vast majority of wife battering cases without arrest or through mediation, often leading to terrible results for the abused wife. This Note supports holding a city and its police liable under the equal protection clause for the inadequate police protection of battered wives. The Note finds the best legal strategy under the equal protection clause would involve showing impermissible gender-based discrimination
Computational Ghost Imaging
Ghost-imaging experiments correlate the outputs from two photodetectors: a
high spatial-resolution (scanning pinhole or CCD camera) detector that measures
a field which has not interacted with the object to be imaged, and a bucket
(single-pixel) detector that collects a field that has interacted with the
object. We describe a computational ghost-imaging arrangement that uses only a
single-pixel detector. This configuration affords background-free imagery in
the narrowband limit and a 3D sectioning capability. It clearly indicates the
classical nature of ghost-image formation.Comment: 4 pages, 3 figure
Going through a quantum phase
Phase measurements on a single-mode radiation field are examined from a system-theoretic viewpoint. Quantum estimation theory is used to establish the primacy of the Susskind-Glogower (SG) phase operator; its phase eigenkets generate the probability operator measure (POM) for maximum likelihood phase estimation. A commuting observables description for the SG-POM on a signal x apparatus state space is derived. It is analogous to the signal-band x image-band formulation for optical heterodyne detection. Because heterodyning realizes the annihilation operator POM, this analogy may help realize the SG-POM. The wave function representation associated with the SG POM is then used to prove the duality between the phase measurement and the number operator measurement, from which a number-phase uncertainty principle is obtained, via Fourier theory, without recourse to linearization. Fourier theory is also employed to establish the principle of number-ket causality, leading to a Paley-Wiener condition that must be satisfied by the phase-measurement probability density function (PDF) for a single-mode field in an arbitrary quantum state. Finally, a two-mode phase measurement is shown to afford phase-conjugate quantum communication at zero error probability with finite average photon number. Application of this construct to interferometric precision measurements is briefly discussed
Long-Distance Quantum Communication with Neutral Atoms
The architecture proposed by Duan, Lukin, Cirac, and Zoller (DLCZ) for
long-distance quantum communication with atomic ensembles is analyzed. Its
fidelity and throughput in entanglement distribution, entanglement swapping,
and quantum teleportation is derived within a framework that accounts for
multiple excitations in the ensembles as well as loss and asymmetries in the
channel. The DLCZ performance metrics that are obtained are compared to the
corresponding results for the trapped-atom quantum communication architecture
that has been proposed by a team from the Massachusetts Institute of Technology
and Northwestern University (MIT/NU). Both systems are found to be capable of
high-fidelity entanglement distribution. However, the DLCZ scheme only provides
conditional teleportation and repeater operation, whereas the MIT/NU
architecture affords full Bell-state measurements on its trapped atoms.
Moreover, it is shown that achieving unity conditional fidelity in DLCZ
teleportation and repeater operation requires ideal photon-number resolving
detectors. The maximum conditional fidelities for DLCZ teleportation and
repeater operation that can be realized with non-resolving detectors are 1/2
and 2/3, respectively.Comment: 15 pages, 10 figure
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