701 research outputs found
Proposal for a QND which-path measurement using photons
A scheme is proposed for experimentally realizing the famous two-slit gedaenken experiment using photons. As elegantly discussed for electrons by Feynman, a particle's quantum pathways interfere to produce fringes in the probability density for the particle to be found at a particle location. If the path taken by the particle is experimentally determined, the complementarity principle says that the fringes must disappear. To carry out this experiment with photons is difficult because normally the act of determining a photon's location destroys it. We propose to overcome this difficulty by putting a type-2 optical parametric amplifier (OPA) in each arm of a Mach-Zehnder interferometer, and observing fringes at the output. An OPA responds to an input photon by increasing its probability to produce a pair of photons with polarization orthogonal to the input, the detection of which allows partial inference about the path taken by the input photon without destroying it. Thus, the measurement is of the quantum nondemolition (QND) type
Tomographic reconstruction of quantum states in N spatial dimensions
Most quantum tomographic methods can only be used for one-dimensional
problems. We show how to infer the quantum state of a non-relativistic
N-dimensional harmonic oscillator system by simple inverse Radon transforms.
The procedure is equally applicable to finding the joint quantum state of
several distinguishable particles in different harmonic oscillator potentials.
A requirement of the procedure is that the angular frequencies of the N
harmonic potentials are incommensurable. We discuss what kind of information
can be found if the requirement of incommensurability is not fulfilled and also
under what conditions the state can be reconstructed from finite time
measurements. As a further example of quantum state reconstruction in N
dimensions we consider the two related cases of an N-dimensional free particle
with periodic boundary conditions and a particle in an N-dimensional box, where
we find a similar condition of incommensurability and finite recurrence time
for the one-dimensional system.Comment: 8 pages, 1 figur
Quantum Frequency Translation of Single-Photon States in Photonic Crystal Fiber
We experimentally demonstrate frequency translation of a nonclassical optical
field via the Bragg scattering four-wave mixing process in a photonic crystal
fiber (PCF). The high nonlinearity and the ability to control dispersion in PCF
enable efficient translation between photon channels within the visible
to-near-infrared spectral range, useful in quantum networks. Heralded single
photons at 683 nm were translated to 659 nm with an efficiency of percent. Second-order correlation measurements on the 683-nm and 659-nm
fields yielded and respectively, showing the nonclassical nature of both fields.Comment: 5 pages, 3 figure
Mesoscopic entanglement of atomic ensembles through non-resonant stimulated Raman scattering
We propose a scheme of generating and verifying mesoscopic-level entanglement
between two atomic ensembles using non-resonant stimulated Raman scattering.
Entanglement can be generated by direct detection or balanced homodyne
detection of the Stokes fields from the two cells, after they interfere on a
beam splitter. The entanglement of the collective atomic fields can be
transferred to the anti-Stokes fields in a readout process. By measuring the
operator moments of the anti-Stokes fields, we can verify the presence of
entanglement. We model the effects of practical factors such as Stokes field
detector quantum efficiency and additive thermal noise in the entanglement
generating process, and anti-Stokes field losses in the entanglement
verification process, and find achievable regimes in which entanglement can be
verified at the levels of tens to hundreds of atomic excitations in the
ensembles.Comment: 35 papges, 6 figures and 1 table, accepted by Phys. Rev.
Design Methodology for Heavy-Lift Unmanned Aerial Vehicles with Coaxial Rotors
This work presents a novel design methodology for multirotor Unmanned Aerial Vehicles (UAVs). To specifically address the design of vehicles with heavy lift capabilities, we have extended existing design methodologies to include coaxial rotor systems which have exhibit the best thrust-to-volume ratio for operation of UAVs in urban environments. Such coaxial systems, however, come with decreased aerodynamic efficiency and the design approach developed in this work can account for this. The proposed design methodology and included market studies have been demonstrated for the development of a multi-parcel delivery drone that can deliver up to four packages using a novel morphing concept. Flight test results in this paper serve to validate the predictions of thrust and battery life of the coaxial propulsion system suggesting errors in predicted flight time of less than 5 percent
A hemispherical, high-solid-angle optical micro-cavity for cavity-QED studies
We report a novel hemispherical micro-cavity that is comprised of a planar
integrated semiconductor distributed Bragg reflector (DBR) mirror, and an
external, concave micro-mirror having a radius of curvature .
The integrated DBR mirror containing quantum dots (QD), is designed to locate
the QDs at an antinode of the field in order to maximize the interaction
between the QD and the cavity. The concave micro-mirror, with high-reflectivity
over a large solid-angle, creates a diffraction-limited (sub-micron) mode-waist
at the planar mirror, leading to a large coupling constant between cavity mode
and QD. The half-monolithic design gives more spatial and spectral tuning
abilities, relatively to fully monolithic structures. This unique micro-cavity
design will potentially enable us to both reach the cavity quantum
electrodynamics (QED) strong coupling regime and realize the deterministic
generation of single photons on demand.Comment: 15 pages, 17 figures, final versio
Neutron wave packet tomography
A tomographic technique is introduced in order to determine the quantum state
of the center of mass motion of neutrons. An experiment is proposed and
numerically analyzed.Comment: 4 pages, 3 figure
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