345 research outputs found
Hong-Ou-Mandel interferometry on a biphoton beat note
Hong-Ou-Mandel interference, the fact that identical photons that arrive
simultaneously on different input ports of a beam splitter bunch into a common
output port, can be used to measure optical delays between different paths. It
is generally assumed that great precision in the measurement requires that
photons contain many frequencies, i.e., a large bandwidth. Here we challenge
this well-known assumption and show that the use of two well-separated
frequencies embedded in a quantum entangled state (discrete color entanglement)
suffices to achieve great precision. We determine optimum working points using
a Fisher Information analysis and demonstrate the experimental feasibility of
this approach by detecting thermally-induced delays in an optical fiber. These
results may significantly facilitate the use of quantum interference for
quantum sensing, by avoiding some stringent conditions such as the requirement
for large bandwidth signals
Ramsey interference with single photons
Interferometry using discrete energy levels in nuclear, atomic or molecular
systems is the foundation for a wide range of physical phenomena and enables
powerful techniques such as nuclear magnetic resonance, electron spin
resonance, Ramsey-based spectroscopy and laser/maser technology. It also plays
a unique role in quantum information processing as qubits are realized as
energy superposition states of single quantum systems. Here, we demonstrate
quantum interference of different energy states of single quanta of light in
full analogy to energy levels of atoms or nuclear spins and implement a Ramsey
interferometer with single photons. We experimentally generate energy
superposition states of a single photon and manipulate them with unitary
transformations to realize arbitrary projective measurements, which allows for
the realization a high-visibility single-photon Ramsey interferometer. Our
approach opens the path for frequency-encoded photonic qubits in quantum
information processing and quantum communication.Comment: 16 page
Real-Time Imaging of Quantum Entanglement
Quantum Entanglement is widely regarded as one of the most prominent features
of quantum mechanics and quantum information science. Although, photonic
entanglement is routinely studied in many experiments nowadays, its signature
has been out of the grasp for real-time imaging. Here we show that modern
technology, namely triggered intensified charge coupled device (ICCD) cameras
are fast and sensitive enough to image in real-time the effect of the
measurement of one photon on its entangled partner. To quantitatively verify
the non-classicality of the measurements we determine the detected photon
number and error margin from the registered intensity image within a certain
region. Additionally, the use of the ICCD camera allows us to demonstrate the
high flexibility of the setup in creating any desired spatial-mode
entanglement, which suggests as well that visual imaging in quantum optics not
only provides a better intuitive understanding of entanglement but will improve
applications of quantum science.Comment: Two supplementary movies available at the data conservancy projec
Frequency Multiplexing for Quasi-Deterministic Heralded Single-Photon Sources
Single-photon sources based on optical parametric processes have been used
extensively for quantum information applications due to their flexibility,
room-temperature operation and potential for photonic integration. However, the
intrinsically probabilistic nature of these sources is a major limitation for
realizing large-scale quantum networks. Active feedforward switching of photons
from multiple probabilistic sources is a promising approach that can be used to
build a deterministic source. However, previous implementations of this
approach that utilize spatial and/or temporal multiplexing suffer from rapidly
increasing switching losses when scaled to a large number of modes. Here, we
break this limitation via frequency multiplexing in which the switching losses
remain fixed irrespective of the number of modes. We use the third-order
nonlinear process of Bragg scattering four-wave mixing as an efficient
ultra-low noise frequency switch and demonstrate multiplexing of three
frequency modes. We achieve a record generation rate of
multiplexed photons per second with an ultra-low = 0.07, indicating
high single-photon purity. Our scalable, all-fiber multiplexing system has a
total loss of just 1.3 dB independent of the number of multiplexed modes, such
that the 4.8 dB enhancement from multiplexing three frequency modes markedly
overcomes switching loss. Our approach offers a highly promising path to
creating a deterministic photon source that can be integrated on a chip-based
platform.Comment: 28 pages, 9 figures. Comments welcom
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