410 research outputs found
Nondestructive Detection of an Optical Photon
All optical detectors to date annihilate photons upon detection, thus
excluding repeated measurements. Here, we demonstrate a robust photon detection
scheme which does not rely on absorption. Instead, an incoming photon is
reflected off an optical resonator containing a single atom prepared in a
superposition of two states. The reflection toggles the superposition phase
which is then measured to trace the photon. Characterizing the device with
faint laser pulses, a single-photon detection efficiency of 74% and a survival
probability of 66% is achieved. The efficiency can be further increased by
observing the photon repeatedly. The large single-photon nonlinearity of the
experiment should enable the development of photonic quantum gates and the
preparation of novel quantum states of light.Comment: published online in Science Express, 14 November 201
A photon-photon quantum gate based on a single atom in an optical resonator
Two photons in free space pass each other undisturbed. This is ideal for the
faithful transmission of information, but prohibits an interaction between the
photons as required for a plethora of applications in optical quantum
information processing. The long-standing challenge here is to realise a
deterministic photon-photon gate. This requires an interaction so strong that
the two photons can shift each others phase by pi. For polarisation qubits,
this amounts to the conditional flipping of one photon's polarisation to an
orthogonal state. So far, only probabilistic gates based on linear optics and
photon detectors could be realised, as "no known or foreseen material has an
optical nonlinearity strong enough to implement this conditional phase
shift..." [Science 318, 1567]. Meanwhile, tremendous progress in the
development of quantum-nonlinear systems has opened up new possibilities for
single-photon experiments. Platforms range from Rydberg blockade in atomic
ensembles to single-atom cavity quantum electrodynamics. Applications like
single-photon switches and transistors, two-photon gateways, nondestructive
photon detectors, photon routers and nonlinear phase shifters have been
demonstrated, but none of them with the ultimate information carriers, optical
qubits. Here we employ the strong light-matter coupling provided by a single
atom in a high-finesse optical resonator to realise the Duan-Kimble protocol of
a universal controlled phase flip (CPF, pi phase shift) photon-photon quantum
gate. We achieve an average gate fidelity of F=(76.2+/-3.6)% and specifically
demonstrate the capability of conditional polarisation flipping as well as
entanglement generation between independent input photons. Our gate could
readily perform most of the hitherto existing two-photon operations. It also
discloses avenues towards new quantum information processing applications where
photons are essential.Comment: 7 pages, 5 figure
Heralded Storage of a Photonic Quantum Bit in a Single Atom
Combining techniques of cavity quantum electrodynamics, quantum measurement,
and quantum feedback, we have realized the heralded transfer of a polarization
qubit from a photon onto a single atom with 39% efficiency and 86% fidelity.
The reverse process, namely, qubit transfer from the atom onto a given photon,
is demonstrated with 88% fidelity and an estimated efficiency of up to 69%. In
contrast to previous work based on two-photon interference, our scheme is
robust against photon arrival-time jitter and achieves much higher
efficiencies. Thus, it constitutes a key step toward the implementation of a
long-distance quantum network.Comment: 6 pages, 4 figure
Photon-Mediated Quantum Gate between Two Trapped Neutral Atoms in an Optical Cavity
Quantum logic gates are fundamental building blocks of quantum computers.
Their integration into quantum networks requires strong qubit coupling to
network channels, as can be realized with neutral atoms and optical photons in
cavity quantum electrodynamics. Here we demonstrate that the long-range
interaction mediated by a flying photon performs a gate between two stationary
atoms inside an optical cavity from which the photon is reflected. This single
step executes the gate in . We show an entangling operation
between the two atoms by generating a Bell state with 76(2)% fidelity. The gate
also operates as a CNOT. We demonstrate 74.1(1.6)% overlap between the observed
and the ideal gate output, limited by the state preparation fidelity of
80.2(0.8)%. As the atoms are efficiently connected to a photonic channel, our
gate paves the way towards quantum networking with multiqubit nodes and the
distribution of entanglement in repeater-based long-distance quantum networks.Comment: 10 pages including appendix, 5 figure
Breakdown of atomic hyperfine coupling in a deep optical-dipole trap
We experimentally study the breakdown of hyperfine coupling for an atom in a
deep optical-dipole trap. One-color laser spectroscopy is performed at the
resonance lines of a single Rb atom for a trap wavelength of 1064 nm.
Evidence of hyperfine breakdown comes from three observations, namely a
nonlinear dependence of the transition frequencies on the trap intensity, a
splitting of lines which are degenerate for small intensities, and the ability
to drive transitions which would be forbidden by selection rules in the absence
of hyperfine breakdown. From the data, we infer the hyperfine interval of the
state and the scalar and tensor polarizabilities for the
state
Cavity Carving of Atomic Bell States
We demonstrate entanglement generation of two neutral atoms trapped inside an
optical cavity. Entanglement is created from initially separable two-atom
states through carving with weak photon pulses reflected from the cavity. A
polarization rotation of the photons heralds the entanglement. We show the
successful implementation of two different protocols and the generation of all
four Bell states with a maximum fidelity of (90+-2)%. The protocol works for
any distance between cavity-coupled atoms, and no individual addressing is
required. Our result constitutes an important step towards applications in
quantum networks, e.g. for entanglement swapping in a quantum repeater.Comment: 9 pages, 7 figures including Supplemen
Increased Dimensionality of Raman Cooling in a Slightly Nonorthogonal Optical Lattice
We experimentally study the effect of a slight nonorthogonality in a
two-dimensional optical lattice onto resolved-sideband Raman cooling. We find
that when the trap frequencies of the two lattice directions are equal, the
trap frequencies of the combined potential exhibit an avoided crossing and the
corresponding eigenmodes are rotated by 45 degrees relative to the lattice
beams. Hence, tuning the trap frequencies makes it possible to rotate the
eigenmodes such that both eigenmodes have a large projection onto any desired
direction in the lattice plane, in particular, onto the direction along which
Raman cooling works. Using this, we achieve two-dimensional Raman ground-state
cooling in a geometry where this would be impossible, if the eigenmodes were
not rotated. Our experiment is performed with a single atom inside an optical
resonator but this is inessential and the scheme is expected to work equally
well in other situations
Efficient Teleportation between Remote Single-Atom Quantum Memories
We demonstrate teleportation of quantum bits between two single atoms in
distant laboratories. Using a time-resolved photonic Bell-state measurement, we
achieve a teleportation fidelity of (88.0+/-1.5)%, largely determined by our
entanglement fidelity. The low photon collection efficiency in free space is
overcome by trapping each atom in an optical cavity. The resulting success
probability of 0.1% is almost 5 orders of magnitude larger than in previous
experiments with remote material qubits. It is mainly limited by photon
propagation and detection losses and can be enhanced with a cavity-based
deterministic Bell-state measurement.Comment: 7 pages, 4 figures, 1 tabl
Innovative applications of associative morphological memories for image processing and pattern recognition
Morphological Associative Memories have been proposed for some image denoising applications. They can be applied to other less restricted domains, like image retrieval and hyper spectral image unsupervised segmentation. In this paper we present these applications. In both cases the key idea is that Autoassociative Morphological Memories selective sensitivity to erosive and dilative noise can be applied to detect the morphological independence between patterns. Linear unmixing based on the sets of morphological independent patterns define a feature extraction process that is the basis for the image processing applications. We discuss some experimental results on the fish shape data base and on a synthetic hyperspectral image, including the comparison with other linear feature extraction algorithms (ICA and CCA)
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