65 research outputs found
Long-Distance Entanglement Distribution with Single-Photon Sources
We present an efficient architecture for quantum repeaters based on
single-photon sources in combination with quantum memories for photons. Errors
inherent to previous repeater protocols using photon-pair sources are
eliminated, leading to a significant gain in efficiency. We establish the
requirements on the single-photon sources and on the photon detectors.Comment: 4 pages, 1 figure, 1 tabl
Macroscopic quantum jumps and entangled state preparation
Recently we predicted a random blinking, i.e. macroscopic quantum jumps, in
the fluorescence of a laser-driven atom-cavity system [Metz et al., Phys. Rev.
Lett. 97, 040503 (2006)]. Here we analyse the dynamics underlying this effect
in detail and show its robustness against parameter fluctuations. Whenever the
fluorescence of the system stops, a macroscopic dark period occurs and the
atoms are shelved in a maximally entangled ground state. The described setup
can therefore be used for the controlled generation of entanglement. Finite
photon detector efficiencies do not affect the success rate of the state
preparation, which is triggered upon the observation of a macroscopic
fluorescence signal. High fidelities can be achieved even in the vicinity of
the bad cavity limit due to the inherent role of dissipation in the jump
process.Comment: 14 pages, 12 figures, proof of the robustness of the state
preparation against parameter fluctuations added, figure replace
Transfer and teleportation of quantum states encoded in decoherence-free subspace
Quantum state transfer and teleportation, with qubits encoded in internal
states of the atoms in cavities, among spatially separated nodes of a quantum
network in decoherence-free subspace are proposed, based on a cavity-assisted
interaction by single-photon pulses. We show in details the implementation of a
logic-qubit Hadamard gate and a two-logic-qubit conditional gate, and discuss
the experimental feasibility of our scheme.Comment: 4 pages, 3 figure
Manipulation and Detection of a Trapped Yb+ Ion Hyperfine Qubit
We demonstrate the use of trapped ytterbium ions as quantum bits for quantum
information processing. We implement fast, efficient state preparation and
state detection of the first-order magnetic field-insensitive hyperfine levels
of 171Yb+, with a measured coherence time of 2.5 seconds. The high efficiency
and high fidelity of these operations is accomplished through the stabilization
and frequency modulation of relevant laser sources.Comment: 10 pages, 9 figures, 1 tabl
Effects of control temperature, ablation time, and background tissue in radiofrequency ablation of osteoid osteoma:A computer modeling study
To study the effects of the control temperature, ablation time, and the background tissue surrounding the tumor on the size of the ablation zone on radiofrequency ablation (RFA) of osteoid osteoma (OO). Finite element models of nonâcooled temperatureâcontrolled RFA of typical OOs were developed to determine the resulting ablation radius at control temperatures of 70, 80, and 90°C. Three different geometries were used, mimicking common cases of OO. The ablation radius was obtained by using the Arrhenius equation to determine cell viability. Ablation radii were larger for higher temperatures and also increased with time. All geometries and control temperatures tested had ablation radii larger than the tumor. The ablation radius developed rapidly in the first few minutes for all geometries and control temperatures tested, developing slowly towards the end of the ablation. Resistive heating and the temperature distribution showed differences depending on background tissue properties, resulting in differences in the ablation radius on each geometry. The ablation radius has a clear dependency not only on the properties of the tumor but also on the background tissue. Lower background tissue's electrical conductivity and blood perfusion rates seem to result in larger ablation zones. The differences observed between the different geometries suggest the need for patientâspecific planning, as the anatomical variations could cause significantly different outcomes where models like the one here presented could help to guarantee safe and successful tumor ablations
Shaping the Phase of a Single Photon
While the phase of a coherent light field can be precisely known, the phase
of the individual photons that create this field, considered individually,
cannot. Phase changes within single-photon wave packets, however, have
observable effects. In fact, actively controlling the phase of individual
photons has been identified as a powerful resource for quantum communication
protocols. Here we demonstrate the arbitrary phase control of a single photon.
The phase modulation is applied without affecting the photon's amplitude
profile and is verified via a two-photon quantum interference measurement,
which can result in the fermionic spatial behaviour of photon pairs. Combined
with previously demonstrated control of a single photon's amplitude, frequency,
and polarisation, the fully deterministic phase shaping presented here allows
for the complete control of single-photon wave packets.Comment: 4 pages, 4 figure
Adding colour-realistic video images to audio playbacks increases stimulus engagement but does not enhance vocal learning in zebra finches
Bird song and human speech are learned early in life and for both cases engagement with live social tutors generally leads to better learning outcomes than passive audio-only exposure. Real-world tutorâtutee relations are normally not uni- but multimodal and observations suggest that visual cues related to sound production might enhance vocal learning. We tested this hypothesis by pairing appropriate, colour-realistic, high frame-rate videos of a singing adult male zebra finch tutor with song playbacks and presenting these stimuli to juvenile zebra finches (Taeniopygia guttata). Juveniles exposed to song playbacks combined with video presentation of a singing bird approached the stimulus more often and spent more time close to it than juveniles exposed to audio playback only or audio playback combined with pixelated and time-reversed videos. However, higher engagement with the realistic audioâvisual stimuli was not predictive of better song learning. Thus, although multimodality increased stimulus engagement and biologically relevant video content was more salient than colour and movement equivalent videos, the higher engagement with the realistic audioâvisual stimuli did not lead to enhanced vocal learning. Whether the lack of three-dimensionality of a video tutor and/or the lack of meaningful social interaction make them less suitable for facilitating song learning than audioâvisual exposure to a live tutor remains to be tested
A Single-Photon Server with Just One Atom
Neutral atoms are ideal objects for the deterministic processing of quantum
information. Entanglement operations have been performed by photon exchange or
controlled collisions. Atom-photon interfaces were realized with single atoms
in free space or strongly coupled to an optical cavity. A long standing
challenge with neutral atoms, however, is to overcome the limited observation
time. Without exception, quantum effects appeared only after ensemble
averaging. Here we report on a single-photon source with one-and-only-one atom
quasi permanently coupled to a high-finesse cavity. Quasi permanent refers to
our ability to keep the atom long enough to, first, quantify the
photon-emission statistics and, second, guarantee the subsequent performance as
a single-photon server delivering up to 300,000 photons for up to 30 seconds.
This is achieved by a unique combination of single-photon generation and atom
cooling. Our scheme brings truly deterministic protocols of quantum information
science with light and matter within reach.Comment: 4 pages, 3 figure
Heralded single photon absorption by a single atom
The emission and absorption of single photons by single atomic particles is a
fundamental limit of matter-light interaction, manifesting its quantum
mechanical nature. At the same time, as a controlled process it is a key
enabling tool for quantum technologies, such as quantum optical information
technology [1, 2] and quantum metrology [3, 4, 5, 6]. Controlling both emission
and absorption will allow implementing quantum networking scenarios [1, 7, 8,
9], where photonic communication of quantum information is interfaced with its
local processing in atoms. In studies of single-photon emission, recent
progress includes control of the shape, bandwidth, frequency, and polarization
of single-photon sources [10, 11, 12, 13, 14, 15, 16, 17], and the
demonstration of atom-photon entanglement [18, 19, 20]. Controlled absorption
of a single photon by a single atom is much less investigated; proposals exist
but only very preliminary steps have been taken experimentally such as
detecting the attenuation and phase shift of a weak laser beam by a single atom
[21, 22], and designing an optical system that covers a large fraction of the
full solid angle [23, 24, 25]. Here we report the interaction of single
heralded photons with a single trapped atom. We find strong correlations of the
detection of a heralding photon with a change in the quantum state of the atom
marking absorption of the quantum-correlated heralded photon. In coupling a
single absorber with a quantum light source, our experiment demonstrates
previously unexplored matter-light interaction, while opening up new avenues
towards photon-atom entanglement conversion in quantum technology.Comment: 10 pages, 4 figure
Vacuum-stimulated cooling of single atoms in three dimensions
Taming quantum dynamical processes is the key to novel applications of
quantum physics, e.g. in quantum information science. The control of
light-matter interactions at the single-atom and single-photon level can be
achieved in cavity quantum electrodynamics, in particular in the regime of
strong coupling where atom and cavity form a single entity. In the optical
domain, this requires permanent trapping and cooling of an atom in a
micro-cavity. We have now realized three-dimensional cavity cooling and
trapping for an orthogonal arrangement of cooling laser, trap laser and cavity
vacuum. This leads to average single-atom trapping times exceeding 15 seconds,
unprecedented for a strongly coupled atom under permanent observation.Comment: 4 pages, 4 figure
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