375 research outputs found
Photon Sorting, Efficient Bell Measurements and a Deterministic CZ Gate using a Passive Two-level Nonlinearity
Although the strengths of optical non-linearities available experimentally
have been rapidly increasing in recent years, significant challenges remain to
using such non-linearities to produce useful quantum devices such as efficient
optical Bell state analysers or universal quantum optical gates. Here we
describe a new approach that avoids the current limitations by combining strong
non-linearities with active Gaussian operations in efficient protocols for Bell
state analysers and Controlled-Sign gates
Near-unity coupling efficiency of a quantum emitter to a photonic-crystal waveguide
A quantum emitter efficiently coupled to a nanophotonic waveguide constitutes
a promising system for the realization of single-photon transistors,
quantum-logic gates based on giant single-photon nonlinearities, and high
bit-rate deterministic single-photon sources. The key figure of merit for such
devices is the -factor, which is the probability for an emitted single
photon to be channeled into a desired waveguide mode. We report on the
experimental achievement of for a quantum dot
coupled to a photonic-crystal waveguide, corresponding to a single-emitter
cooperativity of . This constitutes a nearly ideal
photon-matter interface where the quantum dot acts effectively as a 1D
"artificial" atom, since it interacts almost exclusively with just a single
propagating optical mode. The -factor is found to be remarkably robust
to variations in position and emission wavelength of the quantum dots. Our work
demonstrates the extraordinary potential of photonic-crystal waveguides for
highly efficient single-photon generation and on-chip photon-photon
interaction
Import of ADP/ATP carrier into mitochondria
We have identified the yeast homologue of Neurospora crassa MOM72, the mitochondrial import receptor for the ADP/ATP carrier (AAC), by functional studies and by cDNA sequencing. Mitochondria of a yeast mutant in which the gene for MOM72 was disrupted were impaired in specific binding and import of AAC. Unexpectedly, we found a residual, yet significant import of AAC into mitochondria lacking MOM72 that occurred via the receptor MOM19. We conclude that both MOM72 and MOM19 can direct AAC into mitochondria, albeit with different efficiency. Moreover, the precursor of MOM72 apparently does not require a positively charged sequence at the extreme amino terminus for targeting to mitochondria
Single-photon nonlinear optics with a quantum dot in a waveguide
Strong nonlinear interactions between photons enable logic operations for
both classical and quantum-information technology. Unfortunately, nonlinear
interactions are usually feeble and therefore all-optical logic gates tend to
be inefficient. A quantum emitter deterministically coupled to a propagating
mode fundamentally changes the situation, since each photon inevitably
interacts with the emitter, and highly correlated many-photon states may be
created . Here we show that a single quantum dot in a photonic-crystal
waveguide can be utilized as a giant nonlinearity sensitive at the
single-photon level. The nonlinear response is revealed from the intensity and
quantum statistics of the scattered photons, and contains contributions from an
entangled photon-photon bound state. The quantum nonlinearity will find
immediate applications for deterministic Bell-state measurements and
single-photon transistors and paves the way to scalable waveguide-based
photonic quantum-computing architectures
Characterizing heralded single-photon sources with imperfect measurement devices
Any characterization of a single-photon source is not complete without
specifying its second-order degree of coherence, i.e., its function.
An accurate measurement of such coherence functions commonly requires
high-precision single-photon detectors, in whose absence, only time-averaged
measurements are possible. It is not clear, however, how the resulting
time-averaged quantities can be used to properly characterize the source. In
this paper, we investigate this issue for a heralded source of single photons
that relies on continuous-wave parametric down-conversion. By accounting for
major shortcomings of the source and the detectors--i.e., the multiple-photon
emissions of the source, the time resolution of photodetectors, and our chosen
width of coincidence window--our theory enables us to infer the true source
properties from imperfect measurements. Our theoretical results are
corroborated by an experimental demonstration using a PPKTP crystal pumped by a
blue laser, that results in a single-photon generation rate about 1.2 millions
per second per milliwatt of pump power. This work takes an important step
toward the standardization of such heralded single-photon sources.Comment: 18 pages, 9 figures; corrected Eq. (11) and the description follows
Eq. (22
Spin-photon interface and spin-controlled photon switching in a nanobeam waveguide
Access to the electron spin is at the heart of many protocols for integrated
and distributed quantum-information processing [1-4]. For instance, interfacing
the spin-state of an electron and a photon can be utilized to perform quantum
gates between photons [2,5] or to entangle remote spin states [6-9].
Ultimately, a quantum network of entangled spins constitutes a new paradigm in
quantum optics [1]. Towards this goal, an integrated spin-photon interface
would be a major leap forward. Here we demonstrate an efficient and optically
programmable interface between the spin of an electron in a quantum dot and
photons in a nanophotonic waveguide. The spin can be deterministically prepared
with a fidelity of 96\%. Subsequently the system is used to implement a
"single-spin photonic switch", where the spin state of the electron directs the
flow of photons through the waveguide. The spin-photon interface may enable
on-chip photon-photon gates [2], single-photon transistors [10], and efficient
photonic cluster state generation [11]
Human rhinoviruses enter and induce proliferation of B lymphocytes
Background: Human rhinoviruses (HRVs) are one of the main causes of virus-induced asthma exacerbations. Infiltration of B lymphocytes into the subepithelial tissue of the lungs has been demonstrated during rhinovirus infection in allergic individuals. However, the mechanisms through which HRVs modulate the immune responses of monocytes and lymphocytes are not yet well described. Objective: To study the dynamics of virus uptake by monocytes and lymphocytes, and the ability of HRVs to induce the activation of in vitro-cultured human peripheral blood mononuclear cells. Methods: Flow cytometry was used for the enumeration and characterization of lymphocytes. Proliferation was estimated using 3H-thymidine or CFSE labeling and ICAM-1 blocking. We used bead-based multiplex assays and quantitative PCR for cytokine quantification. HRV accumulation and replication inside the B lymphocytes was detected by a combination of in situ hybridization (ISH), immunofluorescence, and PCR for positive-strand and negative-strand viral RNA. Cell images were acquired with imaging flow cytometry. Results: By means of imaging flow cytometry, we demonstrate a strong and quick binding of HRV types 16 and 1B to monocytes, and slower interaction of these HRVs with CD4+ T cells, CD8+ T cells, and CD19+ B cells. Importantly, we show that HRVs induce the proliferation of B cells, while the addition of anti-ICAM-1 antibody partially reduces this proliferation for HRV16. We prove with ISH that HRVs can enter B cells, form their viral replication centers, and the newly formed virions are able to infect HeLa cells. In addition, we demonstrate that similar to epithelial cells, HRVs induce the production of pro-inflammatory cytokines in PBMCs. Conclusion: Our results demonstrate for the first time that HRVs enter and form viral replication centers in B lymphocytes and induce the proliferation of B cells. Newly formed virions have the capacity to infect other cells (HeLa). These findings indicate that the regulation of human rhinovirus-induced B-cell responses could be a novel approach to develop therapeutics to treat the virus-induced exacerbation of asthma.</p
Quantitative analysis of quantum dot dynamics and emission spectra in cavity quantum electrodynamics:Paper
We present detuning-dependent spectral and decay-rate measurements to study
the difference between spectral and dynamical properties of single quantum dots
embedded in micropillar and photonic-crystal cavities. For the micropillar
cavity, the dynamics is well described by the dissipative Jaynes-Cummings
model, while systematic deviations are observed for the emission spectra. The
discrepancy for the spectra is attributed to coupling of other exciton lines to
the cavity and interference of different propagation paths towards the detector
of the fields emitted by the quantum dot. In contrast, quantitative information
about the system can readily be extracted from the dynamical measurements. In
the case of photonic crystal cavities we observe an anti crossing in the
spectra when detuning a single quantum dot through resonance, which is the
spectral signature of strong coupling. However, time-resolved measurements
reveal that the actual coupling strength is significantly smaller than
anticipated from the spectral measurements and that the quantum dot is rather
weakly coupled to the cavity. We suggest that the observed Rabi splitting is
due to cavity feeding by other quantum dots and/or multiexcition complexes
giving rise to collective emission effects.Comment: 14 pages, 5 figures, submitte
i-SNAREs: inhibitory SNAREs that fine-tune the specificity of membrane fusion
A new functional class of SNAREs, designated inhibitory SNAREs (i-SNAREs), is described here. An i-SNARE inhibits fusion by substituting for or binding to a subunit of a fusogenic SNAREpin to form a nonfusogenic complex. Golgi-localized SNAREs were tested for i-SNARE activity by adding them as a fifth SNARE together with four other SNAREs that mediate Golgi fusion reactions. A striking pattern emerges in which certain subunits of the cis-Golgi SNAREpin function as i-SNAREs that inhibit fusion mediated by the trans-Golgi SNAREpin, and vice versa. Although the opposing distributions of the cis- and trans-Golgi SNAREs themselves could provide for a countercurrent fusion pattern in the Golgi stack, the gradients involved would be strongly sharpened by the complementary countercurrent distributions of the i-SNAREs
Chirality of nanophotonic waveguide with embedded quantum emitter for unidirectional spin transfer
Scalable quantum technologies may be achieved by faithful conversion between matter qubits and photonic qubits in integrated circuit geometries. Within this context, quantum dots possess well-defined spin states (matter qubits), which couple efficiently to photons. By embedding them in nanophotonic waveguides, they provide a promising platform for quantum technology implementations. In this paper, we demonstrate that the naturally occurring electromagnetic field chirality that arises in nanobeam waveguides leads to unidirectional photon emission from quantum dot spin states, with resultant in-plane transfer of matter-qubit information. The chiral behaviour occurs despite the non-chiral geometry and material of the waveguides. Using dot registration techniques, we achieve a quantum emitter deterministically positioned at a chiral point and realize spin-path conversion by design. We further show that the chiral phenomena are much more tolerant to dot position than in standard photonic crystal waveguides, exhibit spin-path readout up to 95±5% and have potential to serve as the basis of spin-logic and network implementations
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