298 research outputs found
Femtosecond Time-Bin Entangled Qubits for Quantum Communication
We create pairs of non-degenerate time-bin entangled photons at telecom
wavelengths with ultra-short pump pulses. Entanglement is shown by performing
Bell kind tests of the Franson type with visibilities of up to 91%. As
time-bin entanglement can easily be protected from decoherence as encountered
in optical fibers, this experiment opens the road for complex quantum
communication protocols over long distances. We also investigate the creation
of more than one photon pair in a laser pulse and present a simple tool to
quantify the probability of such events to happen.Comment: 6 pages, 7 figure
Weak randomness completely trounces the security of QKD
In usual security proofs of quantum protocols the adversary (Eve) is expected
to have full control over any quantum communication between any communicating
parties (Alice and Bob). Eve is also expected to have full access to an
authenticated classical channel between Alice and Bob. Unconditional security
against any attack by Eve can be proved even in the realistic setting of device
and channel imperfection. In this Letter we show that the security of QKD
protocols is ruined if one allows Eve to possess a very limited access to the
random sources used by Alice. Such knowledge should always be expected in
realistic experimental conditions via different side channels
Blood/gas partition coefficients of halothane, isoflurane and sevoflurane in horse blood
Background. Blood/gas partition coefficients (λb/g) for volatile agents in horse blood are reported for halothane but not for isoflurane and sevoflurane. We measured the λb/g of halothane, isoflurane and sevoflurane in the blood of fasted horses. The correlation with age, weight and some haematological and biochemical variables was studied. The temperature correction factor for isoflurane solubility was calculated. Methods. Twenty‐four horses were randomly allocated to halothane (n=8), isoflurane (n=8) or sevoflurane (n=8). Blood samples were taken after 10 h' fasting. Calculation of λb/g was based on the measurement of anaesthetic partial pressures in blood at 37 °C, which was achieved with tonometer equilibration and headspace gas chromatography. Results. Mean λb/g was 1.66 (sd 0.06) for halothane, 0.92 (0.04) for isoflurane, and 0.47 (0.03) for sevoflurane. The λb/g values were all significantly lower than in humans (P<0.001). No correlation was found between λb/g and weight, age, haematocrit, plasma triglycerides, cholesterol or total bilirubin. The change in isoflurane solubility per 1 °C temperature increase was -2.63 (0.13)%. Conclusion. The λb/g values of halothane, isoflurane and sevoflurane in fasted horses are significantly lower than those reported in humans. The λb/g for halothane in this study agrees with values reported in the literature but a positive correlation with plasma triglycerides could not be confirmed. Knowledge of λb/g can refine models of anaesthetic uptake. Br J Anaesth 2003; 91: 276-
Controlled Quantum Secret Sharing
We present a new protocol in which a secret multiqubit quantum state
is shared by players and controllers, where
is the encoding state of a quantum secret sharing scheme. The players may be
considered as field agents responsible for carrying out a task, using the
secret information encrypted in , while the controllers are
superiors who decide if and when the task should be carried out and who to do
it. Our protocol only requires ancillary Bell states and Bell-basis
measurements.Comment: 6 pages, 0 figure, RevTeX4; published version with minor change
High rate, long-distance quantum key distribution over 250km of ultra low loss fibres
We present a fully automated quantum key distribution prototype running at
625 MHz clock rate. Taking advantage of ultra low loss fibres and low-noise
superconducting detectors, we can distribute 6,000 secret bits per second over
100 km and 15 bits per second over 250km
Quantum interference with photon pairs created in spatially separated sources
We report on a quantum interference experiment to probe the coherence between
two photons coming from non degenerate photon pairs at telecom wavelength
created in spatially separated sources. The two photons are mixed on a beam
splitter and we observe a reduction of up to 84% in the coincidence count rate
when the photons are made indistinguishable. This experiment constitutes an
important step towards the realization of quantum teleportation and
entanglement swapping with independent sources.Comment: 5 pages, 2 figures, changes according to referee's comments,
discussions partly rewritte
CD27 is required for protective lytic EBV antigen-specific CD8+ T-cell expansion
Primary immunodeficiencies in the costimulatory molecule CD27 and its ligand, CD70, predispose for pathologies of uncontrolled Epstein-Barr virus (EBV) infection in nearly all affected patients. We demonstrate that both depletion of CD27+ cells and antibody blocking of CD27 interaction with CD70 cause uncontrolled EBV infection in mice with reconstituted human immune system components. While overall CD8+ T-cell expansion and composition are unaltered after antibody blocking of CD27, only some EBV-specific CD8+ T-cell responses, exemplified by early lytic EBV antigen BMLF1-specific CD8+ T cells, are inhibited in their proliferation and killing of EBV-transformed B cells. This suggests that CD27 is not required for all CD8+ T-cell expansions and cytotoxicity but is required for a subset of CD8+ T-cell responses that protect us from EBV pathology
Long distance quantum teleportation of qubits from photons at 1300 nm to photons at 1550 nm wavelength
Elementary 2-dimensional quantum states (qubits) encoded in 1300 nm
wavelength photons are teleported onto 1550 nm photons. The use of
telecommunication wavelengths enables to take advantage of standard optical
fibre and permits to teleport from one lab to a distant one, 55 m away,
connected by 2 km of fibre. A teleportation fidelity of 81.2 % is reported.
This is large enough to demonstrate the principles of quantum teleportation, in
particular that entanglement is exploited. This experiment constitutes a first
step towards a quantum repeater.Comment: 7 pages, 5 figures, Extended version of Nature lette
CD8(+) T cells retain protective functions despite sustained inhibitory receptor expression during Epstein-Barr virus infection in vivo
Epstein Barr virus (EBV) is one of the most ubiquitous human pathogens in the world, persistently infecting more than 90% of the adult human population. It drives some of the strongest human CD8+ T cell responses, which can be observed during symptomatic primary
infection known as infectious mononucleosis (IM). Despite high viral loads and prolonged
CD8+ T cell stimulation during IM, EBV enters latency and is under lifelong immune control
in most individuals that experience this disease. We investigated whether changes in T cell
function, as frequently characterized by PD-1 up-regulation, occur during IM due to the prolonged exposure to high antigen levels. We readily detected the expansion of PD-1 positive
CD8+ T cells together with high frequencies of Tim-3, 2B4, and KLRG1 expression during
IM and in mice with reconstituted human immune system components (huNSG mice) that
had been infected with a high dose of EBV. These PD-1 positive CD8+ T cells, however,
retained proliferation, cytokine production, and cytotoxic abilities. Multiple subsets of CD8+
T cells expanded during EBV infection, including PD-1+
Tim-3+
KLRG1+ cells that express
CXCR5 and TCF-1 germinal center homing and memory markers, and may also contain
BATF3. Moreover, blocking the PD-1 axis compromised EBV specific immune control and
resulted in virus-associated lymphomagenesis. Finally, PD-1+
, Tim-3+
, and KLRG1+ CD8+ T
cell expansion coincided with declining viral loads during low dose EBV infection. These
findings suggest that EBV infection primes PD-1 positive CD8+ T cell populations that rely
on this receptor axis for the efficient immune control of this ubiquitous human tumor virus
Long-distance Bell-type tests using energy-time entangled photons
Long-distance Bell-type experiments are presented. The different experimental
challenges and their solutions in order to maintain the strong quantum
correlations between energy-time entangled photons over more than 10 km are
reported and the results analyzed from the point of view of tests of
fundamental physics as well as from the more applied side of quantum
communication, specially quantum key distribution. Tests using more than one
analyzer on each side are also presented.Comment: 22 pages including 7 figures and 5 table
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