1,510 research outputs found
Testing nonlocality over 12.4 km of underground fiber with universal time-bin qubit analyzers
We experimentally demonstrate that the nonlocal nature of time-bin entangled
photonic qubits persists when one or two qubits of the pair are converted to
polarization qubits. This is possible by implementing a novel Universal
Time-Bin Qubit Analyzer (UTBA), which, for the first time, allows analyzing
time-bin qubits in any basis. We reveal the nonlocal nature of the emitted
light by violating the Clauser-Horne-Shimony-Holt inequality with measurement
bases exploring all the dimensions of the Bloch sphere. Moreover, we conducted
experiments where one qubit is transmitted over a 12.4 km underground fiber
link and demonstrate the suitability of our scheme for use in a real-world
setting. The resulting entanglement can also be interpreted as hybrid
entanglement between different types of degrees of freedom of two physical
systems, which could prove useful in large scale, heterogeneous quantum
networks. This work opens new possibilities for testing nonlocality and for
implementing new quantum communication protocols with time-bin entanglement.Comment: 6 pages, 5 figure
On The Relevance Of Fair Sampling Assumption In The Recent Bell Photonic Experiments
In the experimental verification of Bell's inequalities in real photonic
experiments, it is generally believed that the so-called fair sampling
assumption (which means that a small fraction of results provide a fair
statistical sample) has an unavoidable role. Here, we want to show that the
interpretation of these experiments could be feasible, if some different
alternative assumptions other than the fair sampling were used. For this
purpose, we derive an efficient Bell-type inequality which is a CHSH-type
inequality in real experiments. Quantum mechanics violates our proposed
inequality, independent of the detection-efficiency problems.Comment: 13 pages, no figure, one table. Last versio
Device-dependent and device-independent quantum key distribution without a shared reference frame
Standard quantum key distribution (QKD) protocols typically assume that the
distant parties share a common reference frame. In practice, however,
establishing and maintaining a good alignment between distant observers is
rarely a trivial issue, which may significantly restrain the implementation of
long-distance quantum communication protocols. Here we propose simple QKD
protocols that do not require the parties to share any reference frame, and
study their security and feasibility in both the usual device-dependent
case--in which the two parties use well characterized measurement devices--as
well as in the device-independent case--in which the measurement devices can be
untrusted, and the security relies on the violation of a Bell inequality. To
illustrate the practical relevance of these ideas, we present a
proof-of-principle demonstration of our protocols using polarization entangled
photons distributed over a coiled 10-km-long optical fiber. We consider two
situations, in which either the fiber spool freely drifts, or randomly chosen
polarization transformations are applied. The correlations obtained from
measurements allow, with high probability, to generate positive asymptotic
secret key rates in both the device-dependent and device-independent scenarios
(under the fair-sampling assumption for the latter case).Comment: 12 pages, 11 figure
Quantum memory for non-stationary light fields based on controlled reversible inhomogeneous broadening
We propose a new method for efficient storage and recall of non-stationary
light fields, e.g. single photon time-bin qubits, in optically dense atomic
ensembles. Our approach to quantum memory is based on controlled, reversible,
inhomogeneous broadening. We briefly discuss experimental realizations of our
proposal.Comment: 4 page
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
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