122 research outputs found
Quantum teleportation and nonlocality: the puzzling predictions of entanglement are coming of age
The academic research into entanglement nicely illustrates the interplay
between fundamental science and applications, and the need to foster both
aspects to advance either one. For instance, the possibility to distribute
entangled photons over tens or even hundreds of kilometers is fascinating
because it confirms the quantum predictions over large distances, while quantum
theory is often presented to apply to the very small (see Figure 1). On the
other hand, entanglement enables quantum key distribution (QKD) [1]. This most
advanced application of quantum information processing allows one to distribute
cryptographic keys in a provably secure manner. For this, one merely has to
measure the two halves of an entangled pair of photons. Surprisingly, and being
of both fundamental and practical interest, the use of entanglement removes
even the necessity for trusting most equipment used for the measurements [5].
Furthermore, entanglement serves as a resource for quantum teleportation (see
Figure 2) [1]. In turn, this provides a tool for extending quantum key
distribution to arbitrarily large distances and building large-scale networks
that connect future quantum computers and atomic clocks [6]. In the following,
we describe the counter-intuitive properties of entangled particles as well as
a few recent experiments that address fundamental and applied aspects of
quantum teleportation. While a lot of work is being done using different
quantum systems, including trapped ions, color centers in diamond, quantum
dots, and superconducting circuits, we will restrict ourselves to experiments
involving photons due to their suitability for building future quantum
networks.Comment: This paper is intended to be published in the 2015 fourth issue of
Europhysics News as a "Feature Article
Demonstration of Quantum Nonlocality in presence of Measurement Dependence
Quantum nonlocality stands as a resource for Device Independent Quantum
Information Processing (DIQIP), as, for instance, Device Independent Quantum
Key Distribution. We investigate experimentally the assumption of limited
Measurement Dependence, i.e., that the measurement settings used in Bell
inequality tests or DIQIP are partially influenced by the source of entangled
particle and/or by an adversary. Using a recently derived Bell-like inequality
[Phys. Rev. Lett. 113 190402] and a 99% fidelity source of partially entangled
polarization photonic qubits, we obtain a clear violation of the inequality,
excluding a much larger range of measurement dependent local models than would
be possible with an adapted Clauser, Horne, Shimony and Holt (CHSH) inequality.
It is therefore shown that the Measurement Independence assumption can be
widely relaxed while still demonstrating quantum nonlocality
Towards continuous-wave regime teleportation for light matter quantum relay stations
We report a teleportation experiment involving narrowband entangled photons
at 1560 nm and qubit photons at 795 nm emulated by faint laser pulses. A
nonlinear difference frequency generation stage converts the 795 nm photons to
1560 nm in order to enable interference with one photon out of the pairs, i.e.,
at the same wavelength. The spectral bandwidth of all involved photons is of
about 25 MHz, which is close to the emission bandwidth of emissive quantum
memory devices, notably those based on ensembles of cold atoms and rare earth
ions. This opens the route towards the realization of hybrid quantum nodes,
i.e., combining quantum memories and entanglement-based quantum relays
exploiting either a synchronized (pulsed) or asynchronous (continuous- wave)
scenario
Generalized approach for enabling multimode quantum optics
We develop a universal approach enabling the study of any multimode quantum optical system evolving under a quadratic Hamiltonian. Our strategy generalizes the standard symplectic analysis and permits the treatment of multimode systems even in situations where traditional theoretical methods cannot be applied. This enables the description and investigation of a broad variety of key-resources for experimental quantum optics, ranging from optical parametric oscillators, to silicon-based micro-ring resonator, as well as opto-mechanical systems
High-visibilty two-photon interference at a telecom wavelength using picosecond regime separated sources
We report on a two-photon interference experiment in a quantum relay
configuration using two picosecond regime PPLN waveguide based sources emitting
paired photons at 1550 nm. The results show that the picosecond regime
associated with a guided-wave scheme should have important repercussions for
quantum relay implementations in real conditions, essential for improving both
the working distance and the efficiency of quantum cryptography and networking
systems. In contrast to already reported regimes, namely femtosecond and CW, it
allows achieving a 99% net visibility two-photon interference while maintaining
a high effective photon pair rate using only standard telecom components and
detectors.Comment: to appear in PRA as a rapid communicatio
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