Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session C11: Invited Session: Quantum Communication and Cryptography |
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Sponsoring Units: GQI DAMOP Chair: Mark Wilde, McGill University and Louisiana State University Room: 310 |
Monday, March 18, 2013 2:30PM - 3:06PM |
C11.00001: Limits on classical communication from quantum entropy power inequalities Invited Speaker: Graeme Smith Almost all modern communication systems rely on electromagnetic fields as a means of information transmission, and finding the capacities of these systems is a problem of significant practical importance. The Additive White Gaussian Noise (AWGN) channel is often a good approximate description of such systems, and its capacity is given by a simple formula. However, when quantum effects are important, estimating the capacity becomes difficult: a lower bound is known, but a similar upper bound is missing. Here we present strong new upper bounds for the classical capacity of quantum additive noise channels, including quantum analogues of the AWGN channel. Our main technical tool is a quantum entropy power inequality that controls the entropy production as two quantum signals combine at a beam splitter. Its proof involves a new connection between entropy production rates and a quantum Fisher information, and uses a quantum diffusion that smooths arbitrary states towards gaussians. [Preview Abstract] |
Monday, March 18, 2013 3:06PM - 3:42PM |
C11.00002: Security of continuous-variable quantum key distribution against general attacks Invited Speaker: Anthony Leverrier We prove the security of Gaussian continuous-variable quantum key distribution with coherent states against arbitrary attacks in the finite-size regime. In contrast to previously known proofs of principle (based on the de Finetti theorem), our result is applicable in the practically relevant finite-size regime. This is achieved using a novel proof approach, which exploits phase-space symmetries of the protocols as well as the postselection technique introduced by Christandl, Koenig and Renner (\emph{Phys.\ Rev.\ Lett.}\ 102, 020504 (2009)). [Preview Abstract] |
Monday, March 18, 2013 3:42PM - 4:18PM |
C11.00003: Fully device-independent quantum key distribution Invited Speaker: Thomas Vidick The laws of quantum mechanics allow unconditionally secure key distribution protocols. Nevertheless, security proofs of traditional quantum key distribution (QKD) protocols rely on a crucial assumption, the trustworthiness of the quantum devices used in the protocol. In device-independent QKD, even this last assumption is relaxed: the devices used in the protocol may have been adversarially prepared, and there is no a priori guarantee that they perform according to specification. Proving security in this setting had been a central open problem in quantum cryptography. We give the first device-independent proof of security of a protocol for quantum key distribution that guarantees the extraction of a linear amount of key even when the devices are subject to a constant rate of noise. Our only assumptions are that the laboratories in which each party holds his or her own device are spatially isolated, and that both devices, as well as the eavesdropper, are bound by the laws of quantum mechanics. All previous proofs of security relied either on the use of many independent pairs of devices, or on the absence of noise. [Preview Abstract] |
Monday, March 18, 2013 4:18PM - 4:54PM |
C11.00004: Quantum hacking Invited Speaker: Vadim Makarov - [Preview Abstract] |
Monday, March 18, 2013 4:54PM - 5:30PM |
C11.00005: Complete experimental toolbox for alignment-free quantum communication Invited Speaker: Fabio Sciarrino Quantum communication employs the counter-intuitive features of quantum physics for tasks that are impossible in the classical world. It is crucial for testing the foundations of quantum theory and promises to revolutionize information and communication technologies. However, to execute even the simplest quantum transmission, one must establish, and maintain, a shared reference frame. This introduces a considerable overhead in resources, particularly if the parties are in motion or rotating relative to each other. We experimentally show how to circumvent this problem with the transmission of quantum information encoded in rotationally invariant states of single photons. Our approach exploits multiple degrees of freedom of single photons. In particular, the polarization and transverse spatial modes stand out for this purpose. Just as the circular polarization states are eigenstates of the spin angular momentum of light, the helical-wavefront Laguerre-Gaussian modes are eigenmodes of its orbital angular momentum (OAM). We implement photonic qubit invariant under rotation around the optical axis by combining the polarization with OAM properties. By developing a complete toolbox for the efficient encoding and decoding of quantum information in such photonic qubits, we demonstrate the feasibility of alignment-free quantum key-distribution, and perform proof-of-principle demonstrations of alignment-free entanglement distribution and Bell-inequality violation. The core of our toolbox is a liquid crystal device, named ``q-plate,'' that maps polarization-encoded qubits into qubits encoded in hybrid polarization-OAM states of the same photon that are invariant under arbitrary rotations around the propagation direction, and vice versa. The scheme should find applications in fundamental tests of quantum mechanics and satellite-based quantum communication. We will discuss the potential applications of this scheme to real quantum communication network. [Preview Abstract] |
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