Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session U2: Quantum Cryptography and Quantum Communication I |
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Sponsoring Units: GQI DCMP Chair: Paul Kwiat, University of Illinois at Urbana-Champaign Room: Colorado Convention Center Four Seasons 4 |
Thursday, March 8, 2007 8:00AM - 8:36AM |
U2.00001: Entanglement-Based Quantum Cryptography and Quantum Communication Invited Speaker: Quantum entanglement, to Erwin Schroedinger the essential feature of quantum mechanics, has become a central resource in various quantum communication protocols including quantum cryptography and quantum teleportation. From a fundamental point of view what is exploited in these experiments is the very fact which led Schroedinger to his statement namely that in entangled states joint properties of the entangled systems may be well defined while the individual subsystems may carry no information at all. In entanglement-based quantum cryptography it leads to the most elegant possible solution of the classic key distribution problem. It implies that the key comes into existence at spatially distant location at the same time and does not need to be transported. A number recent developments include for example highly efficient, robust and stable sources of entangled photons with a broad bandwidth of desired features. Also, entanglement-based quantum cryptography is successfully joining other methods in the work towards demonstrating quantum key distribution networks. Along that line recently decoy-state quantum cryptography over a distance of 144 km between two Canary Islands was demonstrated successfully. Such experiments also open up the possibility of quantum communication on a really large scale using LEO satellites. Another important possible future branch of quantum communication involves quantum repeaters in order to cover larger distances with entangled states. Recently the connection of two fully independent lasers in an entanglement swapping experiment did demonstrate that the timing control of such systems on a femtosecond time scale is possible. A related development includes recent demonstrations of all-optical one-way quantum computation schemes with the extremely short cycle time of only 100 nanoseconds. [Preview Abstract] |
Thursday, March 8, 2007 8:36AM - 9:12AM |
U2.00002: Beller Lectureship Recipient Talk: Applications of Quantum Teleportation Invited Speaker: Quantum teleportation, a way to transfer the state of a quantum system from one location to another, is central to quantum communication and plays an important role in a number of quantum computation protocols. Previous experimental demonstrations have been implemented with single photonic or ionic qubits. Very recently long-distance teleportation and open-destination teleportation have also been realized. Until now, previous experiments have only been able to teleport single qubits. However, since teleportation of single qubits is insufficient for a large-scale realization of quantum communication and computation, teleportation of a composite system containing two or more qubits has been seen as a long-standing goal in quantum information science. In my talk, I shall present the first experimental realization of quantum teleportation of a two-qubit composite system. In the experiment, we develop and exploit a six-photon interferometer to teleport an arbitrary polarization state of two photons. Not only does our six-photon interferometer provide an important step towards teleportation of a complex system, it will also enable future experimental investigations on a number of fundamental quantum communication and computation protocols such as multi-stage realization of quantum-relay, fault-tolerant quantum computation, universal quantum error-correction and one-way quantum computation. [Preview Abstract] |
Thursday, March 8, 2007 9:12AM - 9:48AM |
U2.00003: Twenty two years of quantum key distribution Invited Speaker: Following their 1984 invention of quantum key distribution (QKD), Bennett and Brassard and colleagues performed a proof-of-principle QKD transmission over a 32-cm air path in 1991. This seminal experiment led other researchers to explore implementations of QKD in optical fibers and over line-of-sight outdoor atmospheric paths (``free-space''), resulting in dramatic increases in range, secret bit rate, security and availability. These advances have led to, and been enabled by, improvements in sources, single-photon detectors and the deeper understanding of QKD security with practical sources and detectors in the presence of transmission loss and channel noise. Today, QKD has been implemented with unconditional security over ranges greater than 100km, over multi-kilometer distances in high background environments in both fiber and free-space, and at high (GHz) clock rates over shorter distances. In my talk I will review the key enabling advances underlying these developments of experimental optical fiber and free-space QKD over the past 16 years, describe the present status of the field, and compare and contrast different approaches to implementing security against photon number splitting attacks. I will describe some recent results from QKD in dedicated (``dark'') optical fiber using ultra-high efficiency, low-noise transition edge sensor (TES) photo-detectors, achieving ultra-long transmission distances, and unconditional security over 107km through the use of a decoy-state protocol. I will also describe progress in making QKD compatible with all-optical fiber networks, including the co-existence of QKD signals with conventional optical data on the same fiber. I will conclude my talk with a survey of the prospects for QKD transmission distances exceeding 200km, which will include a comparison of the various single-photon detector technologies now becoming available for quantum communications. [Preview Abstract] |
Thursday, March 8, 2007 9:48AM - 10:24AM |
U2.00004: Security of Quantum Key Distribution Invited Speaker: Quantum Key Distribution (QKD) is the most advanced application of Quantum Information Science. It allows extending secret keys over some distances in such a way that the security of the resulting key material can be guaranteed by the laws of quantum mechanics. In contrast to presently used encryption techniques, the security of QKD can be proven in terms of information-theoretic measures. The resulting key can then be used for many tasks, including exchanging secret messages. QKD has been developed in the language of abstract two-level systems, the qubits. They cannot be easily implemented in optical signals. It took some time to bring the protocols and theory of QKD to the point where they fit to the realities of fiber-optical or free-space applications, including lossy channels. Today, QKD schemes can be implemented reliably using standard off-the-shelf components. Information theoretic security is a theoretical concept. Naturally, it is impossible to demonstrate directly that a given experimental set-up indeed creates a secret key. What one can do is to show that the experiment can give data within a certain parameters regime, such as error rate and loss rate, for which a security proof exists. I will discuss what parameter regime gives provable secure key and which parameter regime cannot lead to secret key. It is desirable to prove `unconditional security,' as it is termed in the world of classical cryptography: no assumption is made about the attacks of an eavesdropper on the quantum channel. However, one has to assume that the signal structure and the measurement device are correctly described by the adopted model and that no eavesdropper can intrude the sender or receiver unit. In this talk I will briefly introduce the concept of QKD and optical implementations. Especially I will discuss security aspects of modern approaches of QKD schemes that allow us to increase the covered distance and the achievable rate. [Preview Abstract] |
Thursday, March 8, 2007 10:24AM - 11:00AM |
U2.00005: Towards a practical quantum repeater Invited Speaker: Quantum mechanics provides a mechanism for absolutely secure communication between remote parties. For distances greater than 100 kilometers direct quantum communication via optical fiber is not viable, due to fiber losses, and intermediate storage of the quantum information along the transmission channel is necessary. This lead to the concept of the quantum repeater, proposed in 1998 by Briegel, Duer, Cirac, and Zoller. In 2001, Duan, Lukin, Cirac, and Zoller have proposed to use atomic ensembles as the basic memory elements for the quantum repeater. We will outline our program on the use of atomic ensembles as an interface for quantum information transfer and the prospects for long distance quantum networks. [Preview Abstract] |
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