Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session T5: 20 Years of Quantum Information in Physical Review Letters |
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Sponsoring Units: GQI Chair: John Preskill, California Institute of Technology Room: Ballroom C1 |
Wednesday, March 23, 2011 2:30PM - 3:06PM |
T5.00001: Theory of entanglement and entanglement-assisted communication Invited Speaker: Protocols such as quantum teleportation and measurement-based quantum computation highlight the importance of entanglement as a resource to be quantified and husbanded. Unlike classical shared randomness, entanglement has a profound effect on the capacity of quantum channels: a channel's entanglement-assisted capacity can be much greater than its unassisted capacity, and in any case is given by much a simpler formula, paralleling Shannon's original formula for the capacity of a classical channel. We review the differences between entanglement and weaker forms of correlation, and the theory of entanglement distillation and entanglement-assisted communication, including the role of strong forms of entanglement such as entanglement-embezzling states. [Preview Abstract] |
Wednesday, March 23, 2011 3:06PM - 3:42PM |
T5.00002: Twenty Years of Quantum Error Correction Invited Speaker: Starting around 1991 It became clear that the emerging quantum computer would need error correction to be sensible. Almost immediately, Berthiaume, Deutsch, and Jozsa announced the first key ideas (e.g., allowed codewords should live in a well-defined subset of the Hilbert space), and in less than ten years, the problem was ``solved.'' This solution had many components, involving insights from quantum teleportation, the concept of noisy entanglement and its improvement, creative borrowings from classical binary and quaternary codes, pure group theory, and the reliable working of noisy automata. Actually, this ``solved'' problem continues to produce new difficulties and insights up to the present day, and it is increasingly central for the question of what we do next in the progress towards a functioning quantum computer. [Preview Abstract] |
Wednesday, March 23, 2011 3:42PM - 4:18PM |
T5.00003: Less Reality, More Security Invited Speaker: Bell's inequality makes a seemingly insane scenario possible --- devices of unknown or dubious provenance, even those that are manufactured by our enemies, can be safely used for secret communication. And this is for real! All that is needed to implement such a bizarre form of cryptography is a loophole-free violation of Bell's inequalities. It is on the edge of being technologically feasible. I will provide a brief overview of quantum and post-quantum cryptography and describe how studies of entanglement and the foundations of quantum theory influenced the way we may soon protect information. [Preview Abstract] |
Wednesday, March 23, 2011 4:18PM - 4:54PM |
T5.00004: Twenty Seven Years of Quantum Cryptography! Invited Speaker: One of the fundamental goals of cryptographic research is to minimize the assumptions underlying the protocols that enable secure communications between pairs or groups of users. In 1984, building on earlier research by Stephen Wiesner, Charles Bennett and Gilles Brassard showed how quantum physics could be harnessed to provide information-theoretic security for protocols such as the distribution of cryptographic keys, which enables two parties to secure their conventional communications. Bennett and Brassard and colleagues performed a proof-of-principle quantum key distribution (QKD) experiment with single-photon quantum state transmission over a 32-cm air path in 1991. This seminal experiment led other researchers to explore QKD in optical fibers and over line-of-sight outdoor atmospheric paths (``free-space''), resulting in dramatic increases in range, bit rate and security. These advances have been enabled by improvements in sources and single-photon detectors. Also in 1991 Artur Ekert showed how the security of QKD could be related to quantum entanglement. This insight led to a deeper understanding and proof of QKD security with practical sources and detectors in the presence of transmission loss and channel noise. Today, QKD has been implemented over ranges much greater than 100km in both fiber and free-space, multi-node network testbeds have been demonstrated, and satellite-based QKD is under study in several countries. ``Quantum hacking'' researchers have shown the importance of extending security considerations to the classical devices that produce and detect the photon quantum states. New quantum cryptographic protocols such as secure identification have been proposed, and others such as quantum secret splitting have been demonstrated. It is now possible to envision quantum cryptography providing a more secure alternative to present-day cryptographic methods for many secure communications functions. My talk will survey these remarkable developments. [Preview Abstract] |
Wednesday, March 23, 2011 4:54PM - 5:30PM |
T5.00005: A Brief Prehistory of Qubits Invited Speaker: In the early 1990's, alongside the early work on quantum cryptography, there existed a considerable body of research on the classical information capacity of quantum channels. The strongest and most general result known was the theorem of Holevo giving an entropic bound for the accessbile information in a mixture of quantum signals. This motivated the problem of whether the Holevo bound could be closely approached by suitable choice of code and decoding observable. If so, then the quantum (von Neumann) entropy had a straightforward informational interpretation. When this question was found to be very difficult to answer, quantum data compression and the idea of a ``qubit'' was introduced as an alternate framework for thinking about information in quantum systems and interpreting the quantum entropy. However, the mathematical ideas from the new framework proved essential to solving the original problem of showing that the Holevo bound was asymptotically achievable. This was an early example of the interplay between classical and quantum concepts of information -- an interplay that has been, to say the least, extremely fruitful. [Preview Abstract] |
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