Information-theoretic approach to quantum error correction and reversible measurement

Quantum operations provide a general description of the state changes allowed by quantum mechanics. The reversal of quantum operations is important for quantum error-correcting codes, teleportation, and reversing quantum measurements. We derive information-theoretic conditions and equivalent algebraic conditions that are necessary and sufficient for a general quantum operation to be reversible. We analyze the thermodynamic cost of error correction and show that error correction can be regarded as a kind of ``Maxwell demon,'' for which there is an entropy cost associated with information obtained from measurements performed during error correction. A prescription for thermodynamically efficient error correction is given.Comment: 31 pages, REVTEX, one figure in LaTeX, submitted to Proceedings of the ITP Conference on Quantum Coherence and Decoherenc

Consent v. Closure

Claimants, defendants, courts, and counsel are understandably frustrated by the difficulty of resolving mass tort cases. Defendants demand closure, but class certification has proved elusive and non-class settlements require individual consent. Lawyers and scholars have been drawn to strategies that solve the problem by empowering plaintiffs’ counsel to negotiate package deals that effectively sidestep individual consent. In the massive Vioxx settlement, the parties achieved closure by including terms that made it unrealistic for any claimant to decline. The American Law Institute’s Principles of the Law of Aggregate Litigation offers another path to closure: it proposes to permit clients to consent in advance to be bound by a settlement with a supermajority vote. This article argues that, despite their appeal, both of these strategies must be rejected. Lawyer empowerment strategies render settlements illegitimate when they rely on inauthentic consent or place lawyers in the untenable position of allocating funds among bound clients. Consent, not closure, is the touchstone of legitimacy in mass tort settlements

Consent v. Closure

Claimants, defendants, courts, and counsel are understandably frustrated by the difficulty of resolving mass tort cases. Defendants demand closure, but class certification has proved elusive and non-class settlements require individual consent. Lawyers and scholars have been drawn to strategies that solve the problem by empowering plaintiffs’ counsel to negotiate package deals that effectively sidestep individual consent. In the massive Vioxx settlement, the parties achieved closure by including terms that made it unrealistic for any claimant to decline. The American Law Institute’s Principles of the Law of Aggregate Litigation offers another path to closure: it proposes to permit clients to consent in advance to be bound by a settlement with a supermajority vote. This article argues that, despite their appeal, both of these strategies must be rejected. Lawyer empowerment strategies render settlements illegitimate when they rely on inauthentic consent or place lawyers in the untenable position of allocating funds among bound clients. Consent, not closure, is the touchstone of legitimacy in mass tort settlements

Information transmission through a noisy quantum channel

Noisy quantum channels may be used in many information-carrying applications. We show that different applications may result in different channel capacities. Upper bounds on several of these capacities are proved. These bounds are based on the coherent information, which plays a role in quantum information theory analogous to that played by the mutual information in classical information theory. Many new properties of the coherent information and entanglement fidelity are proved. Two nonclassical features of the coherent information are demonstrated: the failure of subadditivity, and the failure of the pipelining inequality. Both properties arise as a consequence of quantum entanglement, and give quantum information new features not found in classical information theory. The problem of a noisy quantum channel with a classical observer measuring the environment is introduced, and bounds on the corresponding channel capacity proved. These bounds are always greater than for the unobserved channel. We conclude with a summary of open problems

Cell body rocking is a dominant mechanism for flagellar synchronization in a swimming alga

The unicellular green algae Chlamydomonas swims with two flagella, which can synchronize their beat. Synchronized beating is required to swim both fast and straight. A long-standing hypothesis proposes that synchronization of flagella results from hydrodynamic coupling, but the details are not understood. Here, we present realistic hydrodynamic computations and high-speed tracking experiments of swimming cells that show how a perturbation from the synchronized state causes rotational motion of the cell body. This rotation feeds back on the flagellar dynamics via hydrodynamic friction forces and rapidly restores the synchronized state in our theory. We calculate that this `cell body rocking' provides the dominant contribution to synchronization in swimming cells, whereas direct hydrodynamic interactions between the flagella contribute negligibly. We experimentally confirmed the coupling between flagellar beating and cell body rocking predicted by our theory. This work appeared also in the Proceedings of the National Academy of Science of the U.S.A as: Geyer et al., PNAS 110(45), p. 18058(6), 2013.Comment: 40 pages, 15 color figure

Chromospheric Activity of HAT-P-11: an Unusually Active Planet-Hosting K Star

Kepler photometry of the hot Neptune host star HAT-P-11 suggests that its spot latitude distribution is comparable to the Sun's near solar maximum. We search for evidence of an activity cycle in the CaII H & K chromospheric emission $S$-index with archival Keck/HIRES spectra and observations from the echelle spectrograph on the ARC 3.5 m Telescope at APO. The chromospheric emission of HAT-P-11 is consistent with a $\gtrsim 10$ year activity cycle, which plateaued near maximum during the Kepler mission. In the cycle that we observed, the star seemed to spend more time near active maximum than minimum. We compare the $\log R^\prime_{HK}$ normalized chromospheric emission index of HAT-P-11 with other stars. HAT-P-11 has unusually strong chromospheric emission compared to planet-hosting stars of similar effective temperature and rotation period, perhaps due to tides raised by its planet.Comment: 16 pages, 8 figures; accepted to the Astrophysical Journa

Long-Period Giant Companions to Three Compact, Multiplanet Systems

Understanding the relationship between long-period giant planets and multiple smaller short-period planets is critical for formulating a complete picture of planet formation. This work characterizes three such systems. We present Kepler-65, a system with an eccentric (e = 0.28 ± 0.07) giant planet companion discovered via radial velocities (RVs) exterior to a compact, multiply transiting system of sub-Neptune planets. We also use precision RVs to improve mass and radius constraints on two other systems with similar architectures, Kepler-25 and Kepler-68. In Kepler-68 we propose a second exterior giant planet candidate. Finally, we consider the implications of these systems for planet formation models, particularly that the moderate eccentricity in Kepler-65\u27s exterior giant planet did not disrupt its inner system