Stabilisation of Quantum Computations by Symmetrisation

We propose a method for the stabilisation of quantum computations (including quantum state storage). The method is based on the operation of projection into $\cal SYM$, the symmetric subspace of the full state space of $R$ redundant copies of the computer. We describe an efficient algorithm and quantum network effecting $\cal SYM$--projection and discuss the stabilising effect of the proposed method in the context of unitary errors generated by hardware imprecision, and nonunitary errors arising from external environmental interaction. Finally, limitations of the method are discussed.Comment: 20 pages LaTeX, 2 postscript figure

Quantum Reed-Solomon Codes

After a brief introduction to both quantum computation and quantum error correction, we show how to construct quantum error-correcting codes based on classical BCH codes. With these codes, decoding can exploit additional information about the position of errors. This error model - the quantum erasure channel - is discussed. Finally, parameters of quantum BCH codes are provided.Comment: Summary only (2 pages), for the full version see: Proceedings Applied Algebra, Algebraic Algorithms and Error-Correcting Codes (AAECC-13), Lecture Notes in Computer Science 1719, Springer, 199

Changes in hemlock looper [Lepidoptera: Geometridae] pupal distribution through a 3-year outbreak cycle

La distribution des chrysalides de l’arpenteuse de la pruche, Lambdina fiscellaria, a été étudiée au cours d’un cycle épidémique d’une durée de trois ans près du Lac Princeton sur l’île d’Anticosti au Québec. Au total, 10 sapins ont été coupés et toutes les chrysalides ont été comptées sur le tronc et les branches (partie non-foliée vs foliée) de la cime inférieure, médiane et supérieure, ainsi que sur le tronc sous la cime. En condition préépidémique, les chrysalides ont principalement été trouvées sur les branches des cimes médianes et supérieures. Durant l’épidémie, la densité des chrysalides n’a pas augmenté dans ces sites de pupaison et les larves se sont surtout transformées en chrysalides sur le tronc, à partir du sol jusque dans la cime médiane, ainsi que sur les branches de la cime inférieure. Peu de chrysalides ont été trouvées sur la partie foliée des branches en période post-épidémique, la plupart étant trouvées sur la partie basale non-foliée qui apparaît comme un endroit préférentiel pour la pupaison de l'arpenteuse de la pruche. De façon à optimiser la détection des augmentations de populations dans les réseaux de surveillance, des pièges à chrysalides devraient être placés à hauteur de poitrine sur le tronc de sapins baumiers.The hemlock looper, Lambdina fiscellaria, pupal distribution was studied through a 3-year outbreak cycle near Lac Princeton on Anticosti Island in Quebec. Over the 3 years, 10 balsam fir trees were cut and all pupae were counted on the stem and branches (non-foliated vs foliated parts) of the lower, middle and upper crowns and on the stem below crown. In pre-outbreak conditions, pupae were mostly found on branches of the middle and upper crowns. During the outbreak, pupal density did not increase on these parts of the trees, since pupae were mostly found on the stem, from the ground to the middle crown, and on branches of the lower crown. Few pupae were found on the foliated portion of branches in post-outbreak conditions but most were found on the basal non-foliated part of branches, which appears to be a preferred location for hemlock looper pupation. In order to optimize detection of population increases in monitoring networks, we suggest using pupal traps at breast height on balsam fir trees

Demonstration of improved sensitivity of echo interferometers to gravitational acceleration

We have developed two configurations of an echo interferometer that rely on standing wave excitation of a laser-cooled sample of rubidium atoms that measures acceleration. For a two-pulse configuration, the interferometer signal is modulated at the recoil frequency and exhibits a sinusoidal frequency chirp as a function of pulse spacing. For a three-pulse stimulated echo configuration, the signal is observed without recoil modulation and exhibits a modulation at a single frequency. The three-pulse configuration is less sensitive to effects of vibrations and magnetic field curvature leading to a longer experimental timescale. For both configurations of the atom interferometer (AI), we show that a measurement of acceleration with a statistical precision of 0.5% can be realized by analyzing the shape of the echo envelope that has a temporal duration of a few microseconds. Using the two-pulse AI, we obtain measurements of acceleration that are statistically precise to 6 parts per million (ppm) on a 25 ms timescale. Using the three-pulse AI, we obtain measurements of acceleration that are statistically precise to 0.4 ppm on a timescale of 50 ms. A further statistical enhancement is achieved by analyzing the data across the echo envelope to improve the statistical precision to 75 parts per billion (ppb). We discuss methods for reducing prominent systematic effects due to a magnetized vacuum chamber and improving the signal-to-noise ratio. Simulations of both AI configurations with a timescale of 300 ms reached in a non-magnetic vacuum chamber suggest that an optimized experiment with improved vibration isolation and atoms selected in the mF = 0 state can result in measurements of g statistically precise to 0.3 pbb for the two-pulse AI and 0.6 ppb for the three-pulse AI.Comment: 17 pages, 9 figures, 3 table

Experimental Demonstration of Squeezed State Quantum Averaging

We propose and experimentally demonstrate a universal quantum averaging process implementing the harmonic mean of quadrature variances. The harmonic mean protocol can be used to efficiently stabilize a set of fragile squeezed light sources with statistically fluctuating noise levels. The averaged variances are prepared probabilistically by means of linear optical interference and measurement induced conditioning. We verify that the implemented harmonic mean outperforms the standard arithmetic mean strategy. The effect of quantum averaging is experimentally tested both for uncorrelated and partially correlated noise sources with sub-Poissonian shot noise or super-Poissonian shot noise characteristics.Comment: 4 pages, 5 figure

Quantum secret sharing

Secret sharing is a procedure for splitting a message into several parts so that no subset of parts is sufficient to read the message, but the entire set is. We show how this procedure can be implemented using GHZ states. In the quantum case the presence of an eavesdropper will introduce errors so that his presence can be detected. We also show how GHZ states can be used to split quantum information into two parts so that both parts are necessary to reconstruct the original qubit.Comment: 6 pages, revtex, revised version, to appear in Phys. Rev.

Perfect quantum error correction coding in 24 laser pulses

An efficient coding circuit is given for the perfect quantum error correction of a single qubit against arbitrary 1-qubit errors within a 5 qubit code. The circuit presented employs a double `classical' code, i.e., one for bit flips and one for phase shifts. An implementation of this coding circuit on an ion-trap quantum computer is described that requires 26 laser pulses. A further circuit is presented requiring only 24 laser pulses, making it an efficient protection scheme against arbitrary 1-qubit errors. In addition, the performance of two error correction schemes, one based on the quantum Zeno effect and the other using standard methods, is compared. The quantum Zeno error correction scheme is found to fail completely for a model of noise based on phase-diffusion.Comment: Replacement paper: Lost two laser pulses gained one author; added appendix with circuits easily implementable on an ion-trap compute

MuRF1 mono-ubiquitinates TRα to inhibit T3-induced cardiac hypertrophy in vivo

Thyroid hormone (TH) is recognized for its role in cellular metabolism and growth and participates in homeostasis of the heart. T3 activates pro-survival pathways including Akt and mTOR. Treatment with T3 after myocardial infarction is cardioprotective and promotes elements of physiological hypertrophic response after cardiac injury. Although T3 is known to benefit the heart, very little about its regulation at the molecular level has been described to date. The ubiquitin proteasome system (UPS) regulates nuclear hormone receptors such as estrogen, progesterone, androgen, and glucocorticoid receptors by both degradatory and non-degradatory mechanisms. However, how the UPS regulates T3-mediated activity is not well understood. In this study, we aim to determine the role of the muscle-specific ubiquitin ligase muscle ring finger-1 (MuRF1) in regulating T3-induced cardiomyocyte growth. An increase in MuRF1 expression inhibits T3-induced physiological cardiac hypertrophy, whereas a decrease in MuRF1 expression enhances T3’s activity both in vitro and in cardiomyocytes in vivo. MuRF1 interacts directly with TRα to inhibit its activity by posttranslational ubiquitination in a non-canonical manner. We then demonstrated that a nuclear localization apparatus that regulates/inhibits nuclear receptors by sequestering them within a subcompartment of the nucleus was necessary for MuRF1 to inhibit T3 activity. This work implicates a novel mechanism that enhances the beneficial T3 activity specifically within the heart, thereby offering a potential target to enhance cardiac T3 activity in an organ-specific manner

An isotope dilution model for partitioning of phenylalanine and tyrosine uptake by the liver of lactating dairy cows

An isotope dilution model to describe the partitioning of phenylalanine (PHE) and tyrosine (TYR) in the bovine liver was developed. The model comprises four intracellular and six extracellular pools and various flows connecting these pools and external blood. Conservation of mass principles were applied to generate the fundamental equations describing the behaviour of the system in the steady state. The model was applied to datasets from multi-catheterised dairy cattle during a constant infusion of [1-13C] phenylalanine and [2,3,5,6-2H] tyrosine tracers. Model solutions described the extraction of PHE and TYR from the liver via the portal vein and hepatic artery. In addition, the exchange of free PHE and TYR between extracellular and intracellular pools was explained and the hydroxylation of PHE to TYR was estimated. The model was effective in providing information about the fates of PHE and TYR in the liver and could be used as part of a more complex system describing amino acid metabolism in the whole animal

Prolonged refractory status epilepticus following acute traumatic brain injury: a case report of excellent neurological recovery

INTRODUCTION: Refractory status epilepticus (RSE) secondary to traumatic brain injury (TBI) may be under-recognized and is associated with significant morbidity and mortality. METHODS: This case report describes a 20 year old previously healthy woman who suffered a severe TBI as a result of a motor vehicle collision and subsequently developed RSE. Pharmacological coma, physiological support and continuous electroencephalography (cEEG) were undertaken. RESULTS: Following 25 days of pharmacological coma, electrographic and clinical seizures subsided and the patient has made an excellent cognitive recovery. CONCLUSION: With early identification, aggressive physiological support, appropriate monitoring, including cEEG, and an adequate length of treatment, young trauma patients with no previous seizure history and limited structural damage to the brain can have excellent neurological recovery from prolonged RSE