Boundary of Quantum Evolution under Decoherence

Relaxation effects impose fundamental limitations on our ability to coherently control quantum mechanical phenomena. In this letter, we establish physical limits on how closely can a quantum mechanical system be steered to a desired target state in the presence of relaxation. In particular, we explicitly compute the maximum coherence or polarization that can be transferred between coupled nuclear spins in the presence of very general decoherence mechanisms that include cross-correlated relaxation. We give analytical expressions for the control laws (pulse sequences) which achieve these physical limits and provide supporting experimental evidence. Exploitation of cross-correlation effects has recently led to the development of powerful methods in NMR spectroscopy to study very large biomolecules in solution. We demonstrate with experiments that the optimal pulse sequences provide significant gains over these state of the art methods, opening new avenues for spectroscopy of much larger proteins. Surprisingly, in spite of very large relaxation rates, optimal control can transfer coherence without any loss when cross-correlated relaxation rates are tuned to auto-correlated relaxation rates

The Value of Human Capital during the Second Industrial Revolution—Evidence from the U.S. Navy

This paper explores the role of human capital on earnings and other measures of job performance during the late 19th century. During this time, U.S. Naval ocers belonged either to a regular or an engineer corps and had tasks assigned to their specialized training and experience. To test for the eects of specialized skills on performance, we compile educational data from original-source Naval Academy records for the graduating classes of 1858 to 1905. We merge these with career data extracted from official Navy registers for the years 1859 to 1907. This compilation comprises one of the longest and earliest longitudinal records of labor market earnings, education and experience of which we are aware. Our results suggest that greater technical skill translated into higher earnings early in careers, but wage premia diminished as careers progressed. From this evidence we argue that technical progress was more skill-depreciating than skill-biased during this period.

Naval Engineering and Labor Specialization during the Industrial Revolution

This paper explores the roles of capital- and technology-skill complementarities in labor allocation decisions within the U.S. Navy. During the latter 19th century the ocer corps was highly specialized, and was split between groups of line and sta ocers. This was also a time of dramatic technological changes which aected nearly every facet of naval opera- tions. Specically, naval technological developments tended to be \engineering-biased," in that they raised the relative importance of engineer-oriented skills. This created a dilemma for the Navy, as it navigated the balance between the benets of a specialized workforce implementing increasingly complex technologies with rising communication and coordina- tion costs. We rst document the extent of capital- and technology-skill complementarities within the navy which fostered greater labor specialization. We then show how the Navy vitiated the specialized human capital of ocers by blending the corps. The study oers in- sights into how an industry undergoing wrenching technological changes managed its labor and human capital allocation to help the U.S. become a world class naval power.

Extracting high fidelity quantum computer hardware from random systems

An overview of current status and prospects of the development of quantum computer hardware based on inorganic crystals doped with rare-earth ions is presented. Major parts of the experimental work in this area has been done in two places, Canberra, Australia and Lund, Sweden, and the present description follows more closely the Lund work. Techniques will be described that include optimal filtering of the initially inhomogeneously broadened profile down to well separated and narrow ensembles, as well as the use of advanced pulse-shaping in order to achieve robust arbitrary single-qubit operations with fidelities above 90%, as characterized by quantum state tomography. It is expected that full scalability of these systems will require the ability to determine the state of single rare-earth ions. It has been proposed that this can be done using special readout ions doped into the crystal and an update is given on the work to find and characterize such ions. Finally, a few aspects on the possibilities for remote entanglement of ions in separate rare-earth-ion-doped crystals are considered.Comment: 19 pages, 9 figures. Written for The Proceedings of the Nobelsymposium on qubits for future quantum computers, Gothenburg, May-0