Remote State Preparation

Quantum teleportation uses prior entanglement and forward classical communication to transmit one instance of an unknown quantum state. Remote state preparation (RSP) has the same goal, but the sender knows classically what state is to be transmitted. We show that the asymptotic classical communication cost of RSP is one bit per qubit - half that of teleportation - and becomes even less when transmitting part of a known entangled state. We explore the tradeoff between entanglement and classical communication required for RSP, and discuss RSP capacities of general quantum channels.Comment: 4 pages including 1 epsf figure; v3 has an additional author and discusses relation to work of Devetak and Berger (quant-ph/0102123); v4 improves low-entanglement protocols without back communication to perform as well as low-entanglement protocols with back communication; v5 (journal version) has a few small change

Structurally Distinct Active Sites in the Copper(II)-Substituted Aminopeptidases from \u3cem\u3eAeromonas proteolytica\u3c/em\u3e and \u3cem\u3eEscherichia coli\u3c/em\u3e

The aminopeptidase from Aeromonas proteolytica (AAP) was titrated with copper, which bound sequentially at two distinct sites. Both the mono- and disubstituted forms of AAP exhibited catalytic hyperactivity relative to the native dizinc enzyme. Monosubstituted AAP exhibited an axial Cu(II) EPR spectrum with slight pH dependence:  at pH 6.0 g|| = 2.249, g⊥ = 2.055, and A||(63/65Cu) = 1.77 × 10-2 cm-1, whereas at pH 9.65 g|| = 2.245, g⊥ = 2.056, and A||(63/65Cu) = 1.77 × 10-2 cm-1. These data indicate oxygen and nitrogen ligation of Cu. AAP further substituted with copper exhibited a complex signal with features around g ∼ 2 and 4. The features at g ∼ 4 were relatively weak in the B0 ⊥ B1 (perpendicular) mode EPR spectrum but were intense in the B0 || B1 (parallel) mode spectrum. The g ∼ 2 region of the perpendicular mode spectrum exhibited two components, one corresponding to mononuclear Cu(II) with g|| = 2.218, g⊥ = 2.023, and A||(63/65Cu) = 1.55 × 10-2 cm-1 and likely due to adventitious binding of Cu(II) to a site distant from the active site. Excellent simulations were obtained for the second component of the spectrum assuming that two Cu(II) ions experience dipolar coupling corresponding to an inter-copper distance of 5 Å with the two Cu(II) gz directions parallel to each other and at an angle of ∼17° to the inter-copper vector (ℋ = βB·gCuA·SCuA + βB·gCuB·SCuB + [S·A·I]CuA + [S·A·I]CuB + [SCuA·J·SCuB]; g||(CuA,CuB) = 2.218, g⊥(CuA,CuB) = 2.060; A||(CuA,CuB)(63/65Cu) = 1.59 × 10-2 cm-1, Jisotropic = 50 cm-1, rCu-Cu = 4.93 Å, and χ = 17°). The exchange coupling between the two copper ions was found to be ferromagnetic as the signals exhibited Curie law temperature dependence. The Cu−Cu distance of ∼5 Å indicated by EPR was significantly higher than the inter-zinc distance of 3.5 Å in the native enzyme, and the dicopper species therefore represents a novel dinuclear site capable of catalysis of hydrolysis. In contrast to AAP, the related methionyl aminopeptidase from Escherichia coli (EcMetAP) was found to bind only one Cu(II) ion despite possessing a dinuclear binding site motif. A further difference was the marked pH dependence of the signal in EcMetAP, suggestive of a change in ligation. The structural motifs of these two Cu(II)-substituted aminopeptidases provide important insight into the observed catalytic activity

Entangled Rings

Consider a ring of N qubits in a translationally invariant quantum state. We ask to what extent each pair of nearest neighbors can be entangled. Under certain assumptions about the form of the state, we find a formula for the maximum possible nearest-neighbor entanglement. We then compare this maximum with the entanglement achieved by the ground state of an antiferromagnetic ring consisting of an even number of spin-1/2 particles. We find that, though the antiferromagnetic ground state does not maximize the nearest-neighbor entanglement relative to all other states, it does so relative to other states having zero z-component of spin.Comment: 19 pages, no figures; v2 includes new results; v3 corrects a numerical error for the case N=

The Self and the Conduct of the People-Working Professions

This article discusses the evolution of people-working professions through four synchronic eras: 1) the traditional era, 2) the voluntaristic era, 3) the professional era, and 4) the cybernetic era. People-working professions are conceptually distinguished from traditional (craft) professions which serve as the model for most sociological analyses of the professions. In addition to differences in the nature of the knowledge used and the context of the service rendered, a distinction is drawn regarding the focus of the work done. People-workers give service to other selves (egos) while craft professions work with objects or parts of the person. The historical evolution of people-workers, as well as current issues and future prospects for the people-working professions, are considered within the context of this separate identity

Entanglement of a Pair of Quantum Bits

The ``entanglement of formation'' of a mixed state of a bipartite quantum system can be defined in terms of the number of pure singlets needed to create the state with no further transfer of quantum information. We find an exact formula for the entanglement of formation for all mixed states of two qubits having no more than two non-zero eigenvalues, and we report evidence suggesting that the formula is valid for all states of this system.Comment: 10 page

Mixed State Entanglement and Quantum Error Correction

Entanglement purification protocols (EPP) and quantum error-correcting codes (QECC) provide two ways of protecting quantum states from interaction with the environment. In an EPP, perfectly entangled pure states are extracted, with some yield D, from a mixed state M shared by two parties; with a QECC, an arbi- trary quantum state $|\xi\rangle$ can be transmitted at some rate Q through a noisy channel $\chi$ without degradation. We prove that an EPP involving one- way classical communication and acting on mixed state $\hat{M}(\chi)$ (obtained by sharing halves of EPR pairs through a channel $\chi$) yields a QECC on $\chi$ with rate $Q=D$, and vice versa. We compare the amount of entanglement E(M) required to prepare a mixed state M by local actions with the amounts $D_1(M)$ and $D_2(M)$ that can be locally distilled from it by EPPs using one- and two-way classical communication respectively, and give an exact expression for $E(M)$ when $M$ is Bell-diagonal. While EPPs require classical communica- tion, QECCs do not, and we prove Q is not increased by adding one-way classical communication. However, both D and Q can be increased by adding two-way com- munication. We show that certain noisy quantum channels, for example a 50% depolarizing channel, can be used for reliable transmission of quantum states if two-way communication is available, but cannot be used if only one-way com- munication is available. We exhibit a family of codes based on universal hash- ing able toachieve an asymptotic $Q$ (or $D$) of 1-S for simple noise models, where S is the error entropy. We also obtain a specific, simple 5-bit single- error-correcting quantum block code. We prove that {\em iff} a QECC results in high fidelity for the case of no error the QECC can be recast into a form where the encoder is the matrix inverse of the decoder.Comment: Resubmission with various corrections and expansions. See also http://vesta.physics.ucla.edu/~smolin/ for related papers and information. 82 pages latex including 19 postscript figures included using psfig macro

REGIONAL ECONOMIC IMPACTS OF A WATERSHED PLANNING PROCESS TO REDUCE EROSION AND STREAM SEDIMENTATION

Farm-level and watershed-wide land-use changes resulting from policy initiatives are linked to a regional input/output model. As a result not only can the direct economic impacts at the farm and watershed levels be determined, so too can the direct and induced economic impacts at the regional level.Resource /Energy Economics and Policy,

In search of ancient auditors

Auditing is one of the most ancient of all professions. Early civilizations apparently learned to audit almost as soon as they learned to write. Many of the oldest examples of writing are records of possessions, such as livestock, grain, or wine. There is evidence that at least some of these first accounting records were audited. We will examine evidence of auditing in the ancient civilizations of Mesopotamia, Egypt, Greece, and Rome. Our examination will be limited to the lands located around the Mediterranean Sea for it is here that the origin of auditing in Western world can be found. We will then comment on Biblical references to auditing

Phonon Density of States and Anharmonicity of UO2

Phonon density of states (PDOS) measurements have been performed on polycrystalline UO2 at 295 and 1200 K using time-of-flight inelastic neutron scattering to investigate the impact of anharmonicity on the vibrational spectra and to benchmark ab initio PDOS simulations performed on this strongly correlated Mott-insulator. Time-of-flight PDOS measurements include anharmonic linewidth broadening inherently and the factor of ~ 7 enhancement of the oxygen spectrum relative to the uranium component by the neutron weighting increases sensitivity to the oxygen-dominated optical phonon modes. The first-principles simulations of quasi-harmonic PDOS spectra were neutron-weighted and anharmonicity was introduced in an approximate way by convolution with wavevector-weighted averages over our previously measured phonon linewidths for UO2 that are provided in numerical form. Comparisons between the PDOS measurements and the simulations show reasonable agreement overall, but they also reveal important areas of disagreement for both high and low temperatures. The discrepancies stem largely from an ~ 10 meV compression in the overall bandwidth (energy range) of the oxygen-dominated optical phonons in the simulations. A similar linewidth-convoluted comparison performed with the PDOS spectrum of Dolling et al. obtained by shell-model fitting to their historical phonon dispersion measurements shows excellent agreement with the time-of-flight PDOS measurements reported here. In contrast, we show by comparisons of spectra in linewidth-convoluted form that recent first-principles simulations for UO2 fail to account for the PDOS spectrum determined from the measurements of Dolling et al. These results demonstrate PDOS measurements to be stringent tests for ab initio simulations of phonon physics in UO2 and they indicate further the need for advances in theory to address lattice dynamics of UO2.Comment: Text slightly modified, results unchange

High speed quantum gates with cavity quantum electrodynamics

Cavity quantum electrodynamic schemes for quantum gates are amongst the earliest quantum computing proposals. Despite continued progress, and the dramatic recent demonstration of photon blockade, there are still issues with optimal coupling and gate operation involving high-quality cavities. Here we show dynamic control techniques that allow scalable cavity-QED based quantum gates, that use the full bandwidth of the cavities. When applied to quantum gates, these techniques allow an order of magnitude increase in operating speed, and two orders of magnitude reduction in cavity Q, over passive cavity-QED architectures. Our methods exploit Stark shift based Q-switching, and are ideally suited to solid-state integrated optical approaches to quantum computing.Comment: 4 pages, 3 figures, minor revision