Quantum measurement and the first law of thermodynamics: the energy cost of measurement is the work value of the acquired information

The energy cost of measurement is an interesting fundamental question, and may have profound implications for quantum technologies. In the context of Maxwell's demon, it is often stated that measurement has no minimum energy cost, while information has a work value, even though these statements can appear contradictory. However, as we elucidate, these statements do no refer to the cost paid by the measuring device. Here we show that it is only when a measuring device has access to a zero temperature reservoir - that is, never - that the measurement requires no energy. All real measuring devices pay the cost that a heat engine pays to obtain the work value of the information they acquire.Comment: 4 pages, revtex4-1. v2: added a referenc

Quantum communication via a continuously monitored dual spin chain

We analyze a recent protocol for the transmission of quantum states via a dual spin chain [Burgarth and Bose, Phys. Rev. A 71, 052315 (2005)] under the constraint that the receiver's measurement strength is finite. That is, we consider the channel where the ideal, instantaneous and complete von Neumann measurements are replaced with a more realistic continuous measurement. We show that for optimal performance the measurement strength must be "tuned" to the channel spin-spin coupling, and once this is done, one is able to achieve a similar transmission rate to that obtained with ideal measurements. The spin chain protocol thus remains effective under measurement constraints.Comment: 5 pages, revtex 4, 3 eps figure

Work function determination of promising material for thermionic converters

The work done to fabricate Marchuk plasma discharge tubes for measurement of the cesiated emission of lanthanum hexaboride and thoriated tungsten electrodes is described. A photon counting pyrometer was completed and is to be calibrated with a gold standard

Quantum error correction for continuously detected errors with any number of error channels per qubit

It was shown by Ahn, Wiseman, and Milburn [PRA {\bf 67}, 052310 (2003)] that feedback control could be used as a quantum error correction process for errors induced by weak continuous measurement, given one perfectly measured error channel per qubit. Here we point out that this method can be easily extended to an arbitrary number of error channels per qubit. We show that the feedback protocols generated by our method encode $n-2$ logical qubits in $n$ physical qubits, thus requiring just one more physical qubit than in the previous case.Comment: 4 page

Rapid purification of quantum systems by measuring in a feedback-controlled unbiased basis

Rapid-purification by feedback --- specifically, reducing the mean impurity faster than by measurement alone --- can be achieved by making the eigenbasis of the density matrix to be unbiased relative to the measurement basis. Here we further examine the protocol introduced by Combes and Jacobs [Phys.Rev.Lett. {\bf 96}, 010504 (2006)] involving continuous measurement of the observable $J_z$ for a $D$-dimensional system. We rigorously re-derive the lower bound $(2/3)(D+1)$ on the achievable speed-up factor, and also an upper bound, namely $D^2/2$, for all feedback protocols that use measurements in unbiased bases. Finally we extend our results to $n$ independent measurements on a register of $n$ qubits, and derive an upper bound on the achievable speed-up factor that scales linearly with $n$.Comment: v2: published versio

INDIGENOUS LAND TENURE AND LAND USE IN ALASKA: COMMUNITY IMPACTS OF THE ALASKA NATIVE CLAIMS SETTLEMENT ACT

Through the utilization of qualitative methods such as archival analysis, semi-structured interviewing, comparative and extended case studies, and observation, this paper closely examines two related Alaska Native communities. Our purpose is to document the impact of the Alaska Native Claims Settlement Act of 1971 (ANCSA) on land tenure, land use, and community structure. In all, 41 interviews were conducted, focusing on the following issues: (1) the role of the tribal government in relation to the regional and village corporate structure; (2) the recent changes in traditional land uses; and (3) how group decisions are made regarding land management and distribution of resources. By locating ANCSA within a broader context of economic, political, and cultural globalization that seeks to substitute traditional collective rights in land with individual tenure in a "free market" economy, the findings of this research may carefully and cautiously be applied beyond North America to other indigenous-state struggles regarding control of land and resources.United States. -- [Alaska Native Claims Settlement Act], Indians of North America -- Legal status, laws, etc. -- Alaska, Land tenure -- Law and legislation -- Alaska, Indians of North America -- Alaska -- Claims, Indians of North America -- Land tenure -- Alaska, Indians of North America -- Alaska -- Government relations -- History, Land Economics/Use,

Effective one-dimensional description of confined diffusion biased by a transverse gravitational force

Diffusion of point-like non interacting particles in a two-dimensional (2D) channel of varying cross section is considered. The particles are biased by a constant force in the transverse direction. We apply our recurrence mapping procedure, which enables us to derive an effective one-dimensional (1D) evolution equation, governing the 1D density of the particles in the channel. In the limit of stationary flow, we arrive at an extended Fick-Jacobs equation, corrected by an effective diffusion coefficient D(x), depending on the longitudinal coordinate x. Our result is an approximate formula for D(x), involving also influence of the transverse force. Our calculations are verified on the stationary diffusion in a linear cone, which is exactly solvable.Comment: 10 pages, 7 figures, submitted in Phys. Rev.