11,708 research outputs found
Entanglement-enhanced measurement of a completely unknown phase
The high-precision interferometric measurement of an unknown phase is the
basis for metrology in many areas of science and technology. Quantum
entanglement provides an increase in sensitivity, but present techniques have
only surpassed the limits of classical interferometry for the measurement of
small variations about a known phase. Here we introduce a technique that
combines entangled states with an adaptive algorithm to precisely estimate a
completely unspecified phase, obtaining more information per photon that is
possible classically. We use the technique to make the first ab initio
entanglement-enhanced optical phase measurement. This approach will enable
rapid, precise determination of unknown phase shifts using interferometry.Comment: 6 pages, 4 figure
Adaptive Measurements in the Optical Quantum Information Laboratory
Adaptive techniques make practical many quantum measurements that would
otherwise be beyond current laboratory capabilities. For example: they allow
discrimination of nonorthogonal states with a probability of error equal to the
Helstrom bound; they allow measurement of the phase of a quantum oscillator
with accuracy approaching (or in some cases attaining) the Heisenberg limit;
and they allow estimation of phase in interferometry with a variance scaling at
the Heisenberg limit, using only single qubit measurement and control. Each of
these examples has close links with quantum information, in particular
experimental optical quantum information: the first is a basic quantum
communication protocol; the second has potential application in linear optical
quantum computing; the third uses an adaptive protocol inspired by the quantum
phase estimation algorithm. We discuss each of these examples, and their
implementation in the laboratory, but concentrate upon the last, which was
published most recently [Higgins {\em et al.}, Nature vol. 450, p. 393, 2007].Comment: 12 pages, invited paper to be published in IEEE Journal of Selected
Topics in Quantum Electronics: Quantum Communications and Information Scienc
Effects of rotation on coolant passage heat transfer. Volume 1: Coolant passages with smooth walls
An experimental program was conducted to investigate heat transfer and pressure loss characteristics of rotating multipass passages, for configurations and dimensions typical of modern turbine blades. The immediate objective was the generation of a data base of heat transfer and pressure loss data required to develop heat transfer correlations and to assess computational fluid dynamic techniques for rotating coolant passages. Experiments were conducted in a smooth wall large scale heat transfer model
Mixed state discrimination using optimal control
We present theory and experiment for the task of discriminating two
nonorthogonal states, given multiple copies. We implement several local
measurement schemes, on both pure states and states mixed by depolarizing
noise. We find that schemes which are optimal (or have optimal scaling) without
noise perform worse with noise than simply repeating the optimal single-copy
measurement. Applying optimal control theory, we derive the globally optimal
local measurement strategy, which outperforms all other local schemes, and
experimentally implement it for various levels of noise.Comment: Corrected ref 1 date; 4 pages & 4 figures + 2 pages & 3 figures
supplementary materia
An examination of the effects of self-regulatory focus on the perception of the media richness: the case of email
Communication is a key element in organizations’ business success. The media richness theory and the channel expansion theory are two of the most influential theories regarding the selection and use of communication media in organizations; however, literature has focused little on the effects of self-regulation by managers and employees in these theories. To analyze these topics, this study develops an empirical investigation by gathering data from 600 managers and employees using a questionnaire. The results suggest that the perception of media richness is positively affected when the individual shows a promotion focus or strategy.Peer ReviewedPostprint (author’s final draft
Current status and perspectives on anaerobic co-digestion and associated downstream processes
© The Royal Society of Chemistry. Anaerobic co-digestion (AcoD) has the potential to utilise spare digestion capacity at existing wastewater treatment plants to simultaneously enhance biogas production by digesting organic rich industrial waste and achieve sustainable organic waste management. While the benefits of AcoD regarding biogas production and waste management are well established, the introduction of a new organic waste (i.e. co-substrate) with different chemical composition compared to residential sewage sludge is expected to impact on not only the anaerobic digestion process itself but also downstream processing of biogas and digestate. This work critically evaluates the potential impact (both positive and negative) of co-digestion on key downstream processes in the context of AcoD of sewage sludge and organic waste. AcoD can potentially lead to significant changes in biogas quality, digestate dewaterability, biosolids odour and the nutrient balance within the overall wastewater treatment process. The literature reviewed here suggests that effective management of these impacts can enhance the economic and environmental benefits of AcoD. Potential techniques to manage the impact of AcoD on downstream processing include co-substrate selection to minimise sulphur content, co-substrate pretreatment to improve dewaterability, process optimisation to minimize downstream impacts, biological desulphurisation of biogas, and side stream nutrient recovery. These techniques have been investigated and in some cases successfully applied for conventional anaerobic digestion. Nevertheless, further research is needed to adapt them for AcoD. In particular, the issue of nutrient accumulation due to AcoD can be seen as an opportunity to utilise recently commercialised technologies (e.g. Phosnix and Ostara) and currently emerging processes (e.g. forward osmosis and electrodialysis) for phosphorus recovery from food waste and wastewater
Multiple-copy state discrimination: Thinking globally, acting locally
We theoretically investigate schemes to discriminate between two
nonorthogonal quantum states given multiple copies. We consider a number of
state discrimination schemes as applied to nonorthogonal, mixed states of a
qubit. In particular, we examine the difference that local and global
optimization of local measurements makes to the probability of obtaining an
erroneous result, in the regime of finite numbers of copies , and in the
asymptotic limit as . Five schemes are considered:
optimal collective measurements over all copies, locally optimal local
measurements in a fixed single-qubit measurement basis, globally optimal fixed
local measurements, locally optimal adaptive local measurements, and globally
optimal adaptive local measurements. Here, adaptive measurements are those for
which the measurement basis can depend on prior measurement results. For each
of these measurement schemes we determine the probability of error (for finite
) and scaling of this error in the asymptotic limit. In the asymptotic
limit, adaptive schemes have no advantage over the optimal fixed local scheme,
and except for states with less than 2% mixture, the most naive scheme (locally
optimal fixed local measurements) is as good as any noncollective scheme. For
finite , however, the most sophisticated local scheme (globally optimal
adaptive local measurements) is better than any other noncollective scheme, for
any degree of mixture.Comment: 11 pages, 14 figure
Using weak values to experimentally determine "negative probabilities" in a two-photon state with Bell correlations
Bipartite quantum entangled systems can exhibit measurement correlations that
violate Bell inequalities, revealing the profoundly counter-intuitive nature of
the physical universe. These correlations reflect the impossibility of
constructing a joint probability distribution for all values of all the
different properties observed in Bell inequality tests. Physically, the
impossibility of measuring such a distribution experimentally, as a set of
relative frequencies, is due to the quantum back-action of projective
measurements. Weakly coupling to a quantum probe, however, produces minimal
back-action, and so enables a weak measurement of the projector of one
observable, followed by a projective measurement of a non-commuting observable.
By this technique it is possible to empirically measure weak-valued
probabilities for all of the values of the observables relevant to a Bell test.
The marginals of this joint distribution, which we experimentally determine,
reproduces all of the observable quantum statistics including a violation of
the Bell inequality, which we independently measure. This is possible because
our distribution, like the weak values for projectors on which it is built, is
not constrained to the interval [0, 1]. It was first pointed out by Feynman
that, for explaining singlet-state correlations within "a [local] hidden
variable view of nature ... everything works fine if we permit negative
probabilities". However, there are infinitely many such theories. Our method,
involving "weak-valued probabilities", singles out a unique set of
probabilities, and moreover does so empirically.Comment: 9 pages, 3 figure
Does colonoscopy cause increased ulcerative colitis symptoms?
Background: Ulcerative colitis (UC) patients often report symptom flares after colonoscopy. However, this has not been documented in the literature. Objectives: 1. Determine whether colonoscopy is associated with increased UC symptoms. 2. Determine whether there is a need for escalation of UC medications after colonoscopy. 3. Identify baseline variables associated with increased symptoms after colonoscopy. Methods: Firty-five outpatients with a history of UC, intact colon, and quiescent disease were enrolled in a prospective case-crossover study. Subjects were evaluated with the Simple Clinical Colitis Activity Index (SCCAI) before colonoscopy, 1 week and 4 weeks after colonoscopy. A mixed model analysis was used to accommodate nonindependence of repeated measurements on the same patients. Results: Fifty-one (91%) subjects completed the study. Six subjects had clinical relapse defined by a score of 5 or greater on the SCCAI during the week after colonoscopy. Five subjects increased their 5-aminosalicylic acid (5-ASA) medications immediately postcolonoscopy, two of whom had a SCCAI 5 or greater. Multivariate modeling demonstrated a clear association between the week immediately after colonoscopy preparation and increased disease activity, with the time period being predictive of increased SCCAI (week 1 vs. week 4, P = 0.0127). The baseline SCCAI ( P value < 0.0001) and prednisone use ( P = 0.0120) were predictive of increased SCCAI postcolonoscopy. Thiopurines ( P < 0.001) were protective against increased symptoms. Conclusions: In our study, 1 in 8 subjects had UC relapse by SCCAI immediately postcolonoscopy, and 1 in 10 subjects required an increase in their 5-ASA medications. Clinicians should be cognizant of this effect of colonoscopy in patients with UC. (Inflamm Bowel Dis 2007;13:12–18)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55905/1/20049_ftp.pd
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