Quantum limits on phase-shift detection using multimode interferometers

Fundamental phase-shift detection properties of optical multimode interferometers are analyzed. Limits on perfectly distinguishable phase shifts are derived for general quantum states of a given average energy. In contrast to earlier work, the limits are found to be independent of the number of interfering modes. However, the reported bounds are consistent with the Heisenberg limit. A short discussion on the concept of well-defined relative phase is also included.Comment: 6 pages, 3 figures, REVTeX, uses epsf.st

Measuring the Mermin-Peres magic square using an online quantum computer

We have implemented the six series of three commuting measurement of the Mermin-Peres magic square on an online, five qubit, quantum computer. The magic square tests if the measurements of the system can be described by physical realism (in the EPR sense) and simultaneously are non-contextual. We find that our measurement results violate any realistic and non-contextual model by almost 28 standard deviations. We also find that although the quantum computer we used for the measurements leaves much to be desired in producing accurate and reproducible results, the simplicity, the ease of re-running the measurement programs, and the user friendliness compensates for this fact.Comment: 7 pages, 2 figures, 5 table

Entangled-State Lithography: Tailoring any Pattern with a Single State

We demonstrate a systematic approach to Heisenberg-limited lithographic image formation using four-mode reciprocal binominal states. By controlling the exposure pattern with a simple bank of birefringent plates, any pixel pattern on a $(N+1) \times (N+1)$ grid, occupying a square with the side half a wavelength long, can be generated from a $2 N$-photon state.Comment: 4 pages, 4 figure

Cystatins as calpain inhibitors: Engineered chicken cystatin- and stefin B-kininogen domain 2 hybrids support a cystatin-like mode of interaction with the catalytic subunit of μ-calpain

Within the cystatin superfamily, only kininogen domain 2 (KD2) is able to inhibit μ- and m-calpain. In an attempt to elucidate the structural requirements of cystatins for calpain inhibition, we constructed recombinant hybrids of human stefin B (an intracellular family 1 cystatin) with KD2 and Delta L110 deletion mutants of chicken cystatin-KD2 hybrids. Substitution of the N-terminal contact region of stefin B by the corresponding KD2 sequence resulted in a calpain inhibitor of K-i = 188 nM. Deletion of L110, which forms a beta -bulge in family 1 and 2 cystatins but is lacking in KD2, improved inhibition of mu -calpain 4- to 8-fold. All engineered cystatins were temporary inhibitors of calpain due to slow substrate-like cleavage of a single peptide bond corresponding to Gly9-Ala10 in chicken cystatin. Biomolecular interaction analysis revealed that, unlike calpastatin, the cystatin-type inhibitors do not bind to the calmodulin-like domain of the small subunit of calpain, and their interaction with the mu -calpain heterodimer is completely prevented by a synthetic peptide comprising subdomain B of calpastatin domain 1. Based on these results we propose that (i) cystatin-type calpain inhibitors interact with the active site of the catalytic domain of calpain in a similar cystatin-like mode as with papain and (ii) the potential for calpain inhibition is due to specific subsites within the papain-binding regions of the general cystatin fold

Sub-wavelength lithography over extended areas

We demonstrate a systematic approach to sub-wavelength resolution lithographic image formation on films covering areas larger than a wavelength squared. For example, it is possible to make a lithographic pattern with a feature size resolution of $\lambda/[2(N+1)]$ by using a particular $2 M$-photon, multi-mode entangled state, where $N < M$, and banks of birefringent plates. By preparing a statistically mixed such a state one can form any pixel pattern on a $(N+1) 2^{M-N} \times (N+1) 2^{M-N}$ pixel grid occupying a square with a side of $L=2^{M-N-1}$ wavelengths. Hence, there is a trade-off between the exposed area, the minimum lithographic feature size resolution, and the number of photons used for the exposure. We also show that the proposed method will work even under non-ideal conditions, albeit with somewhat poorer performance.Comment: 8 pages, 8 figures, 1 table. Written in RevTe

Maximally polarized states for quantum light fields

The degree of polarization of a quantum state can be defined as its Hilbert-Schmidt distance to the set of unpolarized states. We demonstrate that the states optimizing this degree for a fixed average number of photons $\bar{N}$ present a fairly symmetric, parabolic photon statistics, with a variance scaling as $\bar{N}^2$. Although no standard optical process yields such a statistics, we show that, to an excellent approximation, a highly squeezed vacuum can be considered as maximally polarized.Comment: 4 pages, 3 eps-color figure

High seasonal variability in sediment carbon stocks of cold‐temperate seagrass meadows

Seagrass meadows have a high ability to capture and store atmospheric CO2 in the plant biomass and underlying sediment and thereby function as efficient carbon sinks. The seagrass Zostera marina is a common species in the temperate Northern Hemisphere, a region with strong seasonal variations in climate. How seasonality affects carbon storage capacity in seagrass meadows is largely unknown, and therefore, in this study, we aimed to assess variations in sedimentary total organic carbon (TOC) content over a 1‐year cycle in seagrass meadows on the Swedish west coast. The TOC was measured in two Z. marina sites, one wave exposed and one sheltered, and at two depths (1.5 and 4 m) within each site, every second month from August 2015 to June 2016. We found a strong seasonal variation in carbon density, with a peak in early summer (June), and that the TOC was negatively correlated to the net community production of the meadows, presumably related to organic matter degradation. There was seasonal variation in TOC content at all sediment sections, indicating that the carbon content down to 30 cm is unstable on a seasonal scale and therefore likely not a long‐term carbon sink. The yearly mean carbon stocks were substantially higher in the sheltered meadow (3,965 and 3,465 g m−2) compared to the exposed one (2,712 and 1,054 g m−2) with similar seasonal variation. Due to the large intra‐annual variability in TOC content, seasonal variation should be considered in carbon stock assessments and management for cold‐temperate seagrass meadows.info:eu-repo/semantics/publishedVersio